SansAmp GT2 from Tonepad Issue

[lezerec]

Hi guys, I am writing from France. I ll do my best to explain my problem !

The bypass is ok, LED is on when the pedal's engaged. I have no distortion at all, only clean sound on each of the 3 amp positions (S3, as far as I know). Moreover, the Tweed position needs me to increase volume on the amp (near from the maximum). Someone posted on another topic he had the same problem and found quickly S3 was wired backwards. So, his issue was fixed.
In my case, the 3 rotoswitches (from Musikding) are wired like this :

Pôle - Sx0
Position 1 - Sx1
Position 2 - Sx2
Position 3 - Sx3

Is that right ?

Actually, I tried to invert S3a1 with S3a3 and S3b1 with S3b3.. As I understand from the schematic, it was predictible : I just found Tweed position in first, with the same issue.
I also controlled all resistors, capacitors.. They're all supposed to be at the right place.
I tested all the signal trace with an audio probe. Everything is ok (sometimes it's louder, sometimes it's lighter..). I must precise I had signal on the ground trace (green trace on the layout from Tonepad), on the V and Vb traces (red and orange), and on each pin of the IC's. What does that mean, I don't know !

The pots seems ok too, I can hear their effect. To have the same level as the bypass, Drive and Level need to be at their maximum.

Here are the voltages :

IC1

Pin 1 : 4,48
Pin 2 : 4,48
Pin 3 : 2.26
Pin 4 : 0
Pin 5 : 2.26
Pin 6 : 4.48
Pin 7 : 4.48
Pin 8 : 8.96

IC2

Pin 1 : 4,48
Pin 2 : 5.04
Pin 3 : 4.11
Pin 4 : 0
Pin 5 : 4.48
Pin 6 : 5.04
Pin 7 : 4.48
Pin 8 : 8.96

IC3

Pin 1 : 4,48
Pin 2 : 4,48
Pin 3 : 4.23
Pin 4 : 0
Pin 5 : 4.15
Pin 6 : 4.48
Pin 7 : 4.48
Pin 8 : 8.96


IC4

Pin 1 : 4,48
Pin 2 : 4,48
Pin 3 : 4.48
Pin 4 : 0
Pin 5 : 4.48
Pin 6 : 4.48
Pin 7 : 4.48
Pin 8 : 8.96


I have measured V = 8.96 and Vb = 4.48

Along the PCB,  V is measured as 8.96 everywhere (red trace on the layout from Tonepad), and Vb also everywhere at 4.48 (orange trace on the lay out).

For Q1 :

E = 3.89
B = 4.48
C = 8.96

I am eating my hat, as we say in France  Do someone have an idea ?

Thank you

[lezerec]

I need help, please !

[vigilante397]

Can we get some pictures of your build? Are you using a board you purchased from Tonepad, or is it one you etched yourself? Your voltages look fine, so we're going to need a little more information so we can try to help.

[lezerec]

Thanks for the reply ! Yes, I bought it from Tonepad. Here are some photos. Note that I have already fixed some broken traces with wire and/or solder. The DMM says it's ok now. The pedal is now unboxed for debugging.
I also tried another power adaptator, which delivers 1000 mA. It doesn't change anything.








From a different angle, you can see how one side of S3 is wired :

- purple wire = S3b0 = pole of the switch
- blue wire = S3b3 = position 3 of the switch
- 2 others black wires = 2 others holes (trust me !)
All the 3 switches are wired the same

[reddesert]

You're getting audio (guitar) signal on the ground, on Vsupply and Vb, and on each pin of all the op-amps?  That's really weird and suggests something wrong with the probing technique?  You shouldn't have any signal on the the voltage buses, and also no signal at the inputs of inverting amplifier op-amps (IC4a and IC4b on the tonepad schematic, for example).

[DIY Bass]

OK, so it can be hard to tell just from the photos, but one thing that did I did notice is the top most wire that you have used to replace a broken track is very close to another pad, and may be shorting to it.  That wire connects to a link, that then basically joins to Pin 3 of IC 2.  To make it a bit cleaner I would remove the link, and solder your wire directly to the pad on the other end of that link.  I would try and have less of the wire protruding from the insulation if you can as well.

[lezerec]

https://www.coda-effects.com/2015/07/troubleshooting-guide-for-guitar.html?m=1Well, I am probing with this technique
Here is the audio probe I built :


It seems quite different than the probe from RG at Geofex, as I understand (input and output are inverted, no ?). Well, I am fed up right now and do not want to understand anything

[DIY Bass]

That probe looks good to me

[lezerec]

DIYBass,

Further to your first post, I am sure there's no short ! I have controlled that. But I will try in a few hours. Actually I m at work now.

Well, I have an audio signal between ground and ... ground ! I m so happy..

[Govmnt_Lacky]

Can you provide a link to the rotary switches you are using? Perhaps from Musikding.

[lezerec]

Here it is https://www.musikding.de/Mini-rotary-switch-2P3T
Both 2p3t and 2p4t have 5 pins on each side. The fact is one pin on each side doesn't connect to anything on the 2p3t.

[Govmnt_Lacky]

Here it is https://www.musikding.de/Mini-rotary-switch-2P3T
Both 2p3t and 2p4t have 5 pins on each side. The fact is one pin on each side doesn't connect to anything on the 2p3t.

From the looks of the posted schematic, each of the 2 sections of the switch use a different pin for the common. On one of the switches, it is Pole 1. On the other switch, it is Pole 5.

So, for each Rotary, you should have the poles wired as this:

Rotary #1
Switch 1 Pole 1 > S1a0
Switch 2 Pole 5 > S1b0

Rotary #2
Switch 1 Pole 1 > S2a0
Switch 2 Pole 5 > S2b0

Can you confirm that you have them wired this way?

[lezerec]

Yes, exactly !

[lezerec]

I just audio audioprobed another time. I said a mistake : no signal on the ground of the pedal, neither V or Vb. That's finally better. Sorry for yesterday, I was too tired.

[Govmnt_Lacky]

I just audio audioprobed another time. I said a mistake : no signal on the ground of the pedal, neither V or Vb. That's finally better. Sorry for yesterday, I was too tired.

Sorry but, I don't understand this. Is the pedal working now? Are you having different problems now?

[lezerec]

Sorry, the pedal still doesn't work ! I have the same problem.
I said yesterday I had audio signal on the ground trace and I was wrong : there's as expected  no signal on the ground trace. But my problem is still there..

[lezerec]

Well, I don't know what I am looking for :

- voltages seems correct
- probing doesn't reveal the problem
- wiring seems ok too
- I have no distortion at all, but only a clean sound in each position. The volume of the Tweed is very very low

It's like one stage of the circuit doesn't work. I don't know how to identify the "frontiers" of each stage, if they exists...

[Govmnt_Lacky]

Well, I don't know what I am looking for :

- voltages seems correct
- probing doesn't reveal the problem
- wiring seems ok too
- I have no distortion at all, but only a clean sound in each position. The volume of the Tweed is very very low

It's like one stage of the circuit doesn't work. I don't know how to identify the "frontiers" of each stage, if they exists...

Judging by your explanations and your build pics, my first suspect would be the rotary switches and/or their wiring. If I were you, I would print out the schematic and do a continuity test (with a multimeter) of every switch position. For example.... Let's say you have your S1 rotary in position 1. I would make sure that S1a0 goes to S1a1..... S1b0 goes to S1b1. And so on.

Verify every connection. I bet your problem is somewhere in there.

[lezerec]

Well..
For 2 hours on it..
I tested each side of each switch...
About 10 times each pin, each joint...
I could observe the good sums of resistors around the switches turned off...
I could also observe 0 ohms when switches turned on...
...And it doesn't work...

[DIY Bass]

If the volume of the tweed is very low, then it sounds if if you may have a problem around IC1.  Maybe the IC, but quite likely a problem with one of the passive components around there or a solder joint in that area.