4.5 Pre-amp part numbers

I have a 4.5 pre-amp that has a bad input selector switch. I called customer service and was told that no parts lists or schematics were available for that unit. The representative also told me that that design had been contracted out to a 3rd party company, which made my request even more difficult. It seems very odd to me that PS Audio would not have a parts list for units it sold.

The dealer who sold the unit says he cannot service them, and he does not have any schematics or parts lists either. No one else in San Diego seems to have that information. I really love the preamp because of the fabulous sound using straight wire gain and the moving coil section, so I’d like to continue to use it.

Can anyone at PS Audio supply the part number for the Lorlin switch on the 4.5 preamp input selector?

Thank you in advance!

Best Regards,

Jeff Thayer

San Diego

I’m thinking out loud … was Cullen Circuits involved? The man behind that has retired but his son has a similar business and may have some information. He sells power cords, interconnects, and speaker wire. Cullen Cable is the name I think. I’m not sure if Paul was involved with the company at time either, can’t speak for any of the other current PS Audio employees.

Rick Cullen, Patrick’s father, built all of these products for us back in the day. Rick was our production manager.

The Lorlin switches haven’t been made in decades, unfortunately. There is no replacement I am aware of. Sorry. The one thig that can be done is to replace the switch with a good selector, like a CTS or any decent rotary switch. Then, hand wire from the switch to the PCB. It’s tedious, takes skill, but it can be done.

Wish I had better news.crying_gif

I found an old post from 11/08 on the diyAudio Forum, from mightydub, with part numbers and a schematic for the PS Audio 4.6 pre-amp.

http://www.diyaudio.com/forums/

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:
http://www.alliedelec.com/lorlin-pt6422/70749355/

MANY thanks to mightydub!

Here’s the information mightydub sent me:


Here's the schematic and data sheet 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.
http://uk.farnell.com/lorlin/pt6434-bmh/switch-1pole-12-pos-tht-0-5a-250v/dp/1123674
http://www.newark.com/lorlin/pt6422-bmh/switch-2pole-5-pos/dp/24M6507
http://uk.rs-online.com/web/p/rotary-switches/0352301/
http://uk.rs-online.com/web/p/rotary-switches/0352294/
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
I have a faulty PS Audio 4.5 and need the schematic for repair work. It would be appreciated if any of you can send me a scanned one on my email all@bio-root.com Thanks

Hi scubajeff–I just found this post while looking for answers to a similar problem I have with my PS 4.5. I can’t seem to find mightdub’s post. I’d like to get hold of a schematic and then see if your source still has replacement parts. Let me know if you have a copy of the schematic. Thanks!
chammell@charleshammell.com

Hello
I am looking for the same part for use on the far left selector swirch on the PS audio 4.5. I only see a single wafer and not the dual. Where are the part numbers from? Also, how do you indent them. I assume they are 30 degrees apet.
Anthony

Hello
I wanted to replace my 4.5 switches particularly the selector out far left on the faceplate. What part numbers do I buy to replicate the original. Problem is I don’t know how to indent/index to match the faceplate outputs?
Anthony

Hi Sam,

I’m sorry my reply is almost 3 years late! I don’t visit the forum unless I’m looking for something, and never saw your request. For some reason, your reply didn’t come to my personal email either, or else I would have replied long ago. It’s probably too late, but here is the informal, hand drawn schematic that mightydub sent me. It is actually for the PS Audio 4.6 pre-amp. The 4.6 shared much of the 4.5 circuitry, but the 4.6 had a bigger, beefier power supply. Anyway, that is all I have as far as a schematic. My 4.5 is still working, and I use it daily. I now need to replace the on/off switch, cause it’s quite dirty, and intermittent, a problem common to all 4.5 and 4.6 units.

The PS Audio Forum will not upload pdf files, so I will try to send it to your personal email.

Jeff

Hi Chammell,

As I said to Sam, I never saw your post till today. For some reason the replies to the forum never got forwarded to my personal email account. The forum seems to forbid pdf files, though I have no idea why, so I will send it directly to the address you listed.

Best regards,
Jeff

Hi DocTony,

Interestingly enough, I need to replace that same switch right now. The on/off switch on the far left is the one part number I didn’t get from mightydub, so I will have to research it. If you figure it out first, please post that on/off switch number here for all to see.

As I recall, the switches have a set spacing between clicks. I don’t remember having to set it, or change it, but I may be remembering that incorrectly. The only thing I think I did was set the stop points, and that is pretty obvious once you dive into it.

I should mention I had a terrible time getting the circuit board out of the unit initially. After you remove the 3 screws in the top cover, and slide it off, you also need to remove all the switch knobs. The board felt like it was still screwed in somewhere, but I could never locate where. I finally decided the pre-amp was unusable anyway, so I just pulled the circuit board out very firmly, and it finally came out. Please use caution regarding the volume knob circuit board attachment. It is a funky, jury rigged thing, and just flops around once the unit is removed from the chassis. I broke some of those wires during my repairs, and had to repair them as well.

I have taken photos of the switch, and will contact Lorlin for help identifying that dual wafer (deck), 2 pole switch. I will post the part number here when I have it. I’m not sure how long this process will take. Lorlin was very helpful the last time.

The Lorlin switches rotating arms are too long as they come from the factory. I had to hack saw some off the end to fit the rotary knobs on the unit. It looks like Lorlin changed them slightly, using a longer, dark colored rotating arm, instead of the original, shorter, light colored arms. The switch is perfect after you trim a bit off the end.

BTW, here is a link to the diyforum page about the PS Audio 4.5 Pre-amp:
https://www.diyaudio.com/forums/analog-line-level/133402-ps-audio-question-pre-amp.html

Jeff

1 Like

Helo Jeff

I wanted to thank you for your detailed letter in helping me with the PS Audio 4.5. I have the parts on order, but cannot understand how to set the indent stops matching the selector switch,labeled as follows far left out puts:Off, Straightwire, High Level, Phono. I think there were 2 versions of the PCB layout. Mine has the blue PCB. I spent a lot of time replacing all caps and the TIP transistors. I did not find the switches to be “loose” or corroded. If one decides to keep the original switches, they can be cleaned but tedious. THere is a small 1/4 mm opening between wafers where deoxit can be sprayed… If you can help me to re position the click stops, it would be greatly appreciated.? the inside original blue snap cover has slots where you can set the position (12 positions?). But only 4 indents are needed. Confusing for me??? Does the new lorlin switch already set-up to match the selector switch? The 4.5 I have using 2 ballbearings and a spring through a 2 hole slot on the plastic shaft making 2 opposite click stops. also there is electroyltic cap 2200uf 16V axial located in front of the TIP transistors that attach the negative lead to a bare wire bridge and the other is just inserted into a PCB hole with no solder eylet?? Is this so? If need any help or other on restoration let me know.

Anthony

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Hello Jeff. I don’t know if you received my first message. I wanted to thank you for your detailed letter. I did order the switches which are direct replacement. My PS audio preamp 4.5 may of had 2 versions? I just am frustrating on how to index.align the click stops to match the output faceplate, On/off, straightwire, line. phono. Since there are 12 indents inside the original switch, where is the start point and end-piont? The original was not corroded or faulty, just wanted to upgrade the switch. It used 2 ball-bearing & 1 spring through 2 thu-holes making 2 opposite contacts. also, there’s a 2200uf 16V axial which has the negative soldered to the bare wire bridge on the PCB & the othe apparently had a solder eyelet with no connection (floating) or was it attached to something via a short hook-up wire to another point. See PS forum foe photos.

Hi Anthony,

I got both of your emails today. I’m not sure if I can answer your question, however.

Did you get the correct exact replacement Lorlin switch for the on/off/straight-wire/high level/mono switch? If so, can you please send me the part number, cause I just contacted Lorlin today to see if they can help me find it.

It sounds to me that you used a different switch than the original cause you said you wanted to upgrade it, but I am not sure.

As far as indexing, I am not sure. The stop points are about 10:00, and 2:00 on a clock face. I don’t think you can change the angle of the stops on the original switches, but it has been 4 years since I last played around with the PT6422, which is the only switch I have worked with, and replaced so far.

We should probably take this conversation offline from the forum, and just email directly back and forth until we figure out how to solve your problem. You can contact me at scubapong@yahoo.com

Jeff

<((((°>


DocTony

    April 29

Hello Jeff. I don’t know if you received my first message. I wanted to thank you for your detailed letter. I did order the switches which are direct replacement. My PS audio preamp 4.5 may of had 2 versions? I just am frustrating on how to index.align the click stops to match the output faceplate, On/off, straightwire, line. phono. Since there are 12 indents inside the original switch, where is the start point and end-piont? The original was not corroded or faulty, just wanted to upgrade the switch. It used 2 ball-bearing & 1 spring through 2 thu-holes making 2 opposite contacts. also, there’s a 2200uf 16V axial which has the negative soldered to the bare wire bridge on the PCB & the othe apparently had a solder eyelet with no connection (floating) or was it attached to something via a short hook-up wire to another point. See PS forum foe photos.