Magnavox D8443 Power Blaster Upgrade

[Lasonic TRC-920]

Since you are adding a box for the subwoofer, have you thought of horn loading or manifolding the inner box? Horn loading might be more difficult....

If you manifold the drivers you could use 2 drivers staggered back to back firing in opposite directions - the box could actually be smaller than you would imagine and you wouldn't need to port it.

Similar to this picture from pro Electrovoice speakers... OK this has gone off the rails lol "Go big or go home" is what i always say.

Oh man, that's Way over my head lol

The experience I have is building boxes to the manufacturers specs in regards to volume and some porting. I think I can figure that out. But complex builds like that would be over my head

 

[Lasonic TRC-920]

At this early stage of development, I wouldn't bother with a complex crossover until you've confirmed your speaker selection, cabinet details etc. Just cap the tweeter and leave the mid and sub full range just to get things rolling. Test it, tweek it.

All the theory in the world can be quickly confirmed or denied the second you fire it up!

The amp has a sub woofer crossover, so I'm good there. Do you think the 4's should just be full range?

 

[jimmyjimmy19702010]

I would leave the mids full range initially and see how they sound. Of more concern is making that holey case airtight. I'd also be more inclined to initially try a sealed enclosure that will require less air volume to push bass. You might get lucky and not need to mess with a case spacer! - no guarantees though

 

[Lasonic TRC-920]

I would leave the mids full range initially and see how they sound. Of more concern is making that holey case airtight. I'd also be more inclined to initially try a sealed enclosure that will require less air volume to push bass. You might get lucky and not need to mess with a case spacer! - no guarantees though

I'm right there with you on the case. This weekend I will be out looking for materials to use. I know it sounds crazy but IF I could make an enclosure that houses the 8, is fully sealed and the rear case simply slips over, that would be sweet. Again, I have no idea if it is possible. But then I could build the 8's cabinet, test it, get it tuned and then ad it to the radio case. Or along those lines.

 

[floyd]

I would go with free air speakers they will work the best and what you have nothing else will work better they require more power but that's the only downfall

 

[Lasonic TRC-920]

I would go with free air speakers they will work the best and what you have nothing else will work better they require more power but that's the only downfall

Thanks Floyd, I'll keep my eyes open, see what I can find

 

[kennerithmcguire]

These tweeters might work for you and the price is right... http://www.ebay.com/itm/National-Panasonic-RS-4360DFT-Boombox-Ghettoblaster-Replacement-Tweeters-NP11-/221456315414?hash=item338fd33416:g:ck0AAOxy4t1SkeYJ

 

[Lasonic TRC-920]

These tweeters might work for you and the price is right... http://www.ebay.com/itm/National-Panasonic-RS-4360DFT-Boombox-Ghettoblaster-Replacement-Tweeters-NP11-/221456315414?hash=item338fd33416:g:ck0AAOxy4t1SkeYJ

I wish it gave the dimensions...

OK, new questions...

The tweeters in this ad are 6 ohm. Many of the tweeters I have seen are 6-8 or other....but very few are 4. How does this play in my 8 ohm sub, 4 ohm mids, ? ohm tweeters math equation?

 

[jimmyjimmy19702010]

I don't know the specs of your amp or whether the sub channel is bridged. If not then I would try and get a 4 ohm sub so it will pull the max power out of that amp. BTW, the max watt output quoted by amp manufacturers is almost always measured when connected to 4 ohm speakers. 8 ohm speakers will pull approx half the power than that of a 4 ohm speaker.

Most China amps can handle a 4 ohm load.
Try and get a tweeter that has the same ohm rating as your sub and mid range speakers. Those tweeters the OP linked to look pretty big.

I would be leaning toward car audio speakers where 4 ohm is the norm.

You want to see the perfect 8 inch speaker for this project?:
View attachment 26257
https://www.ebay.com.au/ulk/itm/271380694525
4 ohm, 94 dB sensitivity!! - these things are designed to play as loud as possible from a 12V amp. Not cheap or lightweight I admit! If you can find a cheaper speaker with similar specs, you'll have a genuinely bassy box.

 

[Lasonic TRC-920]

I don't know the specs of your amp or whether the sub channel is bridged. If not then I would try and get a 4 ohm sub so it will pull the max power out of that amp. BTW, the max watt output quoted by amp manufacturers is almost always measured when connected to 4 ohm speakers. 8 ohm speakers will pull approx half the power than that of a 4 ohm speaker.

Most China amps can handle a 4 ohm load.
Try and get a tweeter that has the same ohm rating as your sub and mid range speakers. Those tweeters the OP linked to look pretty big.

I would be leaning toward car audio speakers where 4 ohm is the norm.

You want to see the perfect 8 inch speaker for this project?:

image.jpeg

4 ohm, 94 dB sensitivity!! - these things are designed to play as loud as possible from a 12V amp. Not cheap I admit but no speaker with less than 94dB sensitivity will sound as strong!!
https://www.ebay.com.au/ulk/itm/271380694525
I plan on having a pair of these in my DIY V5.0 box!

DAMN, that speaker looks sick....(looks heavy too )

OK, so the hypothetical plan is, one of those amps, mono'd 30w to 8" 4 ohm sub, second amp is stereo 15w per to 4" 4 ohm full range, tweeter ?" 4 ohm and amp's are happy?
Fricken Math!

I'm hoping to pick up the sub enclosure materials this weekend.

 

[jimmyjimmy19702010]

DAMN, that speaker looks sick....(looks heavy too )

OK, so the hypothetical plan is, one of those amps, mono'd 30w to 8" 4 ohm sub, second amp is stereo 15w per to 4" 4 ohm full range, tweeter ?" 4 ohm and amp's are happy?
Fricken Math!

I'm hoping to pick up the sub enclosure materials this weekend.

Wow, that sounds like a great combo! Should rip it up when and it's done!

 

[Lasonic TRC-920]

Well, you and I are going to figure this out! There is a complex build coming.

IF it can be done, IF there is really enough volume in the cabinet to even BACK UP the BOLD statement the face of this radio makes, we will find it!

 

[jimmyjimmy19702010]

Getting back to reality, this is probably the 8 inch sub I'd go for - cheaper, lighter and still has 92dB sensitivity - around $50 per pair: View attachment 26258

Stick a big chrome cap in the centre and you're rockin! https://www.ebay.com.au/ulk/itm/391091783753

 

[Superduper]

OK, so the hypothetical plan is, one of those amps, mono'd 30w to 8" 4 ohm sub, second amp is stereo 15w per to 4" 4 ohm full range, tweeter ?" 4 ohm and amp's are happy?

Hmm. Partsexpress documentation shows that the amp is rated with 8-ohm speakers. Using 4-ohm speakers will get you higher output at the HF section. Not sure if you can do 4-ohm on the mono'd portion or not. The reason is that I'm pretty sure the mono'd portion is BTL configured which is how it came up with the 30w rating on the 3rd channel. When operated in BTL fashion, the impedance appears to the amps as if it were halved (for example, a 4 ohm speaker will seem like 2-ohm speakers to the amp when operated in BTL config). This is the reason most BTL amps use 8-ohm speakers while SE amps use 4-ohm speakers. For example, the M70 uses 8-ohm speakers with BTL amps. Since you could get more power/volume out of 4-ohm speakers, for sure JVC would've done that since it's such an easy way to double the power without adding any cost. But then they'd probably end up with tons of blown amps too if they did that. Maybe if you could find a sub with dual 4-ohm voice coils, you can series the coils to get an 8-ohm load.

Also, one thing to consider is that this amp requires a minimum of 10volts. In fact one of the reviews stated that the amp starts to distort at 1/3 volume when used with a 12v 5a supply. 5-amps is plenty of current so I'm not sure what type of supply or rating the PS is that was used, but if the supply rail sagged below 12v even with a 5-amp supply at only 1/3 vol, then it's fair to say that with 8-D cells (is that what this boombox uses?), then there is not much supply rail headroom to listen at any listening level beyond moderate. This isn't my personal observation, just noting what the reviewer stated. So with 8-D cells, you are getting 12V with a full charge and no load. As soon as there is a significant load, the voltage will drop. The 1.5v cells only need to sag to 1.25v to get 10v overall. Not good. However, if this is a 15v box, then there should be enough cushion to have some listening fun. For awhile, anyhow. Lowering the stereo speaker impedance is fine and produces higher output (for a given input voltage) but make sure you bench test it with the speakers you plan to use with the real-world power you plan to use to ensure there is enough power to crank without distortion. Would hate to see you mate fancy $259/pair Pioneers in there and see them wiped out by distortion from an underpowered overdriven $10 amp.

 

[Okelly]

^^^What he said, weirdly enough, I understood everything Superduper is saying!^^^

Sent from my VS986 using Tapatalk

 

[jimmyjimmy19702010]

I wouldn't have thought Chris would be seriously intending to power this thing with 8 saggy D cells right?!

 

[Lasonic TRC-920]

Hmm. Partsexpress documentation shows that the amp is rated with 8-ohm speakers. Using 4-ohm speakers will get you higher output at the HF section. Not sure if you can do 4-ohm on the mono'd portion or not. The reason is that I'm pretty sure the mono'd portion is BTL configured which is how it came up with the 30w rating on the 3rd channel. When operated in BTL fashion, the impedance appears to the amps as if it were halved (for example, a 4 ohm speaker will seem like 2-ohm speakers to the amp when operated in BTL config). This is the reason most BTL amps use 8-ohm speakers while SE amps use 4-ohm speakers. For example, the M70 uses 8-ohm speakers with BTL amps. Since you could get more power/volume out of 4-ohm speakers, for sure JVC would've done that since it's such an easy way to double the power without adding any cost. But then they'd probably end up with tons of blown amps too if they did that. Maybe if you could find a sub with dual 4-ohm voice coils, you can series the coils to get an 8-ohm load.

Also, one thing to consider is that this amp requires a minimum of 10volts. In fact one of the reviews stated that the amp starts to distort at 1/3 volume when used with a 12v 5a supply. 5-amps is plenty of current so I'm not sure what type of supply or rating the PS is that was used, but if the supply rail sagged below 12v even with a 5-amp supply at only 1/3 vol, then it's fair to say that with 8-D cells (is that what this boombox uses?), then there is not much supply rail headroom to listen at any listening level beyond moderate. This isn't my personal observation, just noting what the reviewer stated. So with 8-D cells, you are getting 12V with a full charge and no load. As soon as there is a significant load, the voltage will drop. The 1.5v cells only need to sag to 1.25v to get 10v overall. Not good. However, if this is a 15v box, then there should be enough cushion to have some listening fun. For awhile, anyhow. Lowering the stereo speaker impedance is fine and produces higher output (for a given input voltage) but make sure you bench test it with the speakers you plan to use with the real-world power you plan to use to ensure there is enough power to crank without distortion. Would hate to see you mate fancy $259/pair Pioneers in there and see them wiped out by distortion from an underpowered overdriven $10 amp.

Thank you Norm for chiming in...

It's been in the back of my mind that the 8 cell compartment might need to be extended to add two more cells or replaced with something else for power.

This will be the first build, where I plan to build everything on the table before wading it up into the radio, like I normally do.

What are your power thoughts on running two of those little amps. 1 for the sub, 1 for the stereo - 4" mids, plus tweeters?

Too much on one power supply / 15v power pack?

 

[Superduper]

In post #41, Chris posted that "it has to run on batteries" and that he didn't want to duplicate the errors with the louderblaster project. However the more guys chime in on all these fanciful suggestions, the more I see it morphing into Louderblaster #2.

I wouldn't have thought Chris would be seriously intending to power this thing with 8 saggy D cells right?!

 

[Superduper]

What are your power thoughts on running two of those little amps. 1 for the sub, 1 for the stereo - 4" mids, plus tweeters?

Too much on one power supply / 15v power pack?

It's not clear what amp chip module is used since it's not identified, and sits below that heatsink. However, unless I'm mistaken, that chip would have 4 internal amps @ 15w each. 2 of the amps run the stereo speakers and the remaining 2 are bridged to arrive at 30wpc rating. As you cannot unbridge the amp, neither can you bridge the stereo channels without circuit changes, neither can you bridge an amp that is already bridged, so therefore it should be used in its present configuration as designed. If you add another amp, it would not make any improvement in your circumstances because all you'll end up with are idle unused internal amp channels.. In other words, using your proposal, your first amp will only use the 2 of the 4 channels to power the stereo speakers, the other 2(bridged) channels go along for the ride freeloading on the quiescent current. The second amp leaves the stereo channels idle, going along for the ride, again freeloading and sucking up quiescent current without providing any work while only the other 2amps(bridged) drives the subwoofer.... well I think you can see where I'm going and why this won't make things any better in any regards except perhaps allow the chip to run cooler if heating up is a concern.

 

[Lasonic TRC-920]

It's not clear what amp chip module is used since it's not identified, and sits below that heatsink. However, unless I'm mistaken, that chip would have 4 internal amps @ 15w each. 2 of the amps run the stereo speakers and the remaining 2 are bridged to arrive at 30wpc rating. As you cannot unbridge the amp, neither can you bridge the stereo channels without circuit changes, neither can you bridge an amp that is already bridged, so therefore it should be used in its present configuration as designed. If you add another amp, it would not make any improvement in your circumstances because all you'll end up with are idle unused internal amp channels.. In other words, using your proposal, your first amp will only use the 2 of the 4 channels to power the stereo speakers, the other 2(bridged) channels go along for the ride freeloading on the quiescent current. The second amp leaves the stereo channels idle, going along for the ride, again freeloading and sucking up quiescent current without providing any work while only the other 2amps(bridged) drives the subwoofer.... well I think you can see where I'm going and why this won't make things any better in any regards except perhaps allow the chip to run cooler if heating up is a concern.

OK, makes total sense. Tomorrow I will lay it all out on the table and see if I can get a sub signal and stereo signal out of this am and see what it sounds like. I have that tiny Tang Band sub (shown in the video above) and I can wire up some test speakers. I can then power it off of a 10 D cell set up and see where it all goes.