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Old 5th March 2015, 05:25 PM   #301
zfe is offline zfe
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I stand corrected

I used the formula for charging also for discharging the capacitor.
Discharging is as U(t)= U exp(-t/(R C)).
With that we get from the data then C=1200pF.
And with that capacity we get thus as internal resistance 625 Ohm, so the contribution of the DAC ladder only.

So we do not need to think about doing the powersupply better.

It is really hard to find a flaw in Sorens design or specs

Last edited by zfe; 5th March 2015 at 05:37 PM.
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Old 5th March 2015, 09:53 PM   #302
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AS far as the output low pass filter:

Is there any need for it to be where it is? Why not remove the capacitor on the board and place a filter of your choosing at the output? Not sure if removing the resistor would be necessary. Or just consider the value of the resistor when calculating what is required. It will be in parallel.

Not sure if anything is after the filter which would remove the influence of the shunt resistor on the board.

Your choice of resistor and capacitor becomes wide open and much easier to change. Better than taking chances with soldering on the board several times.
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Old 5th March 2015, 10:27 PM   #303
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zfe,

Would you do me a huge favour and take a look at a sawtooth with the stock filter and your reduced filter. It appears that the stock filter - and two of my filters that I've checked - are clipping the peak of the sawtooth with FS input and V+00, but I'd appreciate verification from someone with decent gear.

My "scope" is a bitscope micro - BitScope Model 5 | A tiny USB Mixed Signal Oscilloscope - so my measurement capabilities are very limited.

Add: I've adjusted one of my filters to a gain of x7.8 and it looks like that significantly reduces the "chopped top" on the Sawtooth signal.
AddAdd: Dropped to x7.5 and sawtooth is looking better but it appears the peaks on square waves are being chopped. I've had to drop the output level in signal suite to around 87% to eliminate the clipping.

cheers
Paul

Last edited by spzzzzkt; 5th March 2015 at 10:40 PM.
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Old 5th March 2015, 11:15 PM   #304
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These are screen dumps from bitscope. FS output from SignalSuite, 3000hz sawtooth and square waves. This shows the default Soekris filters, and 44.1khz sampling rate.

You can see the clipped peaks to the waveforms. Sine wave is perfectly fine, so not shown.

Click the image to open in full size.

Click the image to open in full size.

This is one of my filters with the gain dropped to x6 - square wave is still clipping at x7.

Click the image to open in full size.

As I said I'm not 100% confident about the quality of the measurements, so if someone can verify or otherwise it would be appreciated.
The bitscope should handle 12V input but this seems to be clipping at 2V rms.
Attached Images
File Type: png DAM_FACT_ST3K.png (34.1 KB, 829 views)
File Type: png DAM_FACT_SQ3K.png (36.3 KB, 824 views)
File Type: png GainReduction_DAM.png (35.5 KB, 459 views)

Last edited by spzzzzkt; 5th March 2015 at 11:30 PM.
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Old 6th March 2015, 01:15 AM   #305
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Quote:
Originally Posted by spzzzzkt View Post
seems to be clipping at 2V rms.
A correction to this.... The voltage was measured between median voltage and the rms voltage so the clipping is occurring at 4Vrms via the balanced outputs. This is slightly under 6V p-p.

http://www.ap.com/kb/show/367#soundadvice
Quote:
However, digital square waves are useful for exposing certain flaws peculiar to digital systems. For example, systems engineered with inadequate headroom may overload when stimulated with full-scale digital square waves. This is a common problem in interpolation filters.

Last edited by spzzzzkt; 6th March 2015 at 01:19 AM.
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Old 6th March 2015, 03:11 AM   #306
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So this is interesting- the NOSfullbypass 1 doesn't clip when I manually adjust the volume up via the serial manager. I set it to +10 and it is fully usable.
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Old 6th March 2015, 03:52 AM   #307
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Quote:
Originally Posted by spzzzzkt View Post
You can see the clipped peaks to the waveforms. Sine wave is perfectly fine, so not shown.
YEs, this looks like there is some clipping, but I'm not sure if it is the Gibbs effect or genuine clipping.

Quote:
Originally Posted by spzzzzkt View Post

Click the image to open in full size.
This waveform though shows some interesting behaviour in the negative half of both waveforms - it crosses zero in a strange place in the middle yellow waveform and the ripple is flatter in the second half of both the yellow and green traces.
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Old 6th March 2015, 03:59 AM   #308
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Quote:
Originally Posted by robertrowett View Post
So this is interesting- the NOSfullbypass 1 doesn't clip when I manually adjust the volume up via the serial manager. I set it to +10 and it is fully usable.
Square waves don't show the "Gibbs phenomena" on NOS DAC's so it's not an issue.

Click the image to open in full size.
Nice and clean square wave. That is the high point of NOS measurements
Not sure why there is a level difference between the two... but never mind.

Sine waves are not so pretty...
Click the image to open in full size.

NOSfullbypass1 is 12-18dB down on the correct 8 x 1 implementation of a NOS filter, so you can probably crank it all the way to a Spinal Tap-esque "but look this one goes to 15, man" and not get any clipping....
Attached Images
File Type: png DAMNos3K.png (23.0 KB, 432 views)
File Type: png DAMNosSine3K.png (34.8 KB, 434 views)
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Old 6th March 2015, 04:26 AM   #309
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[QUOTE=spzzzzkt;4248589]Square waves don't show the "Gibbs phenomena" on NOS DAC's so it's not an issue.

Click the image to open in full size.
Nice and clean square wave. That is the high point of NOS measurements

The high point of NOS measurements is between my ears!
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Old 6th March 2015, 04:28 AM   #310
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Quote:
Originally Posted by bkdog View Post
YEs, this looks like there is some clipping, but I'm not sure if it is the Gibbs effect or genuine clipping.



This waveform though shows some interesting behaviour in the negative half of both waveforms - it crosses zero in a strange place in the middle yellow waveform and the ripple is flatter in the second half of both the yellow and green traces.
There is a very, very good reason I asked for someone to try to replicate on decent gear. Basically I don't have a high level of confidence in the bitscope. I've seen weird behaviour on the bitscope before it's proved to be a non-issue when checked with a "real" scope.

The tests I did seems to show the clipping occurring at rated RMS output for the balanced stage. Clipping disappears when either test signal is reduced or the digital volume is lowered. Again for the reasons stated above I'd like confirmation from someone with a decent scope before I get too excited about it.
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