How Do I Set Up Lowrey Organ Power Supply Project?

Unfortunately your schematic picture is not very ledgible. I suspect that the large number of voltages you cite are actually DC bias point values on the schematic to assist troubleshooting and not actually seperate supply output voltages. In otherwords these nodal voltages are the nominal DC voltages a repair technician would expect to find with a DC voltmeter while all circuits are in proper working condition.

Have Fun

Nice job! Because GA's are subjective, here ya go.

I uploaded the photos of the Power Supply to flicker. Hopw they have a better resolution.

http://farm2.static.flickr.com/1351/4728958498_a8e6c66b5f_b.jpg

http://www.flickr.com/photos/41228779@N08/4728315709

Thanks,

Rob

Ok, I can read the schematic now from the two links you've provided. The multiple voltages are as I expected, nominal values. Many years back I worked for a company making analog electronic organs. The multiple RC power taps on this schematic are primarily to isolate the types of voices from each other. In other words to prevent the flute, orchestra, reed and timing signals from interfering with each other.

How can I help?

Ok got it.

I need to know how to set this project up as a bench project. I am replacing the caps. Can I fire her up and test voltages without connecting the power supply taps to the various boards? I can't risk damaging the all the newly restored boards if I make a mistake.

I watched a UTube video of a technician that replaced the caps on an Allen Power supply of the same 1970s era. In that instance the power taps were not connected to loads. All he did was measure the taps to ground. He did connect loads to the amps. In my case I can either initally disconnect the amps or hook up four speakers to them.

Can I blow the power regulators without loads? How do I proceed to test after I replace the caps?

Thanks,

Rob

Hi redfred,

This is precisely the information I needed. Now I can go ahead with the project.

All of the electrolytic filter caps on the various boards (RC taps) have already been changed with higher volt capacity caps.

You honed in on the 14V VR which I've had to adjust on the original power supply. And you are correct it was very difficult to adjust as the result of being in one position for 30 years. I cleaned it with Deoxit and was able to get close to the 14V…14.2V but couldn't get closer. The location of the VR is on the "Power Supply Board" which is mounted under the chassis.

Ironically, on the power supply that I intend to work on first as a trial run there is no VR. It is a later production model (1980) and Lowrey obviously did away with the adjustment. There is another component in its place that I assume automatically adjusts the voltage. (I could take photo of it if you like but I won't be at the location of the organ until Sunday.)

Because of the modifications to this second power supply I do not intend to install it in the organ. There is no schematic reflecting the mods. I just want to determine if I am up to the task of replacing the caps and getting correct stable voltages. If I can do it on the trial run then I will change the caps in the original as a separate project.

That's the plan. If it doesn't work out I will leave the original as is.

After doing all this work on the organ it doesn't make sense to leave 30 year old caps to eventually cause a problem.

I do have one more question: What do I have to hook up to the amp inputs to be able to test them? I can provide a schematic if needed.

I'm humbled by your acuity and generosity. Many thanks!!!

Gratitude,

Rob

Well the easiest thing will be to just use a single flute stop of the organ itself. This will be close to a pure sine wave signal. First I would examine the DC voltage output across the speaker with just the audio amplifier operating and no organ signals generated. This should be very close to 0VDC. Now you may have identical DC offsets referenced to ground, for both terminals of the speaker. This will make a 0 voltage difference at the speaker terminals.

With a thirty year old organ, I would seriously consider planning to replace the speaker itself. This will make the most dramatic improvement in sound fidelity. I'm not sure where you could get a direct replacement today. You might consider Madisound for a raw driver. I haven't used their products for a long time. They were not the cheapest source for quality products, they were not exorbitant either. More to the point, they very willing to work with a hobbyist.

Ok

This should be enough to get me started. FYI the speakers have already been replaced. The organ is getting close to it's original sound. There are a few fixes that need to be addressed yet but nothing that can't be handled with some digging and tracing. The power supply caps is the one project that I needed help with.

I will keep you posted.

Much gratitude,

Rob

Threads like this sort of make up for threads like this:Short Circuit in Sea Water? and this: Heavy Load on Low Power Supply and my personal favorite: Personal RF Signals .

Nice work guys!

Thank You,

I wanted to update Redfred and the other members on this forum that were helpful on my Lowrey C500 power supply project. I'm taking it slow. I had to nix the bench project and work directly on the restored organ. So far I've replaced 2 of the large can capacitors which were dual 500uf NP and dual 2500uf NP filtering capacitors for the 4 amplifiers. It was difficult to find non polar caps in those values but I eventually did find them. The result was a definite improvement in the audio.

I've decided to leave the power supply caps alone for the moment. They are working well so it is not a priority.

The old beast is temperamental and fragile after 34 years of existence. After 10 months the project is moving in the direction of "fully functional". There are still at least 3 major repairs left to do and a lot of tweaking needed so there is still a lot to do. Without a technical background I'm flying by the seat of my pants but it's been fun and a good learning experience.

I do have a question:

There are 3 crossover capacitors on the power supply chassis (in the left top photo of the chassis). I tested them with my ER meter and they appear to be OK but I would like to replace them anyway. Those capacitors are clearly marked for AC voltage. 60uf 25V AC, 200uf 25V AC, 50uf 35V AC. What is the significance of the AC marking and what type of capacitor can I use to replace them?

Many thanks,

Rob

I think that the black and red capacitors in the picture are polystyrene capacitors. If I'm correct these capacitors are an obsolete package design which is why you won't find ones that look identical but you can still find exact replacements. Polystyrene capacitors are very stable over temperature. This is why they are used in audio range filter networks of musical instruments. The filter sets the relative harmonic levels of a voice (reeds, flutes, pipes) or can be used to set the amplitude envelope shape for one of these voices. Since you only have a few of these of this size in your organ, I suspect that they set the amplitude envelope.

HI Redfred,

If I get your drift... if I purchase polystyrene caps of the same values and perhaps 5% or less then I am ok.

Thanks

Rob