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My Clarinet and Cornet2 are dead quiet with 102dB/1W/1M horn speakers. Audible hum is not normal, but if at normal listening volumes the hum is audible, then there is an issue. If the hum is only audible at abnormally high volumes and/or "ears to the speakers", then it may be just fine.Cheers,Geary
The balance control is an attenuator. Middle position has both channels attenuated 3dB. All the way to one side is 0dB and 6dB (or something like that, I forget the exact numbers I used). So it does sound like one channel does get louder. jh
HM... I'd not trust such techs. (IMHO) What did the tech check/measured/do? You mentioned a receiver the tech hooked your preamp to... Most receivers have line inputs (which have processor/volume control) and power amplifiers' inputs (which do not have any controls - just like in your power amp). Why the tech connected 2 line stages serially?Such simple line stage should not show any audible noise from the normal listening distance. I absolutely sure about that.
Did the tech use the same pair interconnect cables as you normally do?
Have you tried it at home using cheap or Radio Shack interconnects.Some of my friends speedskate at the Edge ice rink on S. Ward Street.
We swapped the output to ground resistors from 330k to 100k, this kept it from drifting as much. Initially it had up to ~20mV of drift on the output, the 100k resistors dropped this to just a few mV.
Actually, I wonder where was the drift sourced? It means there was some very low frequency oscillation. Normally there should be no such problem. Certainly I can not be sure and completely right, but it seems the main problem was the power filter capacitors in the B+ circuit (dried? had high leakage?...). Second thought - changing the resistors just solved the problem of their connectivity. In earlier measurements there was a strange dependence of the output RCA resistance on the connection of the next device. Third thought - there might be very high input impedance of the next devices and nobody has tried such high resistors on the output for comparable in impedance next device input...In any case - great job, mgalusha! And great attention to the person problem!
The 100k resistors are not in series, they shunt the output after the output cap to ground, so the ZOut should not change much since they are in parallel with the output of the tube. I didn't measure the ZOut before or after the change but I doubt it's very different.
Actually, I wonder where was the drift sourced?
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