Replacing midwoofers in my newly acquired GF-767

[MinerAC4]

I'm new to these forums because I purchased this box from a local record store on the 27th. When I brought it home, only one of the midwoofers was functioning, and upon taking it apart, it was clear that the coil had an internal break, as putting a multimeter onto it showed zero continuity. I bought a cheap generic speaker replacement on eBay as an original was gonna cost me way too much. The next day the other midwoofer decided to conk out too, yelding the same no continuity as the other one. I was wondering if these speakers should be fine replacements and if I'm doing anything dumb here. I have always wanted one of these big chonkers, so I'm excited. It cost me 550$ for the thing, so I'm pretty sure I got a pretty decent deal on it. I'd also like to know if anyone can recommend some cheap and easy to drop in tweeter upgrades. I know the GF-777 came with proper cone tweeters, but they had plastic caps and a capacitor on them, and the only ones I can find available are quite expensive. So I was wondering if anyone had any cheaper alternatives that would either come with everything I need to install them, or also the supplies I need to install them.View attachment 59934View attachment 59932

 

[goodman]

to forum and congrats for this nice SHARP.
I think that this speaker you have chosen is suitable.
For high-frequency speakers, you can use some kind of car kit with suitable filters.

 

[Superduper]

It seems like the factory speakers should not be burning out that easily. The fact that both drivers that failed are tethered to the same amp chip may be a clue (the outside speakers are powered by a different amp). You may want to test the outputs going to the speakers for DC. Speakers work by reproducing AC signals, never DC. If you are measuring DC voltage at the speakers, it’s time to consider replacing that amp chip. Otherwise, you’re just going to continue frying speakers.

 

[Eddy]

Very sweet lookin' 767

 

[MinerAC4]

It seems like the factory speakers should not be burning out that easily. The fact that both drivers that failed are tethered to the same amp chip may be a clue (the outside speakers are powered by a different amp). You may want to test the outputs going to the speakers for DC. Speakers work by reproducing AC signals, never DC. If you are measuring DC voltage at the speakers, it’s time to consider replacing that amp chip. Otherwise, you’re just going to continue frying speakers.

Would I just attach the multimeter on the midwoofer terminals and see what it shows? And if that's the case, how would I go about actually replacing it. I've never done such a thing and I'm not even exactly sure where I can find the part for a non exorbitant price. I'm working with a really small budget here.

 

[Boombox99]

wow looks really nice

 

[Superduper]

Would I just attach the multimeter on the midwoofer terminals and see what it shows? And if that's the case, how would I go about actually replacing it. I've never done such a thing and I'm not even exactly sure where I can find the part for a non exorbitant price. I'm working with a really small budget here.

Yes, just connect a multimeter, set to DC scale, and measure with boombox ON. You may read some voltage if you set meter to AC scale and with music playing -- that's normal, although I doubt a digital multimeter can capture anything because the signal fluctuations is probably too fast for most meters to capture but will be apparent on analog meters as dancing needle. But on the DC scale, the reading will probably be steady you should measure as close to ZERO as possible. If you don't read anything on the volt scale, recheck with the millivolt scale, if your meter has that. Anything over ~50mV (0.050) is concerning. Anything approaching the volt scale can cause speaker damage, especially on smaller speakers such as these. With only a 5W rating, these speakers will have fairly fine voice coil windings.

As for the amp chip itself, it's one of the easier ones to work on. It's situated on the amp board with the small jacks which is the vertical board between the speakers. Many boombox amps are much harder to get to. I can't speak to your budget, it is what it is but you can't really operate it and expect any speakers to last if you have DC at the outputs so it will need to be done. On the GF-777, the amp chip is the Hitachi HA1392 if I recall correctly. These chips aren't too difficult to find but you do need to be careful about getting counterfeit ones, which are probably all over eBay and Amazon or other chinese sellers. Go with a company that has a USA online presence and you are probably OK.

 

[MinerAC4]

Yes, just connect a multimeter, set to DC scale, and measure with boombox ON. You may read some voltage if you set meter to AC scale and with music playing -- that's normal, although I doubt a digital multimeter can capture anything because the signal fluctuations is probably too fast for most meters to capture but will be apparent on analog meters as dancing needle. But on the DC scale, the reading will probably be steady you should measure as close to ZERO as possible. If you don't read anything on the volt scale, recheck with the millivolt scale, if your meter has that. Anything over ~50mV (0.050) is concerning. Anything approaching the volt scale can cause speaker damage, especially on smaller speakers such as these. With only a 5W rating, these speakers will have fairly fine voice coil windings.

As for the amp chip itself, it's one of the easier ones to work on. It's situated on the amp board with the small jacks which is the vertical board between the speakers. Many boombox amps are much harder to get to. I can't speak to your budget, it is what it is but you can't really operate it and expect any speakers to last if you have DC at the outputs so it will need to be done. On the GF-777, the amp chip is the Hitachi HA1392 if I recall correctly. These chips aren't too difficult to find but you do need to be careful about getting counterfeit ones, which are probably all over eBay and Amazon or other chinese sellers. Go with a company that has a USA online presence and you are probably OK.

So I did actually check the reading today, and it was reading 0.014 on both midwoofer terminals. I taped in a pair of Ford car speakers today while I wait on the new proper replacements to come in. I found they were 6.5in and 4 ohms, and they fit well enough and sound decent. Temporary replacement obviously, because they're taped in with cardboard standoffs (lol). So I should be good when the new ones from eBay come in.

 

[Superduper]

That’s good news.

 

[MinerAC4]

That’s good news.

Yep, I've been using it all night to provide music for my family's new years activities.

 

[MinerAC4]

That’s good news.

Very happy in the new year!

 

[Superduper]

Very happy in the new year!
View attachment 59940

Love to see young ones enjoying these boomers like they’re supposed to be used.

 

[MinerAC4]

Love to see young ones enjoying these boomers like they’re supposed to be used.

Yeah, I gotta get me four more rechargable D batteries so I can carry it. Though idk if I'll be able to even pick it up with all the batteries , it's quite heavy as it is. I already need two hands to carry it. My old Sony CFS-1055 was so much lighter in comparison. I used that guy all the time. I don't know if I'd truly call it a "boombox" but it doesn't sound terrible and I still love it.

 

[MinerAC4]

That’s good news.

Btw, what is the rating on the tweeters? Like ohms wise. I know the GF-777 had proper cone tweeters. I was curious if I could find some easy to install and cheap tweeters that would sound good with my new midwoofers. Edit: I did find out they are in fact also 4 ohms, but there is a capacitor on the tweeters in the 777, I was wondering if there was like a cheap set of tweeters I could glue or screw in place or something. Capacitors would also be nice to have as a drop in upgrade.

 

[Superduper]

If you don’t run cone tweeters in series with a bipolar or nonpolar capacitor, you’ll probably damage them. Tweeters are designed to only reproduce certain frequencies, which varies depending on the tweeter chosen. The capacitors will act like high pass filter blocking or severely attenuating the damaging low frequencies. Therefore if you decide to add regular tweeters (non piezo), capacitors are mandatory.

 

[Reli]

I bought a cheap generic speaker replacement on eBay

With a rating of only 5 watts, (nominal? peak?), I doubt those speakers will provide the bass you're wanting. Especially given their very low price. You might want to browse Parts Express, they are one of the biggest sources of speakers. You can search by size and ohms rating. A few people here have also had luck using Alpine speakers, shown here --

GF-777 Alpine upgrade

Inspired by Bklyn sound’s 767 speaker upgrade https://boomboxery.com/forum/threads/767-with-new-speakers.19970/post-243957 Thought I’d give it a go, as I’d picked up a 777 with trashed speakers center woofers warped with a missing dust cap, Both outer drivers blown, well one was I blew the...

www.boomboxery.com

 

[MinerAC4]

If you don’t run cone tweeters in series with a bipolar or nonpolar capacitor, you’ll probably damage them. Tweeters are designed to only reproduce certain frequencies, which varies depending on the tweeter chosen. The capacitors will act like high pass filter blocking or severely attenuating the damaging low frequencies. Therefore if you decide to add regular tweeters (non piezo), capacitors are mandatory.

Oh yeah, I knew about that. That's why I was asking what to look for. I had read about how capacitors are acting as a very crude crossover. Since the main drivers have their own separate amps to act as a crossover. The tweeters in this machine pretty much just piggyback off the midwoofers. Since there isn't any special circuitry for it, the capacitor allows this to work without requiring extra boards and stuff. The pietzos are just super small and don't move very much, so they don't really need capacitors to produce the sounds they're supposed to make. They also don't really produce all that much sound, so that's why I was looking to upgrade them. It's kinda weird how lazily they're installed. They literally just have a foam sticker that's attaching them to the horns where the original comes would go.

 

[MinerAC4]

With a rating of only 5 watts, (nominal? peak?), I doubt those speakers will provide the bass you're wanting. Especially given their very low price. You might want to browse Parts Express, they are one of the biggest sources of speakers. You can search by size and ohms rating. A few people here have also had luck using Alpine speakers, shown here --

GF-777 Alpine upgrade

Inspired by Bklyn sound’s 767 speaker upgrade https://boomboxery.com/forum/threads/767-with-new-speakers.19970/post-243957 Thought I’d give it a go, as I’d picked up a 777 with trashed speakers center woofers warped with a missing dust cap, Both outer drivers blown, well one was I blew the...

www.boomboxery.com

Oh I saw the alpines, I'm currently just using these as a current replacement. I actually am considering doing alpines once I get a job again and can put some more money into it. They look pretty sweet and I'm sure would sound really good too. Especially considering that covers the tweeter situation too. I'm also not using these to replace the woofers. I'm talking about the outer speakers that do the midrange and directional stuff. The woofers are very thankfully still in good shape audio wise.

 

[Superduper]

The pietzos are just super small and don't move very much, so they don't really need capacitors to produce the sounds they're supposed to make. They also don't really produce all that much sound, so that's why I was looking to upgrade them.

The type of Piezo tweeters common in boomboxes don't require capacitors but not because of how much they move. Rather it's an entirely different technology making use of crystals that vibrate when subjected to electric current whereas normal cone drivers use electromagnets instead to make the cone move. Piezos also have their own inherent capacitance as part of their nature therefore, they don't require an external capacitor as that technology naturally limits low frequency due to high impedance at those frequencies.

 

[MinerAC4]

The type of Piezo tweeters common in boomboxes don't require capacitors but not because of how much they move. Rather it's an entirely different technology making use of crystals that vibrate when subjected to electric current whereas normal cone drivers use electromagnets instead to make the cone move. Piezos also have their own inherent capacitance as part of their nature therefore, they don't require an external capacitor as that technology naturally limits low frequency due to high impedance at those frequencies.

Ah, I learned something now. Very interesting stuff. Still, I would like to find some cheap drop in replacements that would sound decent. I saw a post where someone actually found a box with aftermarket tweeters glued over the horns. Which I found pretty interesting.