The Electric Piano Forum

Repairs, Maintenance & Upgrades => Preamps, Modifications & Upgrades => Topic started by: JanneI on September 11, 2019, 01:06:57 AM

Title: DIY Peterson preamp (tremolo) pedal
Post by: JanneI on September 11, 2019, 01:06:57 AM

I made a DIY peterson preamp pedal. It uses vactrols (like VV preamp), otherwise it's identical with original Peterson. Here's a quick demo which compares it to VV model:

Title: Re: DIY Peterson preamp (tremolo) pedal
Post by: sean on September 12, 2019, 05:31:26 PM


18 seconds?  Really?  18 SECONDS!??  That's all you are giving us?

This looks wonderful!  Awesome job.  Did you make only one? 

Can you share the Gerber files for the PCB?

Can you tell us what model Vactrol you used, and where you bought it?

This is really awesome, so we want to hear a whole lot more about the whole project.

Title: Re: DIY Peterson preamp (tremolo) pedal
Post by: JanneI on September 13, 2019, 12:55:23 AM

The whole project started with taking a closer look at Vintage Vibes stereo vibe preamp, which I had purchased long time ago. I got interested in how it differs from the original Peterson schematic and by back-engineering I found out that the only difference was in the tremolo section (bulbs -> VTL5C1's). This simply been just some resistor value changes and a slew generator to simulate bulb behavior.

I opened up their power supply (that red one) and noticed that there's only that mean well supply and some jacks. Preamp current draw is only <30mA with the vactrols. For my pedal I used DC-DC converter (9-36v -> 24v) and now it powers even 9v battery, wall wart being a better option of course.

I designed a pcb and used parts that fit Hammond 1590B enclosure, so no wiring needed. Only expensive parts on the VV preamp (besides vactrols) are the pots, so for this pedal I used single pots instead of dual concentric ones. It needs C50k for depth control (can be modded with b100k&100k res) but for speed control I left out the 82k res for the "slow speed switch" and used b100k instead. So, this pedal has larger scale, which I liked more.

That's basically it. I'll not be sharing gerbers but I can sell pcb for personal use. This as a courtesy towards VV, they do excellent work and I don't want to harm their business. PM if interested.

Title: Re: DIY Peterson preamp (tremolo) pedal
Post by: JanneI on November 14, 2019, 12:40:26 PM

I have some PCBs left, 10Eur each, EU postal fee 6Eur, US/Canada 8Eur. Use Paypal (friends&family!) for payment, email: and send me your address.

Build docs can be downloaded from here:

Some IMPORTANT build notes:
- Please build it following the order of the build guide pictures.
- You need be able to drill and file the Hammond 1590BB enclosure. PCB can be used as a ”drill guide”.
- Only the SPST (/SPDT) foot switch needs wiring. Pots are soldered LAST! and cut the component legs as short as possible under the pots.
- BOM has part numbers for Mouser and Tayda Electronics. Some components have only one source and need to be bought from there. Vactrols need to be bought elsewhere, like: Thonk, Synthcube, Musikding, Banzaimusic, Tubesandmore, Ebay, etc.
- You can build the pedal without the Delta DC-DC converter, but then you should use a quality +24VDC linear power supply.
- Pay attention to the polarity of your power supply. Header J5 can be used to switch between ”center positive / negative”. The most of the guitar pedal power supplies are center negative. The most of the regular DC power adaptors are center positive.
- Current draw is around 25mA (+24VDC). You can test the unit even with a 9V battery (use clip connector), but the battery probably will not last many hours.
- Have fun building!

Title: Re: DIY Peterson preamp (tremolo) pedal
Post by: 4kinga on November 15, 2019, 12:29:52 PM
Count me in!