The Beatdown: A True MIAB

[Ripthorn]

My main amp for many years was a Marshall 5210 solid state from 1983. These were the first solid state Marshalls (along with the Lead series amps) and have always been renowned for sounding particularly good for a solid state amp. I got rid of mine because I got a tube amp that I like and the cleans on the 5210 had a kind of honky quality that i didn't really like too much. But the gain channel was amazing!

So what do we do? Well, we go and take the dirty channel preamp and turn it into a pedal! There are a couple of small changes to it to make it a little more convenient for a pedal build, but it works quite nicely. It does a great classic rock crunch, and I used to get into higher gain territory by putting a Guv'nor in front. I really quite like it, so I thought I would share with you fine folk!

Here is a quick little demo I made of it. I used S-Gear for the clean base and the dirt is from the circuit on the breadboard, so some noise from that, for sure.

https://soundcloud.com/user-45568666/beatdowndemo1

Also, here is the schematic, broken up into the power and signal sections. I'll be working on a two layer board layout soon and will add it when completed. Let me know what you think!

[Ripthorn]

After further tweaking on the breadboard, I have done the following:

1. Eliminate 78L15 along with a cap and diode that were no longer necessary
2. Increase resistor to Gain 1 from 100R to 1k
3. Increase Gain pot to 50 kB
4. Add 2k2 resistor from Gain 3 to junction of 2u2 and 1k

Eliminating the 78L15 was purely for simplification's sake. Tweaks 2-4 all work together to accomplish 1) give more available gain at max, 2) eliminate squealing at max gain, and 3) eliminate complete volume dropout at min gain. Tweaks 2-4 all work together, so changing just one value will not necessarily give a change to the three outcomes.

Here are the new schematics, complete with more logical component numbering:

[Ripthorn]

After some significan thought and breadboarding, I have changed things up some. I changed to a bipolar power supply so that VREF becomes ground. This greatly simplifies things like layouts. I also made a change to how the volume control works. There is a ton of volume/gain on tap, so I changed it to work more like the gain channel and master volume in the Marshall 5210 amp, rather than the gain channel/gain volume in the amp. Here are the updated schematics. Still sounds as glorious as ever!