Add a switch (a true bypass switch) be it manual toggle switch or switch jacks, to the input.
Tbh my advice is based on guitar fx building but the theory is the same. Just Google wiring true bypass. Enjoy
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on another thread 
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I vaguely remember reading somewhere the reasons guitarists want âtrue bypassâ donât actually apply to synthesizers, so the latter can just use an SPDT to switch the input jack between effect and output, or some claim like that, but I canât remember where I saw that. Anyway, DPDT isnât difficult.
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My guess is that passive electric guitars are quite high source impedance, it canât deliver a lot of current. Non-true bypass switching doesnât disconnect the circuit output, often leaving the volume pot and for example ton control and clipping diodes in circuit. These will be in parallel with the input impedance of the amplifier or next pedal. As a result the input impedance that is presented to the guitar lowers, and causes tone sucking.
A lot of synth modules have for example an opamp or a cmos ic at the output. They can deliver a lot more current so are less sensitive to tone sucking.
Also, the input impedance of the next module is probably a lot higher (opamp input vs the 1m resistor usually in guitar circuits) so the combined impedance is a lot higher.
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The opposite, in fact: Typical synth module input impedance is 100k. Often a 100k input resistor to an inverting op amp stage, but if the input stage is non inverting, there will frequently be a 100k resistor to ground. Or, very commonly, a 100k attenuator pot.
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Yes i didnât think of that, still i think the impedance matching is better in this situation.
The input impedance of synth modules is indeed lower, but also the output impedance of the source is a lot lower.
and was i right about the assumption to make this into a dual bandpass or is it more in depth?
It depends on what kind of response you are looking for.
Serial is running the input into the first filter, and then running the first filterâs output into the second filter. The final output is taken from the second filterâs output.
Parallel is running the input into both filters, then mixing the output of both filters.
Serial bandpass, with the same frequency settings will make for a steeper band.
Serial bandpass with different frequency settings will probably just make things very quiet - At the output of the first bandpass there will be a single band, but then that will get filtered by the next one, and if their bands donât align it will just attenuate.
Parallel is probably more interesting, that way you can get two independent bands and probably get some formant type sounds going.
Cheers
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i had no idea there were different types to be honest, parallel sounds more fun to me
I was thinking having separate controls for each would be good, if its worth while anyway
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Hi there, is the band pass filter - thingy still on topic? I build it and ran into some issues.
I compared the Breadboard to the schematics of the cgs30 âŚ
Breadboard
Schematics
âŚand saw the following problem:
The bridge, applied from one Poti to another, would create a connection drawn purple on the schematic. This isnât right, right?
Or may I be mistaken on this?
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Hi, sorry to take so long to get back to you but only just spotted your question.
Wiring the 3 legs of any pot can be confusing and schematics vary in what they assume is standard.
Thereâs a good pot wiring guide somewhere here, just use the search up top.
As for the schematic, it looks right to me and the breadboard too. I see what you mean by not looking right but remember your âbridgeâ contains a diodes and the pot is just acting as an attenuator.
Have you built it?
Can you post a pic of your build?
There are quite a few here who have eagle eyes for what usually ends up staring me in the face.
Keep going.
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Letâs just get the layout and schematic back up here:
Yes, the wiper of the resonance pot is misconnected. It is supposed to connect to 10k resistor, two diodes, and an op amp non inverting input (TL074 pin 5, after hand written correction). Instead it connects to knob 1 legs 2/3. And⌠not so clear which is knob 1 and which is knob 2 but in the original the wiper (leg 2) of one connects to the first TL072 pin 7 while the other connects to a 680R to the second TL072 pin 2. In the stripboard these would be TL074 pin 7 and 9 respectively, and knob 2 wiper does go to pin 7, but knob 1 wiper goes to pin 14 and itâs leg 1 that goes to 680R to pin 9. Basically knob 1 is backwards. Also there should be one dual gang 100k pot instead of two single gang pots, or at least that was what was in the original design. Altogether⌠I think this stripboard layout is beset with errors and is best disregarded, someone should come up with a new one.
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Eagle eyes. Many thanks
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I think the Muffwiggler layout is incorrect.
The 10ÎźF capacitor from pin 8, Vcc+ of the Tl072, and (+15V) should be going to GND, not to the (-15V) rail.
Correct me if Iâm wrong please.
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Youâre right. Though it might not matter much. Itâs a bypass capacitor and best practice is for it to go from one rail to ground, but going to the other rail is not likely to cause anything to break. Still, yes, it ought to go to the next strip higher, GND instead of -15 V. (The other bypass cap goes correctly from -15 V to GND.)
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I think this one might help:
Original link:
https://ua726.co.uk/2011/10/23/stripboard-cgs30-bandpass-filter/
Good stuff can be found on this page. It is worth checking.
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Thanks for the reply.
It can be a bit worrying not having enough experience to know whether other mistakes have crept in
The original stripboard layout by ua726 has the bypass caps placed correctly. Though itâs a bit more spread out.
Samâs layout with all the corrections looks like the way to go.
A triple CGS30 filter, as per Ken Stoneâs guide, should hopefully sound good.
Cheers!
I didnât pay attention, but the ua726 layout had already been posted above. Sorry.
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The ua726 layout you include is shown to work well.
Thatâs where I spotted the bypass capacitor error with Kraggâs layout.
The link out will give newcomers a good place to go.
As the ua726 site itself is a trove of information.
He shows his mistakes as well.
Nice one, thanks
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PS: Iâm coming at this as someone who has gotten their knowledge from books, and online sources. e.g. Dave Jones EEVblog etc.
Where best practice is to add bypass caps close to the ic.
Usually 100nF Multi Layer Ceramic or similar.
Itâs nice to be reminded that the rule doesnât always have to be applied. e.g. Eddy Bergman, and some of his amazing builds comes to mind.
I learn so much here, so thanks again.