Known designs with 1st stage LNFB?

[Reeltarded]

Anyone seen such an animal or possibly have done this along the way?

I have a design that could benefit and spare a bit of gain from the first stage. I don't want to kill it..

I would rather it be Dumble style instead of around the whole stage to keep the coupling RC intact.

[dbeasley]

I haven't seen any with the first stage LNFB. However the 2nd stage A-La Dumble seems to be in a few HiFi designs.

I think no one did LNFB on first stage because most designs are trying to maximize headroom and gain early on. JM2C!

Sent from my moto g(6) using Tapatalk

[Reeltarded]

Yeah I get it, but that is where I want it to work.

[pompeiisneaks]

Not too hard to try, please do report back with results

~Phil

[Reeltarded]

No! This is me trolling you to do the work and report back..

I need a rebuild kit for my Weller.. in other news.

[Tony Bones]

Here's one channel of a Guild Thunderbird. The LNFB is around the first two stages, but I think it qualifies. The slide switch is a single 3P3T unit.



FWIW, this is an amazing amp. Possibly one of the best clean sounds of any amp that I own.

It uses a pair of 7591 in the output stage with 2x12 Jensens. It's the biggest combo I've ever encountered, with the possible exception of that Fender behemouth with 4x12's that I can't remember the name of. It's about the same width as a Super Reverb, but 8 inches taller and 3 inches deeper.

[Reeltarded]

Here's one channel of a Guild Thunderbird. The LNFB is around the first two stages, but I think it qualifies. The slide switch is a single 3P3T unit.



FWIW, this is an amazing amp. Possibly one of the best clean sounds of any amp that I own.

It uses a pair of 7591 in the output stage with 2x12 Jensens. It's the biggest combo I've ever encountered, with the possible exception of that Fender behemouth with 4x12's that I can't remember the name of. It's about the same width as a Super Reverb, but 8 inches taller and 3 inches deeper.

Totally would not work with this amp, but noted and saved! That is super cool!

[Tony Bones]

Totally would not work with this amp, but noted and saved! That is super cool!

Thanks for saying so, though I expect that it actually pissed you off.

Anyway, we could eliminate the fun part (from the plate of the second stage) but keep the local cathode feedback. Unfortunately, it requires cap coupling, but maybe that's not too bad? I'm not sure what will / won't work in this application.

[Reeltarded]

Totally would not work with this amp, but noted and saved! That is super cool!

Thanks for saying so, though I expect that it actually pissed you off.

Anyway, we could eliminate the fun part (from the plate of the second stage) but keep the local cathode feedback. Unfortunately, it requires cap coupling, but maybe that's not too bad? I'm not sure what will / won't work in this application.

Nah, I was being serious about the circuit you posted. I imagine it is bold and stays put. Clean sounds usually have a short useful range of input.

From the second stage to the PI this amp is a 1972 JMP 50.

The first stage is a 100k plate 1k5//22u with a 500p coupler to a 1M pot that has a 6 position bright and a tweed Deluxe tone control. It works great, but it's the last place I can tamper with this amp. Everything from 65% rotation up is a waste, so I imagined I could lose gain but flatten it out and maybe add just a little more sing along the way.

Yesterday, I tried many variations of feedback at the tubes on the second and third (CF driving) stages. Gross! Weird.

If anything happens, it has to be at that first stage. I am using a lot of global feedback. Dumble values at the tail, but different FBR and up a tap.

It might just be done as it is and move on.

[sluckey]

The simplest way to get LNFB is to remove the cathode bypass cap. This will create degenerative feedback AKA negative feedback.

The old Gibson Atlas amps used a 50pF cap between plate and grid on the first triode.

https://el34world.com/charts/Schematics ... dalist.pdf

Sunn used a switched 12pf from plate to grid in a later stage as part of a mid boost circuit. I suppose you could do something similar to the first triode. That's already covered in the Atlas circuit above.

http://sluckeyamps.com/sunn/sunn_sceptre_1971.pdf

[Reeltarded]

The simplest way to get LNFB is to remove the cathode bypass cap. This will create degenerative feedback AKA negative feedback.

The old Gibson Atlas amps used a 50pF cap between plate and grid on the first triode.

https://el34world.com/charts/Schematics ... dalist.pdf

Sunn used a switched 12pf from plate to grid in a later stage as part of a mid boost circuit. I suppose you could do something similar to the first triode. That's already covered in the Atlas circuit above.

http://sluckeyamps.com/sunn/sunn_sceptre_1971.pdf

Does anyone else know if I could do these things?

[Reeltarded]

Actually.. lifting the bypass is elegant and predictable and the other side of my bright switch is empty.

You're brilliant.

[Reeltarded]

I need to lower the resistance after that 1st stage but that absolutely works.

Can anyone else verify that this absolutely works?

lmao

[TUBEDUDE]

From the second stage to the PI this amp is a 1972 JMP

Sounds good right there!!

[Reeltarded]

Every one of them sounds very specifically different, but I swapped parts around until I felt like I had a fair version of the best one ever made. The only place it deviates is no bright over the volume. All the shaping happens in the first pre-stage. It also has paralled mid control. (by the way that is fantastic)

Working on a way to get somewhere between slukey's suggestion of lifting bypass and where it was before right now. I may have to cool the stage down and jack the plate up plus drop the resistance after it. Tiny tiny bits at a time. This thing might need another rotary for selecting 1st stage cathode. I have room, and that would give me a lot of control over response.. we know what the middle is, it's all about what's punching it now. It's so good that I hate to touch it!