Buffered/Tails/Spillover or True Bypass box

[madbean]

Brian, how are you getting those 5-sided tabs (ie: VB).  I thought I had it figured out within Eagle but was wrong.

Those are labels for nets. Just draw a net, and click the label button. Then you can choose the little flag (Xref On button) and name the net you want to connect it to.

For the schematics, I just export them as monochrome @ 300DPI then re-size them in Photoshop.

[benny_profane]

Cheers! Sounds good, thanks!

[Marshall Arts]

Awesome!!! Look what I can do!!!!

[Marshall Arts]

So, today I finally had the chance to try different versions on breadboard. It's complicated, I must say...

To get everybody back on track, the last version was this one here, but replacing the mix pot with a 1M Pulldown resistor.


So I breadboarded this:


Problem with that version was, that I got a muddy signal in bypass mode. I recognized, that I should add a resistor (R16 in the image below).



Still, the signal was impacted in bypass mode, I guess that the output signal's connection to Vb (top right) and the return jack of the delay has some impact on the output signal (even though it's not that bad, but noticable). The phase switch had no noticable impact on the signal (I would have assumed, that if you reverse the phase of the the spillovers it would cancel out the sound of the guitar in bypass mode to some degree in one position).

So I decided to try another approach and skipped the idea of the phase reverse option: Here it is with inverting op-amps:



This one works pretty nice, with R11 it is easy to adjust the volume of the trails in (buffered) bypass mode - 100 k surprisingly created louder trails in bypass than in fx mode. It is a little bit noisy though, so I will try other resistors for R10, R18, R11, R13, R15. Any recommendations?

[Marshall Arts]

I tried all possible versions I can think of (I think). Oh how I sometimes wished a breadboard had an "undo" function ;-).

So, this is the version that to my ears has the least impact to the sound:



It has

- an inverting stage as buffer and
- a second inverting stage as a summing amplifier, which is similar to Jack Orman's simple mixer:



I did not fully understand, why an inverting amplifier is better for summing signals, but my tests tell me that it's true.

I skipped the idea of a phase reversal switch, which is probably overkill (at least with my delays, I did not find one that asked for that feature). I guess that most splitters (for parallel fx-loops) will provide a phase switch anyway, so I leave that up to these devices ;-).

Signal will be always in phase (True bypass, fx - if the delay does not flip the phase, buffered bypass, as it is inverted twice).

Remaining questions for me (more of a general nature...)

- The circuit does not work well without R15 (please tell me why?!)
Input and output coupling caps (C1, C7, C6, C5):
- Do the values in a circuit like this one matter at all? Or could I take 100n non-polarized caps for everything?
- Does the orientation of the polarized electrolytics matter at all (I dont think so, as they pass the AC-signal, but it would be great if somebody could confirm this for me)

If somebody could answer these, I would be really thankful.

[Marshall Arts]

Old thread, but things take time. Here is a simplified picture of ONLY the buffered bypass path. It works great in a standalone setup (except for very little additional op-amp noise), unfortunately, I am using this in a microprocessor controlled looper/switcher . In this setup, it produces some switching noise, which is ok for most setups but can be annoying on higher gain and delay mix settings. I guess, that the switching noise is fed back to the audio path through the op amps via gnd or power, as the microcontroller also switches a lot of LEDs and relays on during program change (and that creates a peak in the power supply). It's not bad enough for me to worry about it (the looper can be switchted to true bypass which works flawless), I am just posting this for information.... unless somebody finds another bug in the schematic ;-)

[gordo]

Not getting an image on this.  I'm on my laptop so will see if I have similar issues at home (mind bending security here at work)