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Pilot SP-210 power supply

vendo81

vendo81

AK Subscriber
Subscriber
If anyone is thinking of building a separate power supply for a SP-210 preamp, you are making the right decision! After a recap of a friends SP-210, and using my rebuilt SA232 amplifier as a power supply, the results were OK at best.

I decided to cut down a Pilot MPX 200 unit to use for the power supply as I have a couple of them that I don't use. I have ACE gold paint that matches the pilot color really well which made things easier. I used a 6X4 rectifier with a C-R-C-R-C filter and drop down to the target 125 VDC. Added a 24V transformer as needed. I happened to have an 11 pin socket as they are used in Seeburg jukeboxes which I have parts. Added a 3/4 amp fuse. I cut down and mounted the original bottom with legs. The SP-210 turns on the power supply and the pilot lamp uses the filament voltage of the 6X4.

The results were amazing! Took the preamp to a new level! Very quiet......... sounds like a different preamp.

Pilot PS.jpg

Pilot PS main.jpg
 
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I wonder if the noise is a ground loop issue. The power supply ground and the signal ground end up tied together in multiple places in these so i can very much imagine it causing issues. I worked on a 210 and used my sa260 to power it. I recall it not being dead silent but it was also only partially restored.
 
Very well could be a ground loop problem as slight hum was an issue with the SA232. The SA232 is very quiet with other preamps.
My recapped Eico HF85 has slight hum which I've heard can be eliminated with a separate supply. I'm going to build one as soon as I get the Eico out of storage.
 
something that might be worth trying as a low effort check, use an audio cable where the shield is only connected at one end. That would have the umbilcal cord as the only ground connection between the units. Worst case it will do nothing or hum and you can build the external supply anyway.
 
I didn't try that. Very good idea! Somewhere around here I have a pair of ground loop isolator cables with in-line transformers that have worked well in the past
 
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