Upupa Epops said:
Thanks for the advice Upupa. I unsoldered them and then twisted them together.
I just finished the second monoblock, and it has similar Vac and Vdc values at output as the first one; open: 2.0 mVac & 182 mVdc, shorted: 0.5 mVac & 1.0 mVdc.
Paul
Those are pretty good as they stand, but with careful adjustment and a quality multiturn DC trimmer then you might be able to get down to 0mV offset. However DC offset will wander a little as the amp warms up, so I tend to tweak when the amp has been running an hour or so.
You should always measure DC offset with the amp's input shorted, leaving it open causes all sorts of spurious nonsense. If you wanted to offset to correct a preamp stage, then you can, as long as it's small, any gross offset could well push the input stage out of it's tolerance. Oh, and remember to alter it back if you plug anything different in. 😉
You should always measure DC offset with the amp's input shorted, leaving it open causes all sorts of spurious nonsense. If you wanted to offset to correct a preamp stage, then you can, as long as it's small, any gross offset could well push the input stage out of it's tolerance. Oh, and remember to alter it back if you plug anything different in. 😉
Probably yes, Andrew... As I see, wiring is correct, so remember, that it is class A and voltage ripples at rails are high in this case ...
Hi all,
if Pink is right
As soon as you remove the shorting plug the offset rises from insignificant to near 200mV.
Plugging in a pre-amp with a DC blocking cap on the output will make little difference to the DC quiescent conditions.
Is this an inherent problem with a power amp that does not have it's own DC block on it's input?
Does it matter? 200mV sounds like a problem to me.
if Pink is right
Then how do we set up KSA?
As soon as you remove the shorting plug the offset rises from insignificant to near 200mV.
Plugging in a pre-amp with a DC blocking cap on the output will make little difference to the DC quiescent conditions.
Is this an inherent problem with a power amp that does not have it's own DC block on it's input?
Does it matter? 200mV sounds like a problem to me.
Hi Jacco,
re post 6169; I read the link from last year.
What are we to read into your comment?
re post 6169; I read the link from last year.
What are we to read into your comment?
shorted: 0.5 mVac & 1.0 mVdc.
Is outstanding.
Has he connected a SOURCE and measured? I don't know why anyone would have an amp on without a source feeding (open).. There would be no sound.
The only relevant mesurements are shorted and connected to a source.
Is outstanding.
Has he connected a SOURCE and measured? I don't know why anyone would have an amp on without a source feeding (open).. There would be no sound.
The only relevant mesurements are shorted and connected to a source.
Hi,
shorted input is relevant as a test only.
Open input is irrelevant, no sound comes out.
Connected to source is very relevant.
But the offset jumps to near 200mV.
How do we set up KSA?
Has anyone else taken similar measurements?
BTW <0.1mVac is outstanding.
shorted input is relevant as a test only.
Open input is irrelevant, no sound comes out.
Connected to source is very relevant.
But the offset jumps to near 200mV.
How do we set up KSA?
Has anyone else taken similar measurements?
BTW <0.1mVac is outstanding.
AndrewT said:
OK OK OK.
I just measured mine-
Input open- L = 15 mV offset/ R = -8 mV offset
Input shorted L = 20 mV offset/ R = 35 mV offset.
I just turned it on for the test so it was not yet fully heated. However, I have measured 20-30 mV with inputs shorted in normal use.
AndrewT said:
A DC-servo has many advantages if layed out properly, just reminding you that you considered using one long time ago. I've just returned from a fattening fish restaurant, need to lay out myself right now. Maybe i'll twist something later on, Pavel style.
Hi Lgreen,
completely different readings, Thanks.
Now can anyone else confirm whether Lgreen (post6175) or Joey (post6162) readings are typical of KSA?
We may need to debugg Joey (the amp not him).
completely different readings, Thanks.
Now can anyone else confirm whether Lgreen (post6175) or Joey (post6162) readings are typical of KSA?
We may need to debugg Joey (the amp not him).
Andrew, as you can see, it is possible to get offset below measurable levels, (see the big blue meter in the link), with careful setting of R105. Just take your time and do it right.
http://www.diyaudio.com/forums/attachment.php?s=&postid=631016&stamp=1114796998
edit: That was with a 1V p-p 10K square wave on the input.
http://www.diyaudio.com/forums/attachment.php?s=&postid=631016&stamp=1114796998
edit: That was with a 1V p-p 10K square wave on the input.
Compared to my A-X, these offset levels are excellent, i.e., they don't stink as much as Jacco and his fish... Hahahaha!
P.S. for that amp, I've decided that I'm willing to accept absolute offset of >4V in exchange for relative offset <.5V. Very tricky amp, but I digress.
P.S. for that amp, I've decided that I'm willing to accept absolute offset of >4V in exchange for relative offset <.5V. Very tricky amp, but I digress.