4th gain stage, I am guilty

[El_Martin]

Hi!

OK, I broke the rule. Couldn't stand one triode being wasted in my two cylinder Liverpool.
Inserted it after 3rd stage. 4n7 coupler, Ra=220k(edited), Rk=4k7 (no bypass cap), 470k to ground on gate. Followed by a ... hm...hum...em...errrm
HRM -there! another rule broken- full tonestack w. trimpots and a 470kOhm (or was it 1MOhm?) volume pot. Ub is somewhere over 300V. No additional C for decoupling.
Guess what? Sounds nice. Can be dialed in to give the clean to mean thingy combined w. some additional gain. Dialed back guitar volume gives a clean trebly sound, while dimed is not at all tinny sounding. Works well with VVR.
Even w. very low wattage the clean to mean works better than before.


I used a lil perf board the size of a stamp for the HRM and a terminal near the tube socket for some additional parts. Adds one shielded wire.

Some of these days I might implement a bootstrapped CF. Just for fun.

OK, now you can sue me or pick at me

Ciao
Martin

[Colossal]

Awesome Martin!! There's no shame in that. The Liverpool is a great amp and a fantastic foundation for going one louder. It can do a killer modern, high gain sound with the right mods. What value did you choose for your slope resistor and treble cap on the HRM board? The bootstapped CF would be a good addition.

[El_Martin]

Hi Colossal!

Tonestack as follows:
470pF silver mica
39kOhm slope
2x22nF=0.022µF
Pots TBM:250k, 1M, 25k

I used different makes of 22nF, because of the colors. I do have more of each type.

Every now and then me likes some gain. Is it the loss of hi frequencies due to getting older? Vanishing playing skills compensated by more gain and compression? Me dunno.

Ciao
Martin

[LeftyStrat]

Preaching to the choir brother!

[roberto]

Tonestack as follows:
470pF silver mica - 39kOhm slope - 2x22nF=0.022µF - Pots TBM:250k, 1M, 25k

This is my choice since around 2007. Balanced both for warm cleans and classic leads. The only difference is that I use ceramic pf value caps.

[Colossal]

Tonestack as follows:
470pF silver mica - 39kOhm slope - 2x22nF=0.022µF - Pots TBM:250k, 1M, 25k

This is my choice since around 2007. Balanced both for warm cleans and classic leads. The only difference is that I use ceramic pf value caps.

Yes, I like 39k too!! Great low end. Roberto, what kind of ceramics do you like?

[garlin]

delete

[roberto]

Yes, I like 39k too!! Great low end. Roberto, what kind of ceramics do you like?

I like the crunchy feel of 500V small cheap class II ceramics (I feel like the higher the voltage, the darker the sound). But it depends on what I can found time by time.

[El_Martin]

Hi!

I do keep old parts, salvaged or NOS. The coupling cap for instance is one of a kind out of the bin.
I think, there's no wrong component, if by any means you get THE sound. Sound and taste may differ, though. Good to have a choice and to use your ears and skills to build your own.

Ciao
Martin
PS: congrats Roberto: you made your 400. post

[roberto]

Absolutely, every piece can be the best one if it helps to nail the sound you have in your head. I agree with the 4n7 to 470k load to feed an extra stage.

220k Rp on 4k7 Rk usually helps to round the sound and add higher harmonics. If you want something with the same gain at lower frequencies but a 3dB boost around 1-2kHz you can try 100k Rp on 10k Rk, then put in parallel to the 10k a 220nF cap in series with a 2k7 resistor (imagine a standard RC at the cathode, but the capacitor is lifted by a 2k7 resistor).

[El_Martin]

Ciao Roberto,

the values of the components were some kind of an educated guess. I did not calculate or simulate anything. It proved me right. After building some amps, one should develop some ideas or models to help you sculpture your desired tone.

BTW, thanks a lot for your valuable simulations and plots in the technical category. Very inspiring! Mille gracie.


Arrivederci
Martin

[Mark]

Did you ever try a cathode follower?

I like the way a CF thickens up an amp. I not sure if I'd put it prior to tone controls. The effect would be more apparent after the third stage. I think Ken did this on the Concorde.

[roberto]

It doesn't sound bad at all with a DC coupled CF after the 100k 10k.
You can change the cathode resistor to obtain different effects (the lower the value, the higher the CF "half wave rounding" effect, and the midrange becomes more "voxey").

[Colossal]

Yes, I like 39k too!! Great low end. Roberto, what kind of ceramics do you like?

I like the crunchy feel of 500V small cheap class II ceramics (I feel like the higher the voltage, the darker the sound). But it depends on what I can found time by time.

Thanks man! I do like to parallel a ceramic onto a silver mica for a bright switch. Adds a bit more clarity in a way. Reason I am asking about ceramics is that I have a superlead build on the bench and was looking for some Muratas or something decent for the mixing resistor/treble peak section.

[roberto]

That's ok, but don't forget that often under the BRAND there are components sold at a lower price with no name on them.