Impedance mismatch question

Hi 2out2sea there is no hard rule here.
We've done experiments with very good equipment with 30 odd audiophiles where we could vary on the fly the impedance ratio from 1:100 down to 1:1 (your case is 1:23)

We started at 1:100 with these listening test, and the group could not detect any change till we got down to 1:5 only then only two of the 30 audiophiles thought they detected a very slight compression to the dynamics but weren't sure, and when we got to 1:1 only 50% of the group detected a slight compression.

This was done using quality interconnects of 1.5mts each long that were 100pf per foot of capacitance both sides of the Lightspeed Attenuator passive pre.

So your 1:23 should be fine so long as your interconnects are good quality low capacitance, which most quality ones are anyway.

Cheers George

Re George's comment, it should be noted that his Lightspeed is a passive resistance-based device. As such it will have minimal if any variation of its output impedance as a function of frequency, especially if it is driven by a source having low or non-varying output impedance.

I would not expect the results of his comparisons to be applicable to most tube preamps.

Regards,
-- Al

Al sorry I should have mentioned at the end of the day a Cymer tube pre with 2k capacitor coupled output impedance was subsituted for the Lightspeed and similar ratio results were observed. Of course as you say being tube tube and capacitor coupled it's output impedance will change a bit according to frequency. All impedance ratio changes were done on the fly on the input of a Cymer tube poweramp using a 32 position switch resistor loading to ground.

Cheers George

2out2sea ... is your OP an academic question or an actual concern based on equipment you own or are thinking of buying? If this is an actual concern, based on Al's post, you may be close. Perhaps a call to the preamp manufacturer is in order.

Btw, I've been there and done this already. I bought a custom designed active impedance buffer for a very similar issue, but in my case only involving the sub-woofer. Check my threads. I doubt my solution would be a good fix if you needed an active impedance buffer like mine to drive your amp. I suspect even if it solved an impedance match issue with the pre, overall sonics might be degraded because you would be inserting an active artifact between the pre and the amp.

Thanks, Georgelofi. As I said earlier, not meeting the 10x guideline (properly defined as described in my post) does not necessarily mean that there will be a problem. But meeting that guideline assures that there won't be a problem.

And as I'm sure you realize, the specific value of the coupling capacitor (which affects the amount of variation of output impedance as a function of frequency), and the deep bass extension of the speakers, and the deep bass content of the source material, are all relevant variables. So I would suggest caution to anyone who might be tempted to apply the results of your experiments in a universal manner.

For preamps that have been reviewed by Stereophile, the measurements and associated comments that John Atkinson usually provides in conjunction with the reviews are a valuable resource in assessing this issue.

Regards,
-- Al