bandpass filter in a stompbox

Stompboxes circuits published in magazines, books or on DIY electronics websites.

Re: bandpass filter in a stompbox

Postby YellowBoy » 09 Apr 2018, 14:24

Hi snk

Something seems horribly off with those voltages. Pins 1,2,3,5,6,7 of both IC's should be around half supply like microbailey said.....somewhere close to 0V.

I'm guessing you have a misplaced component(s), a short, not fully cut through cuts or lastly a bad component.

Try taking out the IC's and measure for continuity (no power plugged in) on all the places that should have it (linked rows etc) and also check for continuity between IC pins (there shouldn't be). I once had a short in an IC socket itself and took hours to track down.

I had a look at the layout vs the schematic yesterday and it looked fine but I'll have another look today just to confirm. In the meantime....recheck every placement, every cut and every link. I'll be back shortly.
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Re: bandpass filter in a stompbox

Postby YellowBoy » 09 Apr 2018, 21:37

ok....I've compared the layout to the schematic and it matches so the problem isn't there. I also can't see anything else obvious in your build so refer to my previous post about that.

If it comes to a rebuild I suggest building my layout attached. It follows more conventional design rules and is much smaller. I've also tried to keep the wiring for all the pots as close as possible. I've gone over it a good few times and I'm confident it matches the schematic. Be aware that I flipped the last 2 opamp channels just to make the layout flow better. This won't alter the function in any way. But....try to get your build up and running first.

A few notes...

This filter was designed for a synth so was expecting a line level signal (or close to it) on the input. For guitar I expect this to be well below unity as is. The inverting input gain stage has a gain of 1 so I'd suggest decreasing the input resistor (47K on input) to maybe 10K and experiment raising the feedback resistor (between pins 1 and 2 of the top IC) between 47K and 100K.

The 4.7K on Res 3 is the resistor labelled 800ish on the original layout

Let us know how you get on. I may give this ago soon as it does sound really good.
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Last edited by YellowBoy on 09 Apr 2018, 22:19, edited 1 time in total.

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snk (09 Apr 2018, 21:44)
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Re: bandpass filter in a stompbox

Postby snk » 09 Apr 2018, 21:50

Thank you, yellowBoy, it's much appreciated ! :thumbsup
Your layout is easy to read indeed. I'm not sure i have enough components left to build one new tonight, but if i get stuck with my first build, i will order some more capacitors and try your layout.

This filter was designed for a synth so was expecting a line level signal (or close to it) on the input. For guitar I expect this to be well below unity as is. The inverting input gain stage has a gain of 1 so I'd suggest decreasing the input resistor (47K on input) to maybe 10K and experiment raising the feedback resistor (between pins 1 and 2 of the top IC) between 47K and 100K.

I will be using it with a synth, too. It will not be a modular, so i'm going stompbox (and not panel), but i'll be usig it at line level so i will keep the original values.

The 4.7K on Res 3 is the resistor labelled 800ish on the original layout

Ok. On my build, i used a switch to be able to use either the original value or a stronger resonance.

Let us know how you get on. I may give this ago soon as it does sound really good.

Yes, it's a simple design but it sounds gorgeous :)

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YellowBoy (09 Apr 2018, 22:20)
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Re: bandpass filter in a stompbox

Postby snk » 09 Apr 2018, 22:55

Ok, so i used an exacto knife to avoid contacts between the veroboards bands, and the circuit is quite cleaner now (picture below).
I still don't get any sound of it, though.

I also processed the continuity test : i have marked in green the parts where the DMM beeps... but i don't know how to make a deduction out of it :hmm:
(PS : the continuity test was performed with the IC still in place. I had one arm of the DMM on the ground, and i was making contact with the other arm on the circuit).

Image

Image
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Re: bandpass filter in a stompbox

Postby YellowBoy » 09 Apr 2018, 23:48

Ok... now it's getting interesting! So I don't really expect this to solve all your problems as your voltages are still off but....

It appears your output wire is somehow connected to ground??? Does that jack socket have a switched contact on the tip? I see 2 legs but is one of those legs connected to ground and therefore did you solder the output wire to the wrong leg? Test the sockets in continuity mode. Basically place the black probe on a ground point and the red probe on each tip leg. If it beeps then one of those legs is connected to ground....solder to the other one.
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Re: bandpass filter in a stompbox

Postby snk » 10 Apr 2018, 12:18

Hi
At first, i used plastic jack sockets. That was the first time i was using such enclosure, it seemed nice to gain a bit more space and to have jack plugs isolated from wires. But maybe it wasn't such a good idea.
I changed them for more classic jack sockets in metal, without any difference.

Sadly, i will not have much time today nor in the next days to debug the circuit (i wasn't expecting to spend so much time on this filter :)), so i will give reports when i'm back.
Thank you very much everyone for your great help ! :thumbsup
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