My GF-777Z ** Project PHAT-AZZZ BASS!!

[Cpl-Chronic]

here's another clip to demonstrate the bass output from different listening points in my bedroom. Notice the bass is strong in most areas, escept directly in front of the box, about a foot & a half back. At this point the horns are really holding their own & the sound is more balanced. I have to point out that in the last couple of videos, the controls are left the same & the 'Super-Woofers' controls are actually trimmed back form 12:00 center to 11:00. The EQ on my computer sound card is OFF & the signal coming into the blaster is flat with no loudness or boost/cut applied. I'm extremely happy with the sound. It has lots of punchy mid-bass just like a good blaster should & it sounds great from a distance too without losing much above 50Hz. That's hard to acomplish with a shallow plastic case.

Turn down your computer speakers before playing this video. It has lots of BASS energy & can damage your desktop speakers:

!!! WARNING PHAT AZZZ BASS!!!!!

I declare Project PHAT-AZZZ BASS a SUCCESS!!!

 

[tshorba]

The aperture of the horn throat should match the driver, when this is the case the horn loaded driver is more efficient than a standard driver. The way sharp has done the mount/aperture creates a lot of refraction behind the plate due to the larger cone.

The sound is not lost inside the box, but the air space in front of the tweeter is forced through the aperture like a port in a bass reflex design

Well, you are right that a professional horn has a driver designed to fit the aperture more closely & the entire diaphram is coupled to the lens of the horn in a traditional design while the SHARP horns are more of a hybrid horn using a cone tweeter. Having said that, for a ghetto-blaster, the GF's horns use a workable trade-off that uses the energy of the tweeter's domes where the higher frequencies emanate anyway & amplify them with a horn aperture like the victrola example I used earlier. In effect, they are damping the mid-range frequencies, say between 1-4KHz & boosting the high frequencies from the dome region of the tweeter & it works quite well & sounds very balanced considering it's D-CELL audio anyway. I definitely hear a lot of high freuency energy from the infinity tweeters I loaded & the domes match the lens aperture perfectly. I bet if you pull the tweeters off the horns & listen to them naked, they'll sound flat with too much mid vs treble...

Not only pro but consumer gear as well

I think you need to rethink your idea about what you call the "dome", it is a dustcap. Apart from covering the voice coil it functions as a quasi phase plug. The dustcap moves the same same as the rest of the driver surface, the tweeter is not co-axial as your explanation would suggest. If you pull the tweeters and found they sound flat and the mid overtook the high frequencies that could easily be rectified with a properly designed crossover.
I am only giving you food for thought

 

[Cpl-Chronic]

The aperture of the horn throat should match the driver, when this is the case the horn loaded driver is more efficient than a standard driver. The way sharp has done the mount/aperture creates a lot of refraction behind the plate due to the larger cone.

The sound is not lost inside the box, but the air space in front of the tweeter is forced through the aperture like a port in a bass reflex design

Well, you are right that a professional horn has a driver designed to fit the aperture more closely & the entire diaphram is coupled to the lens of the horn in a traditional design while the SHARP horns are more of a hybrid horn using a cone tweeter. Having said that, for a ghetto-blaster, the GF's horns use a workable trade-off that uses the energy of the tweeter's domes where the higher frequencies emanate anyway & amplify them with a horn aperture like the victrola example I used earlier. In effect, they are damping the mid-range frequencies, say between 1-4KHz & boosting the high frequencies from the dome region of the tweeter & it works quite well & sounds very balanced considering it's D-CELL audio anyway. I definitely hear a lot of high freuency energy from the infinity tweeters I loaded & the domes match the lens aperture perfectly. I bet if you pull the tweeters off the horns & listen to them naked, they'll sound flat with too much mid vs treble...

Not only pro but consumer gear as well

I think you need to rethink your idea about what you call the "dome", it is a dustcap. Apart from covering the voice coil it functions as a quasi phase plug. The dustcap moves the same same as the rest of the driver surface, the tweeter is not co-axial as your explanation would suggest. If you pull the tweeters and found they sound flat and the mid overtook the high frequencies that could easily be rectified with a properly designed crossover.
I am only giving you food for thought

OK let's talk terminology for a minute. Dome or Dustcap....same thing. The dustcap is in the shape of a dome, not flat felt or a whizzer cone so I call it a dome. Anyway, of course the dustcap/dome moves the same as the cone because it is attached to the cone. I never implied it was co-axial in any way. My point is the horn aperture uses the energy that emanates priamarily from the dome/dustcap which is where the higher frequencies come from & is damping the lower frequencies emanating from the rest of the cone that is covered. In any loudspeaker, the high frequencies come from the center of the speaker where the dome/dustcap is. This is called 'beaming'. That is why I called it a HYBRID horn instead of a traditional horn. Any horn is also a very efficient coupling device & is 5 times as efficient as a normal tweeter so it is performing 2 jobs. If you played those tweeters naked, they would be flat & weak compared to their sound inside the horn. Try it if you don't believe me. I know those horns are a benefit, not a design flaw as some would suggest & the sound I get from my GF is balanced & natural sounding with the horns. Another benefit of a horn loaded tweeter is less distortion althoug these HYBRID types might me a little more noisy as the gap between the lens & dome is bigger.

I think the GF fails in using inferior paper cone dirvers which were the norm for 1983 but if you replace them with better drivers, it really comes alive & the highs are pretty good for a ghettoblaster because it uses the hybrid horn design to naturally boost highs. Don't froget, you have 4 6.5" woofers & only 2 small tweeters so you need the horns to boost the high freq. output & they work quite well.

 

[Reli]

This assumes that Sharp's horns were designed properly by audio engineers.......Shaped and sized to amplify & carry the sound waves as well as possible. Kind of like how an airplane manufacturer would spend great effort testing their designs in a wind tunnel. Somehow I doubt Sharp put that much effort into it, considering that it's just a boombox. Style and cost were the main considerations.

Also, if horns are so great, why are they so infrequently used, even by expensive home audio manufacturers?

I think the only reason Sharp used them on the GF-777 (and NONE of their other boxes) was because there was no room to mount the tweeters against the front case.

 

[Cpl-Chronic]

This assumes that Sharp's horns were designed properly by audio engineers.......Shaped and sized to amplify & carry the sound waves as well as possible. Kind of like how an airplane manufacturer would spend great effort testing their designs in a wind tunnel. Somehow I doubt Sharp put that much effort into it, considering that it's just a boombox. Style and cost were the main considerations.

Also, if horns are so great, why are they so infrequently used, even by expensive home audio manufacturers?

I think the only reason Sharp used them on the GF-777 (and NONE of their other boxes) was because there was no room to mount the tweeters against the front case.

Well, I made my points & they are valid. Either you agree or you don't but unless you listen to those tweeters naked, you won't know the difference they make. Klipsch makes nothing but horn loaded tweeters for their loudspeakers & actually makes a corner horn woofer too because they know the benefits of horns. Look it up on google if you want, or don't but I know these horns work & work quite well for a ghetto-blaster.

Althoug these horns aren't 'Compression drivers' compression horns are much more efficient, have lower distortion & can handle much larger wattages. That's why stage speakers use horns primarily & alot of high-end home speakers do too...

 

[Reli]

I never said horns don't work, I said that many home audio companies don't use them, even when there was nothing stopping them from doing so. You can go into any audio/video store, and the majority of speakers won't have horns. Even ones costing several thousand dollars. It is up to each manufacturer to choose the sound signature they want, and evidently many of them have decided that horns weren't necessary to acheive what they wanted.

 

[Cpl-Chronic]

Also, if horns are so great, why are they so infrequently used, even by expensive home audio manufacturers?

Your statement implies that horns aren't 'great' or better than other types of tweeters when in fact they are far superior in SPL, low noise, transient response & forgiving of abuse. To answer your question, usually home audio speakers, especially woofers with a low FS are less efficient & a properly designed compression horns will actually overpower the mid/low drivers & they are MUCH more costly to make than a simple dome or ribbon tweeter. That's why you don't see many home audio horns but they are virually ubiquetous in pro audio system like monitors, stage speakers etc. In that environment you need a robust tweeter that can put out clean sound at really high SPL's & handle torturous transients that would shred a dome, cone or ribbon tweeter.

I have a pair of Klipsch bookshelf speakers that use a 6.5" woofer & horn & many people have told me already that they are the best sounding bookshelf speakers they've ever listened to. The clarity & strength of the horns really comes through. I'm not making this S#!+ up you know.

Like I said before, these horns aren't a gimmick. The techs at SHARP realized that 2 small cone tweeters won't keep up with 4 6.5" woofers without a more efficient horn design. Besides, molding the horns out of the case doesn't cost much more per unit & gives great results. It isn't just for show, it's science at work. Try it for yourself. Listen to the difference between the naked tweeter & the loaded horn. It's a world of difference & I worked as a roadie for 2 years, built monitor speakers with horns, read all kinds of Electro-Voice white papers on the subject & even made my own basic 2-way cross-overs from scratch. I know what I'm talking about & the GF is way ahead of its time in lots of ways. It's just too bad they cheaped out on the weak drivers. Here's another fun fact:

The recessed super-woofer design is actually quite useful as it strengthens the cabinet & helps keep it from vibrating. Also, it aligns the drivers & keeps the 4 drivers in perfect phase. You car stereo guys know what I'm talking about.

J-SKI

 

[Line Out]

If you want to make the box really stiff, make a mixture of resin and sandblasting sand. Mix the hardener, then pour it to the box, one side at a time. Make just enough for one side and add some glass fibers in the mix to give it a bit more strength. Let it harden. I think maybe a layer of few mm would be enough. When the stuff hardens, its like stone. Acoustically dead and very strong. Glass fiber minimizes the risk of cracking.

This way is quite popular in car hi-fi subwoofer enclosures and in competition use.

 

[Cpl-Chronic]

As a roadie for 2 years in the local band scene & doing odd-ball shows, I worked for a guy who was the Electro-Voice dealer for our area. He learned to build cabinets himself & used fibreglass sheets & resin to strengthen & deaden the box, almost like mounting your woofers inside a concrete box. This works exremely well for vented box cabinets & we used them with 1000w RMS 15 or 18" Electro-Voice woofers.

 

[Cpl-Chronic]

If you want to make the box really stiff, make a mixture of resin and sandblasting sand. Mix the hardener, then pour it to the box, one side at a time. Make just enough for one side and add some glass fibers in the mix to give it a bit more strength. Let it harden. I think maybe a layer of few mm would be enough. When the stuff hardens, its like stone. Acoustically dead and very strong. Glass fiber minimizes the risk of cracking.

This way is quite popular in car hi-fi subwoofer enclosures and in competition use.

You are exactly right about the fiber-glass & sand + resin but my GF already has a weight problem at 40 lbs. loaded with batteries & the new woofers installed. Put some more dynamat & heavy sand/resin finish & we're hitting 50 lbs, easy which may cause the handle to snap eventually.

 

[Line Out]

I think a (can't remember the term, something like "half sealed" or "dampened" or "half breathing" or "baffle") system would work fine also... So that the box would be reinforced, but the openings on the back would only be dampened with a bit heavier plastic foam. For that, the woofers should (if I remember correctly) have a bit higher Qts, meant for sealed box or free-air assembly. But afaik, there is not much high quality free-air woofers on the market anymore.

 

[Cpl-Chronic]

I think a (can't remember the term, something like "half sealed" or "dampened" or "half breathing" or "baffle") system would work fine also... So that the box would be reinforced, but the openings on the back would only be dampened with a bit heavier plastic foam. For that, the woofers should (if I remember correctly) have a bit higher Qts, meant for sealed box or free-air assembly. But afaik, there is not much high quality free-air woofers on the market anymore.

Heyya Line-Out, I already got it covered. The 6.5" Sub-Woofers are good with a small, sealed enclosure & optimal is only 0.16 cu. feet sealed box with an FS of 38Hz. The back of the GF is sealed to keep the back wave from cancelling the bass output & insuation in the crners & gaps to keep rattles minimal. All I need now is a little more deadmat for the back-panel wich will add 1 or 2 pounds to the weight & deaden the rattles off the back panel. I just have to be careful when moving the box so I don't snap the handle off at 40LBS.

 

[Cpl-Chronic]

I think a (can't remember the term, something like "half sealed" or "dampened" or "half breathing" or "baffle") system would work fine also... So that the box would be reinforced, but the openings on the back would only be dampened with a bit heavier plastic foam. For that, the woofers should (if I remember correctly) have a bit higher Qts, meant for sealed box or free-air assembly. But afaik, there is not much high quality free-air woofers on the market anymore.

You just gave me a great idea. You could use fiber & sand with resin on the back panel if you do it right. You would have to cover the brackets for the handle with fibreglass to make the handle stronger too. Would that work? That would add about 5-10 pounds to strengthen & deaden that panel. now were hitting 50-lbs.

 

[spaz815]

Looks and sounds awesome

 

[Cpl-Chronic]

Looks and sounds awesome

Thanx man. I wish I ahd bettter recording equipment instead of my crappy Kodak point & click 1o megger...

 

[Superduper]

I just have to be careful when moving the box so I don't snap the handle off at 40LBS.

Forget the handle. After working on the louder blaster, one of my priorities was to strip some weight to make the project practical again. How many GF's have you seen with shattered front and back cases in stock form? The front case on the GF's are so thin that it's merely a matter of time for cracks and so forth to develop with weight and thumps of subs. Did you retain the original woofer tie braces or did you remove them to accomodate those speakers? If they are gone, I worry about that a bit. Sounds like you still have the stock amps in there? That's probably the saving grace and the only thing keeping the case together. But I do know that the GF-777 only has 4 amps in SE configuration. There is absolutely NO WAY that those amps could use even 1/10th of the capability of those speakers. In other words, the speakers are probably overkill. HA1392's in SE configuration is only spec'd at about 5-7wpc and that is at 10% THD. To see the potential of the speakers, you'd have to replace the amps but like you've noticed, you are already running short of room and those HA1392 chips DO BLOW out, especially now that you've eliminated all the airflow inside the unit. Also, if you study the amp design, you 'll see that they have capacitor coupled outputs. 1,000uf is a good amount but does filter at approx 40hz for 4-ohms and 80hz at 2-ohms. At 4-ohm load, and 1,000uf inline, the optimum low frequency response is 400hz and -3db at 40hz. As you know, with speakers, we are not talking resistance but rather, impedance which varies with frequency. Actual impedance could drop as low as 1+ ohm during actual usage. Understand that while the crossover will help to distribute the low and high frequencies to the respective drivers, this crossover is AFTER the 1,000hz series capacitor. In case you are wondering, do not remove that capacitor to increase low frequency response as this amp chip requires it to protect the amp. A better suited amplifier for amplifying those really low lows is to replace the amps with one better designed for subwoofers.

Now as far as the GF tweeters. I do believe that if the original speakers are unshrouded, they will sound better. The GF-777 is sorely lacking in that department. Shrouding the cone tweeters only exacerbates that deficiency. I know what you say, that you believe that the lens actually helps reinforce the highs. I disagree. Sure, some professional speaker systems do use horns but they have special drivers designed for horns. In the GF, only standard cone tweeters are used and like Reli said, real estate space in the front panel is sorely lacking after those 4 woofers and controls. If you are now experiencing improved highs, it is probably due to the crossover or more efficient drivers and not due to the lens/horn design. On almost any system, merely waving your hand in front of the tweeters cut the highs noticeably. Unlike lows, highs are highly directional and easily affected by shrouding/blocking. BTW, done tweeters disperse better because the sound can radiate all around the dome. Sticking them in a lens seems to be counterintuitive but as long as sound is better than stock, who cares. Some people like bass and some like highs. Me, I like the strong highs on unobstructed tweeter setups like the M90, M70, M9994, etc. The GF comes nowhere close to that. The shrouded tweeters undoubtedly share some blame for that. Most folks that have sub'd the woofers for coaxial ones with tweeters front/center have reported noticable improvement in the highs. If you think shrouded tweets sound better due to less mids, then that's fine for you. But mechanically blocking a range of frequency seems to be an afterthought for a bad design, does it now? No, I think in this particular case, the installation of the tweets in a standoff horn was implemented due to space constraints and for aesthetics, not for critically calculated sound improvements. Because if we believe the latter, then that would suggest that this is a finely calibrated machine and haphazard tampering would generally result in deteriorated performance. Unless you really believe that you somehow was so lucky to swap all of the drivers using the same mechanical layout and improved on this finely tuned machine without benefit of all the gear/equipment etc available to Sharp engineers of the time.

But hey, let's just forget all the data and specs and what not. You said you like the new sound better. In the end, it's your project and if you are happy with it, then that's the only thing that matters. Many GF owners have done nothing more than replace the outboard speakers with coaxial car door speakers and better center bass drivers, and have reported improvement. This without added crossovers, relocating the transformer, or dynomat. In other words, improvement without compromising the structural integrity and practicality of the machine.

Personally, I think for the ultimate blaster, you might want to consider going the route of something along the lines of what JVC Floyd does, without the constraints of working with the original installation.

Do not take this as a knock on your project. Those that knows me also knows I have the tact of a tree. Like I said above, all the above is "......I'm just saying.....". If you are happy, then that's all that matters. I for one have done things to boxes that others have shaken their head at. Good thing I'm not trying to make them happy, just trying to make myself happy.

I suspect you may disagree with 90% of what I said. That's OK too. How boring this world would be if we all were like programmed ants.

 

[Cpl-Chronic]

I just have to be careful when moving the box so I don't snap the handle off at 40LBS.

Forget the handle. After working on the louder blaster, one of my priorities was to strip some weight to make the project practical again.

'How many GF's have you seen with shattered front and back cases in stock form?' --
-- I don't know about that, I only own 1.

"The front case on the GF's are so thin that it's merely a matter of time for cracks and so forth to develop with weight and thumps of subs. Did you retain the original woofer tie braces or did you remove them to accomodate those speakers?" --
-- I kept the braces along the top & all other stock parts. Only the 'cans' were replaced. The front is in great shape & the recessed Woofers add strength to the chassis that other blaster cases lack. The original mounting holes are used with oversized screws. The mounting is genius because you can peel away the mounting paper on the baskets, & the ring of the woofer holes acts like a seal. PERFECT!!!

"Sounds like you still have the stock amps in there?" --
-- Yes, 8 WATTS RMS per channel x 4 @ 4-OHMS is pretty decent power @ 1% THD.

"That's probably the saving grace and the only thing keeping the case together." --
--The case is actually pretty solid if put together right & you don't swing it around like a war-hammer. At 40+ lbs it's not a walk-about, it's a party guest.

"But I do know that the GF-777 only has 4 amps in SE configuration". --
-- Yes, 8 WATTS RMS per/ch. @ 1% THD.

"There is absolutely NO WAY that those amps could use even 1/10th of the capability of those speakers." --
-- Yes, you are correct in general but the SUBS have an FS of 38Hz & that means a low impedance at low frequencies, possibly 1or2-Ohm @ 20-40Hz. Now, that 8 watt amp is pushing 16 or 32w RMS. And I've been around long enough to know that these blasters were made for abuse & can handle 2-Ohm loads in the bass region, even on D-Cells.

"In other words, the speakers are probably overkill. HA1392's in SE configuration is only spec'd at about 5-7wpc and that is at 10% THD." --
-- This point I strongly disagree with. I can't believe an output amp is rated at 10% THD & I'm pretty sure these amps are rated 1% THD as a stanadard. NO? I wanted a combination of woofers with low FS points at 40 & 60 Hz so that the mid/bass will be smooth & blend in well with the horns. Otherwise, what's the point of it all. The cans handle the juice nicely, I get decent SPL running flat & killler BASS at med. to high volumes while the sound is balanced & natural. You watch the videos in full screen & you can see all 4 skins hopping like mad on some tracks but it sounds pretty good, NOT muddy, washed out or distorted. The cam era is crap so it's not a perfect audition but you get the idea these woofers are working hard & sounding good. You tell me how that is overkill if the cans fit the job? Don't forget, 4 drivers coupling in the mid-bass/bass region adds a potential 3db gain for the same amount of watts vs a traditional blaster with 2 large woofers. The only reason the GF's sucked are the cheap paper cones of the early 80's.

"you are already running short of room and those HA1392 chips DO BLOW out, especially now that you've eliminated all the airflow inside the unit." --
-- Yes, the internal temps will go up by a few degress but the heatsinks are adequate & the circuits are well behaved in general. Also, putting 2-way x-overs will even out the load between the woofer & tweeter on the outer 2 amps, anyway which reduces paralell loads to the amp & draw less current than the previous tweeter/capacitor only garbage that was stock. Again, if I sense tha amps fading due to heat, I'll rig a fan from the 15v rail but, so far, everything is running perfect & nothing is getting too hot, even in 90 degree sunny days. I've done extended listening tests & it sounds clear 6 hours later & no fade.

"Also, if you study the amp design, you 'll see that they have capacitor coupled outputs. 1,000uf is a good amount but does filter at approx 40hz for 4-ohms and 80hz at 2-ohms. At 4-ohm load, and 1,000uf inline, the optimum low frequency response is 400hz and -3db at 40hz. " --
-- Well, I don't know aobut the wiring of the unit itself but it has plenty of BOTTOM END & I have dialed the 'Super-Woofer' controls back from the 12:00 center mark to 11:00 & the center-woofers almost reach their FULL EXCURSION & almost ZERO rattles. Again, you can see it in some of the vidoes of my GroundShake Rasta sessions. The unit sounds balanced, bassy & crisp. I really don't know what else to say but I LOVE the sound. It isn't Perfect but it's damn good D-CELL audio, no-matter what you listen to.

"As you know, with speakers, we are not talking resistance but rather, impedance which varies with frequency. Actual impedance could drop as low as 1+ ohm during actual usage." --
-- Yes, I agree that my subs do that in the 20-60Hz band & is actually drawing as much as 16w/ch. RMS @ 2-OHMS & 32w/ch RMS @ 1 OHM & providing great BASS too.

"Understand that while the crossover will help to distribute the low and high frequencies to the respective drivers, this crossover is AFTER the 1,000hz series capacitor. In case you are wondering, do not remove that capacitor to increase low frequency response as this amp chip requires it to protect the amp. A better suited amplifier for amplifying those really low lows is to replace the amps with one better designed for subwoofers. --
-- This is exactly the point I'm trying to make. Nothing in the blaster has changed except the 6 drivers, the LOCATION of the transformer & sound deadening materials to eliminate rattles & resonances from the electronics & casing. The 'Super-Woofer amps are dedicated BASS amps with a 6-db ACTIVE cross-over, you can see in the schematic. It's was made & EQ'd to reinforce the bottom octaves to 40Hz. I can hear the difference with good subs. The power is there @ 2-ohms.

"Now as far as the GF tweeters. I do believe that if the original speakers are unshrouded, they will sound better. The GF-777 is sorely lacking in that department. Shrouding the cone tweeters only exacerbates that deficiency. I know what you say, that you believe that the lens actually helps reinforce the highs. I disagree. Sure, some professional speaker systems do use horns but they have special drivers designed for horns. In the GF, only standard cone tweeters are used and like Reli said, real estate space in the front panel is sorely lacking after those 4 woofers and controls. If you are now experiencing improved highs, it is probably due to the crossover or more efficient drivers and not due to the lens/horn design." --
-- All I can tell you is horns, even the GF design, AMPLIFY sound waves because of PHYSICS tells you so. I've studied horn design & I can see the trade-off SHARP cooked up to boost the treble from the cone tweeter. Yes, a properly designed horn will be far superior to the plastic lens/cone tweeter but the horn DOES improve high frequency response & DAMPENS the mid-range response somewhat, if not perfectly. With the Infinity tweeters, I like the sound & it seems balanced to me & not lacking. You heard the system through a crappy mic but you get the idea if you watched any of those sound tests I posted. Those woofers are really moving hard.& the tweeters have good stereo seperation. The coverage is thin on the vertical axis but very broad on the horizontal axis. I think they did this on purpose so it sounds huge in a concrete courtyard. As you step back from the unit the sound carries much further because of the horns.


On almost any system, merely waving your hand in front of the tweeters cut the highs noticeably. Unlike lows, highs are highly directional and easily affected by shrouding/blocking. --- Yes, you are correct. Horns have a distinct dispersal pattern while domes & ribbins are more omni-directional. This is where design goals differ from person to person.

BTW, dome tweeters disperse better because the sound can radiate all around the dome. -- Yes, domes have a wide dispersal radius & horns are DIRECTIONAL. Of course, they are widely different. Domes wash a room with highs whiles horns carrry further & are louder, watt for watt. These are no different & this is where design asthetics differ.

Sticking them in a lens seems to be counterintuitive but as long as sound is better than stock, who cares. Some people like bass and some like highs. Me, I like the strong highs on unobstructed tweeter setups like the M90, M70, M9994, etc. The GF comes nowhere close to that. The shrouded tweeters undoubtedly share some blame for that. Most folks that have sub'd the woofers for coaxial ones with tweeters front/center have reported noticable improvement in the highs. If you think shrouded tweets sound better due to less mids, then that's fine for you. But mechanically blocking a range of frequency seems to be an afterthought for a bad design, does it now?" --
--You interpret that blocking of mids as a design flaw but I recognize their attempt to create a more efficient & balanced driver by boosting the high frequencies, using a horn & damping the midrange, via the palstic lens. It works well for a cheap solution & they do carry farther than traditional tweeters.

"No, I think in this particular case, the installation of the tweets in a standoff horn was implemented due to space constraints and for aesthetics, not for critically calculated sound improvements." --
-- the Entire cabinet is free from the clutter & if space was at a premium, why create a long horn that increases the driver size by ten-fold esily vs a straight tweeter mount. The horn is a hybrid type that does boost the energy from the dome & dampens the lower frequencies of the cone. It isn't a design that will win nobel prizes but it does the job effectively for a desired effect. To be a more efficient tweeter that carries farthur & sounds somewhat brighter than the naked cone tweeter.

Because if we believe the latter, then that would suggest that this is a finely calibrated machine and haphazard tampering would generally result in deteriorated performance. Unless you really believe that you somehow was so lucky to swap all of the drivers using the same mechanical layout and improved on this finely tuned machine without benefit of all the gear/equipment etc available to Sharp engineers of the time. ---
-- Mmm. They're not exactly building a toaster or an electric blanket. SHARP was making calculators in the 70's 7 80's so the engineering department isn't lacking anything. I updated the drviers with carefully selected pieces to fully utilize the limited but effective power available. I chose a sub-woofer, not for it's efficiency, but it's impedance, FS & sealed box parameters. I wanted a cone that would hit 40Hz in a tiny sealed box for the 'Super-Woofers' & a tight punchy woofer witha an Fs of around 60Hz for the mids/mid-bass. I changed no other aspect of the system. I used roadie experience, lots of fact finding trips to the library & years of studying Electro-Voice white papers on horns, woofers, vented cabs & minor electronics, including building basic 2-way crossovers in a pinch.

But hey, let's just forget all the data and specs and what not. You said you like the new sound better. In the end, it's your project and if you are happy with it, then that's the only thing that matters. --
--RIGHT!!! You can see the woofers hopping & the sound is pretty tight for D-CELL beats.....look ma, no rattles!!!. What's not to like? No matter how much abuse I throw at those cones, they won't die.

"Many GF owners have done nothing more than replace the outboard speakers with coaxial car door speakers and better center bass drivers, and have reported improvement. This without added crossovers, relocating the transformer, or dynomat. In other words, improvement without compromising the structural integrity and practicality of the machine." --
-- The results speak for themselves. I added no new amps or other circuitry, only 2-way corssovers for better seperation & a more balanced load to the amp. The center amps are NO joke sub amps, that are actively crossed before the AMP-out & they just need good skins & a damped sealed enclosure. The horns work good & do boost output vs a naked driver. That is an undeniable fact, due to physics & I can hear the clarity easily vs the raw deal.

Personally, I think for the ultimate blaster, you might want to consider going the route of something along the lines of what JVC Floyd does, without the constraints of working with the original installation. --
-- I don't want to do what someonme else did. YAWN!! I want to do what I want & hopefully it is unique & successful. I'm quite happy & know these cans POUND, POUND, POUND!!

Do not take this as a knock on your project. Those that knows me also knows I have the tact of a tree. Like I said above, all the above is "......I'm just saying.....". If you are happy, then that's all that matters. I for one have done things to boxes that others have shaken their head at. Good thing I'm not trying to make them happy, just trying to make myself happy.

-- What's not to like about it my mod. It looks good, sounds good & has PHAT_AZZZ BASS!!! from across the room or deck, which is friggin' hard to achieve in the mighty GF, oddly...

I suspect you may disagree with 90% of what I said. That's OK too. How boring this world would be if we all were like programmed ants.--
-- I agree & thank you kindly for forging the blunt edge of my ideas sir. It was a pleasure!!!

thumbsup:

 

[Superduper]

I won't bother to respond to anything subjective because such discussions get nowhere.

However, the following are things you can look up:

If you understand about capacitors and frequency, you will know that for audio, they act as filters when installed in series with the load, and rolls off the signal. It's not a hard cut off, so not all of it is filtered off. Typically, capacitors job with an AC signal is to filter off the low frequencies. Do the math and you will find that 1000uf will pass 40hz with a -3db attentuation (80hz @2ohm), and the optimimum low freqency response is 400hz @ 4ohms. This has nothing to do with anything you've done, or your speaker driver specs. It has to do with the amplifier design. If we do not attentuate the signal before the filtered roll off, you will find the frequency HIGHER. See specs below taken from Sharp's own published specifications in their service manual.

As for the amps, I do not know where you are getting your specs from but I can tell you that the MAX specs I quote come directly from the manufacturer of those amp chips. The HITACHI HA1392 puts out 4.3wpc @12v, and 6.8wpc@15v under 4 ohm loads. THAT IS AT 10% THD. You said you strongly disagree. All I can say is look it up and you will see -- it's all there in black and white. Also study the spec sheet as well as the chart and you will see that YES these amps are capable of .5%-1% THD but you will get that at much lower power output levels. In fact, TRY 1/2 wpc at .25%THD, max 1%. Now, if you evaluate the chart diagrams released by the manufacturer, you will find the following approximations:

(1) You will observe 1% THD as power output approaches 2.8wpc
(2) Cleanest power (2% or under) all comes at 3wpc or less. After that, it climbs exponentially.
(3) AS for power output, the rated 6.8wpc comes at 15v supply and freq 500hz up. Power output begins rolling off beginning at approx 300hz. At 100hz, power output drops to approx 5.6wpc. At 50hz, power output drops to 4wpc. At 40hz power drops to 3.2wpc. At 30hz, you are only getting 2.4wpc and at 20h, you are seeing a paltry 1.4wpc. You might be saying NO WAY! But the number do not lie. In practice, the impedance of the speaker system will drop at lower freq operation allowing the power output to sort of keep up, but this comes at an expense.... remember the distortion curve? Well, more power = significantly higher distortion.

BUT forget the manufacturer's chip data which are rated based on Hitachi's test circuits. Let's take the information DIRECTLY from the Sharp GF-777z Service Manual, presumably applicable to the Sharp design:
Output power (GF-777):
Full range: 4 watts per channel minimum RMS at 4 ohms from 100hz to 20khz, no more than 10% THD.
Super Woofer: 3 watts per channel minimum RMS at 4-ohms from 70HZ to 500HZ, no more than 10% THD

Then you speak of the bass amps, that they are dedicated. This is true, that the bass speakers have their own dedicated amps. But you also mention it includes a 6db ACTIVE cross-over. WHERE did you get this from? Are you just making up a number or did you do some calculations based on the interpretation of the design? Normal active crossovers are designed using opamps and works with low level signals. This one does no such thing. The bass amps obtains their input signal from the full range amp outputs, then attentuating the signal to line levels and basically shunts the highs to ground. Anyone can see that is a poor design choice. First off, you are taking amplified signals and attentuating it to be amplified again. We have already established that at high power output levels, distortion figures at the output approaches 10% THD. We take that distorted signal, attenuate it and RE-AMPLIFY IT!. It is what is is, but again, where did you get the 6db stat from? Also, you claim it was made and EQ'd to reinforce the bottom octaves to 40Hz. Excuse me but even Sharps own specifications quote a minimum freq of 70Hz. Again, keep in mind that the capacitor coupled outputs of these amps filters off the low Frequencies so suggesting that this setup was EQ's to reinforce down to 40Hz simply is wrong. Do any 40hz signals pass? Possibly a little. But they would be rolled off to the extent that they certainly would not be considered anywhere near "optimized" for such low frequencies.

So before you give more figures, please do back them up with where you got that information from.

Specs like those above are pretty typical for boomboxes. In hi-fi systems, only the portion of the power output curve that falls under .25% THD will be quoted. The amps are generally capable of much higher output but anything more than .25% is laughable which is why hi-fi amps are rated at the lower range of the curve. Boombox manufacturers figure that hi-fi audio is not of paramount importance. Rather 2wpc would sound rather puny which is why they rate them higher up the curve, to 10% THD. In fact, most all boombox manufacturers rate their products at the 10% THD level, which is horrendous and yes, you CAN hear that distortion and more when you max out the dial.

Now, as for heat -- you can go ahead and operate it in that manner if you like. Successful 6-8 hour bursts do not mean that it's going to be reliable long term. Your boombox is 30 years old. It got there by having sufficient ventilation. Not only for the amps, but also for the appurtenant components. The dust pattern on the back of the ventilation slats are proof that convection activity occurs which would not be the case if convection did not occur. With higher temp operating conditions, electrolytic capacitor life will also be shortened dramatically. And I don't mean 6 hours, or even 6 days. I'm talking years. And the amp life will be shortened too. You should know that those chips are no longer available and originals are very hard to find. Sometimes you see supposed NOS chips for sale on eBay or NTE equivalents. I can tell you from experience that many are counterfeit chips that will not hold up or work at all. The C100 uses these exact same chips in a novel BTL configuration. I have personally witnessed supposed replacement chips literally fry upon application of power. Either they were counterfeit or they aren't up to the specs of the original products. If you don't believe IC chips can be fake or counterfeit, just google counterfeit IC and educate yourself. I have not been able to successfully restore a C100 amp using replacement chips. Only original chips pulled from parted out C100's worked.

 

[Cpl-Chronic]

I won't bother to respond to anything subjective because such discussions get nowhere.

However, the following are things you can look up:

"If you understand about capacitors and frequency, you will know that for audio, they act as filters when installed in series with the load, and rolls off the signal. It's not a hard cut off, so not all of it is filtered off. Typically, capacitors job with an AC signal is to filter off the low frequencies. Do the math and you will find that 1000uf will pass 40hz with a -3db attentuation (80hz @2ohm), and the optimimum low freqency response is 400hz @ 4ohms. This has nothing to do with anything you've done, or your speaker driver specs. It has to do with the amplifier design. If we do not attentuate the signal before the filtered roll off, you will find the frequency HIGHER. See specs below taken from Sharp's own published specifications in their service manual".

--
-- I understand your point but -3db at 40Hz is quite usable & that is why most woofers have a quoted -3db point in usable frequency response. Here is a video of a 20Hz test tone applied to the line-in of the gf. Although the framerate & quality of the video is low you can still see how much the woofers are moving at that frequency without the distortion of hard clipping. Those amps are putting out some serious power & not just 4 or 7 watts at that frequency.
20Hz test tone. Super-woofer controls are FLAT!!(0 boost/cut) Volume set to '3'

I think it's safe to say your assertion that nothing below 70Hz is usable or reproduced, is flat out wrong & you can see the much stronger ouptput of the super-woofers vs the normal outer woofers, even tho the controls are at center or 'FLAT' position.

"As for the amps, I do not know where you are getting your specs from but I can tell you that the MAX specs I quote come directly from the manufacturer of those amp chips. The HITACHI HA1392 puts out 4.3wpc @12v, and 6.8wpc@15v under 4 ohm loads. THAT IS AT 10% THD. You said you strongly disagree. All I can say is look it up and you will see -- it's all there in black and white. Also study the spec sheet as well as the chart and you will see that YES these amps are capable of .5%-1% THD but you will get that at much lower power output levels. In fact, TRY 1/2 wpc at .25%THD, max 1%. Now, if you evaluate the chart diagrams released by the manufacturer, you will find the following approximations:"
(1) You will observe 1% THD as power output approaches 2.8wpc
(2) Cleanest power (2% or under) all comes at 3wpc or less. After that, it climbs exponentially.
(3) AS for power output, the rated 6.8wpc comes at 15v supply and freq 500hz up. Power output begins rolling off beginning at approx 300hz. At 100hz, power output drops to approx 5.6wpc. At 50hz, power output drops to 4wpc. At 40hz power drops to 3.2wpc. At 30hz, you are only getting 2.4wpc and at 20h, you are seeing a paltry 1.4wpc. You might be saying NO WAY! But the number do not lie. In practice, the impedance of the speaker system will drop at lower freq operation allowing the power output to sort of keep up, but this comes at an expense.... remember the distortion curve? Well, more power = significantly higher distortion.

--
--From diigging around on this forum & other sources I get a couple of different spec:
4x8w/ch RMS here: http://www.stereo80s.com/bbx.cfm?id=663
4x7w/ch. RMS here: viewtopic.php?f=2&t=3578&st=0&sk=t&sd=a&start=20
The 7w/ch rating is progbably the right one judging form your statement about the amps putting out 6.8w RMS @ 15v which is what the GF runs at.

It doesn't say at what THD the spec is rated at so I assumed 1% THD which, if I'm not mistaken is a standard measuring point for amplifier circuits. The chips themselves may have a lower rating, I don't know but I don't listen to noise for the sake of loudness & as you can see from my videos, the sound is pretty good with no hard clipping if any at all. Yes, the ear is more tolerant of THD & more sensiitve to transient distortion & intermodulation distortion so it is possible that I may be driving these cans to higher THD levels. I do not know nor pretend to. My ears are the only judge, unfortunately.

BUT forget the manufacturer's chip data which are rated based on Hitachi's test circuits. Let's take the information DIRECTLY from the Sharp GF-777z Service Manual, presumably applicable to the Sharp design:
Output power (GF-777):
Full range: 4 watts per channel minimum RMS at 4 ohms from 100hz to 20khz, no more than 10% THD.
Super Woofer: 3 watts per channel minimum RMS at 4-ohms from 70HZ to 500HZ, no more than 10% THD"

--
-- In your words above, the specs state: 'MIN. 4w/ch' & 'MIN. 3w/ch' @ 4-ohms but the only spec I see in the English Service manual for the GF-777Z, not H, etc. is 'PMPO 90w, AC operation with 4 amplifiers'...which neitehr refutes or proves your statement. Again, no THD numbers at all....If you could send me the PDF you are looking at to E-mail address has been removed, it would be great.

"Then you speak of the bass amps, that they are dedicated. This is true, that the bass speakers have their own dedicated amps. But you also mention it includes a 6db ACTIVE cross-over. WHERE did you get this from? Are you just making up a number or did you do some calculations based on the interpretation of the design?"Normal active crossovers are designed using op-amps and works with low level signals. This one does no such thing. The bass amps obtains their input signal from the full range amp outputs, then attentuating the signal to line levels and basically shunts the highs to ground. Anyone can see that is a poor design choice. First off, you are taking amplified signals and attentuating it to be amplified again. have already established that at high power output levels, distortion figures at the output approaches 10% THD. We take that distorted signal, attenuate it and RE-AMPLIFY IT!. It is what is is, but again, where did you get the 6db stat from? Also, you claim it was made and EQ'd to reinforce the bottom octaves to 40Hz. Excuse me but even Sharps own specifications quote a minimum freq of 70Hz. Again, keep in mind that the capacitor coupled outputs of these amps filters off the low Frequencies so suggesting that this setup was EQ's to reinforce down to 40Hz simply is wrong. Do any 40hz signals pass? Possibly a little. But they would be rolled off to the extent that they certainly would not be considered anywhere near "optimized" for such low frequencies.

So before you give more figures, please do back them up with where you got that information from.

--

-- This is a cut shot of the Super-Woofer outputs from the schematci for the GF-777Z:

If you look at the output, the signals enter the super-woofers pots, VR801 & VR 802, then a filter of some sort is applied before the power amp chip IC802. You can see the 'LPF 6db/oct.' spec for the roll-off. To me, if it is filtered before the amp, I assume it is ACTIVE, maybe not but for sure its 6db/oct. as stated in the schematic & not a passive coil applied to the speakers, after the signal is amplified. If I read the schematic correctly, the pre-amp stage is split & fed to both AMP IC's & the headphone jack, before amplification for the full-range & super woofer sections. If you look closely, you'll see the pre-amp signal is tapped on the pre-amp side of the IC & fed to the headphones jack & then connected over to the 'Super-Woofer' pots, filtered at pre-amp levels & then fed into the amps for the 'Super-Woofers'. This makes sense & is more realistic than amplifying the signal, attenuating it & then feeding it to another PRE-amp/amp chip or the headphone jack. Otherwise, if what you are asserting is true the headphones are getting the full wattage of the amps, which makes no sense at all & the first pair of headphones you use will be grossly over-driven & blow the delicate diaphrams of the phones unless they again use resistors to attenuate the wattage to milliwatts. No engineer in his/her right mind would waste battery power to amplify & then attenute a signal to drive simple headphones or pre-amp another amp stage, when you can use the preamp stage to drive the headphones or second amp & conserve all that power. In reality the preamp stage is used to amplify the headphones & pigggy-backed over to the Superp-woofer amps after filtering the highs out at 6db/oct.. Look at the schematic below carefully & see for yourself. At no point is the high freq. signal shunted which would cause a short circuit above a certain point & the amp would hard clip.

Specs like those above are pretty typical for boomboxes. In hi-fi systems, only the portion of the power output curve that falls under .25% THD will be quoted. The amps are generally capable of much higher output but anything more than .25% is laughable which is why hi-fi amps are rated at the lower range of the curve. Boombox manufacturers figure that hi-fi audio is not of paramount importance. Rather 2wpc would sound rather puny which is why they rate them higher up the curve, to 10% THD. In fact, most all boombox manufacturers rate their products at the 10% THD level, which is horrendous and yes, you CAN hear that distortion and more when you max out the dial.

--
--I did not know this & trust you are correct. All specs I found were without THD ratings so I suspect you are right but I do not overdrive my equipment to gross distortion levels & the sound is quite good but not true HI-FI. It's a ghetto-blsater, not a BOSE system & I'm quite happy with the results as I trust most would. In fact, I have gotten many compliments by people who listened to it in person & as a roadie, I have some real-world experience with a wide range of audio equipment.

Now, as for heat -- you can go ahead and operate it in that manner if you like. Successful 6-8 hour bursts do not mean that it's going to be reliable long term. Your boombox is 30 years old. It got there by having sufficient ventilation. Not only for the amps, but also for the appurtenant components. The dust pattern on the back of the ventilation slats are proof that convection activity occurs which would not be the case if convection did not occur. With higher temp operating conditions, electrolytic capacitor life will also be shortened dramatically. And I don't mean 6 hours, or even 6 days. I'm talking years. And the amp life will be shortened too. You should know that those chips are no longer available and originals are very hard to find. Sometimes you see supposed NOS chips for sale on eBay or NTE equivalents. I can tell you from experience that many are counterfeit chips that will not hold up or work at all. The C100 uses these exact same chips in a novel BTL configuration. I have personally witnessed supposed replacement chips literally fry upon application of power. Either they were counterfeit or they aren't up to the specs of the original products. If you don't believe IC chips can be fake or counterfeit, just google counterfeit IC and educate yourself. I have not been able to successfully restore a C100 amp using replacement chips. Only original chips pulled from parted out C100's worked.

--
-- Again, I defer to your knowledge on this subject but I do know that if amp transistors are having trouble dissipation heat, they fade in power output & start to lose treble over an extended listening session. So far, the GF isn't behaving in this fashion & shows no signs of fatigue at all. I strongly beleive these amps will last without problems & are rugged as hell or spending a 1000 bucks for 1 would be a waste of money & cause alot of pissed off customers to avoid SHARP as a brand in general. So I disagree with you & think it will stand the test of time. If down the road, you prove to be right. I will mention it & apologize for being wrong. Only time will tell. So far so good.

Althoug I disagree with your assertions for the most part, it has been a very interesting discussion & hopefully we both learned more from it. Your challenge has forced me to look into the matter more & so far, I stand by my original assertions, for the most part although I have to agree with you that the amp ratings are probably 7w/ch @ 4-ohms, 15v input & 10% THD.

 

[Cpl-Chronic]

Again, in case you missed it in the last post i edited to include the video:

Here is a video of a 20Hz test tone applied to the line-in of the gf. Although the framerate & quality of the video is low you can still see how much the woofers are moving at that frequency without the distortion of hard clipping. Those amps are putting out some serious power for a beatbox on D-Cells & not just 4 or 7 watts RMS. I susspect at 20Hz the woofers I loaded are probably dipping down to 1-ohm.
20Hz test tone. Super-woofer controls are FLAT!!(0 boost/cut) Volume set to '3'