PAS-2 crosstalk

I've finished work on my PAS-2 project and have enjoyed listening to it for two days now. The strange non-linear volume control will be part of my phase 2 effort. For now I am just enjoying the music. One other oddity is the crosstalk between inputs. The isolation between the "spare" and "fm" inputs is very poor. Is this a known issue with the PAS? I haven't begun testing/debugging this yet.

I'm guessing you are still using the original selector switch? I noticed a little of that before I changed mine out for the plain switch.

When you went through your PAS2 did you remove the tone controls, loudness, speaker switch as part of your cleanup?

Also, I see the power light is on. I read somewhere that it's sonically better to remove that lamp. Not sure why except for maybe the power draw. or it's an old wives tale.

mikeski...

Mikeski wrote:

Also, I see the power light is on. I read somewhere that it's sonically better to remove that lamp. Not sure why except for maybe the power draw. or it's an old wives tale.

mikeski...

I think I would lean toward "old wives' tale", but in any case, here's an option for a LED replacement, see link below:

http://home.comcast.net/~netminer/PAS-3.html

You can also make this yourself (I've done so), but for 12 bucks including shipping, this is a more elegant and easier "drop-in" solution.

Best Regards,
Charlie

I do have new selector switches with 6 positions, it will disable any "special" functions but otherwise is a big improvement over the original.
The indicator lamp problem is NOT an "old wives tale", the original style #53 lamp uses 150ma, as much as any of the tubes.
Replacing it with a 10ma draw LED will boost the very low filament voltage (around 10.5v) up around 11.0v, still shy of the 12.6v rating.
The power transformer (limited current supply) in the PAS2 and PAS3 is THE LARGEST limitation in the entire design.
I have the same LED replacement module listed above.

tubes4hifi wrote:The indicator lamp problem is NOT an "old wives tale", the original style #53 lamp uses 150ma, as much as any of the tubes.
Replacing it with a 10ma draw LED will boost the very low filament voltage (around 10.5v) up around 11.0v, still shy of the 12.6v rating.
The power transformer (limited current supply) in the PAS2 and PAS3 is THE LARGEST limitation in the entire design.
I have the same LED replacement module listed above.

Good Point Roy, I didn't realize the original lamp had that much current draw and would, of course, cause the voltage sag which you mentioned. I've been using a LED for the indicator light in my PAS-3 since building it in the early 90's.

Charlie

As I mentioned in your other thread, the volume control is how they all work. The non-linear response is normal

WntrMute2 wrote:As I mentioned in your other thread, the volume control is how they all work. The non-linear response is normal

This is a case where "normal" is still strange to me . I intend to look into doing something different with the volume control to make it "less normal" I guess. I gave the whole downstairs setup a good listening yesterday with the recently finished Mark IIIs and PAS-2. Not bad at all. I wish I had bothered to buy Mark IIIs years ago. This is my first real experience with them. I have owned ST-70, ST-70-C3 and PAS-3X in the past and they were okay. I am enjoying very low listener fatigue with the Mark IIIs and PAS-2. Maybe it's due to all the work that I did on them over the last six weeks or so!
...j

Try removing the wires from the loudness taps.

ok you said it -"i am stuck with using the ugliest preamp i have ever seen"--be nice pas's have feeling too-- or paint the cover a dark hammertone grey -my pas 2 is in a custom cypress and cherry case-looks better but still not beautiful--i would actually like to put brass knobs on mine-that would help a little more-now for crosstalk -it seems it is a unsolvable issue with the stock pas-i noticed the other day that i have no crosstalk-quite suprised-all the swtches tone controls etc are connected-i have tubes4hifi rca boards -and a curcio selector-one or the other -or both-may be the reason for no crosstalk-i suspect it is the selector-which is the same or similar to tubes4hifi-i also have a FM3zone led-gp49 can probably tell us exactly what the cause may be for crosstalk-GP49???

I personally don't care at all about the crosstalk; I power down unused sources!

They layout of the selector switch probably is the main cause of the crosstalk; you may be able to reduce it by replacing the twisted pair wiring with shielded, but that's a lot more work than turning off whatever I am not playing.

Besides, many times (and not just with the Dynaco PAS), you will find that there is a higher hum level from the phono input, as it can pick up hum fields from the power supply of whatever else is being left powered-up. I have this problem with my Philips CD player; it causes hum in phono when turned on; while my FM tuner, cassette deck and reel-to-reel recorder do not.

So shut 'em off!

[quote="howardnair"]ok you said it -"i am stuck with using the ugliest preamp i have ever seen"--be nice pas's have feeling too-- or paint the cover a dark hammertone grey -my pas 2 is in a custom cypress and cherry case-looks better but still not beautiful--i would actually like to put brass knobs on mine-that would help a little more-now for crosstalk ... quote]

Thinking about it some more... My PAS-2 is not the ugliest preamp I have had. It is about a tie with with the black/gold Audio Research SP3 I had back in my university days. It is certainly better looking than the PAM-1s I owned I am only "stuck" with it because it sounds so good. I would not paint the cover as the factory ivory is in such good shape.
...j

j beede wrote:
My PAS-2 is not the ugliest preamp I have had. It is about a tie with with the black/gold Audio Research SP3 I had back in my university days. It is certainly better looking than the PAM-1s I owned I am only "stuck" with it because it sounds so good.

That's about as good a reason to be "stuck" with it as anyone could think of.

I have a pair of PAM-1 that I haven't used in twenty years. The covers are different colors...which increases the ugly factor. I don't have the stereo adapter that goes with them. That would DOUBLE the ugly factor.

I suppose the PAM-1 pretty much defines ugly. At the other end of the spectrum I think I would place the Fisher 500C and most 1960s and 1970s Marantz. I remember seeing Marantz solids state receivers at the HiFi salons of the day with their blue lighting and "gyro-touch" tuning wheels... electro-sculpture.