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In Reply to: RE: Volume control Dyna PAS posted by mark.korda@myfairpoint.net on June 24, 2023 at 11:54:40
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Have Fun and Enjoy the Music
"Still Working the Problem"
Follow Ups:
Hi Tre', thanks for the help but I didn't understand what that black line was on the schematic.It looked like the same as in my manual.A couple of days ago Van AlStine called me up out of the blue and needed some more info and left me his idea's in an email which I would like to forward to you. He still has me a little confused.
What will solve my problem is the Audio Amateur 1982 #5 issue.It will show just 1 pot for volume like the mod shows and how it is wired.
Tre, I know how to wire the volume with a balance but only having 3 wires, right,left and ground ,I'm baffled.I'll keep trying to send Frank V's answer and see if you can decipher it. Thanks you other guys for the help,present and past and future.......Mark Korda
Your 'sort of' double posting this question on two different Asylums makes it a bit difficult for everyone who's trying to follow, but can't access the same information for what you're trying to accomplish.
As I posted to you in Vintage, here's the Last PAS volume control wiring diagram. There's more information I've posted over there, which shows which wires in the PAS go to which eyelets on your Alps pot board.
For those following, S1 is the source switch (in this case a simple DPDT toggle), and S2 is a stereo/mono switch, the diagram taken from the Last PAS article in Audio Amateur.
Mark, note above that the wires on #3 and #6 (the ground lugs) of the volume control are tied together, just as Tre' said. In the case of the Last PAS, that wire is taken to a star (single point on the chassis) ground.
I hope this helps.
Hi Shovel, I left you a message on another site, vintage. That was beyond help! I had a hard time grasping some other recommendations. The last piece to my puzzle before I solder is a 20K resistor in series with a 510K resistor as in the diagram near the preamps output jacks.I know the 510k's are there as they are still on the un-connected wires.I can't remember if I threw away the 20k resistors when I gutted the jacks before installing the new ones.I don't know if you remember or not if the mod kept that resistor, which I already ordered anyway.I want to send you something for helping me. It will probably have more meaning than value but you the man!, thanks for the help.Here's my email, I need your address (kordamark@gmail.com)...thanks again Shovel...Mark Korda
Hi Mark,
By "diagram", do you mean the schematic? If so, the only resistor I could find close to 510K is the 475K, R26 as shown above. If so, as Tre' said, the 20K won't make any significant difference in that feedback level.
In later correspondence with Dave Vorhis, the author of The Last PAS, here's what he told me about that resistor:
"As far as the resistor values [of R26, 475K] go, the exact numbers are totally non-critical. The two channels should be the same value but other than that you can change them up or down by 20% or so with no effect. [570K/380K]
This circuit is sometimes called an Anode Follower. It basically has heavy feedback which reduces the gain and the output impedance. It's not used as often as other designs but nothing unique about it, and certainly nothing critical.
Like most things, I wasn't the originator of it. My inspiration was the ARC schematic for their old tube crossover. In the ARC design, the feedback was so much that the 12AX7 had unity gain, at least that's how I recall it. I basically just altered the feedback resistor values to give it a bit of gain. The feedback circuit actually includes the volume control so as the control is rotated the overall feedback changes. I remember saying in the article that this was not particularly elegant but it seemed to work ok, so there you go."
Dave Vorhis
Hi Shovel, your the best! I do have a final couple questions before I get sawing and soldering. I got a CK switch,S series, that is going in like the diagram you sent.The picture shows it lying on the chassis near the rotary switch which I will take out. I have to saw the hole a little bigger for the CK switch. I think I need to see what is in the phono board as the PAS manual has 2 750 caps and 2 27K resistors in the pictorial in the manual. That's why in the picture I was going to install 2 5 point lug strips in case they are important in the new Last PAS. I don't know if they w ere in the circuit.I would of saved them but am a little foggy about where I stowed the old rotary systemOne more question Shovel, When your facing the preamp, Is the top green wire the input to the board and same with the top red wire? I owe you big time and I will make sure I get you back....thanks so much for your time and effort, sincerely Mark K.
20k ohms in series with 510k ohms is not going to make any difference.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Hi, Thanks Tre', that was important as now the questions have been answered that kept my project stalled are answered.I got all the pieces in place to get it going thanks to all of you.Thanks Tre'....Mark Korda
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Have Fun and Enjoy the Music
"Still Working the Problem"
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