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Just designed a new amp module for Peterson, 80 W Suitcase, 4 pin

Started by Mike Borish, November 24, 2015, 09:52:16 PM

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Mike Borish

I just finished engineering a drop in replacement amp module for the Fender Rhodes Peterson model.  The original design has been bugging me for years and my buddies at the Chicago Electric Piano Co.  could use a few, so here they are.  I have omitted the interstage transformer because the original design is inferior to mine.   This is an extremely high quality design that elegantly balances fidelity with a low parts count.   This one is a lot more stable and has several protection features.  It has fuses for each rail, a LED that indicates power is on, a volume control, a damping network, extra capacitive coupling, and base driver clamps (that are not installed in the photo.)    I made ten for this run and they are essentially flawless. 

For the most part, it is a drop in replacement that I will assemble.  The TO-3 hardware is salvaged as well as the connection cable.  I designed it so that I can install screw terminals,  but I think soldering is safer for power designs.  You can send me your heat sink ,or I can provide instructions for assembling the final components. 

If anybody is interested, please let me know.  I don't have a problem with wholesale inquiries.  I will also entertain offers for the manufacturing rights / files / intellectual property. 


We're a Chicago company that repairs amps, pro audio, DJ gear & synths!

Mike Borish

So far, I've sold about 8 of these amp kits now and I haven't had any problems.   I'm a lot more confident now about sending these into the wild.

As far as listening tests go, I've been working with the nice folks at Chicago Electric Piano Co. on this project for the past few weeks.  Max and Mike have great ears and know their customers well.  In a brief comparison test, we've discovered:

1.) The original modules have a mid-bass hump in them that throws off the EQ sweep in the bass.   My modules employ negative feedback and are far more linear: They remove this issue and the EQ sweep is smooth now.  For years, I've thought that the EQ circuit had errors in it, and never thought that the power amp could be the problem.   This was a really pleasant surprise for me and my customers too.

2.) The original modules have a much steeper roll off in the treble section.   My modules employ a Zobel network that helps out with this issue.

3.) My modules have a lot less distortion than the originals.  Notes don't sound as muddy in the bass, and the treble sounds a lot more clear.  To my ear, it is a lot easier to transcribe some of the closed voicing jazz chords that are so popular on the Rhodes piano. 

Max suggested that I modify my design to emulate the small mid bass hump present in the original modules.  Does anyone have thoughts on this?  Personally, I like to have a clean slate to start off with and add EQ or change the position of the mic if necessary to compensate.

If anyone is interested in these, or has suggestions, please don't hesitate to ask.


We're a Chicago company that repairs amps, pro audio, DJ gear & synths!


For the Rhodes, the mid bass is the worst place in the spectrum to have a hump.  Don't do it!  The old Peterson amps were a strange design--I'm glad someone finally got around to designing a replacement.


I will turn all my mountains into rhodes.