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PS Audio Question (pre-amp)
PS Audio Question (pre-amp)
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Old 18th November 2008, 10:05 PM   #1
heiman is offline heiman  United States
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Join Date: Nov 2008
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, 10:57 PM   #2
ken.berg is offline ken.berg  United States
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Location: Tempe, AZ
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 18th November 2008, 11:55 PM   #3
mightydub is offline mightydub  United States
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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, 02:15 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, 05:16 AM   #5
mightydub is offline mightydub  United States
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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, 153 views)
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Old 20th November 2008, 12:29 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, 04:39 PM   #7
mightydub is offline mightydub  United States
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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, 11:51 AM   #8
2004tadej is offline 2004tadej  Slovenia
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Location: Ljubljana

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, 03:30 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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Old 18th June 2016, 07:00 PM   #10
scubajeff is offline scubajeff
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Default PS Audio 4.5 & 4.6 Pre-amp switch part numbers & Schematic

Mightydub supplied me with fantastic information, enabling me to fix my PS Audio 4.5 pre-amp. It had the 4.5/4.6 common problem, worn out selector switches. They are Lorlin switches, and contrary to information on the PS Audio Forum, the parts are still made, and readily available.

mightydub's info was specific to the 4.6 pre-amp, but the 4.5 and 4.6 pre-amps shared many parts. The switch part numbers are the same, and worked on my 4.5 pre-amp.

I love the sound of the PS Audio 4.5 pre-amp using the Straightwire setting, which bypasses the line level amp. If your source has a high enough output, you can select Straightwire, which bypasses the entire pre-amp, using only the volume potentiometer. Thus you are only listening to your CD or digital source output, and not the pre-amp. For vinyl records, you can choose to use only the PS Audio phono section, bypassing the line level amp. That assumes the use of a moving coil cartridge with a moderate or high output level. Pretty neat design.

I ordered the switches from Allied Electronics:
Lorlin - PT6422 - 2P 5way wafer switch mechanism-PCB kit - Allied Electronics

MANY thanks to mightydub!

Here's the information mightydub sent me:

Here's the schematic and datasheet on the switches. The switches are a modular system, you start with the basic switch then you can add additional wafers to it. The output, tape feed, and source switches are 2 pole, 5 way though only the input selector uses all 5. The output and tape feed have a stop pin that limits it to 4 positions. The balance switch is two 12 pole wafers. The schematic is hard to follow but it all makes sense once you take the preamp apart and study it a bit.

I found the switches at Allied Electronics, you could also try Farnell in the UK. I just did a google search and see availability at a variety of places.

PT6422/BMH - LORLIN - SWITCH, 2POLE, 5 POS | Newark element14

1 Lorlin SWITCH + 1P 12W Mfr's Part#: PT6434
3 Lorlin PCB SWITCH MECHANISM Mfr's Part#: PT6422
2 Lorlin PCB 2 POLE 5 WAY Mfr's Part#: PT602-003
2 Lorlin PCB 1 POLE 12 WAY Mfr's Part#: PT602-001
Attached Files
File Type: pdf 4.6schematics.pdf (783.8 KB, 129 views)
File Type: pdf lorlinRotaryPT.pdf (495.1 KB, 33 views)
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