so it appears that R95 is input bias compensation and R136 is amp offset. Adjusting in the order Hypex recommended would be the normal order but may not make much of a difference in the real world. Best would be to check both again after adjusting.
to clarify, that is between the non-inverting input (pin 2 on the xlr or J9 pin 1 on the actual NC400) and ground (pin 1 xlr or J9 pin 4 on the NC400)
I have not had a chance to try adjusting them to see the real world effects.
Bruno has discussed the design of the input buffers in this forum before and makes interesting reading.
Cheers
Alan Garren
I do remember something, but I shudder at the thought of going through 340+ pages of messages again... You don't happen to have a link or message number?
Reading all these latest posts it would seem Erland's problems are probably down to him not using the SMPS600. However the problems Robbbbbbbbbbbbbbby's having concern me a little. I am awaiting my cases but when they arrive I am hoping I should be able to just wire them up with care (balanced only), especially in relation to earthing properly and they will work. Will I need to do any testing? I wasn't expecting to have to.
Well, they will probably work. There might be a bit of DC offset - and if it worries you, you might want to measure the DC on the output with a multimeter. Not a very complicated procedure.
By popular demand...
Here are some pictures of the current assembly status of the NCore's..
Here are some pictures of the current assembly status of the NCore's..
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Is it just a case of measuring the dc voltage accross the red and black speaker terminals with the amp switched on but no source connected?
Without measuring, you don't know... So just speaking for me, I definatly will measure it when I have them up and running!
You don't need an oscilloscope to measure DC...
mine arrived with something like 20mv on one and 50mv on the other, quite fine.
I gave them a complete checkout before hooking them up to a speaker, including an overnight burn-in with load at a couple hundred watts, only mildly warm when I came back the next day.
You can wait if you want, but I see no reason (obviously I didn't)
........................
you don't want DC because its wasted energy in your system, if its too much it can heat up your voice coil(s) and cause damage. It can also cause "premature" clipping as you are offsetting the signal from the centerline (DC) so its not as "far" to one of the rails. (again if excessive)
However if you're clipping this amp please wear earplugs!
.............
sort by Bruno first then input buffer or some such thing, should come up right away.
I used to say google is your friend, now I'm not so sure.
Alan
I gave them a complete checkout before hooking them up to a speaker, including an overnight burn-in with load at a couple hundred watts, only mildly warm when I came back the next day.
You can wait if you want, but I see no reason (obviously I didn't)
........................
you don't want DC because its wasted energy in your system, if its too much it can heat up your voice coil(s) and cause damage. It can also cause "premature" clipping as you are offsetting the signal from the centerline (DC) so its not as "far" to one of the rails. (again if excessive)
However if you're clipping this amp please wear earplugs!
.............
sort by Bruno first then input buffer or some such thing, should come up right away.
I used to say google is your friend, now I'm not so sure.
Alan
28th July 2011, 01:11 PM #257
31st July 2011, 03:30 AM #258
1st August 2011, 12:00 AM #261
2nd August 2011, 07:59 AM #267
3rd August 2011, 08:46 AM #271
27th September 2011, 12:41 AM #410
8th February 2012, 07:07 AM #1941
Thanks, I will try it again but this time with the input and speakers disconnected. I just don't understand why this isn't adjusted before they're shipped, adjusting these pots would probably be best served to do with a o-scope for the best accuracy.
Alright, just tried everything out
Unplugged both speakers as well as the input and was able to adjust both the input and output dc voltages to 0 with the two potentiometers.
Plugged everything back in and turned the amp on "POP".
Measure again with everything connected 0.5VDC.
Unplugged input and left speakers connected 0VDC
Plugged in input and unplugged speakers 0.5VDC
So even though I adjusted everything to 0, as soon as I plug my input in output DC jumps to 0.5?
I used this source (dac) with the temporary amp I was using while waiting for my ncores and it had 0VDC on the outputs, now when plugged into these amps 0.5?
I'm so confused!
Edit
Well after adjusting both monoblocks down to 0 with speaker/input disconnected I now have one with ~490mVDC and the other ~390mVDC with input plugged back in.
Unplugged both speakers as well as the input and was able to adjust both the input and output dc voltages to 0 with the two potentiometers.
Plugged everything back in and turned the amp on "POP".
Measure again with everything connected 0.5VDC.
Unplugged input and left speakers connected 0VDC
Plugged in input and unplugged speakers 0.5VDC
So even though I adjusted everything to 0, as soon as I plug my input in output DC jumps to 0.5?
I used this source (dac) with the temporary amp I was using while waiting for my ncores and it had 0VDC on the outputs, now when plugged into these amps 0.5?
I'm so confused!
Edit
Well after adjusting both monoblocks down to 0 with speaker/input disconnected I now have one with ~490mVDC and the other ~390mVDC with input plugged back in.
Last edited:
So, with the pre disconnected you were able to see the voltages swing thru zero and to adjust them.
then you plugged you pre in and it went to hell again.
you must have a source of offset from the pre.
try another pre and see what happens
or put a cap in series with the output from the pre and see, just temp, don't worry about audio quality
if the cap solves it, its from the pre, if switching the pre does not change/solve it, then.....?
Alan
Ya with input/speakers disconnected I could bring the DC on the input and output down to zero. Soon as the input is plugged back in jumps to the 0.5.
I don't have another pre to test, my old cambridge audio poweredpre took a dive, all I have now are audio/video receivers and pro amps and none of the have balanced outs.
And in regards to putting a cap in series with the dacs output, not sure how comfortable I am doing that. I have a couple caps kicking around but I have no idea if the values are right, how to properly connect them between the source and amp and lets not forget polarity, I see lots of blown up caps in my future
I'm curious what the third pot does? Would I need to adjust any voltage between ground and the clear wire (pin 3) on the input?
I don't have another pre to test, my old cambridge audio poweredpre took a dive, all I have now are audio/video receivers and pro amps and none of the have balanced outs.
And in regards to putting a cap in series with the dacs output, not sure how comfortable I am doing that. I have a couple caps kicking around but I have no idea if the values are right, how to properly connect them between the source and amp and lets not forget polarity, I see lots of blown up caps in my future
I'm curious what the third pot does? Would I need to adjust any voltage between ground and the clear wire (pin 3) on the input?
Just checked again with the amps on and the input cable plugged in but the dac/pre off and the voltage is really low ~0.008. But when I turn the dac/pre on goes up. what the heck is causing this and can it be fixed? Like i mentioned I never had this problem with my other amp and this same dac, though I was using rca cables instead of the balanced outputs.
Well, fortunately it is pretty clear what is causing it, and it is easy to fix.
Your DAC/pre very clearly has a DC offset on it's output. You won't be able to measure it with a multimeter, because your multimeter has a much lower input impedance than the nc400 - so low it effectively shorts away the DC.
The solution is a capacitor (well, one per input, so 2 + 2 in total for your two amps). Use any decent caps of 0.47 uF (and voltage doesn't matter, anything above 10V is fine), so you don't have to worry about LF cutoff. They go between the XLR pins 2 and 3 and the corresponding nc400 input pins.
Actually, now that I've had my morning coffee... As the input impedance of the nc400 is as high as it is, you can get away with a much smaller capacitor if you want.
And an input capacitor is a normal thing to have. The nc400 is DC coupled - effectively making it a great DC servo. You have to have a cap that isolates the DC *either* at your DAC/pre output, or at the nc400 input. It seems your DAC/pre doesn't have one. Your other power amp (that worked OK with the DAC/pre) probably has one. It is also possible that your other amp has a lower input impedance that, just like the multimeter, puts enough load on the DAC/pre to "kill" the DC.
And I would assume that is standard practice for any DIY project - at least have a quick check (with a multimeter) that all voltages are OK.
Absolutely. I would like to emphasize the "excessive" here. The 500 mV or so some people have been seeing would still only result in 0.06W into 4 ohms, and about 1% less "headroom" because of the offset from the centerline, so not something I would stay awake at night for.
The most annoying effect of the DC is probably the pop from the speaker when turning the amp on or off. So you don't actually even need a multimeter to check for the problem. No pop - no problem!
- Status
- Not open for further replies.