Author Topic: Question about analog octave circuits  (Read 1153 times)

matmosphere

Question about analog octave circuits
« on: November 02, 2017, 12:21:20 AM »
Is there a way with any analog octave circuits to split the output into two signals with one being the non-octave effected signal and the other being only the octave sound that's being generated?

If my understanding of transformer based octaves is correct then you couldn't split the signal in that way on that type of circuit. But I've never look closely at other types of octave pedals.

Pedal love

Re: Question about analog octave circuits
« Reply #1 on: November 02, 2017, 12:50:08 AM »
Is there a way with any analog octave circuits to split the output into two signals with one being the non-octave effected signal and the other being only the octave sound that's being generated?

If my understanding of transformer based octaves is correct then you couldn't split the signal in that way on that type of circuit. But I've never look closely at other types of octave pedals.
Are you talking about octave up or octave divide? They are very different.

Sent from my SM-S327VL using Tapatalk


PRR

Re: Question about analog octave circuits
« Reply #2 on: November 02, 2017, 12:59:35 AM »
The non-effected signal is easy, of course.

Most octave-up circuits leak a large amount of "raw uneffected" signal at lower levels. Getting an only-octave signal could be way too much trimming and filtering to be practical or musical.

Octave-down seems simpler but I am less familiar with those.

Mark Hammer

Re: Question about analog octave circuits
« Reply #3 on: November 02, 2017, 09:43:31 AM »
In referencing transformers, I take it that matmosphere is referring specifically to octave-up.

The most straightforward way of creating a clean/octave blend is to tap the clean signal from an earlier point in the circuit.  Often there will be some sort of gain stage as a "front end", before the signal gets to the near-inevitable phase-splitter - identifiable as a transistor stage with equal-value emitter and collector resistors, and outputs from both collector and emitter.  The Fender Blender provides a nice illustration of this principle.

You can see in this drawing that an attenuated version of the clean signal is tapped from the ground end of the "Sustain" pot.  That gets fed to one side of the "Blend" pot, which will adjust the balance of clean and octave-fuzzed signal.
Where could we do a similar thing on, say, the Foxx Tone Machine?

The front end, here, is more complex than that found on the Fender Blender, but I think we can find a tap point from the emitter of Q2.  Since we don't want that tap to interfere or interact with the octaving, it might be best to stick yet another 10uf cap on the emitter, and run the signal from the negative side of that cap to some form of blend pot, just ahead of the Volume pot.