PS Audio 4.5 Power Supply

blairfrischx

I just recently picked up a PS Audio 200CX amp and PS Audio 4.5 Preamp from Craigslist. The Preamp came without the accompanying power supply. It's fully capable of working as a passive preamp (granted, phono doesn't work in passive mode), but I was wondering if it would be possible to make a new outboard power supply.

All rectification and filtering seems to be handled inside the preamp chassis, so it really only requires the specs of the transformer used. It's a long shot, but does anybody know or have any rough estimate? :razz:

On an unrelated note, the 4.5 and 200CX together sound very good. It's a lot more amp than I currently need, so I will probably end up selling it before too long; it was just part of a package deal. I'd like to keep the preamp around.

If it'd help, I could take and post some pictures of the preamp.

FTGV

If the rectification and filtering are already in the pre chassis then it should be a piece of cake.I 'm not sure of the secondary voltage needed but will do some digging.Pic's would help.

I assume the active gain stage is switchable so it can be bypassed?

blairfrischx

FTGV wrote: »

If the rectification and filtering are already in the pre chassis then it should be a piece of cake.I 'm not sure of the secondary voltage needed but will do some digging.Pic's would help.

I assume the active gain stage is switchable so it can be bypassed?

I can say for certain that there are 2200uF 50V caps immediately attached to the four-pin power umbilical inlet. I saw them when I had it open earlier, but I didn't take any pictures. I will have to take pictures tomorrow. I don't recall if there were any diodes or bridge rectifiers there, but I don't see why they would be separated from the rest of the circuitry.

The guy I bought it from said that the guy who originally owned it had had the external power supply go bad on him and couldn't find a suitable replacement for the transformer. Mind you, that advice was ca. 1995, so there may be something matching the specs that is available today.

I've been Googling about it but haven't found anything conclusive. I might email one of the guys over at PS Audio to ask.

Edit: one of the comments here states "The external power supply is a 56VAC center tapped power transformer. The bigger the better."

FTGV

Ok looks like it needs 56 center tapped(2x28VAC ) so the DC rails are high- ish for a preamp.Due to age you may also want to look at replacing those filter caps and any other electrolytics.




He He looks like I found the same quote from Paul McGowan,the P of PS.

blairfrischx

FTGV wrote: »

Ok looks like it needs 2x28VAC. so the DC rails are high ish for a preamp.

I see you found the same source I did. I edited my comment above pretty much right as you posted.

Avel Lindberg doesn't have anything at 2x28VAC or 56VAC center tapped. Their closest are 2x25V and 2x30V.
Edcor doesn't have anything even remotely close from what I can see.
Hammond has some 60VAC center tapped. They also have some 56VAC center tapped in this range which cost ~$15-20 on Mouser. That's not so bad.

I had debated replacing the capacitors inside the preamp as well. It would certainly make sense that they are long overdue - especially those in the power supply which have just been sitting unused ever since the outboard transformer died.

From what I saw inside the preamp, the soldering was done on the underside of the board (one-sided pads), so it'll probably have to be completely removed from the enclosure to do much of anything.

blairfrischx

Here's a picture from Google of the insides:


Power supply section on the right side

FTGV

There should be voltage regulators for the DC so even if the secondary voltage is a bit high the regulators will just need to drop a few more volts.

FTGV

blairfrischx wrote: »

Here's a picture from Google of the insides:


Power supply section on the right side

I see what appears to be regulators with heatsinks,but don't see any bridge or rectifier diodes.

blairfrischx

I took some pictures of the inside. There is indeed a little bridge rectifier right in front of the voltage regulators.

Here's an album of pictures.

I also need to find a good way to dust it off. Hazards of having a perforated grating on top, I guess. :frown:

SCompRacer

blairfrischx wrote: »

I also need to find a good way to dust it off. Hazards of having a perforated grating on top, I guess. :frown:

My 20+ year old Krell pre has a fully vented top. It was pretty dusty, canned air just wasn't blowing it off. When I recapped it I washed the entire board with 99% Isopropyl alcohol. Looked like new after.

FTGV

blairfrischx wrote: »

There is indeed a little bridge rectifier right in front of the voltage regulators.

Indeed there is,so now you just need an appropriate tranny and a little enclosure for it.If you like the sound I would seriously consider replacing all those lytic's and De-Ox-ing those connectors.

blairfrischx

FTGV wrote: »

Indeed there is,so now you just need an appropriate tranny and a little enclosure for it.If you like the sound I would seriously consider replacing all those lytic's and De-Ox-ing those connectors.

I do like the sound. It'll take a little bit of work to get it back in "like new" shape. There was a post on the PS Audio forums with the identities and manufacturer parts numbers for all the switches used on the front (not the pot, which is of Noble make); he said full replacement was under $40-50 for the switches. On top of that, I count 24 electrolytics throughout. Maybe it'll give me something to do over the summer!

FTGV

blairfrischx wrote: »

I do like the sound.

I meant when you get the active section up and running.

I count 24 electrolytics throughout...

A good low impedance lytic like Panasonics FCseries available from Digi Key are very economical.http://www.digikey.com/

opusk2k9

Oddly, I recently picked up a PS Audio 200cx and PS Audio 4.5 and 5.0 in a CL package deal too. I can open the power supply box tomorrow and email you some photos. The power supply for the 5.0 is much beefier.

The guy kept excellent records, so I actually have a copy of the manuals for both the 4.5 and 5.0. I can PDF them next time I am at work.

He also kept the copy of Stereophile where they reviewed the PS Audio 200cx, I can only find the review of the 200c online.

opusk2k9

Here are a copy of photos of the inside of the power supply.

opusk2k9

If you are interested, I scanned the operation instructions for the PS Audio 4.5, 5.0, and 200c. I also scanned the Stereophile review of the PS Audio 200cx.

Email me if you want a copy.

blairfrischx

I completely missed your past few responses until just now. Thanks for the help! I'll send an email your way.

On another note, have you noticed the behavior that is supposed to be typical of the 200cx - pop and fizzle on power down, etc? It's a great amp, but I think mine might be due for a thorough servicing.

An overhaul on the innards of the 4.5 will be a project for me. I'll have to see if the switches are still available online.

Bob in WI

Interesting thread. I believe I just bought one of the 200 CX's referenced above. After a good cleaning, it makes a small discharge on shut down but nothing excessive - I'm certainly not worried about the speakers. It was pretty dusty in there & there are some contacts & terminal blocks that can get corroded. Don't know if cleaning made a difference but it sure looks spiffier under the cover now. I'm pretty impressed with the amp. The pre I sampled hummed something crazy - I would like a reasonable pre at some point. Noticed the PS Audio pre's have no tone controls/ not sure I like that.

joosoof

opusk2k9 wrote: »

Here are a copy of photos of the inside of the power supply.

It looks like it is 28V-0-28V (56VAC) power supply. Do you know the power rating of the power supply (Amp or Watt)?

wkclaw

opusk2k9 wrote: »

Here are a copy of photos of the inside of the power supply.

Hi opusk2k9,
I know this issue happened long time ago, I am just wondering if you still have the copy of PS 4.5 instruction or you still have the preamp. I would like to have a picture of the front of the 4 pin connector on the power supply if you still have it. I have the same unit buy lost the power supply during the move. I email PS but have no response from them, may be I should call them instead. Thanks.

agfrost

Hi wkclaw, welcome to Club Polk.

I have the PS Audio 5.0, which likely has the same connector (?).

Diameter of the black plastic portion of the plug is ~12.5mm. note the crescent-shaped cutout.

Hope this is of some assistance.

gyosa

My ps audio 4.6 is the same, FWIW ..

BK

wkclaw

agfrost wrote: »

Hi wkclaw, welcome to Club Polk.

I have the PS Audio 5.0, which likely has the same connector (?).

Diameter of the black plastic portion of the plug is ~12.5mm. note the crescent-shaped cutout.

Hope this is of some assistance.

Thanks you guys for the info. Since I have to buy a new transformer, I need to get a new connector as well to replace the existing one. Do you guys know by any chance what type of oem transformer is it and what is the KVA(W) rating? I believe the original transformer may be 50 to 100W the most, I am thinking to buy a 150W to 200W toroidal transformer but I don't want to over kill. Thanks.
wkclaw

emmett518

First off, the power plug is a standard, 4 pin CB / Ham Radio mic connector. You can get them anywhere.

Second, I have a PDF of the 4.5 owners manual, and the service manual for the 6.1. I have a schematic for the 6.1, and am working on one for the 4.5. Happy to email them to anyone.

Also heard that Lorlin (a British company) still makes the switches for the 4.5, but they seem to be out of stock at Allied and Mouser.