McMartin LR-1004C Service and MODS

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The McMartin LR-1004C is a diode limiter with ton's of "Flavor" (Distortion/clipping). Works great on drums. One downside is the undersized output tranny, which probably does not have that great of a frequency response. But if all you want is "Flavor", It's got it. It is an older piece of gear and will most likely need a complete recap.

Attack/Release Relocation MoD:
- This moves the attack and release controlls to the front panel.
- Drill 2 holes in the front panel and put in a 1K Linear attack pot and a 750K (or 1M) Linear Release pot . Remove the old pot's from the Compressor board, solder wires from board to the new pots and make sure to twist the wires.

Capacitor/resistor MoD:
(Compressor Board)
- Replace c5 with a .47uf 10mm spacing polypropelene capacitor
- Replace c1 with a 4.7uf 15mm spacing polypropelene capacitor
- Replace c3 with a 47uf 35v or 50v bipolar capacitor
- Bypass that with a .47uf film cap
- Put a 10uf 50v cap across B+ and GND
- Bypass that with a .1uf polypropelene capacitor

- Replace r1 with a 100 ohm metal film resistor
- Replace r2 with a 22k metal film resistor
- Replace r3 with a 1k 2 watt metal film resistor
- Replace r4 with a 270 ohm metal film resistor
- Replace r5 and r6 with 330 ohm metal film resistors
- Replace r7 with a 2.2k metal film resistor
- Replace r9 and r14 with 100k metal film resistors
- Replace r12 with a 47k metal film resistor
- Replace r8, r10, r15, and r16 with a 1k metal film resistors

(Line Amplifier Board)
- Replace c1 with a 4.7uf 15mm spacing polypropelene capacitor
- Replace c3 with a .47uf 10mm spacing polypropelene capacitor
- Replace c4 with a 220uf 35v or 50v bipolar capacitor
- Bypass that with a 2.2uf film cap
- Put a 10uf 50v cap across B+ and GND
- Bypass that with a .1uf polypropelene capacitor

- Replace r2 with a 1.5M metal film resistor
- Replace r3 and r4 with 47k metal film resistors
- Replace r5 with a 680 ohm metal film resistor
- Replace r7 with a 8.2k metal film resistor
- Replace r8 with a 10k metal film resistor
- Replace r9 with a 820 ohm metal film resistor
- Replace r10 with a 150k metal film resistor
- Replace r11 and r12 with 10 ohm 1 watt metal film resistors

PSU MoD: (Power supply Board)
- Change the diodes D1 and D2 to Fast (UF) diodes. UF4004's will work.
- Replace c2 with a 1000uf or greater 63v capacitor (axial)
- Bypass that with a .1uf 63v film cap
- Replace c1 with a 1000uf or greater 50v capacitor (axial)
- Bypass that with a .1uf 63v film cap
- put a .1uf polypropelene cap across + and - output

Here are some images:
         Schematic PDF
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Disclaimer: I encourage people to DIY and I'm here in a informative role.
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ModDefecation is about making equipment sound better, providing knowledge and support, repairing that awesome piece of gear, and custom builds. Send me you questions or Ideas.