Another Cool Custom Pre-amp! Cloning the Peavey Decade

I got a request for a pedal that recreated the pre-amp portion of the Peavey Decade amplifier. The Peavey Decade is an old-school solid state amp that has been used by a lot of bands. It has waxed and waned in popularity over the years, but it is popular enough that there are a couple of fairly boutique guitar pedals that emulate it's preamp section. PedalPCB makes a preamp board, called the Decadence Preamp. So with board in hand, I got cracking!

The overall circuit is really pretty basic. It has a basic 3 band equalizer, but most of the actual work is done by the diodes which are set up in both soft and hard clipping configurations in different parts of the circuit. For this build I went with all new production components. The resistors are all 1% metal film. The pF range capacitors are all MLCC. The nF range capacitors are all film capacitors - mostly WIMA and KEMET. There are a few electrolytic capacitors which are all Nichicon. The diodes are all NOS 1N4148 from my local source. There is also a single IC which I socketed.

The PCB is fairly large and roomy, but is well laid out so final assembly looks very clean and neat. I decided to relocate the LED from the location on the main PCB to the daughter board (I used one of my "Steggo" daughter boards I had made up based on a layout originally done by Drunk Beaver Pedals) largely to accommodate the art I wanted to use on the pedal. The jacks are all connected using aviation grade wire from Tube Depot and insulated with heat shrink tubing. I used 2.54mm pitch ribbon cable to connect the main PCB to the daughter board.

For the dinosaur mascot this time around I went with Pachycephalosaurus - or in this case just "Pachy" - for obvious reasons. According to Wikipedia:

"Pachycephalosaurus was among the last species of non-avian dinosaurs on Earth before the Cretaceous–Paleogene extinction event. The genus Tylosteus has been synonymized with Pachycephalosaurus, as have the genera Stygimoloch and Dracorex, in recent studies.[4][5]

"Like other pachycephalosaurids, Pachycephalosaurus was a bipedal herbivore, possessing long, strong legs and somewhat small arms with five-fingered hands. Pachycephalosaurus is the largest-known pachycephalosaur, known for having an extremely thick, slightly domed skull roof; visually, the structure of the skull suggests a ‘battering ram' function in life, evolved for use as a defensive mechanism or intra-species combat, similar to what is seen with today's bighorn sheep or muskoxen (with male animals routinely charging and head-butting each other for dominance). This hypothesis has actually been highly disputed in recent years."

The pedal itself sounds pretty good overall and has quite a bit of range - especially if you're into especially early through late 80's hard rock. Getting the pedal to unity takes a little cranking, but the tone is good. If you flip the "Saturation" switch you go from a slightly dirty overdrive at higher volume levels into full distortion. The three band EQ allows you a lot of freedom in shaping your tone as well. The pedal will also run at 18V - so next I'm going to try to up the voltage and see what difference it makes. I'm guessing it is going to like 18V better.

Along the same lines, I really like the benefits of a 3-band equalizer. I'm honestly looking at a couple of designs I want to add the 3-band EQ to. However, those are future projects! So stay tuned!

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