Amp #4 – Something JCM800-like

I’m going to be short and to the point since I’m poor at writing. It was finally time to build amplifier #4! This time I wanted to have another go at something high-gain (because I think that’s pretty cool).

I started out with the JCM800 #2204 schematic and used that as the general structure for the gain channel. I wanted a 30W-ish EL34 push-pull output stage, so I reused (with appropriate modifications) the output stage I put together for amp #3. I also had the output and power transformers ready as I scrapped amp #2 (it didn’t work properly, go figure…); a Hammond 1750Q and 372FX, which gave me some design directions.

After prototyping and going through several iterations I ended up with a two channel amp, high-gain and clean, with a blending phase inverter because I thought that would be fun. But since blending both channels in the P.I. would prevent the use of negative feedback, I also added, again for fun, a passive switching scheme that could take the amp between blending both channels, and muting one channel while giving the active channel the option of having negative feedback applied.

I had great fun and success building the previous amp on fiberboard, so I wanted to do the same this time, foregoing the point-to-point disaster that was amp #2 😉

I always forget how much work goes into building an amp from scratch. I must have been working on this six months straight, not counting the idea and drawing phase. And the shear price of all the parts had to be divided across many months anyway. This is certainly not a cheap hobby…

Lots of more or less interesting images of the amp taking form.

Spent some time designing nice face- and back plates, and got them etched in acrylic plastic from . Came out really great at a reasonable price. And of course I ended up bothering the circuit and ditching the “Mid” control in favour of an “Output” not long after. Typical! 🙁

No big, complicated build without figuring out what’s wrong and doing some changes along the way. Notice the fire extinguisher.

Had to build a house for it as well. Not the most exiting part of the project, but it’s nice seeing everything coming together.

And finally, done.

I’m pretty happy how it ended up. Here’s a quick, off-the-top-of-my-head feature list:

  • High-gain channel in the spirit of the JCM800.
    • James tonestack with shift control (based on idea from Merlin Blencowe’s books).
    • Less bright than the JCM800, because I don’t like too bright.
    • Gain into- and out of the gain channel for some added possibilities (turned out essential for being able to blend the two channels).
    • Parallel FX-loop
  • Clean channel in the spirit of the DC30.
    • “Big muff”-style tilt control for single adjust of both bass and treble.
    • Not enough amplitude compared to the gain channel. Next time…
  • Master volume and presence control in the output stage.
  • 30-ish watts of cathode biased EL34 push-pull output. I like cathode bias for the additional fail-safe. And it sounds good 🙂 Oh, and no manual bias adjustments required.
  • Blending of gain and clean channels possible (no NFB).
  • Single channel output (with or without NFB).

The schematic isn’t 100% when it comes to drawings of transformers, impedance switch etc. I didn’t want to spend time drawing more components in EagleCAD, so I just went with something close.

 

Updated: 29 November, 2017 — 00:06

A long overdue update

Hi. Long time, no see.

I’ve been dreading this moment. Opening up my inbox and seeing all the comments and emails I’ve been missing. I haven’t spent a minute on this site for well over a year, maybe two, and I’m not sure I will ever get the time to sift through and reply to all of you, of which I am sorry.

You’ve heard the story many times before, and it’s not particularly exciting. I’ve been struggling with personal issues and went through a really rough time, which is not to say everything is now going great, but I am slowly trying to pick things up again. Maybe not exactly where I left them, but we’ll see.

I know a few of you ordered pre-programmed tap-tempo chips, and I hope I managed to send them all out.

I haven’t been keeping up on the features and updates on my vero/stripboard app. I have some ideas and a lot of bugs; if I do find the time I will get to that.

I haven’t stopped doing projects, it’s one of the things that has kept me sane, but I haven’t felt like doing all the work that goes into sharing it. Hopefully that will change a bit.

Updated: 28 November, 2017 — 22:48

Just for fun – Jazzmaster pickups

20140809_141438351_iOSYou might remember I tried my hands at pickup winding a while ago (was it more than a year ago already?) creating a set of pickups for my Jazzmaster. Or maybe I never posted that, but anyway.

With some major help from my friends I finally got around to do a proper pickup comparison! And here’s the result:

The setup:
  • Three different Jazzmasters20150524_121010489_iOS
    • (J) A japanese Fender Jazzmaster (CIJ) with stock japanese pickups.
    • (S) My own japanese Fender Jazzmaster (CIJ) with custom pickups as mentioned above (see lovely picture, it’s the left one).
    • (A) A modern AVRI Fender Jazzmaster with stock pickups.
  • No effects, guitar straight to amp (happened to be the one I most recently built, which, in my subjective opinion, sounds just great). The amp is connected to a 1×12 open-back cabinet with a G12H element.
  • A Soundelux U195 microphone straight to a CI2 Steinberg interface for recording.
The result:

Note: No post-processing effects were used, to retain the actual sound as much as possible, but all samples have been trimmed down and given a light touch-up to attenuate excessive fret noise spikes (equally for all samples).

Neck pickups only:

(J):

(S):

(A):

Middle position/both pickups at the same time:

(J):

(S):

(A):

Bridge pickups only:

(J):

(S):

(A):

Credits:
  • All guitar playing by Ronny Yttrehus of Captain Gone.
  • Recording engineer: Jon Bjørnstad, also of Captain Gone.
  • Minor editing and post processing by myself.
Updated: 14 May, 2016 — 14:31

Tap-tempo v3

I’ve been working on (still am to be honest) a new version of the tap-tempo LFO. There’s a few new features, like:

  • Rotary encoder input toggling between and selecting multiplier, waveform and tempo adjustments.
  • The just mentioned speed adjustment – You can now micro-adjust a given tempo rather than having to tap in a new one.
  • New “random” waveform – I hope to get some fun out of this one myself.
  • Many new multipliers (Base tempo is 4/4):
    • Whole notes
    • Dotted half notes (new)
    • Half notes
    • Dotted quarter notes (new)
    • Quarter notes (1:1)
    • Dotted eighth notes (new)
    • Eighth notes
    • Dotted sixteenth notes (new)
    • Triplet notes (new)
    • Sixteenth notes
  • LED indicators for both base tempo and actual tempo (current multiplier).

Source code is now available for free on github under GPLv3.

It’s not done yet, but getting there. I plan on also bringing the attiny85 up to the same standard (minus a few features). As earlier, I’ll also try to keep a few pre-programmed chips available for those who prefer not to get into the programming side of things.

Keep watching this space for more info soon.

Updated: 26 March, 2016 — 00:56

StripboardCAD version 1.2

stripboardcad_app_iconThe second update to StripboardCAD is finished and awaiting publishing on the App Store.

This update s focused on improving the parts list and how you interact with it. There’s lots of small improvements and a few large ones as well.

Head over to the changelog page for the Download_on_the_App_Store_Badge_US-UK_135x40details.

Updated: 7 February, 2016 — 14:15

Status update

You haven’t heard much from me lately, and I’ve been busy with a disproportionate amount of real-life stuff, but there are things to come yet.

I started working for a new company a few months ago. While this leaves me with less free time I can use for electronics and noodling, I’m fortunate enough to now be working professionally with things related to electronics, circuits, audio signal processing and microphones! I’m hoping this will have a positive effect on my DIY tinkering as well smile emoticon

I’m actively working on the next update for my pet project, the StripboardCAD app. This time around I aim to improve workflow related to the parts list, entering of data/values etc., fueled by myself starting to use the tool actively and noticing a few short comings.

A few of my good musician friends have been trying out the “Workhorse” project I put together, and they’re so enthused about it that I’ve now built a few units for sale. That was a pain in the *behind*, and took much more time than I would have wanted, but hopefully it’ll come out well in the end. I even hear some plans about a demo video; a first for anything I’ve been involved with, and only (potentially) happening because I’m not doing it wink emoticon More to come on this soon (I hope).

I’m also revisiting the tap-tempo LFO stuff. While it has resulted in some very cool effects (I’m most happy with the tremolo), it has also disappointed on a few occasions (the phaser, to name one) due to overly noisy design etc. There’s two things to take away from this:
1) I need to learn more about proper grounding in digital effects, and how to lay stuff out on a vero/circuit board.
2) There are still things I would like the chip to do, like integrating a manual tempo adjust pot, a random wave form, and more options in the multiplier department (triplets etc).

And, of course, there are a number of other ideas I’m also playing with, that might result in something further down the road. We’ll see.

I’ll try my best to post more news before the year is over, but just in case:

Merry christmas and a happy new year! Thanks for your support in 2015!

Harald

Updated: 5 December, 2015 — 13:36
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