102 Feedback City

[talbany]

How about injecting a sine wave at OD2, then OD1, etc while monitoring if a signal comes up in the previous stages? That should be 10 minute test.

And it will tell you if there is significant crosstalk happening.

Good Idea I will try this.. First I want to slave the amp again and ground out the PI on my 102 eliminate any cross talk to the output section..see what this does first..

Tony

[talbany]

How about injecting a sine wave at OD2, then OD1, etc while monitoring if a signal comes up in the previous stages? That should be 10 minute test.

And it will tell you if there is significant crosstalk happening.

jelle
Injected 1k wave into OD2 flat line into OD1 (which makes sense since the feedback is also present in clean)

Inject signal into OD1 flat line to CL2

Inject signal in CL2 flat line to input

Tony

[ayan]

Tony, so has your amp stopped feeding back then? If you haven't torn down your set up, you might want to go higher than 1K. Since we're speculating that you have capacitive coupling going on, the higher the frequency the more clearly you'd see that on a scope. Of course, chances are we're looking in the wrong places and Dumble -- assuming he lurks here -- is having a good lough at our expense.

Gil

How about injecting a sine wave at OD2, then OD1, etc while monitoring if a signal comes up in the previous stages? That should be 10 minute test.

And it will tell you if there is significant crosstalk happening.

jelle
Injected 1k wave into OD2 flat line into OD1 (which makes sense since the feedback is also present in clean)

Inject signal into OD1 flat line to CL2

Inject signal in CL2 flat line to input

Tony

[swt]

Hey talbany! have you checked the last cap filter?. i used to build amps with stiffer power supplies, something like 40uf in preamp stages, and sometime ago i decided to try something different, and used 10uf. there was a lot more feedback, and looser sound, perfect for the strat and tele i was using, and also a lot more vintage sounding, and natural sounding.
maybe a loose joint at filters so there's some ac reference lost or something like that...
also been thinking of feedback...how about a feedback network as in fender's tweed twin...with a 10meg resistor from cl2 out to cl1 in...or other options...you know...

[swt]

how about a resistor from cl2 cathode to cl1 input ala fuzz face?? maybe with a cap or 2...is it possible?

[zimm]

Something particular with the OT specs?

[10thTx]

sometime ago i decided to try something different, and used 10uf. there was a lot more feedback, and looser sound

I found the same thing to be true on my Tweed Overdrive Special. Lower filtering on V1 helped the tone, harmonics and blooming, IMO.

With respect, 10thtx

[ayan]

how about a resistor from cl2 cathode to cl1 input ala fuzz face?? maybe with a cap or 2...is it possible?

Hmmm... CL2 cathode is out of phase with CL1 grid, so I don't think that'd get the desired effect. The Tweed Twin has a negative feedback loop: output form the stage (which will be out of phase with respect to the input), followed by cathode follower (does not change the phase), feed back into the input of the previous stage, so definitely a negative feedback loop.

Gil

[talbany]

Hey talbany! have you checked the last cap filter?. i used to build amps with stiffer power supplies, something like 40uf in preamp stages, and sometime ago i decided to try something different, and used 10uf. there was a lot more feedback, and looser sound, perfect for the strat and tele i was using, and also a lot more vintage sounding, and natural sounding.
maybe a loose joint at filters so there's some ac reference lost or something like that...
also been thinking of feedback...how about a feedback network as in fender's tweed twin...with a 10meg resistor from cl2 out to cl1 in...or other options...you know...

I thought the same thing so I switched out the newer TVA's( which were in Screens/PI/V1) with the older yellow TVA's like in 124..To be honest I didn't notice that much difference!!..So Axe the filters..

I really don't want to do anything too invasive here..

Tony

[llemtt]

Please Tony,

did you tested playing guitar in one room with the speakers in another one?

otherwise this thread is a joke...

thanks
teo

[llemtt]

@Gil

I don't get what's your current hypotheses, do you think that the clean preamp (v1a+v1b) is an almost "self oscillating" circuit?

so that when fed by a signal from guitar it starts oscillating by themselves?


thanks
teo

[talbany]

Please Tony,

did you tested playing guitar in one room with the speakers in another one?

thanks
teo

Teo
Chill man I am still scoping this thing I'll get to it

T

otherwise this thread is a joke...

Teo.. If you built an amp that acts like mine (standing 6ft away at living room volumes)in the same room.. please post it as I would love to hear it..

Tony

[boldaslove6789]

Please Tony,

did you tested playing guitar in one room with the speakers in another one?

otherwise this thread is a joke...

thanks
teo

IMHO having the speakers with in range of the pickups does factor in the this equation too.

From experience recording in an isolated console room at a pro studio , putting the speaker cab and guitar in separate rooms concealed from each other will most likely not induce this natural harmonic feedback that the 102 circuit can produce.

Self oscillating feedback is almost impossible with this style amp (102/183) without some kind of proximity pickup interaction. Even if the guitar pups are facing in the opposite direction 10+ feet away from the cab it still has an effect.

[talbany]

Please Tony,

did you tested playing guitar in one room with the speakers in another one?

otherwise this thread is a joke...

thanks
teo

IMHO having the speakers with in range of the pickups does factor in the this equation too.

From experience recording in an isolated console room at a pro studio , putting the speaker cab and guitar in separate rooms concealed from each other will most likely not induce this natural harmonic feedback that the 102 circuit can produce.

Self oscillating feedback is almost impossible with this style amp (102/183) without some kind of proximity pickup interaction. Even if the guitar pups are facing in the opposite direction 10+ feet away from the cab it still has an effect.

Greg
I agree the feedback has to start from somewhere It still will be an interesting experiment I want to try to see how much natural sustain the amp has..Chances are it won't feedback as much in another room,, But we will see..

Tony

[boldaslove6789]

Greg
I agree the feedback has to start from somewhere It still will be an interesting experiment I want to try to see how much natural sustain the amp has..Chances are it won't feedback as much in another room,, So we will see..

Tony

Exactly, it's not whether the amp can feedback or not, cause at higher volumes and close pickup approximation most will, even if the amps lead dress doesn't follow the original 1:1.

What makes a great #102 circuit so special is the effect certain areas & notes on the fretboard start to bloom into very "musical" harmonic feedback. And I say musical because #102 has an almost envelope opening like effect. Call it what ever you will, note flipping, bloom, violin tone, etc.