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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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In Reply to: RE: Hey Mark posted by mark.korda@myfairpoint.net on July 2, 2023 at 21:20:26:
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
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Follow Ups
- "510K resistor as in the diagram near the preamps output jacks" - 1973shovel 08:05:07 07/05/23 (1)
- RE: "510K resistor as in the diagram near the preamps output jacks" - mark.korda@myfairpoint.net 09:32:10 07/10/23 (0)
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