What does your bias measure on each side?
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What does your bias measure on each side?
I also had a channel on a Rev.A that had high offset. It turned out to be a bad solder joint on a resistor, which I believe was R12, so you might recheck
all of your joints. The bad one on mine looked perfectly fine until I pushed down on the top of the resistor, when I discovered that the solder didn't adhere
to the board foil. Sneaky little bugger.
The problem is coming from the tube itself - swapping the tubes
brings the high offset to the other board and vice versa.
Bias is ~200mV each side after warming up.
Alex says that this is within the normal behavior.
The servo has to be that slow.
Well, seems that I will have to get an e12 and stuff it into the
already packed case :-( (There's room left, but wiring is tricky)
What brings me to another question - why do you use two e12s for the Ehha?
The relay can delay up to four channels - so one board should be sufficient?
Nonetheless - I'm happy that the amp lives now :-D
I'm back with another problem.
I have now wired the inputs, the pot and the headphone jack.
It plays music without any flaw - but I have a very loud hum one the left
and a more quiet one on the right channel.
I used wiring method one and all the signal carrying wires all fully shielded.
I'll post a picture of the inside of the amp tomorrow.
the hum problem you are describing most possibly is a grounding issue... like a ground loop because you have two ground points (probably not) or something else.
In one of my builds I had hum because I attached the shield of the input wiring on both sides... duh. Took me forever to find it (glad it's years ago ).
Anyway good to hear that your EHHA is playing music now!
Concerning the offset - of course I could always disconnect phones.
I'll do that anyway.
But I also use the EHHA as PreAmp for my active speakers
AND I am not the only one using it, my wife has a bad influance
on technical gear ;-)
So it's just to be sure - and to have the delay.
I also understand why I should use to of them after some reading,
but as you see, the case is more than packed and two would not
really fit. (The small sheet of paper is about the size of an e12)
Concerning the hum:
First, a picture:
I have one star ground, all ground connections got to that point
and from there another wire goes to the ground connector on the AC input.
(Yellow lines ;-) )
If I disconnect the wire from SG to the AC-inlet, the hum is still there.
Input ground is isolated from the chassis (using neutrik jacks) and just
conncted to the pot (and SG on the boards from there.)
The output wiring is just temporary.
Any idea where to start from?
I have 4 possible suggestions. One of your RCA's is very close to one of your transformers. You mention that one channel has a louder hum than the other. Is that the channel? Your on/off switch wiring runs very close to one of the amp boards. Again, is that the channel with the loudest hum? On mine, I used an IEC connector with a switch built in to avoid running AC wiring in what is a rather confined enclosure. I can't really tell from your photo, but you also might try running a ground wire from one of the screws on your volume pot to ground. Seems that a number of people had issues with the pot causing hum. Lastly, I ran all my circuit board grounds through a ground loop breaker and then to chassis ground. Mains ground is attached directly to the chassis.
My build had a very faint hum on both channels with one being slightly louder than the other. Turned out to be a ground loop problem.
Hope this helps and good luck!
Hate to tell you this but I'd bet good money its the proximity of those transformers to the amp. Especially with the low-level signal/tube socket extension wires (acting like antennas).
Lots of examples of hum problems happening w/various DIY headamps when transformers are very close to amp channels. Google & you will find them.
E.g. If the LEFT channel board is the LEFT one in the picture, see how those 2 transformers are "ganging" up on it? Perhaps their overlapping electromagnetic fields are bathing the left channel & feeding your tube-extensions/antennas. In less extreme cases, rotating the transformers to try to lessen hum is something to try.
Switching to expensive, possibly larger shielded & encapsulated transformers could help some, as could mu metal shields perhaps BUT nothing works like physical distance. It's why I transitioned to 2-box builds soon after (re-)starting audio DIY years ago.
OK, I'll bud out. What you say about commercial gear is spot on. My post was more anecdotal based on my own experiences (CK²III, β22s & my EHHA) & those of others that have posted fairly frequently, e.g.:
And I don't see how your suggestions + review of his build picture otherwise explain the large difference in hum heard between his left & right channels.
Also, I've found it fun to listen to hum level differences in my DIY amps on the bench as I move/rotate their (unshielded, non-encapsulated) toroidal transformers about them. Esp. noticeable w/high-sensitivity cans.
But carry on, I really need to stop posting here:)