Bbe sonic stomp vero issue

[JebemMajke]

http://www.sabrotone.com/?attachment_id=533

Hello guys

I've built this pedal using madbean's layout in the past, and everytime it worked from the getgo.

Currently i am stuck in the vero world, because i hate ironing .

Pedal works fine, sound is beautiful, but the lo pot doesn't work in the last 1/4 of a turn. And it actually kills all the signal.

I've changed the pot, and no difference.

However i didn't change the other pot, and since they are connected like siamese twins maybe i should.

Any suggestions?

[ElectricDruid]

Schematic please? I can't debug anything from a layout alone, sorry.

Maybe someone else is more able with veroboard, but that confuses the hell out of me.

Sorry!
Tom

[JebemMajke]

here you go

http://s197.photobucket.com/user/bajaman002/media/BajaBBESonicStompschematic.png.html

[JebemMajke]

Well, I've changed both pots, no difference

So here are the voltages. 9v regulated power supply

Measurement was done with lo pot to the max.

ic1 tl071
1  0.13
2 4.12
3 4.03
4 0
5 0.13
6 4.12
7 8.22
8 0

ic 2 tl072

1 4.15
2 4.15
3 3.75
4 0
5 4.15
6 3.75
7 7.56
8 8.24

ic 3 tl074

1 4.16
2 4.13
3 4.12
4 8.24
5 4.15
6 1.4
7 7.44
8 1.34
9 4.5
10 4.16
11 0
12 4.34
13 4.17
14 4.17

Any ideas?

[samhay]

>ic3
...
6 1.4
7 7.44
8 1.34
...
The area around the 'bottom' of your TL074 is not right (these 3 pins should all be ~4.5 V). Check for shorts and mis-placed jumpers in this corner of the board.
Alternatively, you may have a wiring issue with the LO pot - check it isn't grounding on something.

[JebemMajke]

I've cleaned some traces 6 is now 4.35

7 1.35
8.7.54

I ll continue to clean

Thnx for your reply samhay

I really appreciate it.

[JebemMajke]

It doesn't work.

[samhay]

Might be time to post pictures

[JebemMajke]

So i've used the old pcb board, because i like this box's appearance much better.

But it worked for some time and after i hooked it up second time it started having some issues. For example if i ground it to the box bass pot doesn't work for the first 1/5th and last 1/3rd. But if i remove ground from the chassis bass pot works so so but process pot doesn't do anything.

So i guess it is the internal wiring.

[ElectricDruid]

So i guess it is the internal wiring.

Sounds like it. Something connected up wrong, or something shorting out on something.

Have a careful look around it and see what you can spot.

Tom

[JebemMajke]

I've changed 2 ics to tl22 series, so tl 2272 tl 2274 and I changed tl071 for another tl071

Bass ( lo contour ) pot now works. And it adds a lot of volume when it is maxed.

Treble ( process ) pot does nothing. Any idea?

edit:

Changing treble pot does nothing.

[ElectricDruid]

Changing random parts in the hope that it fixes things isn't usually a great idea. I mean, you *might* get lucky, but generally you won't, and the changes mean that things you thought you knew about the circuit are no longer guaranteed. That makes debugging much more difficult.

If we work through the circuit from left to right and follow the audio through, we ought to be able to find out where it's going wrong. The first stage is a simple buffer. Presumably you've got clean audio at the output of that op-amp.
The second stage is another buffer on the top schematic (gain=1), and a non-inverting op-amp(gain=2) on the bottom schematic. Again, check you've got clean audio at the output of that stage.

The next part is where it gets interesting. This is a static state-variable filter. The cool thing about state variable filters is that they provide a high-pass, a band-pass, and a low-pass response - all at the same time. The first stage is a mixer (well, ok, differential amp really), and the output from there is a high-pass signal. The next two stages are integrators, which serve as filters. The output from the first one is the bandpass signal, and from the second (last) stage is the lowpass signal. You should be able to check the audio from each of these op-amps and hear if it's what we expect. The filter is interesting in that they've tweaked the filter caps so the two stages aren't the same.

The final op-amp is another mixer, which mixes the signals from the filter back together in variable proportions to give you the final tone.

I would guess that the problem lies in the filter, since it would be very easy to wire up either the feedback paths (one from BP, one from LP) or one of those filter output connections wrong. If those aren't right, the knobs won't get the signals they need and the final mix won't sound right at all.

HTH,
Tom

[JebemMajke]

I will post pictures later.

But i have a question could film box capacitors or resistors die or go bad?

[ElectricDruid]

I will post pictures later.

But i have a question could film box capacitors or resistors die or go bad?

It's possible, but unlikely. You can melt the film in film caps if you overheat them when soldering, but it takes a lot. Similarly, although I've once come across a resistor where the end cap had come away from the body (thereby making a *very* high resistance!) it doesn't generally occur. You can fry resistors with too much current, but that's usually pretty obvious from the burnt smell and interesting "toasted" look they get...

A dodgy solder joint on a resistor or capacitor gives the same effect though, and that's much more likely.

T.

[Cozybuilder]

Changing random parts in the hope that it fixes things isn't usually a great idea. I mean, you *might* get lucky, but generally you won't, and the changes mean that things you thought you knew about the circuit are no longer guaranteed. That makes debugging much more difficult.

If we work through the circuit from left to right and follow the audio through, we ought to be able to find out where it's going wrong. The first stage is a simple buffer. Presumably you've got clean audio at the output of that op-amp.
The second stage is another buffer on the top schematic (gain=1), and a non-inverting op-amp(gain=2) on the bottom schematic. Again, check you've got clean audio at the output of that stage.

The next part is where it gets interesting. This is a static state-variable filter. The cool thing about state variable filters is that they provide a high-pass, a band-pass, and a low-pass response - all at the same time. The first stage is a mixer (well, ok, differential amp really), and the output from there is a high-pass signal. The next two stages are integrators, which serve as filters. The output from the first one is the bandpass signal, and from the second (last) stage is the lowpass signal. You should be able to check the audio from each of these op-amps and hear if it's what we expect. The filter is interesting in that they've tweaked the filter caps so the two stages aren't the same.

The final op-amp is another mixer, which mixes the signals from the filter back together in variable proportions to give you the final tone.

I would guess that the problem lies in the filter, since it would be very easy to wire up either the feedback paths (one from BP, one from LP) or one of those filter output connections wrong. If those aren't right, the knobs won't get the signals they need and the final mix won't sound right at all.

This is a jewel of a response, the kind that forces you to look at the circuit as individual blocks with the mindset of what each section actually does. Thanks for posting!

[PRR]

> it worked for some time and after ...started having some issues.
> changed 2 ics to tl22

These ICs are essentially identical.

It worked, and then it didn't work. It didn't work, and then it worked (partly).

THE MOST LIKELY fault when it works/not-works for no reason, or not-works/works when you change a part that should make no difference, is bad solder joints.

It is nothing to be too ashamed of. Samsung/IBM sold me a monitor with a bad joint that failed in a few years. Smacking the monitor sometimes "helped". Going inside and cleaning then re-soldering the joint was a forever fix. Bogen sold friends three large tube amps they used 24/7 (motor driving). One of the 200+ joints had NEVER been soldered, was holding on the wirer's crimp, then let go and started a fire. I won't admit how many bad joints I have made, but I will say that once I admitted it was A PROBLEM, and started being ULTRA CAREFUL about my joints, my work improved and problems reduced.