Zen -> Cen -> Sen, evolution of a minimalistic IV Converter - Page 143 - diyAudio
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Old 12th April 2013, 05:24 PM   #1421
EUVL is offline EUVL  Europe
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I am pretty sure I do not agree with the R4 in your sim, which is the main contributor of the distortion.

In the real PCM1704, the output current does not go through the 1k internal impedance, and the internal impedance only have a secondary effect on the accuracy of the current source. If you want to sim this properly, you need to put in the entire equivalent circuit of the R2R DAC.

In real life, the distortion of the cascode SEN is unmeasurable on my AP system 1. We have access to a Rhodes & Schwarz UPV, but that means shipping the entire circuitry across continents. Postage and insurance are too much to justify generating numbers for the sake of it. We like the sound (for ourselves), which is all I care.

Rechargeable drill batteries are just NiCd, unless you use the newer Lithium ones. I have only changed my NiMH for my preamp once in 6 years. So for me batteries are no issue. And the beauty of the SEN, as described in the article, is that it draws constant current in a separate loop as the signal. So impedance of the power supply has next to no effect at all.


Just my biased opinion, without saying,
Patrick
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Last edited by EUVL; 12th April 2013 at 05:28 PM.
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Old 15th April 2013, 05:55 PM   #1422
q-rz is offline q-rz  Austria
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Regal, Patrick, heb1001, thanks for your replies.

Here are my quick measurements, sorry for the noise and hum. From left to right: Cen (2SK170 and 2SJ74), Sen (paralleled 2SK170's), Sen (paralleled BF862's).

Cen has vanishingly low distortion, it clearly beats the Zen I had before.
Somehow I didn't have any luck with the Sen. With 2SK170's its not that bad, but with BF862's the harmonics above 2nd rise remarkably. Maybe the parts aren't matched tight enough, or I've done something wrong. Could somebody help me with this?

I would happily buy a kit with matched fets, if there is any available. Maybe it would work better.

Peter
Attached Images
File Type: png cen.png (88.9 KB, 604 views)
File Type: png sen_2x2sk170.png (90.3 KB, 476 views)
File Type: png sen_2xbf862.png (39.6 KB, 471 views)

Last edited by q-rz; 15th April 2013 at 06:06 PM.
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Old 15th April 2013, 06:23 PM   #1423
EUVL is offline EUVL  Europe
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Your measurements do not totally disagree with ours.
CEN is push-pull, and have some even harmonic cancellation.
But SEN has 2nd harmonics below -90dB, and what I call a health distribution down to 5th to give good sound.
I personally would be very happy with it as is.
If you want to chase numbers, then try cascoded SEN.

We can only support SEN V18 right now with matched 2SK369Vs.
I am not sure whether it will give you even better numbers than paralleled 2SK170s for you application.
Suggest you try to get 2SJ74 / 2SK170 matched sets from Spencer.

Do some listening first ?


Patrick
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Old 15th April 2013, 07:15 PM   #1424
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Patrick

what Is your choice by listenning - Sen (single ended class A) or Cen (Push Pull)
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Old 15th April 2013, 07:24 PM   #1425
EUVL is offline EUVL  Europe
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Cascoded SEN in balanced mode.


Patrick
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Old 15th April 2013, 10:46 PM   #1426
orelli is offline orelli  Italy
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What's CASCODED Sen?
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Old 16th April 2013, 02:50 AM   #1427
EUVL is offline EUVL  Europe
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Sen with cascode on all the JFETs.


Patrick
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Old 16th April 2013, 10:50 AM   #1428
q-rz is offline q-rz  Austria
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Quote:
But SEN has 2nd harmonics below -90dB, and what I call a health distribution down to 5th to give good sound.
My results with BF862 are much worse. Could it be the lazy matching?

Quote:
If you want to chase numbers, then try cascoded SEN.
Quote:
what Is your choice by listenning - Sen (single ended class A) or Cen (Push Pull)
Quote:
Cascoded SEN in balanced mode.
No offense, but if the cascoded sen is your favorite, then cascoding must be more than number chasing

Quote:
Do some listening first ?
Did already, it sounds the best I've ever heard (DIY). I'd like to thank you for sharing it with us!
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Old 16th April 2013, 10:57 AM   #1429
EUVL is offline EUVL  Europe
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> but if the cascoded sen is your favorite, then cascoding must be more than number chasing

I need a small PCB and hence SOT23 devices.
And every now and then I also chase numbers as a hobby.




Patrick
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Old 16th April 2013, 06:02 PM   #1430
heb1001 is offline heb1001  China
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[QUOTE=q-rz;3456396]My results with BF862 are much worse. Could it be the lazy matching?

If the devices are badly matched or you have any DC out of the DAC then you will see higher distortion. Also if you have high frequency oscillation (but that looks different from your current results).

Assuming your signal is where it seems to be at about -14dB and not actually at 0dB then the -84dB mains hum you have is not a good result. Also there seems to be quite a lot of high frequency noise in there too - certainly the 3rd picture has higher noise than the first two which wouldn't be the case if it were an artifact of the measurement.

On batteries you can get hum down below -110dB for single ended Sen and -125dB for balanced.

Some of my earlier measurements looked a bit like yours with mains hum and high frequency noise before I eliminated all the ground loops.

How have you wired up the L+R channel input and output signal and grounds? Also, how are you doing the measurement?
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