DIY RA-200 suggestions?

[nmi8080]

Hi

I've just started thinking about how to DIY the "top half" of a Yamaha RA-200 and wanted to see if anyone has thoughts or suggestions on how to get there. The interesting thing about the RA-200 is the set of three 8 ohm rotating speakers (I've acquired three from old Yamaha organs):

http://www.stefanv.com/electronics/hammond_rotary/speaker.jpg

I want a clean, warm Fenderish sound and don't need lots of volume.

David Gilmour uses these as so: guitar->Alembic F2B preamp->RA-200 solid state power amp. He seems to know what he's doing so I was thinking about the same approach.

Since I don't have an RA-200 power amp, I was looking at these:

1 x 600W Class D Audio Amplifier Combo Kit w MW 48V 600W Power Supply TAS5630 | eBay

and a DIY one-channel Alembic to feed it.

Any thoughts?

Regards,
mike.

 

[jazbo8]

It seems that you got the most difficult part sorted - the rotating speakers. Since you do not need lots of volume, why use such high-power amp? For that matter, why even solid-state?

 

[nmi8080]

The set of three 8 ohm speakers is the complicating factor. I could only find one tube amp (tweed Bandmaster) that used a setup like that and it wired them parallel for 2.6 ohms, used a 4 ohm OT, and supposedly had a "unique" tone because of the mismatch.

I just want a nice warm clean tone - I get dirt from pedals, so a solid state power amp seems to be the simplest and cheapest way to go. 600W sounds like overkill but from what I can find out the amp type is unusably distorted anywhere near 600W.

I'm hoping someone has looked at these power amps and can offer an opinion about how well they'll work in the preamp & speakers scheme I'm thinking of, or has a better/simpler idea.

 

[jazbo8]

If you go with the SS amp, you don't need a OT, since it has no problem driving 2.6 Ohm. OTOH, if you wire 2 of the speakers in parallel then put them in series with the other one, you will have 12 Ohm, which can be easily driven with a tube amp with the right OT (a 8 Ohm or 16 Ohm tap should work fine as well), Even a 50W tube amp can drive them to pretty loud levels. Before you order any amp, you can use whatever you have or can borrow, to test out the various combinations.

 

[nmi8080]

Progress!

I've made quite a bit of progress on my project:



I went with this power amp, one channel per speaker.

4x100W @ 4 Ohm TK2050 Class-T Audio Amplifier Board Only | 320-335

Which sounds great as a music amp, not so good as a guitar amp - flat and lifeless. So I'm working on the second part of the project, an Alembic F2B clone. I like the build shown here:

Dual Channel 1U bass/guitar preamp with low impedance transformer balanced output

But am wondering about the amp input levels. Jon's project writeup says the attenuated mono output gives "6V P-P into a 600 ohm load" and says that it would be "desirable to be able to drive lower-level inputs without overload" and would need a pad to do so.

I think I may run into this problem since the TK2050 amp has an 520 mV input sensitivity.

Can anyone point me in the right direction to understand this issue? Thanks!

 

[Nigel Goodwin]

But am wondering about the amp input levels. Jon's project writeup says the attenuated mono output gives "6V P-P into a 600 ohm load" and says that it would be "desirable to be able to drive lower-level inputs without overload" and would need a pad to do so.

I think I may run into this problem since the TK2050 amp has an 520 mV input sensitivity.

Can anyone point me in the right direction to understand this issue? Thanks!

Two resistors as an attenuator, or simply alter the existing attenuator to drop it even further.

With no schematic, I can't really suggest values.

 

[jazbo8]

Looking good! But I'm not sure the Alembic is the right choice for this application, since it's designed for relatively clean bass amp. What you are looking for is pre-amp distortion since the T-Amp should not be over-driven. I suggest that you build a distortion pedal like the Tube Screamer, Big Muff or RAT, all of which has volume control, so you can easily match the input sensitivity of the T-Amp.

 

[Leondr255]

Hi There...
I am new here.
I olso have a problem with the ra 200. One of the three amplifiers makes a schortclosure. I dont have a good schematic. I onley have the schematic of the ra 100.
Does anyone know of there a great diferance is between the those two models? Appart from the one but three rotating speakers? Can i juse the schematic from the ra 100 for the ra 200? Already thanks for answering. Greetings from Holland.

 

[Roody91]

Did you finish the project?

Hey,

Were you successful finishing this project? Can you provide some pics, sound/video?

Thanks