How to replace volume pot in Dynaco Pas

thanks V

Thanks V. I have used a 25k stepped attenuator and built myself a little one input passive preamp (no autoformer)and it sounds pretty nice using the Pas2 as a phono stage only. The weird this is;I don't have to turn on the tape monitor,it just works.
Is this normal?

e

Viridian: a St70,though very interesting to me,would never work with my speakers (Acoustat 2s).
Correct me if I am wrong,but Joe's circuit removes some of the caps to be replaced by wire? He seems to have a handle on the RIAA curve. I will send you some picts of my Pas board.
In the meantime, I definetly plan on changing out the rectifier for a new power supply cap board,and change out the pilot light for a diode. I feel like the volume pot is way off from where it should be. Honestly I really don't have a grip on that yet.Will having a 100k pot make it less sensitive?

I love it that Ralph jumps in on these strings. It proves to me that he has genuine interest in our hobby and makes me more interested in his products than others.(not to mention the great write ups his amps get)

thanks again

e

I noticed that when I started looking at the values.

This Pas has been rebuilt, but it was done before I bought it. The 250k pot is too sensitive and the pre sounds very good. I am wondering if the guy that did the mods changed the values toward the good. Should I start over and make sure that everything is ok? This is where I am leaning.
I feel like this little Preamp has alot to offer for a beginner hacker.
I really appreciate your help V.

e

I looked up Orange drops online and I must not have them because mine are redder than what they show. I can't see anyone's name on them.Also I would say that this pre doesn't have a harsh bone in it's body.

I noticed on the Dyno Doc's image what looks like a 470pf shunt on the 2200pf (flat looking)caps.Is this right?

e

Regarding the Dynaco Doctor image: is this mod to bring the RIAA curve closer to spec?

As for the caps: what voltage should the phono board caps be?
I am thinking of doing the Dayton foil caps.Good price and easy (1 day) delivery.

e

I bought a kit for my hafler and most of the caps were Daytons. The amp sounds better than new.
I am curious about the russian oil and paper.

There is not that much on these boards, so I imagine it is pretty cheap to recap.
How about the resistors?

e

Thanks guys. I will change my order on the attenuator.

This mod doent' look too bad to perform.

Do you guys recommend any particular caps?

e

Viridian: Do you think I should use a 100k pot? I am not using the loudness feature.I have been looking at the math and I am unsure.
The low level input is 50k and the high level input is 250k and the output is 1k.

I have been reading up on pots and attenuators and I will admit that I am a little confused.I was never very good at math and the equations (as expressed in the white paper I am reading) are beyond me.I understand the concepts but am having a problem putting numbers to formulas.

If you or anyone has experience with this or a recommendation I would be very grateful.

rank beginner hack

e

Viridian: I was thinking I would just purchase on of the upgraded power supply mods from Audio Regenesis. Here is there link:
http://www.audioregenesis.com/projects/index.html

Not expensive and a easy conversion and makes the amp much safer and with better power supply.

I am also going to try my 25k stepped attenuator.I will let you know how it goes in the next day or so.

e

I figured it out. Thanks Viridian.

I disconnected the loudness circuit,and installed a new 250k pot that came with my new Pas 2. The pot was way too sensitive,so I put some 10k resistors between the output and ground to refigure the taper.It is still too sensitive but it is much better.I will get some 32k resistors which should put it in the sweet spot for pot taper.

I am also thinking of installing a stepped attenuator but I want to figure out the best pot value to use before I do that.
I am thinking that 100k is probably where I should be.

I have a power supply upgrade coming too.

Since replacing the pot the sound is much more balanced,with much better imaging.The tone seems less colored while still maintaining the tube transparency.
A very nice sounding little preamp.

e

I went back to Dynaco Doctor and I couldn't find anything about the volume pot.If you have a link,could you post it up?

thanks

e

Thanks for the help. I have done the tone control defeat. I have been to the Dynaco Doctor site and it is quite helpful, but I didn't see anything on the volume pot. I will go back and look again.
My Pas 2 is the later model that looks just like the Pas 3 and all the caps have been replaced. I didn't do the work so I am not sure what they were replaced with.
Any and all help is very appreciated.

thanks so much.

e