New Amp Modules - Peterson Amp Redesign Kit - Unboxing and review

Started by Cookymonster, January 23, 2017, 04:02:36 PM

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Sorry for my English. It's not my first language.

My new 1975 suitcase – Peterson- Rhodes  is a great instrument  in very good condition.

It is "all-original"  except of course for the small parts (grommets,
hammer-tips, action mod, washers, felts..)
I intended  to keep it that way.  

But to be honest, some flaws and issues kept bothering me.
Like a lot of old suitcasesit suffered from modest volume, unwanted distortion, especially when pushing the volume, crackling noise, a bit of hum...
And of course the well-known  "muffled" suitcase sound...
OK, it's charming in a way. But I would rather reach  that particular sound by turning my tone control
button to the left... but also be able to have some brilliance and transparency when it is turned to the right...

As I wanted to keep my suitcase original  I decided to "replace" some parts, rather than to repair or modify.
And I would keep the original components stored safely in a dry place.
Everything should be reversible.

So I replaced  the old alnico speakers for some new Jensen CH/Mod 12-50
I doubt this was a good choise. I will explain later.

I replaced the old Peterson pre-amp for a new  Vintage Vibe pre-amp
Great product, sounds like the old Peterson pre-amp, but without the noise, humm, crackling etc.

And recently I installed  the new amp modules designed by Mike

Fender Rhodes 7054 "Peterson" Amp Redesign Kit

Mike offered two things:
-              Sending just the printboards with the transistors
-              Installing  the PCB's and transistors to my current Peterson modules (which I had to send to him)

As I wanted  to be reversible, there was only option 1.
So I ordered a pair of modules from Borish electronics.

Meanwhile I ordered a pair of Indonesian good quality heat-sinks for about
20 $, shipping included. They are a bit shorter but thicker, but look and feel very well.

The heat-sinks arrived a few days later.
Belgian Customs clearing kept the amp modules for  more than one month   :o :o >:(  tsss....

Anyway.After this month, both PCB's arrived well, together with 4 new silicon transistors and fuses.

I  have very modest notice of electronics.
On Borishelectronics' website the modules are called  "drop in replacement".

This would surely be the case if  I would have sent in my old Petersons, to receive ready-made modules.
But I had to install the transistors and do some wirings.  Also I had to check  for regulating the bias and offset.  :-[
After Mike's  first e-mail with instructions regarding this,  I concluded I  would  depend on my local amp tech.

But when the modules finally arrived,  my amp tech  went on holidays...for three weeks.  
I have been patient enough with the customs - delay,  so I decided to try it myself.

To install the transistors to the heatsink, well there was Youtube and Google  ;D.
It looked pretty obvious, so I felt rather confident about that.
The wiring made me doubt a bit. I was not sure about 2 wires.  (only 4 wires, one wire is ommitted in this design)

But I managed to install them.

I was very eager to test my modules.
I don't have a "variac" like Mike suggested (who does anyway?) so I plugged
them directly into the power section of the suitcase...with speakers connected of course.

You can see the new modules attached to (temporary long wires  connected to) the Power supply.
And in front the old Peterson modules.

I kept the power switch between my shaky fingers in case  the modules would show up as smoke generators  ;)
What was / is  the result ?
Just one short sound ? With some visual firework effects ?
Or will I finally  make my point and just describe the qualities of the amp modules ?

 That is for my next post...if you still would want to read it. It is already
a lot of writing for me and reading for you ::)

This was the UNBOXING part. Next is the review.  Hope to see you back...
I will turn all my mountains into rhodes.


Not a single response? Looks like nobody is viewing this forum any more ... ???
At least...not much happening on it in general.
Or is this not interesting ?
I still wil do the post with the review soon anyway in case somebody in the future would want the information.
I will turn all my mountains into rhodes.


We were waiting to hear the next installment!

I bet that it didn't blow up in your face.  I bet the new modules sound great, because you were inspired to write about it.


Tim Hodges

Quote from: sean on January 26, 2017, 12:02:27 PM

We were waiting to hear the next installment!

Same! I really enjoyed reading it, I was just waiting for the next part. So far sounds like everything is going well, I've spoken to Mike about getting some replacement Super Satellite amps made, I should get back in touch with him as he seems to know his stuff.
Bristol Electric Piano



I have enjoyed reading your post, as others, simply waiting for the results. I would imagine they sound very nice.


OK. Thank you for the response.
The file is on my other computer. I will upload it monday or tuesday.
I will turn all my mountains into rhodes.


Yes of course...I would not advertise a preview of just some smoke.

To be honest, I did make a small mistake in my wiring of the transistors  in one module ???
But that was just inattention of me. I was fast enough to put that right. 

What happened when I turned the switch on ?
Nothing. Except for 2 green LED bulbs lighting up on the amp modules.
This was OK. But no sound except for just one soft "click/plop"  coming out of the speakers ...
I reached over to touch some keys on the keyboard and guess what ?
An F Sharp diminished or something like that ... full sounding with a nice body...
I was surprised first ...and then extatic.

With a volume level at about 2 on a scale of 10 (in fact there are no figures on my volume-pot. Just an estimation).
EDIT feb 1th: there ARE figures on the volume scale. They are just small ... and I need glasses...

This speaks for itself already, doesn't it ?
No more hiss or hum at a this relatively low volume level.
This is a major difference. Turning the volume up makes the next difference: it can go incredibly loud.
No comparison with my former original amp modules. 
Without amp-distortion. 
What happens over level 5 (half of the volume-pot reach) is real overkill in my room.
At level 6  my son's drum set is easily overruled. 
To be honest, at a level above 5, a lot of things start rattling.
EDIT feb 1th:  above level 6... but the speakers keep performing well.

This is resonance of both the instrument (especially the suitcase cabinet and components) and all kinds of things in the room.

Clean sound from the amp up to high volumes, that's new to me.
Much cleaner and transparent than the old modules. 

I had to  readjust volume in the high pickups.
They sounded too hard and sharp.

But then, for the rest of the keyboard, sound is nicely balanced . 

The brightness and bass tuner-pots of my pre-amp seem to react more  gradual and smooth in combination with these modules. 

Is it more brilliant and clear ? Definately yes.
Is it "high-fidelity" transparent ?  No.
Not yet ?

I plugged my CD-player directly into the suitcase-input, and this does not generate  a real hi-fi sound neither.

OK, these are 12 inch guitar speakers. We can not expect Wilson-audio sound of it.
But my Silverface Twin Reverb seem to go way beyond that in terms of transparancy.

So I wonder if I chose right in buying the (vintage) Jensen CH/Mod 12-50 speakers recently.
They were definately an upgrade to my old worn-out Eminence Alnico's.
I tested two kinds of Jensen speakers (the CH/MOD and the C12N)
View my other post

With the old amp modules it didn't make that much of an difference.
That's why I chose the cheaper and lighter MOD's.
The C12N's had brighter mid's . But not all that much difference on the old modules.
On these modules it surely would have made the difference...
I am convinced that a combination of these amp modules with other speakers can raise the suitcase to a new level.

So, I will do some experimenting on speakers soon.

It's a huge upgrade already.
It's is nice sounding. Full-body. Full control.
The dynamics are fantastic.
Such a pleasure to play the suitcase now.

I mounted them back into in the cabinet again.
As the heat-sinks are a bit deeper and shorter I mounted them on  small L-profile brackets.
I will shorten the wires soon. and solder them instead of the temporary connectors.

By the way, the amp – modules stay cool.
Even when playing very loud for some time, the sinks just get "hand-warm".

I think this design is very mature.
Way better,  more safe,  operational and reliable than the original, that is for sure.

What did I pay for the modules ? I payed about 150 EURO for both modules.
But as far as I understand, this price could be temporary as it  is still  a kind of Beta – testing.
It didn't cost me more than having both my old Peterson Modules repaired by an amp tech.
And it was way cheaper than the alternative on the market.
(I haven't tested these, so I can't judge them... )

But to my opinion,  these amp modules a high-end design.
It is a new circuit that deals with  some problems of the old design and uses evolved insight and technology in an effective, musical and functional way. 
It is ready to be commercialised. I am sure it will make a lot of suitcase-owners happy.

The only thing Mike should work on ... is a simple installation manual...for  dummies like me  ;) 

I will turn all my mountains into rhodes.

Mike Borish

Thanks for the write up.  Your English is very good.  You installed the speakers incorrectly.  I can see that you are employing a parallel connection when they are supposed to be series.  This is why your new amps are extremely loud: Your effective load is 4 ohms instead of 16. :)  My modules should take a 4 ohm load but it is not recommended and you will probably destroy your speakers.

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

Mike Borish

Where did you find those heat sinks?  Can you post the link?

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


Quote from: Mike Borish on January 29, 2017, 04:08:55 PM
You installed the speakers incorrectly.  I can see that you are employing a parallel connection when they are supposed to be series.  This is why your new amps are extremely loud: Your effective load is 4 ohms instead of 16. :)  My modules should take a 4 ohm load but it is not recommended and you will probably destroy your speakers.

Hello Mike,

They used to be 32ohm speakers connected in parallel. Which makes a load of 16 Ohms per channel.
I changed them for 8 Ohm speakers which I connected serial. That should also make a load of 16 Ohms per channel.
I am pretty sure I hooked them up right, but I will check this again next week ..better safe than sorry.

I will turn all my mountains into rhodes.


There are lots of aluminium heatsinks on Ebay.
Probably also in a size that fits even better.

I think I used this one.

But I remember considering to buy a longer heatsink (for 4 transistors) and cut them in the exact size.
That would make it very close to the original heatsink.

Oh I forgot to mention. I had to drill two more holes in the base of the sink.
Just to fit the PCB 4 mounting holes.

I will turn all my mountains into rhodes.

Mike Borish

I saw those heat sinks a few months ago and noticed that the dimensions of the top holes were slightly off.  I also noticed that I would have to drill bottom holes too.  I'm seriously thinking about designing the next batch of modules around those heat sinks. 

It looks like they don't fit in the base without modification either.

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


I  checked the speaker cables. They are OK.  Your modules just go louder and clearer, Mike. That's not a shame  ;D
I pushed the volume to 10 (and played softy). Loud, but under control.
The volume is really gradual.   At volume 10, quite a bit of hiss comes up... which I think is normal at that level.
These are good modules Mike. You may be proud.

As for the heatsinks. Yes, they are a bit deep. I also had a pair of flatter, longer sinks.
But these looked and felt better. And drilling the holes was very easy with my 10 dollar cobalt drill.
I was even able to mount them back the same way in the cabinet. But that would only leave a distance of half an inch from the grill cloth... 

The top holes were fine. The PCB is mounted on teflon spacers
I will turn all my mountains into rhodes.