[Ishcabible]

  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.

 

[Mullet]

So I'm in the process of finally building up my EHHA Rev A. It's been a long time coming. A few questions...
 
I plan on adding sockets for the gain resistors. Is it safe to say that R10 doesn't need to be socketed. I'm thinking that R11, R13, and R14 are what would be changed anyway.
 
For power management, I'm thinking two 4 position wire-to-wire terminals would be appropriate. One for IEC socket to both trafos. The other for 30-0-30 power management. I'm thinking it might not be necessary for the heater trafo though. Then I'd get another 4 pos. barrier terminal for SG management.
 
The only other thing that I can think of right now is how to wire up the 2 E12s. I know about the ±30v. I'm assuming the Left channel goes to L+ on one E12 and the Right channel goes to R+ on the other E12. But what about SG connections? I'm not quite there yet in terms of having the build ready, but want to have it figured out fairly soon.

 

[proid]

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?

 

[gurubhai]

  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.

 

[proid]

  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?

 

[Mullet]

So no one has answers to my questions...
 
I'm going to guess that I don't have to socket R10. Looks like it will always be stationary. So scratch that one off. Power management wise... I'm sure I'll just wing it and see if what I bought was the right parts for the job.
The E12s are where I'm still not sure of proper wiring. I'll have to reach out to Amb's forum and inquire there.

 

[gurubhai]

  Thanks for you helpful comment, so you did change not only the servo booster but all the transistor to BC546/556?

Ahh, didn't notice that you were enquiring only about the servo, I doubt that changing that would have any effect on sound.I had used only the BC devices in that particular amp, since I didn't have the Toshiba transistors at hand at that point of time.

 

[proid]

I have finished my EHHA RevA, both channel sound fine but it has very annoying noise like a sine wave at 5khz, it increase a bit if i turn the volume up. Everything measure fine, my build using bc546/556 for the servo booster and the current source for tube like the EHHA 1 (because i don't have the CRD), 1145/2705 for the rest and i use a shunt regulator to power it. I use both the original wiring and alternative wiring but nothing change. The tube i'm currently using is 6h6n which is an equivalent to 6h30.

 

[Mullet]

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.

 

[proid]

  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.

No, it's not 60 or 120hz hump, it's like some one playing sine wave at some where between 4k-6khz. What do i need to compensate for higher heater current tube? My tube sound fine in another amp so the problem must come from the EHHA.  I currently haven't cased it up so i can't do the ground loop breaker.

 

[Mullet]

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.

 

[proid]

  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 use a 9V 2A transformer and the regulator is heatsinked well so that's not the problem. 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.

 

[stixx]

 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.

I guess 6H6N is the same as 6N6P... anyway this tube is usually biased at higher supply voltage (from 80V up). The important bit is: where is the 6N6P biased with the given parts in the EHHA RevA?
Theoretically this could put the tube at a bias point it doesn't like, though I don't think it would produce a high pitched noise like you are describing... rather just higher distortion.
Still worth checking.and I'll also advise to get some tubes the circuit was designed for (6N27P are still reasonably priced last time I checked... I am using them in my build).

 

[cfcubed]

It's silly but did you try moving the amp to a different location? Just to rule out interference from a nearby device.

 

[Sathimas]

Very basic electronics question:
 
I got 2 new transformers (custom wound, two identical ones now with 9V and 30V each)
 
Due to my unpreciseness in the order, I got them 2x12V instead of 12-0-12 center tapped.
 
Now I tried to figure out how to connect them to the PS but got more confused the more I read ^^