Schematic for my ridiculous amp is partly complete.

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Illinest

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Joined 2014
Greetings. :D This is my big project. It is an Asymmetric Split-Stereo Guitar Amp. 7 Valves, 4 Transformers, 2 Tone Stacks, 2 Channels,2 Speakers, 11 Pots, 5 Switches and a special cross-connect system. Class A and AB simultaneously. Single-ended and push-pull at the same time. There's a lot of ground to cover. I learned (and borrowed) quite a bit from DvNator at "Chasing Tone". DvNator's Amp Projects | Tube Guitar Amp Stuff He's got an excellent website that he frequently updates with lots of schematics, sound-clips and explanations.

The cross-connect system allows the user to mix pre and power amps. I'm going to make this easier on myself by establishing terms. The top pre-amp is called "Pentode", the bottom pre-amp is "JCM". The top power-amp is "SE", the bottom power-amp is "PP".


  • Pentode starts with a bypassable EF86 gain stage. This stage also features a tone shaping trick that I borrowed directly from DvNator. When S1 is open, the stage adds a treble peaker. When S1 is closed, the stage adds a mid-scoop. Closing the bypass switch removes the stage from the circuit. The next gain stage leads into a Baxandall tone stack, and then a gain recovery stage and into the cross-connect.


  • JCM starts with a typical Marshall gain stage, the standard treble peaker and a second gain stage which leads into the cross-connect.


  • SE goes from the cross-connect to a 6V6 SE output stage. There is an 8 ohm speaker wired into the circuit and an Ext. Speaker out.


  • PP goes from the cross-connect into a gain stage, a cathode follower stage and then into a FMV tone stack that features another trick that I learned from DvNator. The Brit/American switch alters the character of the tone stack, from an approximation of the Fender frequency response on one end to an approximation of the Marshall frequency response on the other. (If anyone is curious - the American notch is a pretty close match for Fender blackface. The Brit side is much like the Marshall tone stack, but lossier.) Then on to a LTPPI with Presence control, a PPIMV (installed on the back of the amp) and ECL84(6F4P) power tubes. The output tubes will be controlled by VVR, (power amp only). Then on to the OT, speaker and Ext. Speaker out as it was for the SE circuit.

When the cross-connect is wired straight across you've got two amps in stereo. The first is basically a Fender Champ with a Baxandall tone stack and the option to goose it up by using an extra gain stage. The second is essentially a small-scale Marshall amp, loosely based on a JCM.

When you cross-connect them though, it gets a little bit interesting.
The JCM circuit drives the SE power amp with no tone stack in the way. The Pentode pre-amp on the other hand progresses through both a pre-distortion Baxandall tone stack and the post-distortion, post-cathode follower FVM tone stack.

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I

Illinest

Member
Joined 2014
JonSnell Electronic said:
An ECL84 was designed for MF use but I dare say will work as an audio amplifier. Don't forget to connect the G3 with Cathodes!
Click to expand...

Will do.

If you haven't heard an ECL84 power amp yet, you should definitely peruse DvNator's website. He's got a fair number under their own heading (using the Russian designation) and more importantly I think, he's also got a good variety of other circuits to listen to as well. All recorded with the same device, same speakers (for the most part) same player, same room.

I think that you can tell the difference between (for example) his dual-triode push-pull (ecc99, iirc) and the ECL84s. They sound pretty good!
 
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