Sunday, 14 February 2016

Apocalypse Audio Thunder Tone

From RnFR:

here's something i churned out the other day. i have been thinking about modeling the Supro Thunderbolt with FETs, but then thought- i just got in these cool new Tesla GE's, why not use those? so that's what it is, the preamp section of the legendary amp used by Page and supposedly Hendrix, done up NPN germanium style. i had to eliminate a few resistors towards the end to bring up the volume and lowered the value of an emitter resistor to up the gain a bit. also, i made the resistor on the input variable so you can adjust the input impedance for guitars with different pickups.

the real gem of this circuit is the tone pot- totally counter-clockwise you get a nice full range tone with plenty of mids. as you go clockwise it goes to a very muffled tone, and as you go even further, it goes to a very thin, cutting tone. there are some very cool sweet spots, and a lot of versatility. i like it better than a regular muff style control, but it does cut plenty of signal- hence the two gain stages after it.

it's a cool sounding circuit. nicely voiced and does a good overdrive type sound. if you don't have the trannys, you could change out the 33K Rc's to trimmers and adjust to taste. the tesla trannies are extremely consistent, so no trimmers needed. the layout below uses some large axial caps and is yet unverified, but hopefully i'll get it done sometime soon.


Posted by at 03:22
Tags: , ,

4 comments:

  1. giudis15 February 2016 at 08:54

    Nice!
    What is the value of Pre pot?

    ReplyDelete
    Replies
    1. Iago21 February 2017 at 02:50

      That would be 50K, according to the schematic.

      Delete
    2. Zach21 February 2017 at 03:00

      didn't realize i forgot that in the notes, updated the layout.

      Delete
  2. Kris10024 September 2026 at 21:57

    few issues I found on this - 2.2k resistor next to 100k should be connected between Q2 emitter and ground, paraller to 2.2uf cap. Per the original schematic, 1n cap is connected between 33k resistor (or trimmer if you choose to use one) on Q1 and ground. Currently this is located at 33k biasing Q3 and it's parallel to the resistor rather than connecting the resistor end which goes to collector with ground. 500R resistor doesn't exist on the schematic, perhaps this was put instead of a jumper / link to avoid shorting gain to ground at min setting, at the same time without this link to ground the same strip connects one end of the 10nf cap to ground - which per the vero goes to ground through the 500R resistor. On my build, I moved the 2.2k to right from Q2 between Q2E and ground. 500R got replaced with a link and 1nf got moved to E column (just under the new jumper replacing 500R) and ground from other end which conveniently can be the bottom strip in left corner. Biasing wise this seems to be interesting, I built a PNP version with electrolytics flipped and a negative V inverter to feed it with -9V. With 3x AC128s of about 60-80hfe and relatively low leakage I biased by ear, following typical half the Vcc (-4.5V in my case) seems to produce rather low output volume

    ReplyDelete

Subscribe to: Post Comments (Atom)