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Project: L5 Preamp

Build description

ALL PARTS: HQ & all purchased from Mouser & Small Bear Electronics based on the Aion supplied BOM

OpAmps & ICs: OPA2134, OPA134, LM741P, CA3080

I was able to buy the 16mm 2.5KA Alpha pots from a UK distributor from a link supplied by Aion. Pots were not the right angle type though. I wired both of ’em to the PCB.

It took me a number of weeks to carefully sort parts, measure the values & populate the board. I had to wait for 3 back ordered items from Mouser for a long time but just in time when the Aion enclosure was ready to order. I had to buy a same size & value box cap (0.0082uF) & install ‘em while waiting for the last backordered cap so I could test the “Mother of All Pedals”. I’ll change those in a later time.

I used a shielded wire for the IN, OUT & LED pads / additional ground pads. I also added the experimental (100K) resistors for the off-board switches. It made the Channel switching very quiet although I could still hear a little bit of pop noise when the Bypass Mode switch is engaged/disengaged. I opted for the quieter Always On LED operation. On the other hand, the Bypass-Off LED operation confuses me because the 3 LEDs on the offboard switches don’t turn off at all and a loud pop is always present in spite of the experimental resistors.

Using the Signal Generator app on my iPhone 6 yielded mixed & inaccurate voltages so I used the ToneGenerator app instead but measuring the required 1kHz 30mV sine wave with a multimeter was hard to achieve. So, I just connected the iPhone output directly to the test points and adjusted the Distortion trimpot to 4.4VAC which was easily and accurately achieved. I know this isn’t the right way but it was my last resort.

TESTING EQUIPMENTS: Marshall JVM 205H head / Marshall 1960A cab / Fender Metalhead Amp & cab / IBANEZ S5470Q guitar. Jackson Japan-made Warrior guitar with genuine SD Invader humbuckers. Only Lab Series is connected — to the power amp input and alternately used as a pedal.

TEST RESULTS: A very quiet preamp for me as long as it’s used on an equally quiet power amp or is used as a pedal & connected to the front of a regular amp. The compressor / limiter & the distortion works fine for my rig. The 2 Channel tones sound great! Lots of headroom & very tweakable!

Thanks to Kevin for resurrecting the great Lab Series L5 Preamp amazingly reduced to Lilliputian specs.

Are you tired of carrying heavy rig to your gigs? Try the Mother of All Pedals, hook it up to the PA and tell us all about it……… Gulliver!


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All Modes Are Beast Modes

Project: L5 Preamp

Build description

This was one of the cleanest, most well thought out “big” projects I’ve ever built, and I come from the synth DIY world so I’ve seen some properly big ones! Kudos, Kevin. Fantastic work.

Everything worked perfectly at the first power-up aside from the bypass LED, which stayed lit no matter what state the bypass switch was in. 2 minutes of web searching yielded the answer – don’t connect the two switch boards together with the wire as shown in the diagram, just run one from the mode switch PCB to its own ground on the main board. (Maybe that’s in the docs?)

I’m a modular synthesizer manufacturer, not a guitarist, so I could only test it on the Eurorack, but I’m happy to report that it sounds just as fantastic on synths as it does on guitar. Time to build the second one, which I’m absolutely keeping for myself. =)

Modifications or part substitutions

None. I like faithful recreations to be as faithful as possible. I had almost all of the parts in stock but the few that needed to be ordered were available straight out of the BOM.