Ishcabible
Headphoneus Supremus
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- Jan 19, 2009
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High DC-offset at amp startup - have you ever measured that?
Sorry, I just got time to remeasure it! It's 1.5mV, and it's never done anything at start up, but randomly.
High DC-offset at amp startup - have you ever measured that?
I was wondering can i change the transistor in the servo booster from C2705/A1145 to BC546/556? I use spice to simulate and it's working fine but in real world performance do you guy think it will affect the sound quality?
I used them in my original EHHA -1 and it worked fine. Its been a while so I can't remember the details but at that time I felt that the one with Toshiba devices sounded slightly cleaner(not much of a difference though).
P.S. - Don't forget to twist the legs of BC devices to match the pin orientation.
Thanks for you helpful comment, so you did change not only the servo booster but all the transistor to BC546/556?
Do you mean a 50 or 60hz hum? 5Khz would be a pretty high whine. Several posts mention to use a Ground Loop breaker to get rid of Gnd loop hum.
Also, have you compensated for the higher heater current required for the 6H30? I know from EHHA I you needed to do this. Also, there was a trimpot required to use alternate tubes. I would use the 6GM8 first to test if it's a tube problem.
The tube requires more current to work properly. In the EHHA directions (not Rev A) on the Cavalli Audio site, it states that you need to compensate by providing more current on the heater supply. Also, there is mention of a trimpot that is used to balance the triodes. This is because you're running the tubes at a lower voltage than what they normally require and at a lower voltage the triode balance is off. I'd buy some 6GM8s or the Russian 6N27Ps, which are the 6GM8 equivalent. Plus, I'm not sure if there is a part equivalent to R6 on the Rev A, so how would you balance out the triodes.
This is what the Cavalli sites says:
6922, 6H30 and other compatible tubes
Tubes designed for higher operating voltages than the 6GM8 will tend to have more triode imbalance at low voltages. To compensate for this possibility install the trimpot R6. See the Instructions page for steps in making out of balance tubes work.
Beware that the heater current for a single 6H30 is approximately 800mA. Increase the size of the heater transformer according.
I wonder what will happen if the triode a not balance, can it make that noise? I don't have 6GM8 or 6n27p so i can only use 6h6n now.