SSS-style DCCF, independant bias? LND150?

[sds1]

Howdy,

Questions about the DCCF found on the SSS:


1) How would you modify this circuit to use 2x separate bias trimmers (one for each side)?
2) Thoughts/personal experiences swapping in directly LND150 for the 12AX7 here?

TIA

[JD0x0]

An LND150 wont behave the same as a tube CF. Unless you dont want the added harmonic content of the tube CF, and purely want the impedance buffer, I would avoid the LND150's here.

[pompeiisneaks]

An LND150 wont behave the same as a tube CF. Unless you dont want the added harmonic content of the tube CF, and purely want the impedance buffer, I would avoid the LND150's here.

It was my understanding that a cathode follower is near or under unity gain, and for recovering losses from the tone stack and matching impedance etc. Therefore, it would seem to me that it's doing very little if anything to 'color' the sound and is functioning as a 'bridge' between segments of the circuit. They perform exceptionally linearly (per the valve wizard) and therefore to me seem like a perfect place to replace them with a mosfet if one should choose to do so? No? It seems that other tone shaping parts of the circuit would definitely not be optimal like gain stages, or phase inverters that drive hard into power sections, etc are very optimally chosen as tubes....

Or am I mistaken?

~Phil

[erwin_ve]

An LND150 wont behave the same as a tube CF. Unless you dont want the added harmonic content of the tube CF, and purely want the impedance buffer, I would avoid the LND150's here.

It was my understanding that a cathode follower is near or under unity gain, and for recovering losses from the tone stack and matching impedance etc. Therefore, it would seem to me that it's doing very little if anything to 'color' the sound and is functioning as a 'bridge' between segments of the circuit. They perform exceptionally linearly (per the valve wizard) and therefore to me seem like a perfect place to replace them with a mosfet if one should choose to do so? No? It seems that other tone shaping parts of the circuit would definitely not be optimal like gain stages, or phase inverters that drive hard into power sections, etc are very optimally chosen as tubes....

Or am I mistaken?

~Phil

Tube CF defenitly has some added compression/harmonics beside the unity gain.

[pompeiisneaks]

An LND150 wont behave the same as a tube CF. Unless you dont want the added harmonic content of the tube CF, and purely want the impedance buffer, I would avoid the LND150's here.

It was my understanding that a cathode follower is near or under unity gain, and for recovering losses from the tone stack and matching impedance etc. Therefore, it would seem to me that it's doing very little if anything to 'color' the sound and is functioning as a 'bridge' between segments of the circuit. They perform exceptionally linearly (per the valve wizard) and therefore to me seem like a perfect place to replace them with a mosfet if one should choose to do so? No? It seems that other tone shaping parts of the circuit would definitely not be optimal like gain stages, or phase inverters that drive hard into power sections, etc are very optimally chosen as tubes....

Or am I mistaken?

~Phil

Tube CF defenitly has some added compression/harmonics beside the unity gain.

Could you explain how/why? If it's operating in a completely linear fashion and not amplifying the signal, what causes compression in a non driven tube that's in it's linear section? I thought the compression is caused when a tube starts getting out of the linear zone, and is amplifying past it's optimal 'linear' range. I also am under the impression that the 'tone' from a tube comes from the non linearities, that cause the other harmonic distortion etc. If the stage is in a non amplifying, very linear operating point, how does it color it? I honestly want to have detail/data that explains this. I trust you're probably right, but just because you say it is so, doesn't mean it is so. And no offense meant, I'm just looking for knowledge and understanding, and although I trust you, I still don't understand the 'why' and want to.

Thanks,

~Phil

[erwin_ve]

Phil, no offense taken !

A ecc83/12ax7 maybe not the best lineair choice for a cathode follower.
I dont have the time to do a load line right now, anyway the 220k is fairly big and at higher volumes explain what I might be hearing, non linear fashion.
Bear in mind Valve wizard is explaining how to get the most linear out of a cathode follower and choose the Ecc82 for that purpose with a lower load on the cathode.

I can do a test with my SSS feeding a signal in the PI and see what it does after the cathode follower. Should be easy to see on the scope

Erwin

[pompeiisneaks]

Oh so you're saying the CF in the SSS to the power sections are biased in a different way to actually be more gainy/cause some tonal impact...

gotcha, I'd definitely like to see some of the detail when you have time.

~Phl

[JD0x0]

ValveWizard has a pretty solid write up on DCCF and explains how the 'flawed' operating points contribute to the
performance, which many find desirable, in guitar amps.
http://www.valvewizard.co.uk/dccf.html# ... to%20cause

[Roe]

ValveWizard has a pretty solid write up on DCCF and explains how the 'flawed' operating points contribute to the
performance, which many find desirable, in guitar amps.
http://www.valvewizard.co.uk/dccf.html# ... to%20cause

his book also discusses the Mosfet substitutes for cathode followers (LND150)

[erwin_ve]

ValveWizard has a pretty solid write up on DCCF and explains how the 'flawed' operating points contribute to the
performance, which many find desirable, in guitar amps.
http://www.valvewizard.co.uk/dccf.html# ... to%20cause

his book also discusses the Mosfet substitutes for cathode followers (LND150)

With flawed operating points?

[ericlc]

Merlin states that a MOSFET can be used instead of a valve in case you don't want the CF to contribute towards any tonality of its own.
Contribution towards tonality in case of the valve CF is due to clipping of the CF (top) and grid-current limiting (bottom) of the gain stage in front of the CF.

[Roe]

ValveWizard has a pretty solid write up on DCCF and explains how the 'flawed' operating points contribute to the
performance, which many find desirable, in guitar amps.
http://www.valvewizard.co.uk/dccf.html# ... to%20cause

his book also discusses the Mosfet substitutes for cathode followers (LND150)

With flawed operating points?

not that I'm aware of no

[sds1]

Not cloning a SSS here, actually a 100W high-gain new design and I wanted to put this on a switch and see what it does for me.

While this stage may (or may not?) provide harmonic color in the SSS, I think I'm mostly interested in the benefit-effects of change in impedance and lack of coupling cap/power tube grid interaction.

Regarding harmonic color though, I thought this feature was to push SSS/SVT circuit into more of a hi-fi cleans type power amp?

I will build it and report back but I'd really like to split the bias if it's possible.

Looking at RG's MOSFET DCCF driver configuration as well, but does anyone know what Vs+ and Vs- can be? I thought they would be at HT-ish potential but someone elsewhere noted the dissipation at the source resistor goes up to like 10W or some nonsense with the higher VDC supply.

[ericlc]

I must warn you that I have never build such a circuit.
I guess if you just replace that valve for a set of MOSFET's and keep the same resistor values that the current is not that high.
-280V over 220K gives about 1.2mA / 356mW.