Tech 12 Bass Driver, needing help to debug

[stucliff]

Hi everyone, this is my first post, about (yes you guess it) my first project. I'm building a Sansamp Bass Driver Di. I know it's not a "beginners" project, but I'm a bass player, and this is the one and only effect I like.

So, to say it straight, the most logical thing happened, and I'm having trouble with it. And taking in count that I don't have good skills on electronics, I need some help to make the effect work. I've checked already all that I can... I'm going to post it because I'm sure it could mean something, but I don't know what it could be...

So, to make things right, the Debugging report:

1.- The effect works at a really low volume. Checking for loose IC I've noticed that in you touch the circuit where the C21 and R23 are soldered the

volume goes up at almost "normal volume". I don't know if this is important or not.

2.- Tech 12 Bass Driver from Plexilandia

http://www.plexilandia.cl/foro/viewtopic.php?t=5775&postdays=0&postorder=asc&highlight=sansamp&start=0#top

3.- Schematic, PCB & layout

http://sites.google.com/site/plexilandia/tech12bassdriver.zip

This is the PCB I've made with the parts already soldered (the original image has a very nice resolution so you can zoom it and see if there's anything wrong)



I've checked the "suspicious" tracks and soldering points, and everything seems to be OK.

4.- NO modification to the original circuit

5.- NO parts substituted

6.- NO positive ground to negative ground conversion

7.-Battery voltage 9.11
Voltage at the circuit board end of the red battery lead = 9.00
Voltage at the circuit board end of the black battery lead =0

IC1
1= 4.51
2= 4.51
3= 2.25
4= 9.06
5= 3.69
6= 5.06
7= 4.49
8= 4.40
9= 4.73
10=4.50
11=0
12=4.22
13=4.44
14=4.45

IC2
1= 4.42
2= 4.42
3= 4.08
4= 9.01
5= 4.46
6= 4.48
7= 4.49
8= 4.48
9= 4.48
10=4.24
11=0
12=4.32
13=4.42
14=4.42

IC3
1= 4.42
2= 4.48
3= 4.45
4= 0
5= 4.40
6= 4.47
7= 4.48
8= 8.99

IC4
1= 4.46
2= 4.46
3= 4.46
4= 0
5= 4.45
6= 4.47
7= 4.47
8= 8.98

I've also checked the electrolytic caps, all the negative pins where at 0 volts except the C21, that was 4.39V at the positive and 0.29V dropping fast to 0.13V.

I've checked all the resistors too, and all were OK, except  R13, that reads 45k when it's on the board, I've replaced it for a new and checked one, but all remained the same, the resistor reads 45k, and the one that was at 45k it's OK and reads 330k.

I don't know if this it's important or not... But i think it's worth mention it.

OK, that's about all, thank you very much. Let's see what happens

[PRR]

Does it work (pass straight signal) in "bypass"?

> in you touch the circuit where the C21 and R23 are soldered the volume goes up at almost "normal volume".

That is very strange.

Bad joint "fixed" by finger pressure. Re-re-recheck the solder joints around here. Even take out resistors and caps, use new ones, pre-scrubbing and pre-tinning the legs before you stuff and solder to the board.

Get a helping hand. Get DC voltage readings at IC3 pins 5 6 7 with and without finger at C21 R23 area ("sick" and "normal"). Do they change much?

[stucliff]

Thanks Paul,

I haven't put the switch yet, for what I've read it's better to first test it that way, because you have less "potential trouble factors" to deal with. So the effect is without switch nor led and DC power neither.

I've replaced the parts and checked the entire area for bad connection between the parts and the PCB, they're all OK, I mean I've checked the joint from the PCB side, and also checked that the connection was good between the "components side" and the tracks. So I think, IMHO that the solder is good...

My impression is that my finger is acting like a "bridge", so to speak, and this is what makes the volume go up...

I'm suspicious about some of the capacitors, I live in Europe and the notation here is kind of different from what is used in USA (The notation used on the parts list is in "American" values",  so I think I don't have all the correct values on some caps (a confused seller with a hurry, and me getting very confused about notations). I'm gonna check this today and, if it doesn't work, gonna wait for the "helping hand" and see what the voltages are on the IC3

Whatever happens I'm gonna post it here...

[PRR]

The signal goes through the switch. No switch, no signal.

[stucliff]

Ok, I have all the correct cap's (that's what I think after a long talk with the guy at the electronic components shop).

I've connected the switch (DPDT, I've connected the SW1, SW2, SW1 to the correspondent terminals in the switch, and nothing more). But no signal, not clean or effects signal. However i receive noises if I touch the circuit, and the effect that I've mentioned before about C21...

This is gonna make me crazy... I've re re re re checked the connections to the plugs, re re re checked the IC's, I know already that the resistors are OK.

I'm really  stuck, don't know what to do...

[stucliff]

OK, for knowledge's sake. There are 2 versions of this PCB, one is dated 08-21-2007 (21/08/2007 in the PDF) and the other one 12-09-2007 (09/12/2007 in the document). The first one doesn't have the connection between the switch output and the circuit. Be aware of that and use only the December version...

The rest is OK, as long as I fixed the issue everything is working OK...

Keep looking at the skies!

Regards