 
|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
|
|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
72.224.232.198
In Reply to: RE: Hey Mark posted by 1973shovel on July 01, 2023 at 15:10:49
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
Follow Ups:
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
| FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
||||||||||||||
This post is made possible by the generous support of people like you and our sponsors:
Top of Page ]
[ Contact Us ]
[ Support/Wish List ]
[ Copyright © 2024, Audio Asylum, all rights reserved ]
