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Putting a different power amp into a peterson cabinet

Started by billulsund, September 05, 2008, 01:37:38 PM

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billulsund

I have 2 suitcase rhodes with peterson amplifiers. One of the peterson amplifiers works great. The other peterson amplifier does not work and both power amps are toast. I was originally going to just rebuild the dead power amps, but have been thinking about doing something different. The power supply does work so I was thinking that I could use the power supply to power the preamp, and install a different stereo amp within the cabinet. I was wondering if anyone has done anything like this before and has information on good power amps to use. It would be cool to try it with tube amplifiers, but I am open to any suggestions. I do have quite a bit of electronics experience and would even be open to the idea of building my own amps if someone has a good schematic.
1974 Suitcase 73, 1975 Suitcase 88

Rob A

http://sound.westhost.com/projects.htm

When I was where you are at, I was considering building a pair of the 60W amps from here known as project 3A.

Pluses:
+ solid design
+ plenty power assuming oyu buy efficient drivers for your project
+ PCB available (!!!)
+ dead simple power supply
+ uses cheap, readily available output transistors
Minuses:
- no short circuit protection on the outputs

I can't think of a better choice myself.

I would strongly suggest modern drivers too--no point in wasting those beautiful 120W.

billulsund

Thanks Rob, that is exactly what I was looking for. Did you build these amps for your project? If so I was wondering how it turned out. The power supply circuit looks pretty simple, but I was wondering if you know  whether or not I can use the original Rhodes power supply. That would save some time and money. I will test the power supply to see if it will work as I believe it does provide a +-35v output. I think I will be ordering 2 of the PCBs for this amp today. It will be nice to have a more reliable amplifier. I was also wondering if you have any reccomendations on what drivers to use.
1974 Suitcase 73, 1975 Suitcase 88

Rob A

Man you are really opening up a can of worms now.

Let me just say this much about design. I think it's important to be clear what you are trying to accomplish. I'm pretty sure that my design goals wouldn't line up entirely with yours in several respects (and that's okay).

The big design decision, before the driver spec, is open or closed cabinet.

My opinion is that one reason that the stock suitcase bottom has really pretty dire performance is that it's an open design like a guitar amp, not a closed ported enclosure like a PA type cabinet. But now we're right back to the idea of design goals. If one primary goal was to use parts already on hand from your guitar amp operation, the suitcase bottom looks pretty good. I just don't share that goal.

Anyhow, I didn't carry out my project, because installing the piezos in my stock suitcase bottom convinced me that it would be a lot smarter not to have the speakers aimed at your knees. I know that's a radical theory, but I'm going to stick with it.

So I figured for what I'd invest in a suitcase bottom project (I was gonna biamp mine, and so 4 of those 60W amps plus an active xover), I would be better off buying a commercial power amp and a pair of floor wedges with 12s in them. I'd get better separation and a lot more bang for my buck, plus no real fear of messing up the design somehow. Plus all that kind of stuff is up for sale used all the time (I bought a QSC power amp used for a couple hundred bucks that was essentially new in box and had a six year warranty).

Some really good info about speaker cabinets is available here:
http://www.partsexpress.com/resources/speaker-replacement.cfm
http://www.partsexpress.com/resources/build-a-speaker.cfm
http://www.partsexpress.com/resources/pro-sound-driver-selection-guide.cfm

billulsund

Rob,

Thanks for the reply. I have been researching this all day and after reading your latest post have come to a similar conclusion. For the time and effort it would take me to put this together and the un-certainty of the results I am not as sold on this project as I was earlier (plus you make a great point about the speaker location on suitcase amps). I will probably be better off just using my power amp and floor monitors for now (or my working suitcase amp), and then somewhere down the line I may try this project or go back to the original plan of rebuilding the old amps. For the purposes of resale I imagine the piano is worth more with an original spec amplifier anyway.
1974 Suitcase 73, 1975 Suitcase 88