Voltage regulators and input impedance

Definitely contact Audio Research… last time I had a question I called. They were very helpful. I don’t remember the tech guys name now.

I owned a REF 5SE… I changed one tube after 2,000 hours only because it was recommended. I upgraded to the REF 6SE before any other tubes needed changing.

Definitly something is wrong.

Well, it’s not that the bass will roll off, although I guess it would at a barely measurable rate since the midrange input Z is stated to be 23K ohms, as that once you get below a ratio of 1:10 for output Z vs input Z, you start to lose more signal voltage to ground, which could eventually, as the ratio gets progressively lower, result in noticeable loss of gain.

That is absolutely correct - when I distributed tube gear in the 80’s we provided a modification service to customers power amps to increase the input impedance to provide an optimum load to match the tube preamps - a significant benefit in terms of "apparent gain" and overall sound quality.

what gs5556 said.

1V/15k ohms = .00007 amps = .07mA = teensy weensy

I just want to correct what I wrote on 06-01.  I guesstimated the output impedance of the PH5SE at 200 ohms, based on the recommendation to mate it with an amplifier of not less than 20K ohms input Z.  In fact, if one applies the 1:10 rule of thumb, I should have guessed the output Z at 2000 ohms, not 200 ohms.  In fact, ARC say its output Z is 300 ohms unbalanced/600 ohms balanced. Mea culpa. But in view of the facts, I wonder why ARC recommend to drive an amp with not less than 20K ohms input Z.  In theory, the PH5SE could work just fine with an input Z much lower than 20K ohms. Could be that the output Z of the PH5SE rises at frequencies other than 1 kHz, where the measurement is usually done.  Also, input capacitance presents an impedance that is in parallel with the resistance.  This can cause a high frequency roll-off if the input/output impedance ratio is not a healthy greater than 1:10 ratio.  Anyway, the main point is that the matching of the two components is almost certainly not causing the 6550s in the ARC PS to blow or wear out prematurely.

Thanks for the sharing of considerable expertise here. I will contact ARC and see what they say.