Passive & Tubed pre-amps to power amp at same time?

Al - thanks for the reply. I meant to specify the meter used in my earlier note but it slipped my mind. It is a Craftsman Model 82015. I'm thinking the 20K setting I used is good for measuring resistances in the range of 20-200K ohms. The next lower setting is for 2000 ohms. The next higher for 200K. Not sure why things are "denominated" in 2s vs 1s. Sorry if I introduced some confusion - there is no 'x' symbol associated with the scale labels for the meter dial. What multiplier to use was my question only. Let me know if you find something helpful - or other thoughts. Thanks as always. (I well might repeat the measurements taking care not to hold the leads while doing so...I hadn't taken this precaution earlier - but am hopeful they won't change things significantly if current values are sort of "as expected).

It looks like it is what is known as a 3-1/2 (three and a half) digit multimeter, which means that it can display 4 digits but the one on the left (the most significant digit) can be only a 0 or a 1, rather than any value from 0 to 9. So the maximum numeric reading it can display is 1999. That being one very tiny increment less than 2000, which explains why the scale choices all begin with 2. And the maximum possible indication with the 20K setting would be 19.99, corresponding to a resistance of approximately 19.99K (or approximately 19990 ohms). And, similarly, with the 200K setting the maximum possible indication would be 199.9, corresponding to a resistance of approximately 199.9K (or approximately 199990 ohms).

So as you can probably see the scale numbers are not multipliers. They are the maximum amount of resistance that can be measured on the particular scale, with the decimal point having to be adjusted by the user to get the approximate number of ohms. And as you can probably see the best resolution (and presumably the best accuracy) can be obtained by using the lowest scale number that is higher than the resistance being measured.

So it seems likely that the 6.77/6.75 and 2.19/2.18 and 8.97/8.95 numbers represent approximately 6.77K/6.75K ohms, 2.19K/2.18K ohms, and 8.97K/8.95K ohms respectively ("K" denoting thousands). Those numbers are all much less than the resistor values used in the Rothwells. That would work in the direction of making them an even better impedance match than the Rothwells with respect to the tube preamp, but a less good impedance match with the CDP. Although in this case that less good match would most likely still be good enough, given that the unspecified output impedance of this particular solid state CDP is most likely low. I would not drive those attenuators with many and probably most tube-based signal sources, though, as well as some lesser solid state components, because their higher and often frequency dependent output impedance would not do well when working into 8.97K/8.95K (and actually a bit less than that, due to the additional loading presented by the preamp or other destination component).

To be sure that the measurements are meaningful, though, and weren't taken on a scale that was lower than what was being measured, I'd suggest repeating the measurements on the 200K scale and verifying that the results are consistent. (Although I suspect that if the measurements were taken on a scale that was lower than what was being measured the meter would probably have given some sort of error or overload indication). On the 200K scale you'll probably see a reading of around 6.8 when measuring between the input and output center pins, corresponding to the 6.77/6.75 numbers on the 20K scale. And likewise for the other measurements.

Best regards,
-- Al

Al - thanks for the follow up. I did some on-line reading after posting and found similar info as in your explanations for interpreting the measured impedance values and scale upper limits being multiples of 2. I can indeed take some further readings using the 200K scale setting. As noted previously, putting the Harrison Lab attenuators on the TEAC CDP outputs did give more usable volume control "range" on my pre-amp. None of my sources are tubed so if those low resistance numbers aren't likely to harm the TEAC, I'll continue to use them.

None of my sources are tubed so if those low resistance numbers aren't likely to harm the TEAC, I'll continue to use them.

To clarify, no harm (in the sense of damage) would be done even with the kinds of components I mentioned as being unsuitable for use with these attenuators. The issue with components having high output impedances, and/or output impedances which vary greatly as a function of frequency, would be adverse sonic effects, such as deep bass rolloff.

Best regards,
-- Al

A follow up on use of the -12 dB attenuators. The Harrison Labs attenuators have indeed been beneficial in the system. They provided extra control range on the pre-amp volume control when the CDP was in use as noted earlier. I did NOT think I heard a sonic benefit in this application however, just easier fine control of volume...but no negative effects, either. Recently, I had been bothered by what seemed like upper frequency distortion when playing at higher volumes (mid to upper 80 dB at the listening position) CDs ripped to hard drive. ICs from CDP to pre are Cardas Parsecs. ICs from the Gungnir DAC to pre are Morrow Audio MA-4s. Today after switching the attenuators to the DAC ICs at the pre-amp, I enjoyed a very satisfying listening session with no trace of harshness or distortion at sound levels similar to what had been annoying 2 days ago. I'm wondering if the attenuators are doing a little "tone control" - rolling off the top end just a very little bit (by increasing the impedance of the MA-4s?). Not 100% certain the cause but did order another pair of the attenuators from Parts Express so I won't have to swap them out between CDP & DAC. We'll see if listening continues to be as pleasant and free of harshness going forward. (BTW - Al, I did come across similar values as what I measured being reported on Amazon for the Harrison Labs attenuators).