Development of Variable Negative Feedback Mod

[NewReligion]

Development of my Variable Negative Feedback (VNFB) Mod.

Actually changes the character of the amp from Dark & Chewy feeling (Hopkins Pandora) to Tighter & Brighter (Hopkins MorningStar).

Amp also is equipped with my V-Mod (Voltage Dissipation) Mod, SAT Clipper, Depth/Resonance Mod. Thank you George Metropoulos for the very transparent Metropoulos Zero Loss Effects Loop.

 

[scottosan]

Different than using a pot in place rather than a resistor, like Friedman’s “Response” control?

 

[NewReligion]

Different than using a pot in place rather than a resistor, like Friedman’s “Response” control?

Yes it is different. I didn’t realize DF had the “Response” control. I imagine there are many variations to this simple idea.

It is more in depth than just a couple of resistors on a SPST switch. A rotary IMO would be too much in addition to limiting other options in this part of the circuit which I feel necessary.

I once had a modded Marshall from someone we all know that had a 5 way rotary switch which paralleled caps over a coupler. I could never settle on a choice. I disconnected it and boom total improvement.

Point being I get creative in order to reach a goal as opposed to just goofing around. Kind of relative to The mother of invention quote. There are so many places to work in the NFB circuit.

Thanks for the interest & question.

David

 

[psychodave]

My Cameron Aldrich mod from around 2011 has an adjustable NFB instead of a presence pot. It’s on a push pull pot. It’s not just a simple circuit either, there is a lot going on with it and the push pull adds additional tonal changes. I think the adjustable NFB really makes an amp versatile.

 

[scottosan]

The Friedman control is a variable resistor in place of the NFB resistor. In series with the depth control is pretty much the same effect you describe. This is vs the 3 way dark switch on a CCV

 

[NewReligion]

The Friedman control is a variable resistor in place of the NFB resistor. In series with the depth control is pretty much the same effect you describe. This is vs the 3 way dark switch on a CCV

Very interesting how 3 guys approached the same desired outcome differently.

Thank you for the detailed data.

Much respect, David

 

[NewReligion]

My Cameron Aldrich mod from around 2011 has an adjustable NFB instead of a presence pot. It’s on a push pull pot. It’s not just a simple circuit either, there is a lot going on with it and the push pull adds additional tonal changes. I think the adjustable NFB really makes an amp versatile.

I absolutely agree. This is a part of the circuit I will spend more time with. I am currently working with simple switching relays as so much can be accomplished there as well.

Thanks for taking time to listen and posting feedback.

David

 

[glip22]

Very cool Dave! I recently did a three way switch with 2 resistors on the switch paralleling my existing 100K resistor on the board. I have approximately 50k in one setting, middle is stock 100K and position 2 is approximately 25K.
When I switch to the 50K the volume and highs drop significantly. When I switch to the 25K it drops even more. I have the NFB going to my 8 ohm tap.

I was very surprised at the effect. I'm still not sure it's correct. I checked my readings and I read correct resistance on my
meter. I have to completely adjust my settings for each but can get a big variety in tones and feel. Thoughts? Low end gets really cool in the lower settings but the EQ changes a lot for each.

 

[NewReligion]

Very cool Dave! I recently did a three way switch with 2 resistors on the switch paralleling my existing 100K resistor on the board. I have approximately 50k in one setting, middle is stock 100K and position 2 is approximately 25K.
When I switch to the 50K the volume and highs drop significantly. When I switch to the 25K it drops even more. I have the NFB going to my 8 ohm tap.

I was very surprised at the effect. I'm still not sure it's correct. I checked my readings and I read correct resistance on my
meter. I have to completely adjust my settings for each but can get a big variety in tones and feel. Thoughts? Low end gets really cool in the lower settings but the EQ changes a lot for each.

Hello Glip! Great to hear from you. When you get that low of a resistance it is going to lose a lot of treble , tightness and signal volume. Try disconnecting the presence altogether and you will likely find it is quite similar.

I worked in the opposite direction from the Pandora. So I increased the NFB significantly while utilizing a depth mod of sorts in one position and non on another while leading to multiple taps. This in conjunction with the V-Mod which changes the dissipation % rate of the power tubes gives the user the feeling of have two completely different circuits at hand.

The TMB does not need to be touched nor the Presence but as you see in the video if the Presence is increased from 5 to 7 it becomes more Metal which was the goal as the guy plays Hair Metal & more Modern Metal but still wanted clear singing lead lines. So we ended up with the VNFB which requires little change when switched.

I hope I answered your question.

David

 

[glip22]

Very cool Dave! I recently did a three way switch with 2 resistors on the switch paralleling my existing 100K resistor on the board. I have approximately 50k in one setting, middle is stock 100K and position 2 is approximately 25K.
When I switch to the 50K the volume and highs drop significantly. When I switch to the 25K it drops even more. I have the NFB going to my 8 ohm tap.

I was very surprised at the effect. I'm still not sure it's correct. I checked my readings and I read correct resistance on my
meter. I have to completely adjust my settings for each but can get a big variety in tones and feel. Thoughts? Low end gets really cool in the lower settings but the EQ changes a lot for each.

Hello Glip! Great to hear from you. When you get that low of a resistance it is going to lose a lot of treble , tightness and signal volume. Try disconnecting the presence altogether and you will likely find it is quite similar.

I worked in the opposite direction from the Pandora. So I increased the NFB significantly while utilizing a depth mod of sorts in one position and non on another while leading to multiple taps. This in conjunction with the V-Mod which changes the dissipation % rate of the power tubes gives the user the feeling of have two completely different circuits at hand.

The TMB does not need to be touched nor the Presence but as you see in the video if the Presence is increased from 5 to 7 it becomes more Metal which was the goal as the guy plays Hair Metal & more Modern Metal but still wanted clear singing lead lines. So we ended up with the VNFB which requires little change when switched.

I hope I answered your question.

David

Thanks Bro. Some cool things can be done in the NFB. I'll have to experiment some.

 

[Monomyth]

Switchable taps are really cool Dave, there’s so much tone and character in the nfb circuit. I’m working on some new things too.

 

[NewReligion]

Switchable taps are really cool Dave, there’s so much tone and character in the nfb circuit. I’m working on some new things too.

Thank you brother Shea. Everything you are engineering sounds great. The BlackSun at times Sounds like the Gower Killer Kali ++ but more articulate.

David...♫

 

[nzsteve]

My amp tech installed an adjustable one for me on my Mojave, but like he said, once you adjust it to where you like, your probably never move it again so it was going to be a wasted spot for a push pull, so he left it there for a few weeks I dialed it in, never touched it and he did set the values in the amp but he did add a push pull for either a 4 ohm or 8 ohm tap.. I think thats correct, or its 16 and 8, I am not a tech and now I cant recall but its the normal tap and one lower I think.. and I never change it, not sure how to use it correctly or where that would come into play the best.. Thats one mod that didnt do too much for me after we set it.. just my experience..

 

[NewReligion]

My amp tech installed an adjustable one for me on my Mojave, but like he said, once you adjust it to where you like, your probably never move it again so it was going to be a wasted spot for a push pull, so he left it there for a few weeks I dialed it in, never touched it and he did set the values in the amp but he did add a push pull for either a 4 ohm or 8 ohm tap.. I think thats correct, or its 16 and 8, I am not a tech and now I cant recall but its the normal tap and one lower I think.. and I never change it, not sure how to use it correctly or where that would come into play the best.. Thats one mod that didnt do too much for me after we set it.. just my experience..

Right. That is actually a technique used to identify what sounds great as you dial it in. Then the tech carefully removes the wires (takes it out of circuit) measures the value. A tech then can replace the potentiometer (which is a variable resistor) with a resistor of the desired value. No need for drilling holes for an option that will remain static.

My guy wanted the tone and feel of two of my amps which are similar. Therefore adjustments are necessary but minimal. It was nice to satisfy that request of giving the amp the ability to change such drastically in character.

The rest of the mod is very in depth and can take 9-14 hours to perform depending on options. Then I let the amp burn, in order to settle resistors and flow capacitors. This process is no less than 8 hours with a signal being put through it at times.

Before my Oscilloscope died on me I always took a look for things that may not be heard as high gain analog tube amp modifications are beautiful to me when done properly.

Oops, rant lol.

Thanks for taking an interest and posting nzsteve

David

 

[nzsteve]

All good, so what is the standard nfb tap, is it on the 8ohm output usually? If so, what would the difference of having the ability of using it on the 4 ohm tap, mine is on the push pull so I can use either but im not actually sure what to look for sound wise, would it need to be a certain volume to realize the difference etc?