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108.20.111.121
Just picked up a nice PAS2 dynaco preamp.
Then I founsd out it is looking for an amp with >250,000 imput impedance.
Other than Dynaco, is there such a creature?
Follow Ups:
Most tube amps from the 60's had high input impedances. The MC225 was 200,000 ohms and the PAS3x worked well with it.
A few SS power amps are up around 100k, also. Adcom GFA 535II for one. Dynaco ST120 for another. And the Phase Linear 700 into the Normal inputs. Lots more, I'm sure.
Jerry
Thinking path of least resistance (no pun) might be rebuilt dyna or Bob Latino's take on them. Any reviews by non buyers of the latter?
What do you think?
The PAS series were designed for use with the Dyna power amps; which have a 470,000 ohm input impedance. For use with lower impedance power amps, say under 100k ohms, the PAS series badly needs an output buffer stage. Like a good cathode follower.
Jerry
....using the broad rule of thumb that the input impedance should be a minimum of 20X the output impedance, you get a figure of 20K ohms minimum. 50K ohms would be better still.
Since if the caps are original they would need to be changed, you can easily go up to .47 for the output coupling caps. I have even gotten away with 1.0 with no motorboating. This will improve the drive at the low end.
If the (PAS) unit is rated for 10K, 50K should be fine. Even 20K will work and we might like the sonics. However, the 10K rating was proven wrong, way back when, when reviewers tried the PAS with various vintage ss power amps.
I remember a shootout in my home, in the seventies, when my brother had all ss Dyna while I had the PAS 3X, St.70 and the Soundcraftsmen 2217 preamp/EQ along with an SAE XXXIB. The ss units I had were quickly sold, as was the St. 70 after I recapped a pair of British RCA UL monoblocks.
The PAS is versatile and may work well with many ss amps...
According the the PAS 2 manual, 250k is the input impedance for the high level input (non phono stage) and > 100k is the recommended input impedance for the amplifier. So any amplifier with an input impedance greater than 100k will be fine.
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