Hoffman Amplifiers Tube Amplifier Forum

Other Stuff => Solid State => Topic started by: TIMBO on September 06, 2014, 07:51:25 pm

Title: Lowrey Organ Doner
Post by: TIMBO on September 06, 2014, 07:51:25 pm

Hi guys, I got one of these for niks. Not tube, solidstate with reverb and leslie.

I'm looking to build another ROTOSONIC with a built in reverb and its own amp.

Is it possible to adapt a preamp to the existing power amps.

Title: Re: Lowrey Organ Doner
Post by: PRR on September 08, 2014, 06:55:03 pm

I like Note 9.

Otherwise: what a mess!! 4 power channels, 6 speakers, one spinning?

Title: Re: Lowrey Organ Doner
Post by: TIMBO on September 16, 2014, 03:24:11 am

Thanks PRR, I like note 9 as well, sometimes you DO have to read the small print.

My understanding of SS stuff is as limited as my tube knowledge, so I have trimmed it to what I think is needed for the moment.

The power supply required for the Leslie Output Amp is +12v and +15.5v and the Leslie Amp +38v, -37v and +14v,-14v and looking at the power supply circuit board layout these can be isolated.

This preamp http://www.altronics.com.au/p/k6044-champion-pre-amp-kit/ (http://www.altronics.com.au/p/k6044-champion-pre-amp-kit/) uses 4-13.5v dc and can be tapped off the Leslie Output amp +12v supply.

This EQ  http://www.altronics.com.au/p/k5305-sc-1995-5-band-graphic-equaliser-kit/ (http://www.altronics.com.au/p/k5305-sc-1995-5-band-graphic-equaliser-kit/) needs 15-0-15 supply and I think that a separate transformer would be the easiest way to go.

I am hoping that is a case of the Preamp-> EQ -> Leslie Output Amp -> Leslie Amp -> Speaker.

The Reverb is NOT a must have but I was only going to include it as it was a bonus FX.

Does this look like it is a workable setup. Thanks

Title: Re: Lowrey Organ Doner
Post by: TIMBO on September 24, 2014, 04:14:27 am

Hi guys, Had some time to CUT n PASTE parts and I have been able to get the power supply running to close to the desired voltages.

I trimmed the circuit board for the Leslie output amp and replaced the Ecaps as they were a bit iffy.

Mounted on a board for some testing.

Preamp and EQ has arrived, these are kits so some neat soldering needed. :icon_biggrin:

Title: Re: Lowrey Organ Doner
Post by: TIMBO on October 03, 2014, 03:12:42 am

Hi guys , No big surprise that this would fizzle, no magic smoke or anything. It does work after bypassing some of the circuit (Leslie output amp) and plugging the EQ straight into the main amp. This was quite loud but unfortunately the added noise (static/hum) was more than I was prepared to put up with. I rebuilt the whole main amp board, replacing the CC resistors with CF resistors and the NP Ecaps, this still was very noisy. The transistors remained as there is no ID on them so I have no idea what they are.

Off to the local store and they have great 50w module, so I am in the process of wiring it up and eager to here it.

Title: Re: Lowrey Organ Doner
Post by: TIMBO on October 03, 2014, 11:40:38 pm

Hi guys, I was informed that the aluminium chassis may not be the best heatsink ,so a proper is now in place.