Repairs, Maintenance & Upgrades > Preamps, Modifications & Upgrades

Preamp-less suitcase 88 for studio - what to do?


I'm putting together a small personal project studio and just picked up a cheap 1978-ish MkI 88 for it. It's a suitcase, but the preamp had been removed entirely and there's just a cable plugged into the harp, through the power cable hole, with a 1/4" on the other end. It sounds and plays great!

I would like to clean it up a bit, though. At the minimum I'd like to replace the cable with a 1/4" jack, add a volume pot, and get a sheet of aluminum or something to cover all the holes I'm not using up. There seems to be some debate as to the best impedance of volume pot to use, so I'm wondering if anyone has advice on what's best if I just want it to sound like it sounds straight off the harp, but with adjustable volume. Or would I really be selling the thing short without a preamp?

Second, right now I'm playing it into my Boss Katana guitar amp, and it sounds excellent. The plan is for it to live plugged into my Apollo 8p, and I'll be able to apply amp modeling and reverb there as needed, but I'd like to have at least drive and tremolo sitting on top of the board. One approach I can see working is to just grab like a Soul Food and a Stereo Pulsar, into a stereo (active?) DI box, into the Apollo. Should I also be looking at some sort of preamp pedal? Alternately, I could get something like a Boss GT-001 or Line6 POD tabletop guitar processor and have access to a bunch of stuff beyond drive and tremolo (although in a less hands-on package.) That would also give me a headphone amp and the ability to send line-level signal into the Apollo, alleviating the need for a DI box. Does anyone use a digital-multieffects thingy with their piano? Would the desire to plug it into something like that vs. a pedal vs. a DI box impact what choice I make for the volume pot? (I know what I would pick for a guitar or a bass, but it seems like the way the pickup array on these things works differently!)

Lastly, it's a suitcase without the speaker cabinet, so I need a sustain pedal of some sort. What's the preferred solution for conversion? The Vintage Vibe one appears out of stock.



If this were mine, I would probably split my goals into short-term goals and long term goals:

Short-term goals:
Get this piano playable and gig-able by putting a 1/4" jack and volume control on the rail.  If you just want volume, put the 1/4" jack where "accessory 1" would be, and put the volume pot where the origianal volume pot would go.  If it were mine, I would put the volume and bass boost pots in the place where speed and intensity would go.

Seller "AmplifiedParts" has nice-feeling "Alpha Potentiometer, 10K Audio (Log)" pots for sale on Amazon.  Same seller has the 50K Reverse-Audio pot for bass boost.  These Alpha (Taiwan) pots are not flimsy-feeling units, they feel like hydraulic-oil-damped pots from years ago.  Mouser sells the same pots, but I will be damned if I can figure out which part number exactly to buy, and Mouser isn't any cheaper than AmplifiedParts.  Sadly there is industry confusion with the California company using the same "Alpha" brand, and the Tiawan company does not have a very good web presence (minimal documentation, zero narrative in English).

The Alpha (Taiwan) pots from AmplifiedParts have plain round 1/4" shafts.  I have used the Fender 1972 Telecaster knobs with the setscrew.  Fifteen bucks for two volume, two tone.  These knobs look good, and I can't come close to this price ordering knobs individually from Mouser or Digikey.

Lots of pots with 1/4" shafts are available with the 3/8"-32TPI bushing threads (which you want), but nowadays many have metric bushings as small as 7mm.  The metric threads leave a lot of slop in a 3/8" mounting hole, but you can make it work.

Maybe some day, long-term goals:
Call around looking for the preamp you want.  If you don't find it on craigslist or ebay, call Vintage Vibe, RetroLinear, Chicago Electric Piano, Avion Studios, CAE Sound, and everybody else, and ask them if they have one to sell.  (Or wait ten minutes, and they might reply to this thread.)

Find a used or rebuilt Rhodes Janus preamp (with sliders) to install in your namerail.  I can't imagine a working one selling for less than $300.  Or, maybe buy a new-design replacement preamp and power supply when you stumble upon $500 to $800.  You would need the power supply, control/face plate, and the preamp.  Ideally, you really want the metal box that goes around the circuit board, not just the circuit board unprotected.  If you get just the circuit board, figure out a way to protect the underside of the board from accidental contact.  My unprotected preamp circuit board has nice burn marks from some sort of foolishness with the power applied (or the caps still energized).


If you like the sound of your harp plugged directly into your electronic chain, you may well not like the sound of the Janus amp or the standard stage-piano schematic.  Both have input impedances of 10k, which will definitely make the piano sound duller, with less of the hammer-impact sound.  The stage-piano circuit can be mostly cured of that problem by scaling the components.  For example use a 50k audio-taper pot for the volume control, a 250k reverse audio-taper pot for the bass control, and a 0.01 uF capacitor.  To my thinking, the Janus preamp is pretty much a waste of money.  I'd put in the stage piano circuit using the values I mentioned, and then make a front panel to cover the unused holes.  Another benefit of doing that is that you won't have to run power to the piano, which is a PITA.

Thanks for the feedback, folks!

I came to the conclusion that trying to add an active preamp - either an original or something like a Vintage Vibe - will probably be more money and trouble than it's worth because it IS a pain to get power to the preamp. So, I'm going to start with the original passive preamp design and go from there. I think I'm also going to try out the Boss GT-001 first. It seems to be the cheapest, most elegant solution to get the piano + some effects into my interface. Passive + pedals + stereo DI or Preamp + power adapter both seem to be substantially more expensive options vs. just going with a small amp modeler with line outs.

Any suggestions on sustain pedal? Can I just get the stage sustain pedal and put a cap on the end of it?


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