102 Feedback City

[ayan]

The whole thing is that the amp appears to be on the verge on instability. Dave Funk talked about deliberately building instability in his amps via lead dress/layout. I had encountered that with my early Fender conversion amps back in the day; it started off as a problem, because I would get this "whistling sound" in OD mode. Once I found the problem area I could "fix things" and was left with an amp that would also take off almost all by itself.

To me, however, that didn't readily translate into the Dumble lead dress too much since it seems to be pretty much a "left to right" type of layout, such that there isn't any "obvious" in-phase coupling anywhere. Or, is there, and we have been missing this all these years? Dumble does hint at that in the 80s GP interview, where he says very small distances in the lead dress are crucial: "A distance of half a centimeter makes a big difference in the way something sounds. It's a science involved with what's called circuit constants."

I have absolute faith that you will make some pretty good discoveries, having the know how to poke around in the right places as you do. I will be patiently waiting to read about your progress. We need you, Tony.

Cheers,

Gil

Gil
Thanks for checking out the clips and joining the discussion..This amp has totally changed my view on having to use certain tubes dialing in the sweet spot on the trimmer and that type of compulsive behavior we sometimes obsess ourselves with.. If the fundamental property exists the rest is icing on an already sweet cake.. Wonderful idea on the loop inputs to determine where and hopefully what is contributing to this amps ability to take off.. I can say with some certainty that most of the feedback that is occurring is happening inside the amp and not so much as one being acoustically driven like most amps I have played.. I have to go out of town a few days but will do the experiment and will report my results to you..Yes I will crack this if it KILLS ME!!

All The Best...

Tony

[passfan]

Yes , thanks Tony. A couple of us experimented with a higher bias and while it seemed to make my amp want to take off, it didn't. I have yet to drop down to 50uf yet either. Thanks for your experiments and I look forward to the results.

[talbany]

The whole thing is that the amp appears to be on the verge on instability. Dave Funk talked about deliberately building instability in his amps via lead dress/layout. I had encountered that with my early Fender conversion amps back in the day; it started off as a problem, because I would get this "whistling sound" in OD mode. Once I found the problem area I could "fix things" and was left with an amp that would also take off almost all by itself.

To me, however, that didn't readily translate into the Dumble lead dress too much since it seems to be pretty much a "left to right" type of layout, such that there isn't any "obvious" in-phase coupling anywhere. Or, is there, and we have been missing this all these years? Dumble does hint at that in the 80s GP interview, where he says very small distances in the lead dress are crucial: "A distance of half a centimeter makes a big difference in the way something sounds. It's a science involved with what's called circuit constants."

I have absolute faith that you will make some pretty good discoveries, having the know how to poke around in the right places as you do. I will be patiently waiting to read about your progress. We need you, Tony.

Cheers,

Gil

Gil
Thanks for checking out the clips and joining the discussion..This amp has totally changed my view on having to use certain tubes dialing in the sweet spot on the trimmer and that type of compulsive behavior we sometimes obsess ourselves with.. If the fundamental property exists the rest is icing on an already sweet cake.. Wonderful idea on the loop inputs to determine where and hopefully what is contributing to this amps ability to take off.. I can say with some certainty that most of the feedback that is occurring is happening inside the amp and not so much as one being acoustically driven like most amps I have played.. I have to go out of town a few days but will do the experiment and will report my results to you..Yes I will crack this if it KILLS ME!!

All The Best...

Tony

Gil
I agree with you!!.. Believe you me I have thought about this what might I have done differently on this build?.. Looking over everything a 3rd and 4th time there is nothing that jumps out at me at this early stage..Although my instincts tell me PI/ power section but I do not want to speculate..All the voltages and common Dumble lead dress techniques have been incorporated as with all my builds..However this build did use some NOS parts Dumble used but I have a hard time believing this is the main reason for the amps instability like you mention... Hopefully we will discover the missing link soon!!...Welcome to the next level I guess! BTW..We need you too..

Thanks a TON!!

Tony

[boldaslove6789]

Sounds Great Tony!

Indeed I've found too with the #102 and #183 type circuits that the notes seems to build up a certain way and maintain a certain harmonic feedback that other circuits don't quite produce.

(Maybe his is what Tag had refereed to when he called it ie "Note flipping" LOL.)

Not that they play the biggest role in increasing harmonic feedback in #102 but I've found the best results with a Ge short plate (12ax7wa) in V1, a Telefunken Smooth plate in V2, and a Ge short plate in V3.

I've found that you almost have to teach yourself how to play without making notes taking off into feedback when playing regularly (Especially at a gig when the amp is loud and there's a band). Robben Ford has definitely mastered this technique.

[ayan]

Uber cool.

Gil

The whole thing is that the amp appears to be on the verge on instability. Dave Funk talked about deliberately building instability in his amps via lead dress/layout. I had encountered that with my early Fender conversion amps back in the day; it started off as a problem, because I would get this "whistling sound" in OD mode. Once I found the problem area I could "fix things" and was left with an amp that would also take off almost all by itself.

To me, however, that didn't readily translate into the Dumble lead dress too much since it seems to be pretty much a "left to right" type of layout, such that there isn't any "obvious" in-phase coupling anywhere. Or, is there, and we have been missing this all these years? Dumble does hint at that in the 80s GP interview, where he says very small distances in the lead dress are crucial: "A distance of half a centimeter makes a big difference in the way something sounds. It's a science involved with what's called circuit constants."

I have absolute faith that you will make some pretty good discoveries, having the know how to poke around in the right places as you do. I will be patiently waiting to read about your progress. We need you, Tony.

Cheers,

Gil

Gil
Thanks for checking out the clips and joining the discussion..This amp has totally changed my view on having to use certain tubes dialing in the sweet spot on the trimmer and that type of compulsive behavior we sometimes obsess ourselves with.. If the fundamental property exists the rest is icing on an already sweet cake.. Wonderful idea on the loop inputs to determine where and hopefully what is contributing to this amps ability to take off.. I can say with some certainty that most of the feedback that is occurring is happening inside the amp and not so much as one being acoustically driven like most amps I have played.. I have to go out of town a few days but will do the experiment and will report my results to you..Yes I will crack this if it KILLS ME!!

All The Best...

Tony

Gil
I agree with you!!.. Believe you me I have thought about this what might I have done differently on this build?.. Looking over everything a 3rd and 4th time there is nothing that jumps out at me at this early stage..Although my instincts tell me PI/ power section but I do not want to speculate..All the voltages and common Dumble lead dress techniques have been incorporated as with all my builds..However this build did use some NOS parts Dumble used but I have a hard time believing this is the main reason for the amps instability like you mention... Hopefully we will discover the missing link soon!!...Welcome to the next level I guess! BTW..We need you too..

Thanks a TON!!

Tony

[sonicmojo]

Very cool clips, thanks! Your amp has made me experiment quite a bit on mine too. Since I have a couple of third gen amps with the 50uF filter section that don't go off like yours I too think it must lie somewhere else or in a combination of many things. I would also be interested to hear if you get any type of similar results plugging into the power in on another amp or vice versa.

[Max]

Wonderful idea on the loop inputs to determine where and hopefully what is contributing to this amps ability to take off..

Tony, as I did comparisons like this rather often, here are some suggestions:

AFAIR some of your customers are studio players. So if you should have access to HQ recording equipment, you cold perhaps try things like these to find out more about the influence of different sections of the circuit of an amplifier on its global tone and feel:

Instead of playing when comparing, what perhaps bears the risk, that you might adapt your touch etc. in a way that may affect the validity of the results of such a comparison, you could perhaps think about recording a dry guitar signal in some kind of re-amping approach (perhaps some alternative versions, e.g. using a splitter between your guitar and amp when playing etc.).

Then you can e.g. feed this recorded dry signal into different amps when comparing them, to make sure, that the input signal is always the same. But to do so, IMO you'll of course need first class recording and playback equipment.

In regard to your #102 clone the playback of a dry signal, that was recorded without a possibilty of any acoustic kind of feedback between guitar and amp/speaker, and then is fed into the input, would IMO e.g. isolate all effects of the amp on the amount and kind of feedback from any possible actual acoustic kind of feedback between guitar and amp/speaker and from any possible influence of a possible adjustment of your touch etc. on the amount and kind of feedback.

Or you could perhaps think of recording the signal present at the pre-out of some amp or at the send output of a Dumblelator. If you do so, you can at any later time play back this recorded preamp out signal or Dumblelator send signal into the power amp in of some power amp(s) or into the return input of a mono or stereo Dumblelator conected with one or two power amp(s).

Recordings like these could e.g. perhaps be helpful to be able to compare two versions of the same preamp after and before some tweaks without having to rely only on your memory of the tone before the tweaks. Or you could perhaps use recordings like these to document the timbre of amps you've sold or altered, even for a long time.

When comparing complete amps, or preamps, or power amps, or different combinations of preamps and power amps etc., it's IMO a must to be able to switch as quick as possible between the structures that shall be compared, because AFAIK the human sound perception sytem is rather cheesy when we try to compare an actual sound with one we only remember, even already after some minutes or even seconds.

I found the results of experiments like those explained in these few examples to be rather educational, but this may of course be just my personal subjective impression.

Have fun!

Max

[wokkel]

Hi Tony,

I think you struck gold. Congratulations. Now just dig it up !

On a side note, on the layout of 102 I see two snubbers on V2.
But it seems you don't have them on this amp.
I'm I wrong?

Harald

[vibratoking]

Max has good input regarding using a fixed input and recording the results to make useful comparisons. I don't always trust my aural memory. I use a looper quite often for the input. I have found that I haven't been able to record well enough to trust that side of it.

In the original thread on Tony's 102, he stated that he did not use snubbers on V2.

The feedback in the clips is interesting, but something I am hearing makes me wonder if the feedback is caused the traditional way through acoustic coupling from speaker to guitar or if the amp itself is getting vibrations through coupling in the cabinets. I notice that Tony has the amp on top of the stack in the clips. I have experienced the blatty sound characteristic in the past with the head on top of the cabinet. I have noticed that if I move the head off the cabinet, the blattiness (word?) goes away. I think what happens is the vibrations are coupled into various components inside the amp and cause 'extra' sounds. For instance, I could imagine caps and transformer windings rattling around and adding spurious artifacts to the timbre. Just some info from my past experience.

[talbany]

Max
Great idea...unfortunately my friends with the killer studios live in Nashville.. About 10 hours drive.. I do have a fairly nice Boss Sampler I use to practice with so I will use Vibro's recommendation and use it to conduct my test..I'll get back with my results..Other expierments I want to try is to see if by adding a LNFB on V1B how this effects the amps ability to feedback..also to see if by moving the anode/cathode wires further apart how this effects feedback..I think it's safe to say the wood grain Formica has not much to do with the amps ability to take off!!..
My next build will be a 123 using the same components and lead dress to see if I can replicate it...Wish me luck!!!

Tony

[vibratoking]

Other expierments I want to try is to see if by adding a LNFB on V1B how this effects the amps ability to feedback..also to see if by moving the anode/cathode wires further apart how this effects feedback..

Tony, I would be interested to hear about your results with LNFB on V1B. I have mine on a switch and it certainly beefs up the amp and allows for maybe a bit more feedback, although it is not a huge difference in that category, at least for my amp.

I have also previously experimented with the anode/cathode wire dress on V1, V2, and the PI. It did make changes in the overall timbre of the amp. Making it smoother and less harsh in the highs. I didn't notice any difference in feedback, but I wasn't specifically looking for it. I would hope I would have noticed, but who knows? Don't let my input stop you from your own experiments. You may notice something very different with your amp.

BTW, what do you think about my comments regarding placing the amp on top of the speaker cabinet vs placing it somewhere else?

[M Fowler]

Wish me luck!!!

Tony, your so talented that you don't need luck to build great amps.


Mark

[Structo]

That is very interesting.
Was the amp cranked up really loud?

I think Scott and Shad have reported that 102 does indeed do that to an extent but perhaps yours even more so.

Is that picture how the amp is now?

No V2 snubbers, no footswitch wired?

Ceramic sockets?

I was trying to read the color codes on your resistors on the PI.

The tail is 22K?
What about the cathode?

And I seem to recall you did something different on the feedback resistor value (norm 4K7).

Thanks Tony!

[erwin_ve]

Tony that clip was great.
I know Shad talked about it when he had a Bludo #102 copy on his hands, Scott raved about it.
But actually hearing this; for me it's a dream to have that kind of feedback under the hands. I'm really looking forward to your experiments.

[BobW]

This is a great discussion.

Tony, if not already suggested, consider removing any mechanical coupling as well (take the amp off the spkr cab). A simple experiment to try, but Gil and Max's suggestions seem the most reasonable approach to isolate the cause and effect.

Good Luck!