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Old 18th November 2008, 11:05 PM   #1
heiman is offline heiman  United States
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Cool PS Audio Question (pre-amp)

Hi Folks:

Newbie Bruce here:

I have a PS-4 pre-amp and it intermittently develops a ~60hz hum/buzz, largely regardless of the input selection.

It is not other appliances--I have the circuit nicely isolated via a UPS/surge protector/line conditioner.

Has anyopne had similar issues with PS Audio gear?

Thanks for your kind consideration.


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Old 18th November 2008, 11:57 PM   #2
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Look for contact problems in the 4 pin connector from the power supply umbilical. I had intermittent mute relay surprise operation a few years ago that traced out to this.

You can either clean the contacts and retension the pins, or replace - Radio Shack carried the plug ans socket the last time I checked.
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Old 19th November 2008, 12:55 AM   #3
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Is this the PS 4.5/4.6?

Do the rotary switches still work reliably, or are they intermittent? Mine are in need of replacement but there's no drop-in substitute so it is either a major project or I scrap it.

PM me if you want the schematic for the 4.6, it is too big to post.
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Old 19th November 2008, 03:15 AM   #4
heiman is offline heiman  United States
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Default Good catch on rotary switches

I have the 4.5, and the rotary switches are showing serious signs of wear (increased hysterisis is the main sympton)--this results in intermittence. It is not a very user-friendly feel versus when the pre-amp was new...though I can still find the detents/stops for the switches. The locking allen screw in the rotary knobs is giving me trouble (slippage) too.

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Old 19th November 2008, 06:16 AM   #5
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If you have your 4.5 apart and can take some measurements of the rotary switches and figure out the connections, I can design and etch a little adapter pcb for a Greyhill or Electroswitch rotary to replace the existing ones. Basically I'd need the same set of information shown in the attached data sheet.

this is something on my "to-do" list that hasn't made it to the top yet.
Attached Files
File Type: pdf electroswitch_rotarypdf.pdf (82.7 KB, 104 views)
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Old 20th November 2008, 01:29 PM   #6
heiman is offline heiman  United States
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Default INformative responses--thx

Hey folks:

Thanks for the help! This resource is amazing.


Ken Berg: Awesome suggestion! That is a really good idea. I think this may be an issue. The disadvantage that I only NOW see (thx to you) to a separate hi-current power supply is the connection. I originally loved this pre-amp for the isolation of the potentially highly noisy power electronics. Oops.

mightydub: The hinky rotary switches have been an issue for some time, but I have been highly uncertain regarding them as a source of noise. Given the likely power supply issue above, I hope to try the slighly less tricky fix initially. The switches ARE a mess, and that might be the signal for me to consider buying a new pre-amp (I am thinking, BTW of a Bryston as a reasonable, well-built replacement for the PS Audio). ALSO: thanks for the schematic and the offer on the pcb--for now that is beyond my available time. Ummm...since I have still to discover my previous repair guy's contact info, do you ever fix oldish (late 70s and 80s vintage)
B&O gear? It is a pretty highly specialized pursuit.

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Old 20th November 2008, 05:39 PM   #7
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I'm not in the repair business - I just DIY for a hobby, and fix what I have when it breaks because I can't bear to throw it away. If/when I finally get a replacement switch solution for the 4.5 I'll post it here.
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Old 27th July 2013, 12:51 PM   #8
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I looking for schematics for 4.6 preamplifier or exactly psu voltage as acquired preamplifier without Psu
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Old 27th July 2013, 04:30 PM   #9
tvi is offline tvi  Australia
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The switches look like blue lorlins to me, now they are black and lead free.

Lorlin Rotary Switch PT 6477 | Alltronics
The small part of ignorance that we arrange and classify we give the name of knowledge.
Ambrose Bierce
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