'Deluxe' active blended and buffered Feedback Looper advice

[Viktor Von Doom]

Hello everyone-

Longtime lurker, first time poster.

I have a question about something I have seen posted here previously. I have been playing around with a similar circuit on a breadboard, and I accidentally came across this thread https://www.diystompboxes.com/smfforum/index.php?topic=95089.0. I know; it is really old.

This is pretty much exactly what I have on my breadboard, except that I have been using 'utility boards' (Link: https://shop.pedalparts.co.uk/product/invertingbuffer) to achieve this function.

I would like to have a PCB made for this project, but need some help with the schematic first. In the thread linked above, there was no option to invert the phase of the 'WET' signal or the 'FEEDBACK' signal. This is important (IMHO) as some effects are inverting [and would become self-cancelling if looped], and sometimes the option of an inverted signal provides an interesting sonic choice when desired.

I have attached two schematics below. One is the original, and one is annotated. I believe I can substitute a TL074 for the areas highlighted and use them with an SPDT switch to provide the phase reversal option- but I would like to hear from the experts here (as I am only a rank amateur ).




Thanks for reading. Any ideas, help, snarky comments, or brutal criticisms are welcomed.

[PRR]

Welcome!

There's three opamps. We usually buy opamps as duals. So use a fourth opamp as a final inverter.

Quads exist but the usual advice (and in most commercial gear!) is to do duals for easier layout.

[Viktor Von Doom]

Thank you, Paul. There are many, many clever and knowledgeable folks here, and I am very happy to be included amongst your ranks (though I still have so much to learn).

Perhaps I was unclear in my previous post- a 'Master' phase switch at the output of this circuit wouldn't be that desirable, IMO. The ability to invert (or not) the phase of the signal at two specific points (the 'Op Amp A,' and the 'Op Amp B,' as annotated above) seems like it would be provide the most usable sounds (due to the way the Input signal is bounced around between the Send and Return jacks).

I chose this circuit to use as my first PCB design project because it has a (relatively) simple signal path, but that it would also force a deeper understanding of Op Amps and their multiple uses (in this case: a simple buffer, and also as a summing amplifier).

As stated above- any input, advice, harsh criticisms, etc., are welcomed. Thanks for your your welcome, Paul, and I hope to grow into a valued member of this wonderful resource

[bluelagoon]

Onya Viktor, Not as knowledgeable as a lot here, so likely not as helpful, But nice to see you onboard, Welcome.

Like the look of your first project, looks interesting. Good luck with it

[Viktor Von Doom]

Thank you.

I cannot take credit for the schematic, though. It was drawn and posted here by a user named earthtonesaudio (back in 2011. But it doesn't seem like he has logged on recently). He was even kind enough to post it as a Falstad Simulation link in the original thread.

I had breadboarded a nearly identical circuit (but mine had phase reversal on the opamps), but I did it by using 'add-on' PCBs (utility? I don't know what the right term would be) vs. placing all the individual components. Two phase inverting buffer boards, a buffer/splitter board, and two buffer/blender boards. Kind of cheating; I know.

I accidentally found that link while hunting around and thought it would be better to share than my crappy hand-drawn schematic before I asked anyone for help, ha ha

[Viktor Von Doom]

So, after taking a closer look at the schematic I posted earlier, it seems like Mr. earthtonesaudio is more clever than I was on my breadboard. Would someone please verify what I see to be the Op Amp functionality in this circuit?

There's three opamps

Yes, I know that. I originally thought I could pull off my idea with one single Op Amp and a single Quad Amp, but I now see where that wouldn't work. If we let the annotated schematic stay with the drawn-on 'Op Amp A,' and 'Op amp B,' nomenclature, can we call the first unnamed component 'Op Amp -1?'

As I understand it:

* 'Op Amp -1' Is utilized as a non-inverting buffer
It-

1) Buffers the audio signal entering from the 'INPUT JACK'
2) And sends its output to A) the DRY MIX pot, and B) to 'Op Amp A'


* 'Op Amp A' is utilized as an inverting summing amplifier
It-

1) Sums the output of the FEEDBACK POT and 'Op Amp -1'
2) And sends its output to the 'SEND JACK'


* 'Op Amp B' is utilized as an inverting summing amplifier
It-

1) Sums the outputs of the WET and DRY pots
2) And send its output to A) one lug of the FEEDBACK POT, and B) to the 'OUTPUT JACK'


Do I read this correctly?

[ElectricDruid]

Do I read this correctly?

Yes, you do.

[Viktor Von Doom]

Yes, you do.

Thank you