Sansamp gt2 debug

esmifra · August 25, 2015, 02:29:10 PM

The last measurements i posted are done with the jack tip inserted in the jack INPUT abd they seem fine. The problem now it that there is no sound coming out, only a heavy hmmmm but if i touch the guitar the sound intensifies.

The switches are correctly mounted ( i believe)

michauorin · August 25, 2015, 03:06:22 PM

Quote from: esmifra on August 25, 2015, 02:29:10 PMtouch the guitar the sound intensifies.

Potential ground problem. Apart from checking every ground connection You can think of (also input jack, aren't the ground an hot path switched?) I still recommend to use the audio scope to isolate the problematic part of the circuit.
The hum is generally supposed to lower when You touch the guitar, not the other way around.

esmifra · August 25, 2015, 03:23:14 PM

Actually, its the other way aorund, if i otuch the strings, the hmmm gets lower, sorry my bad

this is how i wired the jack input and output + batery
http://i.imgur.com/9lZbhPV.jpg
edit: forgot link

esmifra · August 25, 2015, 03:38:27 PM

I've made an Audio Probe. If i'm thinking correctly, the only thing connected to the amp is the Audio Probe right? i plug the guitar in the input jack and leave the output idle, correct? Then i just touch whereever the signal goes ( if i can follow it) with the tip of the capacitor while strumming the strings, correct?

Cozybuilder · August 25, 2015, 03:42:00 PM

The stereo jack normally is the input jack. If that is your intent, then it looks like you have the output jack wired to the input & vice versa. Just for grins, plug your amp into the "Input" jack and guitar into the "Output" jack- see if it works then.

Edit- My mistake, sorry

Kipper4 · August 25, 2015, 03:48:40 PM

Quote from: esmifra on August 25, 2015, 03:38:27 PM
I've made an Audio Probe. If i'm thinking correctly, the only thing connected to the amp is the Audio Probe right? i plug the guitar in the input jack and leave the output idle, correct? Then i just touch whereever the signal goes ( if i can follow it) with the tip of the capacitor while strumming the strings, correct?

you got it

esmifra · August 25, 2015, 03:50:12 PM

the black wire that connects both input and output jacks is suposed to be the ground

esmifra · August 25, 2015, 04:16:31 PM

OK first thing i found is that the signal doesn't reach the DRIVE pot. There is a signal in the switch S3A1, S3A2, S3A3 but not in S3A0. i believe this is the problem and tomorow i'm going to buy new switches. I'll continue probing and posting results tomorow.

Thank you all for your help, i'm very gratefull

Cozybuilder · August 25, 2015, 04:48:57 PM

Does the switch have lugs you can access? If so, I suggest you simply short S3A0 to your choice of S3A1-2-3 (1 is coupled with 10nF, 2 with 2n2, 3 has 100K then 22nF) and see if you get noise out.

esmifra · August 27, 2015, 01:08:22 PM

YES!! i found the problem using the Audio probe. I found that i don't get a signal on S30, so i think its the switch fault. After i shorted SA30 with S2A0, i get a clear audio at the output. Unfortunatly, the store from where i buy eletronic stuff doesn't have these switches, so i'll wait a bit ^^

Once again, thank you guys very much for your help, you've been very usefull!

Cheers!! \o/

Kipper4 · August 27, 2015, 01:24:52 PM

I'll just leave this here

predok13 · September 21, 2015, 12:52:14 PM

Hi all! I have strange problem with an original Sansamp GT-2. It's have a short circuit between ground and +9V power trace (35 Ohm resistance between them). I've desoldering and checked all electrolitic caps - they are all working ok. TL072 is ok too. Maybe I should check out the rest of the ICs... What do you think, what may be the reason?

PCB (not my but it's looks the same): http://www.pisotones.com/GT2/imgs/GT-2board(J.Luja).jpg
Scheme: http://www.axiomdrift.com/schematics/GT-2pn.gif

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Sansamp gt2 debug