2. amps-preamps
  3. 1337738447

Relocating power transformer in PS Audio GCPH

I just recently completed a project to relocate (or actually disable) the torodial power transformer in my PS Audio GCPH phono pre-amp.

I built a separate outboard power supply with a similar torodial transformer (so I could leave the stock one installed but disconnected) that has 132,000 mfd of capacitance. I run the V+ , V- and Gnd busses up to the GCPH and feed them through the chassis using an Amphenol connector, and run wiring from the connector to a molex style three pin that matches the connector on the original GCPH transformer. I removed the IEC AC connector (and associated circuit board) and mounted the Amphenol connector to a blind off plate that mounts in place of the IEC.

After the modification, the hum (60/120/240 Hz) noise component is completely gone. Much quieter on the 60 dB and 66 dB gain settings. I can also use more of the volume control than before.

This setup allows me to go back to stock if desired, as I did not disturb the position of the PS Audio power transformer (which is critical). But I doubt if I will go back beacuse the new noise performance is so much better.
dhl93449

Showing 4 responses by dhl93449

dhl93449 OP
455 posts
 
Rrog:

I can't comment yet as I am still putting my turntable/arm/cart together. I would not expect it to be worse than stock, however. The noise was such a big issue for me that I felt I needed to deal with it if I was going to continue consideration of the GCPH.
dhl93449 OP
455 posts
 
Swanny:

I'll email you further details. Too bad we cannot post pics on Agon. I can take some for you if you wish.
dhl93449 OP
455 posts
 
Swanny:

I sent an email to your address. Did you get it?

For pics maybe I can post something on vinyl engine, if you guys subsrcibe to that forum.
dhl93449 OP
455 posts
 
M297904:

Yes, the outboard capacitance is about 2.75x the stock level of 48,000 mfd (which is also quite a lot for a pre-amp).

Re the Underwood mods, I could not really see what "input resistors" they were replacing, as all the passive components (except the power supply caps, diodes, and voltage regulators) on the input stages are all surface mount and you cannot replace surface mount resistors with leaded components. That is practically impossible. Unless they are going inside the GC modules themselves? There are four smaller electrolytic caps that act as bypassing caps for the IC pre-amp that I understand they may also be replacing.

Certainly any mu metal/mag shielding placed between that transformer and the circuit board will help reduce hum levels. But relocating the transformer will do more than any shielding can IMHO, as distance is your friend where field strength is concerned.

It's no coincidence that remotely packaging the power supply is practiced by a number of phono pre-amp manufacturers, including Byston and others. It's too bad that PS does not follow the same practice, but I understand their concern for cost (the Bryston is many times the cost of the PS Audio).
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