Category: Build

Amp #3

Update (18.05.2014): I’ve made a few changes, mainly removing the FX-loop, and also put together a basic layout since I’ve had several requests for that as well. But to keep in mind this isn’t a simple color by numbers project; you need to know how to wire all of this properly, and you also have to keep safety in mind working with high voltages!



Updated: 18 May, 2014 — 13:56

Amp #2

I finally got around to finishing my second amp build, and as I promised here are the details.

Amp2 outsideAmp2 inside 1Amp2 inside 2Amp2 inside 3Amp2 inside 4

I’m reasonably happy how the internals ended up given that it was all laid out more or less as I went, though I am a perfectionist at heart and this really is far from good enough. Gives me a lot of room for improvements for my next amp, though 🙂

Amp2 Schematic

So this all began several years ago when a colleague lent me a Bad Cat Xtreme-tone preamp effect (the one with tubes inside) which I liked a lot. I got my feet wet converting the same preamp circuit to a JFET variant some time after that with the thought of eventually building a full amplifier for myself. To make a long and boring story shorter and less boring I started reading books on the subject, and ended up adding to and modifying the original idea to what you see above.

I’d like to bring your attention to a book that, more than any other, helped me understand a lot of this stuff. “Designing Tube Preamps for Guitar and Bass” by Merlin Blencowe is a surprisingly well written and downright enjoyable book made to help novices like myself getting into this great hobby/addiction (I can also recommend his book on power supplies). I found a lot of the changes and modifications here.

So the basis for the amp is the Hot Cat 30, which again is , I believe, based on a Matchless, which again is based on a Vox AC30. So it has the AC30 power section lacking the typical negative feedback that many other amps have.

I replaced the clean channel with a gain stage borrowed from the Dr. Z Carmen Ghia (a favorite of my friend). Then following this I added a standard BMP tone control with two added switches giving the option of a mid- scoop or boost (or a frequency shift towards bass when both are engaged) that I arrived at by experimenting with Duncan’s Tone Stack Calculator.

For the gain channel I replaced the tone stack with a Marshall one (bass, mid, treble), and followed it by an active parallel/serial FX-loop I got from Merlin’s book. I also got rid of the “edge” control and consolidated the two gain controls into one dual pot. And lastly I replaced the odd first gain stage with a more standard cathode biased one.

The schematic lacks a proper symbol for the output transformer and the following wiring, as well as the input power socket wiring, the heater wiring, the indicator LED + resistor, and the humdinger trimpot. There are also small tweaks to the power supply section as well as a “tube rectifier emulation” switch, all of which was borrowed from Merlin’s book (as far as I remember).

So to sum up, it’s a two-channel clean/high gain amp with an FX-loop, running 5x 12AX7/ECC83 and a push-pull power section with 2x EL34. It’s very loud and very cool, though being a perfectionist there are things I would like to improve/change.

Initial thoughts/lessons learned:

  • It’s too loud for home use (I knew this though). Maybe an attenuator will help. Some kind of power scaling would have been nice.
  • The FX-loop, though fully functional, could probably be scaled down a bit/made simpler.
  • I didn’t get much out of the “tube rectifier emulation” so will probably just stick with plain silicon rectifiers next time.
  • The point-to-point-layout-as-I-go ended up looking less tidy than I would have liked. Maybe this amp was a bit too much for such a small enclosure (8″ x 16″). Bigger enclosure or less components next time maybe.

If there’s requests for it I’ll add parts list and voltages. I also welcome suggestions, advice and criticism on anything from schematic and design to building and what not.

I’ll add more pictures when the amp is fully dressed up in tolex etc.

Update (01.05.2013): Here’s a rough overview of the various sections within the amp.


Updated: 2 May, 2013 — 00:44

Request: Marshall ShredMaster

Here’s a quick vero layout for the Marshal ShredMaster. I’m assuming this is a distortion of some kind just from the name alone. Let me know what you think if you build it.


Update (22.02.2013): Built this one tonight and it works. Thanks to Timothy for verifying this one as well. There seems to be an oscillation issue with the drive at max. Placing a resistor in series with the “Drive 3” connection fixed it for me (I used 22k).

Update (23.06.2013): So apparently there’s two schematics of this effect floating around, and they’re slightly different. Since a few people have had trouble building this I decided to make a layout for the second schematic as well. With a bit of luck this is the one that works 😉


Both schematics can be found in this thread over at My initial version is based on the “1992” schematic, and this new one is (obviously) based on the other one, dated “4/17/02”.

Update (25.06.2013): Just built this second version and it works as advertised without any modifications. There was a bit of oscillation with all controls dimed, but this is not surprising with long test leads attached to the pots flying everywhere, and I expect this to be gone once properly boxed.

If you’re thinking of building this effect I’d go for the second layout, though both work.

Update (26.12.2013): I’ve had this thing around for some time now, but didn’t put knobs on it until today. Here’s how it came out. I’m quite liking it 🙂

ShredMaster buildShredMaster gut shotShredMaster board

Updated: 26 December, 2013 — 14:44

My take on an envelope controlled State Variable Filter

So a colleague of mine asked me if I could build him an auto-wah type effect, and specifically something that sounds similar to the MuTron III and it’s brethren. Another goal was to simplify the controls a bit by getting rid of unnecessary switches and pots.

Having just recently managed to successfully debug and build the MuTron III vero properly (with the frustration that came with it fresh in mind) I was a bit reluctant to go straight to that one. Rather I wanted to try the DOD440 circuit first. I got it working, but not in a satisfactory manner.

In the end I decided to sit down, read and understand the relevant circuit blocks in more detail and put an effect together piece by piece. R.G.Keen’s “Technology of…” article on the auto-wah was of course spot on, but I also found this article by Elliott Sound Products to be a great resource. Along with the schematics for R.G.Keen’s Neutron project and the Lovetone Meatball I ended up with a State Variable Filter I was quite happy with, getting rid of most of the controls only keeping a potmeter for “Q” and only using the band-pass output.

Next up was the envelope detection circuit which was a lot harder to get right (it’s probably still not right, mind you). Again I ended up with a derivative of several circuits, keeping pots for “sensitivity”, “attack” and “decay”. I also somehow made it work with a standard TL072 and not the LM1458 that the Meatball uses, but had little luck with any current limiting adjustments for the LEDs and nothing worked as I wanted it to. In the end I was inspired by the Tremulus Lune LFO and put in a trim pot set up as a voltage divider to control the LEDs off-ness. This actually worked surprisingly well and I was able to use all of the optocouplers I had at hand (VTL5C4s, NSL32s and two flavors of home-made ones).

My first take on a vero layout used 2n2 caps for C2 and C3 which I found a tad bit too trebly and switched them for 4n7 ones. R9 and R11 (both 220k) sets the lower limit for the filter sweep, and R10/R12 sets the upper. I tried using 330 ohm resistors for the upper limit, but that made the sweep way too high and I changed it to 10k.

I’ve now built this successfully using cheap LDRs from smallbear (the 9203 variant) and 3mm high-brightness clear red LEDs (5mm LEDs may not fit on this layout since the optocouplers are so close) and I’m very pleased with how it sounds! Tuned the trimmer to where the LEDs were just barely off with no signal.

Final build images coming as soon as I get around to boxing this…

Update (08.12.2012): Build complete and I’m pretty happy with how it came out in the end. And it quacks nicely too 🙂

It was a snug fit and I had to cut off one of the corners of the board to pull it off, which annoyed me somewhat.

Also, I’ve updated the schematic. I had left an extra trimmer in there that I never ended up using.

Update (24.01.2013): Layout rev. 1: I forgot to update C6 on the layout which should be 470n (like the schematic). Fixed now.

Updated: 24 January, 2013 — 23:39

Request: BK Butler Tube Drive

This one was requested a long time ago. Here’s an overdrive pedal that uses an actual preamp tube, which is quite exciting.

Based on Bajaman’s schematic I created a layout with wiring for the tube pins (since I can’t imagine a tube socket fitting neatly on a piece of vero board). I left as much space as I felt was necessary for the large supply caps, but I’m afraid it could still end up being a bit crowded. The effect uses a preamp tube of type ECC83 / 12AX7, and I guess you would need some ventilation in your enclosure. The wiring explanation is a bit convoluted as well, sorry. I really should draw a proper diagram for this.

Do note that this effect requires 12v AC power and not DC like most other effects. Use a small mains transformer or a good 12v AC power supply, and be careful when playing with mains power. Don’t do it if you’re not sure how to do it safely.

Update (09.09.2012): Thanks to several of you for verifying this one!

There’s also been reports of this being quite noisy, and I’m happy to pass on coi2001’s suggested fix; leave the heater resistor off the board since that’s the main noise source. Run the 10 ohm resistor (R16) from the 12VAC source (probably a trafo in most cases) straight to the heaters.

Update (09.05.2013): Here’s my own build, in a slightly taller 1590BB enclosure I got from smallbear (I think they call it the 125BB) which gave just enough room for the tube. Left the heater resistor off the vero board, as was previously suggested, and set it up to receive 12VAC external power (no room for a transformer and power socket obviously).

TubeDriver buildTubeDriver gut shot

Sounds great and there’s very little hum, just a small amount when drive is full on! 🙂

Updated: 10 May, 2013 — 00:22

SabroDrive Two

I’m still learning the basics and this one is a (small) step up from my first adventure. It’s still a dirt pedal, but with a novel and not very useful idea.

It’s made up of more or less well known sections. The input buffer/gain stage was borrowed from the AMZ mosfet boost. I can’t remember exactly where I got the EQ section from, but I do believe I took it from Merlin Blencowe’s preamp book and changed it to an active tone stack. The dirt section is basically half of a BSiaB2 circuit, and the output buffer is a straight forward source follower.

The signal always starts by going through the boost section and always ends at the output buffer, but I added switching so that the EQ- and dirt sections can be swapped (based on the juggler article on In other words you get to choose whether the EQ section goes before or after the dirt stage, and you can hear the difference, no really 🙂

Anyway, here’s a working vero layout for this thing.

And here’s how my build came out. Compared to my first one this feels kind of useful!

Updated: 21 December, 2012 — 22:33
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