Pos and Neg Regeneration (i.e. Phase 100)

[moosapotamus]

I'm fixin' to tinker with a Phase 100, and have a couple questions before I get started...

Can someone explain the difference between negative regeneration and positive regeneration? How would one be implemented, compared to the other (in a Phase 100, for example)?

Is the Phase 100 an example of negative feedback, because the regen path taps from the output back to the inverting (negative) input of IC6b?

JD's Phase 100 scheme: http://www.generalguitargadgets.com/v2/diagrams/mxr_p100_sc.gif

If someone wanted to add a mod that allowed for switching between positive and negative regeneration, are there certain circumstances under which they might not sound very different from each other? Conversly, can things be done to accentuate the difference in how pos regen sounds compared to neg regen?

One of the Phase 100 mods recently discussed here involved returning the regen path back to different stages. Would connecting the regen path to a non-inverting input sound any different than returning it to an inverting input?

Finally, true or false... regeneration and feedback mean the same thing, but are not necessarily the same thing as resonance.

OK, place your pencils on your desks and close your test booklets.

Thanks!
~ Charlie

[toneman]

HiYa

**Can someone explain the difference between negative regeneration and **positive regeneration? How would one be implemented, compared to the **other (in a Phase 100, for example)?

A1:  pos regen is "in phase"  , or zero degrees signal shift.
A2: neg regen is "out of phase"  or 180 degrees signal shift.

note: out-of-phase can B 45, 90, 180, 270, etc.
at 360, it's back in phase again.....

in phase makes signals "add"
out phase make signals "subtract"

each inverting stage shiifts signal 180degrees.
with an even number of inversions,
signal out has same phase as signal in.

**Is the Phase 100 an example of negative feedback, because the regen **path taps from the output back to the inverting (negative) input of IC6b?

the phase100 schematic  referenced looks like 6 phase shift stages.
The stages with the VR's in them(Variable Resistor)
BUT, notice the signal goes to + input of all opamps.
Each opamp itself has (negative)feedback.
Output & input are IN phase.   The VRs act a variable resistors
to control the frequency response of each phase.

**JD's Phase 100 scheme: **http://www.generalguitargadgets.com/v2/diagrams/mxr_p100_sc.gif

**If someone wanted to add a mod that allowed for switching between **positive and negative regeneration, are there certain circumstances **under which they might not sound very different from each other? **Conversly, can things be done to accentuate the difference in how pos **regen sounds compared to neg regen?

check out R.G.Keen's Phase90/180 for feedback examples.
check out  R.G.Keen's  article on Phasers and Flangers.

To have regen, can B reinforcing or non-reinforcing.
Since in & out are both in phase, use limiting resistor and pot for
feedback.   For out-of-phase feedback, add inverting opamp.
When U find suitable levels, pos and neg, add a switch to
change from one to the other, or put both into a noninverting
mixer and mix in a little of both...(?)
In the schematic, feedback is thru R16, back to the IC6b.
IC4a is a preamp.  IC6b does shift frequency phase, but
it is not variable.   Same with IC2a and IC3b.

Check out The Phase45 and Korg Phaser schematics.
All phasers are similar, just do shifting with different
components.  B sure to read Keen's article.

**One of the Phase 100 mods recently discussed here involved returning **the regen path back to different stages. Would connecting the regen **path to a non-inverting input sound any different than returning it to an **inverting input?

Probably.  Less stages, different sound.
Pleasing?  Musical?  don't know.

**Finally, true or false... regeneration and feedback mean the same thing, **but are not necessarily the same thing as resonance.

Correct.  
But,
Feedback can B "regenerative" or "degenerative".
adding or subtracting, respectively.

Resonance usually refers to the "bandpass" or "Q" of a filter.
Feedback can cause resonance & resonances, good or bad.
Too much resonance, too much feedback of either kind,
can cause circuit to "howl" or break into oscillation.
Watch those speakers!

staytuned
tone

[toneman]

HiYa

**Can someone explain the difference between negative regeneration and **positive regeneration? How would one be implemented, compared to the **other (in a Phase 100, for example)?

A1:  pos regen is "in phase"  , or zero degrees signal shift.
A2: neg regen is "out of phase"  or 180 degrees signal shift.

note: out-of-phase can B 45, 90, 180, 270, etc.
at 360, it's back in phase again.....

in phase makes signals "add"
out phase make signals "subtract"

each inverting stage shiifts signal 180degrees.
with an even number of inversions,
signal out has same phase as signal in.

**Is the Phase 100 an example of negative feedback, because the regen **path taps from the output back to the inverting (negative) input of IC6b?

the phase100 schematic  referenced looks like 6 phase shift stages.
The stages with the VR's in them(Variable Resistor)
BUT, notice the signal goes to + input of all opamps.
Each opamp itself has (negative)feedback.
Output & input are IN phase.   The VRs act a variable resistors
to control the frequency response of each phase.

**JD's Phase 100 scheme: **http://www.generalguitargadgets.com/v2/diagrams/mxr_p100_sc.gif

**If someone wanted to add a mod that allowed for switching between **positive and negative regeneration, are there certain circumstances **under which they might not sound very different from each other? **Conversly, can things be done to accentuate the difference in how pos **regen sounds compared to neg regen?

check out R.G.Keen's Phase90/180 for feedback examples.
check out  R.G.Keen's  article on Phasers and Flangers.

To have regen, can B reinforcing or non-reinforcing.
Since in & out are both in phase, use limiting resistor and pot for
feedback.   For out-of-phase feedback, add inverting opamp.
When U find suitable levels, pos and neg, add a switch to
change from one to the other, or put both into a noninverting
mixer and mix in a little of both...(?)
In the schematic, feedback is thru R16, back to the IC6b.
IC4a is a preamp.  IC6b does shift frequency phase, but
it is not variable.   Same with IC2a and IC3b.

Check out The Phase45 and Korg Phaser schematics.
All phasers are similar, just do shifting with different
components.  B sure to read Keen's article.

**One of the Phase 100 mods recently discussed here involved returning **the regen path back to different stages. Would connecting the regen **path to a non-inverting input sound any different than returning it to an **inverting input?

Probably.  Less stages, different sound.
Pleasing?  Musical?  don't know.

**Finally, true or false... regeneration and feedback mean the same thing, **but are not necessarily the same thing as resonance.

Correct.  
But,
Feedback can B "regenerative" or "degenerative".
adding or subtracting, respectively.

Resonance usually refers to the "bandpass" or "Q" of a filter.
Feedback can cause resonance & resonances, good or bad.
Too much resonance, too much feedback of either kind,
can cause circuit to "howl" or break into oscillation.
Watch those speakers!

staytuned
tone

[moosapotamus]

HiYa
A1:  pos regen is "in phase"  , or zero degrees signal shift.
A2: neg regen is "out of phase"  or 180 degrees signal shift.

note: out-of-phase can B 45, 90, 180, 270, etc.
at 360, it's back in phase again.....

in phase makes signals "add"
out phase make signals "subtract"

each inverting stage shiifts signal 180degrees.
with an even number of inversions,
signal out has same phase as signal in.

Yeah! OK, cool!

In the schematic, feedback is thru R16, back to the IC6b.
IC4a is a preamp.  IC6b does shift frequency phase, but
it is not variable.   Same with IC2a and IC3b.

Are you sure? To me, it looks like feedback is through R1 (15K), into IC6b pin 6 (inverting). And, are you sure that IC6b does not have variable phase shift? To me, it looks like it does. Aren't the six variable phase shift stages IC6b, IC5a, IC4b, IC3a, IC2b, and IC1a?

B sure to read Keen's article.

Fo' shoe!

Pleasing?  Musical?  don't know.

Well, I guess I'll let you know.

Feedback can B "regenerative" or "degenerative".
adding or subtracting, respectively.

Resonance usually refers to the "bandpass" or "Q" of a filter.
Feedback can cause resonance & resonances, good or bad.
Too much resonance, too much feedback of either kind,
can cause circuit to "howl" or break into oscillation.
Watch those speakers!

staytuned
tone

Yeah, I've heard that! :shock:
Thanks, tone dude!

Anybody else?

Thanks!
~ Charlie

[toneman]

U R right on the 6 stages.
I was flipping back and forth from message to schematic.
Now i printed it out 2 write this  :-P

Now as 4 feedback....
U R also right about R1 being a feedback R.
Didn't see that it was switched in/out with SW2.

But R18 *is* feedback also.
Technically, R3, R5, R7, R9, R11, R30, R28, R26, R24, R22, R20, R56
are "feedback" resistors also.
Why?
Bcause they couple/feedback Output-2-Input.
Notice also, except for IC1b, the feedback is negative or out-of-phase.
How much?
108deg out, or "degenerative".
In opamp circuits, feedback determines gain or amplification.
In this case, a "phaser" or "phasor", feedback is used to
emphasize-deemphasize certain frequenceies.
this gain or reduction is controlled by the LowFrequencyOscillator(LFO)
which is composed of IC1b and the transistors.
But U knew that.
staytuned
tone

[Mark Hammer]

Regeneration, feedback, resonance, color, emphasis are used almost interchangeably on a variety of effects for what is essentially the same control.  What they share in common IS feeding back a portion of the output of some audio path back to an earlier point in that path.  

The names applied to that will depend partly on what the audible consequences are.  In the case of delays long enough to produce audible echoes, there might be a certain boxiness to the sound but not specific emphasis of frequencies or frequency bands.  In the case of flangers and phasers, though, that feedback DOES result in an audible emphasis of certain frequencies over others.  Presumably because there are doofuses out there who will think that "Feedback" means that if you turn it up your amp will feed back, the name is changed for different products to make it sexy-sounding or to convey the change in tonal character it produces.

In some instances, feedback/regeneration is applied before dry/wet mixing (i.e., solely within the wet path).  In other instances, the feedback is applied after wet/dry mixing, while in others it is a hybrid.  For instance, although the typical practice with phasers is to feed back the output of the last phaseshift stage to the second one in the series, so that the feedback always travels 1 stage less than the total number of stages in the pedal, in the Small Stone the "Color" switch feeds back the output of the wet path to the input stage of the pedal so that it travels through all 4 allpass stages.  I gather this has to do with the polarity of allpass stages in general and the polarity of the SS input stage.

Personally, I've never understood the difference between sum/difference mixing, and regeneration polarity.  In the sum/difference case, the wet signal is either added to the dry signal or subracted from it.  Variations in regeneration simply determine the height of any peaks or dips, whereas summing vs differencing turns a peak ito a dip and vice versa.  Of course, if the recirculation path comes AFTER the wet/dry mixing, then polarity of the recirculated signal matters.

[moosapotamus]

Cool, I'm going to go hack into my Phase 100 now.

Thanks for the input.  

~ Charlie