I've bought a few small amp boards off eBay in the past, and usually has a range like my TPA3116 amp I bought for an arcade project that says 8-25v. I used a 19v laptop power supply because plenty of volume, had a few kicking around, and low enough not to push the amp and pop caps.

I have an old Synsonics Terminator guitar. '80s guitar, built in 3" speaker, built in amp (maybe distortion) with headphone jack as well. Few parts missing, rusted, etc... so I've never had the chance to try it out. Full rebuild/restore project. No one would ever restore/improve one of these, except me because it's what I do for fun.

It takes 2 x 9v batteries, I think parallel. I'd like to grab something like a 12v lithium pack and maybe a buck converter, a USB recharge chip and 3D Print a new battery box for it so it can be recharged with a cell charger.

Also upgrade the speaker, looks like a Sharp 3" 6w 8ohm, could be .6w, or 1.6w... the stamp is pretty distorted.

Anyways, if the amp can handle more than 12v, with a bit of overhead (no blowing caps), then no need for a buck converter, maybe get more volume.

Here's a photo of the board... any way of knowing? Use the buck converter and play it safe?

(assuming running 9v, will have to test later, maybe it's 18v).

 

Can you read the alphanumeric code on the side of the long black IC?

 

A single-ended amplifier powered from 12V produces about 1.5W into 8 ohms when clipping distortion begins. It heats with about 1.3W so it might need a small heatsink. Edit.

 

Indeed!! That black SIP is the power amplifier, in fact it is the only active component on the PCB. With the part number you should be able to find the specifications. Do not exceed the with the supply the voltage on those four polarized capacitors or the max voltage for the amp, seen in the specifications.
And with an old small 5 inch speaker, that amp will not deliver a half watt.
But certainly the headphone jack can drive a line input on a big amplifier and give you lots of sound with all the quality of the original system. Enjoy it!!!

Can you read the alphanumeric code on the side of the long black IC?

 

OK... hard to see, carefully bent a few things and got the jeweller's loupe out... Best guess is

KA2212
948A

So, if correct then 3-12v? best use the buck converter then? Also then likely a 0.6w speaker in there... 3", small magnet and shallow. Was going to replace with this speaker which probably will work... the 3" was too deep to fit.

I'll post again... just need a bit to gather up links of what I think will work.

Supply voltage		3 to 12 volts
Output power		0.5 Watts
THD @ 0.5 watt		10%
Bandwidth		100Hz to 10KHz
Input resistance		15K ohms
Voltage gain closed		75dB

 

The output power depends on the supply voltage. Good, you found the amplifier part number of KA2212. it produces about 1W with fairly low distortion into 8 ohms with a 12V supply or about 0.7W into 8 ohms with a 9V supply that drops to 0.3W into 8 ohms when the battery drops to 6V. The datasheet shows its output power at a horrible10% of clipping distortion.

 

So, the cavity for the old battery is about 46mm wide, 72mm long and 28mm deep. Not a lot of space but enough I hope.

I was thinking of grabbing a lithium battery, one with the 3-cells, 12v, 3500mah. I noticed most have 2 wires coming out... some of these lithium packs have 2 sets of wires, assuming power out, recharge in... trying to find one this size "cheap" but just finding 2 lead batteries or sites like in my link where they sell in bulk I think. Should fit with some wiggle room and space for the other chips.

I have a few buck converters bought for a fan upgrade on a PS2 because the fans were 5v or 12v, and the PS2 source was 7v. People were adding 12v fans and being amazed at the quietness... ya sure, because probably running half speed. Anyways, I have Mini DC-DC 12-24V To 5V 3A buck converters. Can drop a blob of solder on the back and make it 9v.

Then I guess a USB-C recharge module... something like this maybe?

Then I suppose run the battery wires to the USB module IN, and then the USB module OUT to the buck converter IN, and from that to the amp board?

 

Yes, 3 to 12 volts, but read the capacitors and limit the voltage to the rating of the caps.

 

Yes, 3 to 12 volts, but read the capacitors and limit the voltage to the rating of the caps.

Well, currently takes 2x9v batteries and the battery box is just the 2 wires and metal tabs, no electronics in there at all, so assuming running parallel... I guess average '80s 9v was what, 400-55mah? so parallel means 9v 800-1100mah?

Newer rechargeable pack should easily double the play time on that guitar, or more.

That and just easier to recharge a battery via USB than grabbing 9v batteries all the time. Suspect with lost of play, this would go through batteries quick.

The buck converter has a 9v option on the back... dial on the front too so could do 10v even but, if designed for 9v and buck converter has a 9v solder spot, I'll just leave it at 9v.

 

If you look, you can find rechargeable 9 volt batteries.

 

If you look, you can find rechargeable 9 volt batteries.

Saw those with the little plugs on the side but for the project I'd rather have a port added for charging. Not enough room in there to add a y-splitter to the 2 x 9v and run to a single charge port. Debated that. 3D printing a new tray seemed easier and cleaner.

 

Sounds good.

 

is the order of the wiring ok? battery to charger to buck converter?

 

It might be that the noise from a switcher power supply will be a fair potion of what comes out of the system powered by that setup.
The very big benefit of battery supply is that it is quiet. And in an electric guitar system of any kind, the only sound you want is from the strings, not the power source.

 

It might be that the noise from a switcher power supply will be a fair potion of what comes out of the system powered by that setup.
The very big benefit of battery supply is that it is quiet. And in an electric guitar system of any kind, the only sound you want is from the strings, not the power source.

Switcher power supply... is the buck converter?

What would be a better setup? Drop to 7.4v? I see some that say "10.8v 11.1v" but also on the label say "max charge voltage 12.6v" which is too high else that would have worked.

Hmm, maybe the 9v batteries with USB ports on the end vs sides might work? be a tight fit though.

 

How long would you be playing this guitar in one session?? The rechargable should be good for at least an hour.It is possible that the 2x 9 volts were fed thru a resistor. I suggest tracing out the circuit to understand what voltages it will work from. If the two batterys were in series then it could use 18 volts, so it would play fairly well on 12 volts.

 

if amp max voltage were 12v, would not 18v be a bad thing?

and not long sessions... it's more of a fun project than a real guitar. It's a 3/4 scale guitar with a speaker built in... this project is more of a "why would you do that?" upgrade.

 

The KA2212 amplifier in post #5 has a maximum supply of 14V. It will be destroyed with an 18V supply but it might last tor milli-seconds or hours.

 

So my suggestion for a 12 volt battery was appropriate. And if it used two nine volt batteries they were not in series.

 

So what was the suggestion? Battery Supply? Is that different from a battery? You don't mean like an ac adapter? Because that defeats the whole built in speaker no need for a cable to an amp thing.