In your experience is matching the output and input impedance critical? My amp's input impedance is only 22.1K and I'm considering building a tube pre with a fairly high output impedance. In your experience will a "mis-match" in theory result in anything audible, like weak bass?
You'll need around 0.47uF or larger for the preamp's output coupling capacitor, just to have a LF
bandwidth of 20Hz. A low amplifier Rin can also increase distortion in the preamp's output stage.
bandwidth of 20Hz. A low amplifier Rin can also increase distortion in the preamp's output stage.
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There is almost never a reason to match impedances in audio, but if the preamp isn't meant to drive a 22.1 kohm load, you could lose bass, get gross distortion or just get some reduction of the signal level. It depends on the output stage of the preamp.
Yeah, I have a PAS2 with direct plate from 12AX7 output (through capacitor) and it won't drive most SS amps.
Look at the schematic of a dynaco ST120 to see how they made it compatible with their PAS2 & 3 preamps. Took a BC108c transistor on the input. Fortunately most modern transistors like MPS8099 have huge gains already, and no popcorn noise from the hair & skin of the operators.
I modified an AX6 circuit for this high gain, see this page: Retro Amp 50W Single Supply - Page 22 - diyAudio
I've parked the PAS2 in the attic. It draws 100 W heating up the music room, and after a paper cap went bad, the replacment mylar caps sounded bad. My RA-88a op amp mixer sound much better & draws 6 watts: after replacing the hissy 4558 op amps with ST33078 then bypassing PS rails locally & cutting ultrasonic gain to eliminate the resulting 1 mhz oscillation.
Look at the schematic of a dynaco ST120 to see how they made it compatible with their PAS2 & 3 preamps. Took a BC108c transistor on the input. Fortunately most modern transistors like MPS8099 have huge gains already, and no popcorn noise from the hair & skin of the operators.
I modified an AX6 circuit for this high gain, see this page: Retro Amp 50W Single Supply - Page 22 - diyAudio
I've parked the PAS2 in the attic. It draws 100 W heating up the music room, and after a paper cap went bad, the replacment mylar caps sounded bad. My RA-88a op amp mixer sound much better & draws 6 watts: after replacing the hissy 4558 op amps with ST33078 then bypassing PS rails locally & cutting ultrasonic gain to eliminate the resulting 1 mhz oscillation.
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