Thanks, g1 (pentode control grid?  )
I'll measure the preamp's current draw and see how much or how little it is.
Have a good one.

@Umlaut
Hi, in practice, what's the maximum signal amplitude coming from that GIVE stage? Is there a limit?
Best regards,
M.

Greetings, oh, collective wisdom.
I've got this solid-state guitar amp from the 1980s. It's operational, or at least it was last time I checked, but it's not quite the kind of tone I like. So, a thought of modifying it popped into my mind.

I was thinking of leaving the power section alone and changing the preamp to the one inspired by Joe Davisson's designs switchable to something else. It's not decided yet.

The amp as it is now uses a bipolar power supply and the preamp I was considering runs on a single PSU.
I'm wondering if it's not going to upset the power amp's PSU rail balance due to the extra current draw, which compared to the PA section is minuscule, I know, but it's still there.
Am I being paranoid here?

¡Muchas gracias, Señor Fahey! 
That definitely makes life easier, doesn't it? This info will come in handy one day, once I feel I'm ready to design and build my first high power transistor amplifier. I'm not going to rush it, though 😅

Here's the schematic for the iteration presented in reply #24. I plugged the output straight into the high-impedance input of a tube amp. The cable's capacitance is 530 pF according to my DMM.

No problem. I breadboarded it to see how it sounds and shared my findings for others to have a point of reference because I had trouble finding any. Maybe my recordings will not get lost over time.
NB: I plugged the output of the preamp directly into the effects loop return of my DIY tube amp for this recording. Later I ran it through a buffer (a bypassed Boss DS-1) and it sounds different than in the sound sample.
EDIT: Of course, I can post the schematic if anyone's interested.

I added another gain stage and tweaked it again. Here's how it sounds now

https://m.soundcloud.com/user-996907905/joe_davisson_preamp_modded_bc3

EDIT: Again, I'd like to apologize for the sloppy playing.

Another update.
I have tried running this circuit at 18V. The tone is a little bit different, definitely brighter. It has a tad more headroom, although that might be my perception only. It puts out more volume too. Not by a lot, but noticeably more.
Note that I didn't bother rebiasing anything.
I also tried using BC550's. With these transistors installed, there's more juice on tap, more hair. I think I like it better with the 337's.
There's another thing I'm going to try soon, namely adding another gain stage. I'll keep you guys posted.

Here's a schematic of Joe's preamp tweaked to my liking. It's the way it is on my breadboard at the moment. To date, I have tried a few different combinations and this is one of my favorites.
Here's the original design
https://www.diystompboxes.com/analogalchemy/sch/v4preamp.html

As you can see, aside from different transistors and their collector resistors, I ditched two emitter bypass caps (3rd and 4th stages) and changed the values of the other two (1st and 2nd stages). I added bright caps here and there and changed tone stack capacitors. Also the TS potentiometers are higher value because these are the only ones I have. Oh, and my mid pot is 50k.
Many thanks to Joe Davisson for sharing his idea with the interwebs.
M.

Thanks a lot for the reply, Loudthud.

Hello, everyone.
First of all, I'm sorry if this question has been asked and dealt with before. I have done some searching, but haven't been able to figure out a straightforward answer. I'm new to solid state amplification. Now, to the point.
I've been looking at Rod Elliott's 40W power amp design and I don't know which components should be matched. I started reading teemuk's book, but for now it's quite a bit to digest, so I'm taking my time.
So, should I look for matched pairs of any devices found here?
The whole article:
https://sound-au.com/project215-p27-revisit.htm

Circuit diagram:
https://sound-au.com/p215-p27-revisit-f6.gif

Thanks for any input.
M.

Quote from: edvard on June 01, 2024, 10:45:18 PMI've asked before on other forums that if there were such thing as a "clean channel" pedal, what would it consist of, and most folks suggested either completely dry, like plugging into the power section with a tone control, or light-to-medium compression with no clipping.

Thanks for the tip. There are a couple of ideas I've been looking at, like the Fetzer Valve with a tone stack, Rod Elliott's preamp, or Umlaut's Keelhauler. I'll start a new thread once I've found what I'm looking for.

QuoteHe hangs mostly at diystompboxes.com, maybe pop in there and send him a personal message.  At the very least, I'd say draw your own schematic and highlight the differences, so you won't be straight-up copying.  Maybe include "modified from Joe Davisson's Vulcan" and a link to his page.
IANAL, so I'd ask him about it first.

I sent him a PM this morning. We'll see what he says.

Update

So, I have been tweaking the circuit for the past couple of days and I think I've got it where I like it. Actually, there are a few versions that I'm fond of, so I'm going to make it a switchable two or three-channel preamp. Honestly, this design has enormous potential, afaic. I haven't tried it on 18V yet. That's still on my to-do list.
Now I'm going to need a nice clean channel to pair with it. Any suggestions are welcome.

Is it OK to post a schematic with my changes? On his site, Joe Davisson put the 'do not copy / all rights reserved' clause, so I wouldn't like to infringe his copyrights, annoy him or anything like that, hence my question.

Hi, joecool85.
Sorry about not posting the schematic or link. I should have done it in my first post. My bad.
Actually, it's this one
https://www.diystompboxes.com/analogalchemy/sch/v4preamp.html
The one you provided shows the 3-stage bjt Vulcan overdrive pedal and they sound completely different.
As for the diodes, I used 1N4148.

EDIT: the link posted previously was strange. To say the least. Now it should be fine
https://m.soundcloud.com/user-996907905/joe_davisson_vulcan_preamp_bc3

Ok, here it is.
Guitar: LTD MH 50 with pickups from Dean Vendetta 2
Amp: single-ended EL91 Fender Champ-a-like
Speakers: some 1980s 12" marked Celetion (sic!)
Settings change as I go. I do not touch the guitar's volume knob, I just play with the knobs on the preamp.
The values of I used for the tone stack, presence and level are different than those on Mr. Davisson's schematic because I only had pots for tube amps. All caps have been scaled accordingly.
Enjoy.
Oh, and please forgive my sloppy playing 😅 I don't play as much as I used to...