just finished the amp. Have some nasty humm in it. Noise is low though. Not a very hot(temp) amp. Lars, where are the 2.4 ohms ,grounlift resistors, situated(diagramm), just before the bias resistors of the opamp(LM6172)?Or is the 7812 also behind it?
Your amp. sounds nice
This blue LED...wow? Blinds your eyes The humm is noticable when I connect both channels, inputs. 1 is ok, but 2 creates humm, when putting your ear on the speakers, 86Db/1mtr. System is 1 transf. with split rails, psu's, grounded at the input RCA's. Picture tomorrow 
Your amp. sounds nice
This blue LED...wow? Blinds your eyes The humm is noticable when I connect both channels, inputs. 1 is ok, but 2 creates humm, when putting your ear on the speakers, 86Db/1mtr. System is 1 transf. with split rails, psu's, grounded at the input RCA's. Picture tomorrow 
yep, that's right.novec said:
The amp. has some sqeak when switching off, even before the protection relays switches off.
This amp. has to do some hours before comparing it to the UCD's.
The UCD's have absolutely no humm or noise at all(Coldamp. has some humm/noise also). There are some differences here. Same setup(except the groundlift resistors which are 10ohms in the UCD, on the 1 transf. setup!!not the dual mono). My UCD's have 35Db gain so that's not too much difference from the NCD's gain of 45Db.
Still some testing/mods. to do. Crosstalk is also a bit worse than the UCD setup. Have to make the humm go away. This is worse than the noise.
If I am obliged now to make it dual mono to get rid of the humm I am not happy. Chriss do you have humm??You have a 1 transf. setup also I thought?
here is the pic.
An externally hosted image should be here but it was not working when we last tested it.
It is done as your cookbook, grounded at the RCA inputs, no starground, - input directly shortcutted to ground at the pcb terminal like you suggest. Crosstalk at 15khz=-60db.Lars Clausen said:
Now, when doing it the way I connected the UCD's(with the 10 ohm groundlift resistors and starground) the humm almost disappears, not completely but acceptable, and crosstalk at 15khz=>-100Db. Lars, don't you use 100ohm input resistors on the input opamp IC?
Sound is getting better after many hours of playing
Bgt said:
I would not say that the difference between 35 and 45dB gain is not so different. That is a factor 3.16 in gain. Could that be the reason that you have a bit more hum with the same groundlift resistors? The higher noise level may also be due to the higher gain? Whay is the gain so high on the NCD? 45dB sounds like far too much gain for most applications. I know, UcD is supersilent the lowest of any Class D amp I have heard (Tripath, Zappulse and UcD) and equal or better than my Accuphase E407 integrated amp (very silent amp,now gathering dust).
Best regards
Gertjan
Best regards
Gertjan
Lars Clausen said:
If I do it like your cookbook, its 50/100 hz. But the 50 hz is dominating.
When doing the starground(with groundlift resistors) scheme it is 100hz and much softer.
For the Vgate I am using a small bridge rectifier with an add. 1000uf smoothing. Each channel has a sep. isol. winding, so psu, for the Vgate input. It is fed by the small transf. in the middle.
The main supply is a bridge per channel, giving -/+ output lines, with the 0V as common 0V for both amps.
Dont have a sketch ready. I'll make 1 later.
ghemink said:
Thats sad, sell it. I did that with my 4 months old NAD C162+C272 also. It was too expensive to keep it gathering dust.
Whats nice about the high gain of the NCD is it is easy to use with a passive pre or pot. When using the setup I use for the UCD's(starground with 10 ohm groundlift resistors) I loose the 50hz humm which is ok. As a benefit my crosstalk figure went up like crazy(positive). It seems that even though the NCD uses 2.5 ohm groundlift resistors on the NCD PCB the crosstalk still suffers.
Don't know if this has anything to do with the way the input amp. is setup.
I will build a dual mono also to see if it is any better. But that 1 later.
And high gain should not give any problems. I have this on my Crescendo also without any hum or noise.
http://www.grotel.nl/photo/wiringschemecrescendo2.jpg
After having modified the UCD's for higher gain they became very unstable and that is why I changed the input wiring to the 1 I use now with the groundlift resitors. There was no way for me to have it properly done otherwise and I got the id from the Crescendo which used the groundlift resistors also. And if you look carefully at the input differential of the Crescendo you will see I use it in exactly the same way.
t. said:Looking forward to reading your guys opinions of the NCD's sound, the thing a lot of people would like to know is if the NCD is a worthwhile upgrade over something like the UCD etc.
Hopefully the thread won't turn into arguments, all we want is honest opinions
Nice work btw Bert!
It's well worth to upgrade over 2.3SE and Jeff Rowlands or other ICE-power based amps.I have not heard any UCD (yet).
0V is not floating if you use starground.novec said:
If I use a single supply for 2 channels my sonics will be worse.
Did you ever scope the power rails when 2 channels are on 1 supply? The amp. must have an enormous PSR to remain ok.
Also crosstalk suffers. And crosstalk is ugly distortion.
Remember the UCD's I use with the same supply are dead quiet at 35Db.
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