Synsonics guitar amp help

Tube or solid-state, this section goes to eleven!
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fortj3
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Post by fortj3 »

I have a Korean made Synsonics 12 volt DC solid state guitar practice amp.
I know nothing of the ownership or usage history. I got it cheap with some cables, strings, and a stompbox.
Anyway, when I plug it in and turn it on it hums.
However, the power-on LED does not come on.
Also, when I plug my guitar into it, and play, no sound comes out.

I am in need of diagnostic/repair advice.
Any help is greatly appreciated.

If this post is in the wrong place, I apologize.
I haven't been a member here for very long and don't really know my way around this forum.

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fortj3
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Post by fortj3 »

OK. i have found an issue with my 12 volt power supply.

I don't have another 12V wall wart.
I do have a PC power supply.
Only thing is, the output voltages I'm getting are 5 VDC (correct), 10.7 VDC :scratch: , and 14.5 VDC :scratch: .
It should output 5 VDC at the red and black wires, and 12 VDC at the yellow and black wires.
The 14.5 VDC is output at the orange and blue wires. That would work for a battery maintainer for my motorcycles, but I'm not sure if it's going to cause problems with the amp.

I wonder if I can safely run the amp off of 10.7 VDC or 14.5 VDC?
I don't want to let the smoke out of any of the circuits, because it's hell to try to stuff it back in.

I'm not new to electrical or electronic troubleshooting/soldering/repairing.
HOWEVER, I am very rusty. I will be relearning a lot of things along the way.

I plan on building some stompboxes, because I'm cheap and stompboxes aren't.
Plus, it's fun to build things.

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deltafred
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Post by deltafred »

Look up the datasheet for the output chip and you will have almost everything you need to know, including half of the schematic.

14.5v may be ok but PC power supplies are not ideal for powering low power circuits because they often need to supply a minimum current, usually on the +5v output, to operate correctly.
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fortj3
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Post by fortj3 »

How do I tell which chip is the output chip?

BTW, the PC power supply is a no-go.
I'll figure something else out.

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Post by deltafred »

fortj3 wrote:How do I tell which chip is the output chip?

BTW, the PC power supply is a no-go.
I'll figure something else out.
If it is a GA-150 or similar it's the one attached to the aluminium heatsink in the photo below on the right hand side.
SynsonicsGA150guts.jpg.jpg
SynsonicsGA150guts.jpg.jpg (64.54 KiB) Viewed 1622 times
Photo from https://reverb.com/uk/item/4822613-syns ... cuit-board
Politics is the art of so plucking the goose as to obtain the most feathers with the least squawking. - R.G. 2011
Jeez, she's an ugly bastard, she makes my socks hurt. I hope it's no ones missus here. - Ice-9 2012

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fortj3
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Post by fortj3 »

Is this amp a copy/clone of any other, more well known, practice amp?

I got it working.
I found an old Dell 12 volt laptop charger I had lying around.
The only problem was that the output jack was the opposite polarity of the amp 12 volt input jack.
That, and the pin in the center of the input jack was loose in the terminal. A quick solder job fixed the loose pin.

So, I desoldered the 12 volt input wires from the input jack, reversed their polarity to match the power supply, and soldered them back on.
It now works perfectly, except for a slightly scratchy sounding pot and the fact that the speaker sounds rather cheap.
I'll clean the pots. No worries.
I tried it out with one of my guitars and with my bass guitar.
It actually sounded better with my bass than with my 6-string electric guitar.
I think it could be a good one to use for some blues harp. We'll see.
Maybe I'll put a better speaker in it. Maybe I won't.
Maybe I'll dope the speaker and seal the cab to use it as a bass practice amp. Probably not.

Thanks for the advice.

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Post by deltafred »

Good to hear that you've got it working, and thanks for letting us know.

I remember when I was Googling for details of it I found on a forum somewhere that someone said it was their first amp and described something like "not sound good and couldn't even fart properly!". :lol:
Politics is the art of so plucking the goose as to obtain the most feathers with the least squawking. - R.G. 2011
Jeez, she's an ugly bastard, she makes my socks hurt. I hope it's no ones missus here. - Ice-9 2012

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