Has Anyone Ever Upgraded a Dynaco PAS?

[jeff e.]

I have a Dynaco PAS-2 that I got off of eBay a while back and all of the parts seem to be original. Would it be worth my while to replace all of the caps and resistors? I've noticed that one channel of the phono stage has louder hiss than the other. Since that is probably a resistor problem, I'm wondering if I should just go ahead and replace everything. Also, does anyone know of an online source with instructions on how to replace the selenium rectifier with diodes? I can't seem to find anything. I did find out how to bypass the tone controls, so if I decide to take the upgrade path, I may do that as well.

I know that Curcio sells some well-reviewed PAS circuit boards that are supposed to make a dramatic improvement, but I can't afford to take that route. The cost of new resistors and caps would not be a problem.

[Richard Feirstein]

I would start with the resisters and leave it at that. See what you hear at that point. It is not always easy to find in the wild components of the proper values, but the power supply stage is a good place to start because it is not as critical so long as you observe heat (current) values.

Richard.

[Shakey]

Try looking over these sites:

http://www.enter.net/~cae/index.htm
http://store.yahoo.com/triodeel/index.html

[jeff e.]

Shakey, thanks for the links. I've actually visited the Curcio site a few times. As a matter of fact, I just disabled the tone controls on my PAS using the directions on their site and it made a world of difference.

Triode Electronics is another great site. I've actually visited their store in Roscoe Village a couple of times to buy tubes. Very cool place... :cool:

[indy mike]

There's lotsa documentation on Dynaco stuff online - search around some more. Ask Mr. Curcio questions - he is VERY helpful, and his handy flow charts for pinpointing problems are excellent. I got a pair of MK IV amps up and running properly using a voltmeter, a schematic, helpful email from Mr. C. AND A VERY CAUTIOUS APPROACH AT ALL TIMES!!! You will be dealing with very high voltages, and those 525 volt caps can hold a charge a LONG time. Work in short periods of time when you are wide awake, no booze til your fix-it session is done. I found that I had to replace resistors, caps and tubes as I went, but it's not hard to repair Dynas if you are careful. Sckott is also a great resource right here at the site, and even kindly traded a nice NOS rectifier tube I needed.
What did you hear once the tone controls were removed from the circuit? I have a PAS-3X and have been contemplating that mod...

[jeff e.]

Thanks for the reply, Mike. I know all of the precautions about working with high voltages--right now, I'm only looking at replacing the caps on the PC boards. I know a power supply upgrade on the PAS is supposed to make a big difference, but I don't want to get that deep right now.

I was amazed at the difference when I disabled the tone controls. The sound opened up considerably--the upper end and even the bass sound much more natural and smooth. It had an ugly, "constipated" sound before the mod. The tone controls on the PAS-2 are atrocious: it is very hard to figure out if they are set dead center and it seems like the slightest turn of any of the four knobs affects the sound considerably. I'm not sure if the tone control mod would make such a big difference on a PAS-3X, though. From what I've read, putting the tone controls in the center position removes them from the circuit. It sounds like it's much more user-friendly.

Another mod I made the other day, just for the hell of it, was converting the "special" input into a second phono input. For some reason, this input sounds much cleaner than the regular phono input on my unit.

I'm just taking it one step at a time. As I said, I'll probably order some Orange Drops and replace the caps on the line and phono boards and see if that makes it even better.

Maybe one of these days I'll even work up enough courage to try to fix my beloved Sherwood S-5000 integrated amp with the hum problem... :rolleyes: