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I'm continuing my Exar collection tracing, this time I traced Exar HR-03 Hammer.
Before opening it up, I thought it might be some Big Muff variation as it sounded pretty fat. My curiosity was high so when I got some free time, I finally started tracing. It is quite easy to trace Exar's single-sided PCBs, they are easy to look at traces on the light.
The PCB was labeled as SM-03, but according to Effects Database, it was announced but never released.
It had nothing similar to Big Muff, but a mix of Boss DS-1 and Rat circuits. Circuit blocks included: FET buffer, BJT gain stage (something you might see in DS-1), op-amp gain stage with hard clipping diodes (kinda Rat arrangement), fixed gyrator-based bass boost, passive lowpass filter (Rat-style tone control), and two BJT buffers (two were required because of buffered bypass). My friend pointed out that it looks similar to Ibanez TM5 Trash Metal circuit, and it is. A lot of values are different, but the overall layout is the same. I don't think they would sound identical due to all the changes.

Attached is the schematic without parts related to buffered bypass switching.

I emulated it, but the effect of the Tone pot seems really small, and just in the most higher frequency: over 7k.
It's weird because the tone cap is the 3.3nF, that we can see in the pictures.

In general, the schematic drawn like that, boost mid and high frequency. At least in my emulation.

Ichabod_Crane wrote: ↑13 Nov 2022, 15:08 I emulated it, but the effect of the Tone pot seems really small, and just in the most higher frequency: over 7k.
It's weird because the tone cap is the 3.3nF, that we can see in the pictures.

In general, the schematic drawn like that, boost mid and high frequency. At least in my emulation.

It is basically a tone stack similar to Rat one (just tone pot wired differently), it's a simple lowpass filter - it has a pretty wide range from 471Hz to 22kHz.

It's very strange. I'll try to look the schematic in my emulator again. Or there's some mistake or my emulator lies.

At least to my eyes, this seems like quite the high gain distortion that could be really cool.

Although. I was wondering about the collector resistor on the gain transistor. 47K feels a bit high ohm value for a high gain device..

Anyway, here's a layout for HR-03. Unverified for now... (updated, fixed a missing cut from putput stage...)