When you lift the right leg of the 0R47 you avoid the relays....and could measure if there is enough juice,
but the 10nF and 47R are no more connected ......
but the 10nF and 47R are no more connected ......
That's a relief!
Any other way to measure that, without a sound card and REW?
My relay is not working, so I bypass it as follows: (the blue wire connects directly to the headphone jack)
The 2nd blue wire connect to the caps in front of the pre-amp out...
ANY help from anyone is welcome 🙏
VERY likely it is unique to me. I used 24V relays by mistake, and I believe it is the root cause for all the issues I am having 😢
I see, the BOM doesn't state which relays and the rail is 24V. What should be used instead, 25V ?
I see in Jeff's (and others) builds - the relay is 12V part. Not 24V.
Thanks @JeffYoung and @generg for all your suggestions and help!!! 🙏
I will try that and report back... hopefully tonight (depends on work schedule).
Apologies, but another quick question before moving forward with this suggestion:
One potential problem with this approach is if we disconnect R23 lead - we lose GND path via C6/R28.
Wouldn't that be problematic, at least in theory? What's the function of C6/R28 anyhow? Act as a load in absence of headphones?
If so, and without the dummy load - what is the risk to the amp (if any) when operating without a headphone or dummy load?
Thanks.
@JeffYoung
best wishes for your operation.
I had mine done -- new main aortic valve and four bypasses -- nearly three years ago.
I believe I had the surgery in Egypt because people kept telling me I was in de Nile.
seriously turning from the elephant in the room and not worrying helped. of course that might also have contributed to my condition too (though the valve was a birthright)
never got the cookies ... [sigh]
best wishes for your operation.
I had mine done -- new main aortic valve and four bypasses -- nearly three years ago.
I believe I had the surgery in Egypt because people kept telling me I was in de Nile.
seriously turning from the elephant in the room and not worrying helped. of course that might also have contributed to my condition too (though the valve was a birthright)
never got the cookies ... [sigh]
C6/R28 are a Zobel network to make the resistance of the headphones appear constant. (In reality the headphones resistance will be somewhat dependent on the frequency; the spec given is just the average.)
I suspect the absence might make the amp less stable (ie: more prone to oscillation), but it should be fine for a quick test.
Someone here might be able to provide a better answer; this level of theory isn't my strong suit....
I suspect the absence might make the amp less stable (ie: more prone to oscillation), but it should be fine for a quick test.
Someone here might be able to provide a better answer; this level of theory isn't my strong suit....
Progress report:
- I managed to remove the relays for headphones and preamp outputs, and added a rework as shown in the photo below.
- As a result - the rework of connecting R23 to headphone jack, is not needed and was removed. No lifting R23 lead, so no compromise to the Zobel network! 🙂
Good news / bad news:
Good - now, the amp is definitely getting loud. Yay!
Bad - it sounds weird and totally off... Playing Sultan of Swing - not only guitars and drums sound weird, but vocals sound like they're VERY far and VERY quiet. Something is definitely wrong. 🙁
A friend suggested a theory:
If phase is inverted between channels you can get null in centre image which will effect vocals.
Do others agree with this theory, or do you have other theories / ideas on what to do next?
If we move forward with my friend's phase inverted between channels theory - how do I prove or refute this theory? (and what mistake in my build could cause it?)
Thanks in advance for any help 🙏
Negating waves is absolutely a real thing but it would be beyond a longshot to say that could happen with a headphone amp because the waves are never intersecting unless you have holes for ears and an empty chamber for a skull that would allow the sound waves from each side to actually meet somewhere ... anyway, you get the point.
Way to test if this is the problem, you simply listen to one side at a time and if it's playing low with only 1 side at a time, it's not a problem of wave cancellation. For subs in a room, nulls are definitely something to look out for but not for a headamp.
Way to test if this is the problem, you simply listen to one side at a time and if it's playing low with only 1 side at a time, it's not a problem of wave cancellation. For subs in a room, nulls are definitely something to look out for but not for a headamp.