Debugging a Blues Pro on vero

[T-Dub]

Hi folks, I was just building a blues pro up on vero and I have the weirdest issue.

All the knobs work (Gain does *something*, tone and vol work as they should) but it doesn't amplify the signal, but instead cuts out every second, like a slow tremolo. I changed out all the power caps just in case that was the problem but no dice.

I was using this layout:


Things I did differently; I did not include the fuzz or fat switch. I instead put a jumper between that trace that both switches connect to and the + of the 22uF cap going to ground. I also used a 51pf in place of the 30pf. I then decided to try and just build it as it's laid out, apart from adding the switch and now it just squeals like crazy!

Voltages on the IC are:

1 bounces around
2 0.07
3 0.01
4 0
5 0.65
6 0.09
7 bounces around
8 9.02

I've changed IC's no difference too. Something weird is happening though! Sometimes I just hate vero 

[Kipper4]

Looks like your not the only one to have had trouble with this one


http://www.diystompboxes.com/smfforum/index.php?topic=82008.20

A schematic would be helpful
maybe pictures too or the board

[Kipper4]

I'm  guessing it's based around this

https://www.gearslutz.com/board/attachments/geekslutz-forum/294785d1338688669-op-amps-output-volume-guitar-pedal-blues-pro-schematic.png


The mods (fuzz and fat) are not included in this schematic.
It looks pretty much like a TS drive topology.
I would check the you Vr ( node between the two 22ks) because pins 1,2,3,5,6,7 should all be in the region of 4.5v.
I don't really do vero.
Happy debugging.

[T-Dub]

Thanks mate, very much appreciated!

[Kipper4]

Question for the gurus please What kind of filter is this?

[Cozybuilder]

I traced out the Vero and came up with this schematic. I wonder if the problem is related to the Fat switch branch being located on the wrong side of D2?

[Groovenut]

I traced out the Vero and came up with this schematic. I wonder if the problem is related to the Fat switch branch being located on the wrong side of D2?

Russ I had a quick look at the layout and this is what I see for the amplifier/switch section. Maybe I've missed something though

There's a cut under the 1k that's easy to miss and the 1k/220n to ground is a little convoluted but I see it there.

edit:oops looks like I left out the 1M at the input

[Groovenut]

Question for the gurus please What kind of filter is this?

I would hazard a guess at a dual step low pass filter (low pass since it's in the negative feedback loop). With the signal feeding back from output to neg input, you get an initial LPF from the 330k/10p RC combo then a second LPF with the 330k/1n5 RC. These work in conjunction with the 100k at the neg input to set the gain of each filter.

my 2 cents...

edit:
The 330k/10p has a -3dB knee at around 45KHz, the 330k/1n5 has it's knee at around 325Hz. Here's a plot

[Cozybuilder]

Law-
I agree with your schematic 

[Groovenut]

Law-
I agree with your schematic 

I think the OPs issue is as was mentioned earlier, the bias network.

[Kipper4]

Thanks guys.
I breadboard ed it earlier and it sounds ok I can't say I noticed a remarkable difference from a ts I had as a side by side in the test.
The tone stack is not not much more effective than the ts.
I tried some German diodes as hard clipping to ground and it improved a bit.
Haven't done the switch mods yet

[Cozybuilder]

If I'm reading the OP's posting correctly, it looks like he missed the cut under the 1K also. He says he connected the + of 22uF to the trace that both switches are connected to. I think he means he soldered a wire directly between where the Vero indicates Fuzz Sw2 and Fuzz Sw1, and connected that to the 22uF. If that is correct, then essentially he connected 22uF to the output of the Op-amp to ground.

It would be a lot easier if there was a clear photo or two.

[T-Dub]

Cuts seem to be in the right place having scoured the board last night. I cleaned up the board with some isopropyl alcohol, ran a knife between the traces, and found I'd put 300k resistors instead of 330k resistors. That stopped the pulsing/cutting out. I added the switches and things to see how it went, and they seem to work. I was excited when I plugged it in but soon realised, it still doesn't seem to be actually raising the volume above unity for some reason. I'll get a picture of the board when I get home.

I will admit that I had to do some remedial work where I'd cut the traces in the wrong place...