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Old 26th October 2012, 02:43 AM   #5271
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Default Adjusting for DC offset.

Can I just confirm that when I have finished building the amps, I measure across the +/- of the speaker posts for 0 mV, and only have to adjust R95/R136 if itís off. Thanks.
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Old 27th October 2012, 03:34 AM   #5272
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Quote:
Originally Posted by Johanson View Post
Can I just confirm that when I have finished building the amps, I measure across the +/- of the speaker posts for 0 mV, and only have to adjust R95/R136 if it’s off. Thanks.
Yes wait until they have settled for a few minutes and Nampon grounded then test - within +/- 10mv is perfect.
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Old 27th October 2012, 12:23 PM   #5273
Henkjan is offline Henkjan  Netherlands
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Quote:
Originally Posted by Turbonsx View Post
I really need to raise the input gain so I can attenuate the output of my Phasure NOS1 more to lower the DC offset and keep the NCores from going into protect without adding coupling caps.
I'm not an expert, but woudn't adding a couple of high quality couple caps be much easier and flexible? what's the problem with couple caps?
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Old 27th October 2012, 01:44 PM   #5274
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Default Lowering NC400 output gain

Quote:
Quote:
Originally Posted by Turbonsx
I really need to raise the input gain so I can attenuate the output of my Phasure NOS1 more to lower the DC offset and keep the NCores from going into protect without adding coupling caps.
I'm not an expert, but woudn't adding a couple of high quality couple caps be much easier and flexible? what's the problem with couple caps?
I tried 4 high grade Mundorf caps(balanced inputs). Unfortunately, the NOS1 is so resolving, the caps had a negative effect on the resolution. It certainly sounded better without them. I'm just not able to listen at a volume that I'd like to. Decreasing the digital attenuation(raising the output) on the NOS1 beyond a certain amount increases the DC enough to throw the NC400s into protect.
And adding a preamp is not an option as it also negatively effects the resolution. It seems like lowering the resistance on resistor 141(RG) would have less impact on the system's resolution, but I've only seen examples of NC400s lowering the amplifier gain by removing R141.
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Old 27th October 2012, 02:18 PM   #5275
Julf is offline Julf  Europe
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Quote:
Originally Posted by Turbonsx View Post
I really need to raise the input gain so I can attenuate the output of my Phasure NOS1 more to lower the DC offset and keep the NCores from going into protect without adding coupling caps.

The gain of the nCore (or rather input sensitivity) is already pretty high - several of us have had to lower the gain. While Bruno & co have commented on lowering the gain, I am not sure what the effects of increasing the gain will be - decreasing feedback? Increased instability? Definitely increased sensitivity to noise.

The problem is the DC offset from the NOS1 - you should deal with that problem, and not try to band-aid over it by increasing the nCore gain. A DAC with significant DC offset is badly designed.

Also be aware of the fact that the NOS1 can have a significant amount of unfiltered HF noise on the output - it might cause intermodulation in the amplifier.
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Old 27th October 2012, 02:43 PM   #5276
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Thanks for the reply Julf,

The DC on the NOS1 is do to the Phase Alignment feature of the XXHighend software. The DC offset is quite low without this feature engaged and plays fine at all volumes. I just like the effect the phase alignment feature has on improving the realism of bass instruments and soundstage.
I'll play around some more with the coupling caps. I certainly don't want to do anything that affects the additional focus and clarity that the NC400s provide.

Remember I'm not trying to increase the gain of the NC400, just to change the differential buffer stage sensitivity to increase the gain relative to a given input voltage. I'm really looking to gain about 6-9db of of input sensitivity and the slight decrease in signal to noise might be worth the trade off instead adding coupling caps, not to mention the $'s

Todd
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Old 27th October 2012, 03:18 PM   #5277
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Default turbo...

which Mundorf caps did you try which were too degrading to you, and what value? Into the impedance of the nCore I suspect you would only need 2 uF or so, right?
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Old 27th October 2012, 03:47 PM   #5278
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Barrows,

Just the M-cap supremes, 1 mf. I didn't want to outlay to much money initially.

The NCore's are only running the mid/high. The bass and sub- bass are handled through separate amps running through an active x-over that is Jensen transformer coupled, so no DC issues on those.

The Jensen coupling on the mid/high drivers was killing the resolution of the NOs1' so I'm running them straight from the NC400's with a passive x-over between the mid/tweeter and no x-over on the bottom end of the mids.
I should mention these are Audio Artistry Beethoven Grandes, so full dipoles on all drivers.(Premier design of Linkwitz before he left the company and started doing the DIY Orion's.)

Todd
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Old 27th October 2012, 04:08 PM   #5279
Julf is offline Julf  Europe
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Todd,

Quote:
Originally Posted by Turbonsx View Post
The DC on the NOS1 is do to the Phase Alignment feature of the XXHighend software. The DC offset is quite low without this feature engaged and plays fine at all volumes. I just like the effect the phase alignment feature has on improving the realism of bass instruments and soundstage.
Yes, I understand the DC offset comes from the "magic" Phase Alignment feature, but I still view it as a design problem - it should not be too hard to do the required processing while maintaining (or restoring) the DC balance.

Quote:
I'll play around some more with the coupling caps. I certainly don't want to do anything that affects the additional focus and clarity that the NC400s provide.
A pair of smallish high-quality caps should not have a major impact on the sound quality.

Quote:
Remember I'm not trying to increase the gain of the NC400, just to change the differential buffer stage sensitivity to increase the gain relative to a given input voltage
i am not sure I understand the distinction. 6-9db of increase in input sensitivity (and thus gain) will result in a corresponding loss in signal-to-noise.
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Old 27th October 2012, 10:19 PM   #5280
Regnad is offline Regnad  United States
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I received a pair of Veritas amps yesterday and am quite surprised (and pleased) at how much better they are than my DIY NC400s.
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