Tube Amp Archive

..The FX send is not that big concern since it’s simple buffer, but I’m not sure about the performance of this BJT return stage.. it’s rarely used and bettered by FETs and OPAMPs. I don't know well but I guess a discrete circuit with more sophisticated design would be needed to achieve clean recover...

To me, R42 becomes a 10k pot for the send level, then stick a common collector MPSA20 stage after it as a buffer. Few fx pedals put out sufficient signal level to drive a power amp to full output, so an additional recovery stage may be a good idea. eg a MPSA20 common emitter stage set up for a gain...

I realized that I don’t need the return stage, since this is a preamp version. It was stupid to implement whole FX loop circuit in the stand alone preamp.. Now I need a proper line out with adjustable level, and it’s a little bit problematic to add a pot after GEQ output simply. Maybe the side effec...

Whenever someone wants to add and or even use an existing effects loop I need to ask if you intend to use anything wired into it that has any time delay to it. Reason being that any time delay put on your signal that is again distorted by a down stream amp stage will sound pretty bad, at least by m...

I am currently preparing to build a Mesa Mk4 preamp. (basically Mk2C with switching circuit of Mk4) I‘ll omit the stock loop and reverb, and add an ZL fx loop after GEQ. IMG_5719.jpeg IMG_5718.jpeg However, since the GEQ circuit itself has a low impedance output, It could be FX Send with just a simp...

I’v collected various Mesa EQ circuits converted to gyrators such as OPAMP or TRs, But since I already bought the set of inductors from the official Mesa parts shop without thinking when I first planned this build(they are quite cheap).. and this is my first Mesa build, I am going to implement the o...

Thanks for your reply, nuke!
I couldn't understand it perfectly though, I'm starting to get the concept.

the keyword ‘anti-whump’ was a good hint.
Again, thank you!

There are no reason to match two cap values. Since the current is very small, 10uF is sufficient.

Smaller cap has advantage for faster charging.

Slow discharging also important for stablity, it could be achieved by the diode//resistor combo as shown on that page of Merlin’s.

I‘m currently planning to build a Mk4 preamp. It’s basically implementing the channel switching of Mk4 on the Mk2C circuit. There are some questions remained while organizing the circuits. Older Mark series(before 5) used LDRs for switching, mostly VTL5C1, and partially used VTL5C4 for its slower de...

As a general note, new-manufactured LDRs have become problematic worldwide. Environmental restrictions In the manufacturing countries - first world and China, for instance - have make the use of cadmium sulphide and cadmium selenide compounds illegal. Even where they can be manufactured, they're il...

I bought some FAKE VTLs from Aliexpress. Not surprisingly, there are problems with them. Relatively well known issue; the package is not sealed properly. It leaks, so additional work is needed to seal it.. with black heatshrink tube or tapes, paints etc. The dark resistance is high(over 40M), on res...

Thank you for the reply! I’ll keep that in mind. Actually, I'm a bit skeptical now about OT replacement for ‘lo-fi thing’. As far as I gather information, including your advice, it would be not that worth it I suppose.. And the more crucial part is; I think the problem was on PT, not OT. I suddenly ...

I apologize for making sloppy statements based on only fragmentary information.

Thank you guys for sharing valuable information from your long experience. I learned a lot.

I believe the larger OT's were interleaved. Based on the post on DiyAudio I linked; https://www.diyaudio.com/community/threads/guitar-vs-hifi-output-transformer.315451/#post-5260982 the Schumaker OT was from 80’s, rated 80w. So it could be tweed twin, maybe late CBS era.. hard times. And usually Fe...

How that? Oh I was half joking.. maybe the tone was wrong, limited English thing.. :oops: just on the fact that old Schumaker OT of Fender was obviously not interleaved. I wouldn't say that. Both started out using audio transformers that could be sourced locally. Again, half joking :oops: And, Mars...