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Old 25th October 2011, 10:55 PM   #1001
dsdjoy is offline dsdjoy  Germany
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Default UGS Frequency Response

Hi,

here is a Audio Precision Frequency Response measurement of my UGS all-inclusive build (all-inclusive means PCB set including volume control, input selector, CPU and display boards from french HCFR forum).

The measurement was provided as a free-of-charge service by Mr. Fuchs from Volpe-Audio Electronics - electronics development at the Analogue Audio Association event in Krefeld/Germany. Thanks a lot for the nice talk and measurement session !

Measurements revealed that the frequency response is flat between 10hz and 80khz (-3dB point with 2V input and 2 Volt output)
Frequency response of UGS Preamp shows dependency on the volume setting.
Cause is probably parasitic capacitance (here: Vishay Dale CMF-55) of the resistor network - maybe to some extend also switching relais or PCB circuits.

Red Line: Volume attentuator set to 0dB - no attentuation.
-3dB point is beyond 200khz.

Other lines: Frequency response at different volume levels. -3dB point varies with volume level with minimum at 80khz.

Based on a lot of listening sessions, my impression is that the preamp sounds very neutral - the difference between the amp and amp-bypass at same loudness is minimal. But I also find that when bypassing the amp - or when setting volume attentuation to 0db (none) - the sound is a bit better.

Not sure where to look for, but the volume attentuator resistor ladder and relais circuits could be an option........
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File Type: jpg frequency_response_vs_level_s.jpg (87.6 KB, 962 views)
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Old 25th October 2011, 11:09 PM   #1002
dsdjoy is offline dsdjoy  Germany
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Default UGS THD+N

Hi,

here is a Audio Precision THD+N over frequency measurement.

THD with 500khz Bandwidth is ~ 0.004%.
As this distortion curve is independent from frequency, it seems to be dominated by background noise.

Limiting the bandwith and excluding the high-frequency portion of the noise result is:
THD with 22kHZ Bandwidth is ~ 0.001%

I am not an expert in THD figures of preamps, but I'd say it looks very well...

[Measurement kindly done by Mr. Fuchs from www.volpe.at]
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File Type: jpg THD+N over Frequency.jpg (140.7 KB, 923 views)
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Old 25th October 2011, 11:13 PM   #1003
dsdjoy is offline dsdjoy  Germany
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Default UGS CCMR and FFT measurement

Last but not least the CCMR and FFT measurements:

Common Mode Rejection

Common Mode Rejection on the symmetrical input is around -60dB.
Not too bad, but maybe some even better matching of transistors and some resistors is required here to lower CMRR ?

FFT with suppressed ground/base wave

Residual 50hz AC-line-noise is at approx. -100db - looks fine.

FFT shows some -115dB noise at 5.9khz and it's K3 at 17.7 khz.
There is a small noise-generator hidden somewhere in my circuit layout.
Measurements with different inputs and separate ground-reference of the audio-precision
indicate that there is a grounding problem in my layout.
However at -115db level of this noise - it is probably not really audible on the speakers ?
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File Type: jpg CCMR symmetrical input_s.jpg (82.8 KB, 885 views)
File Type: jpg FFT Preamp_s.jpg (84.4 KB, 878 views)
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Old 26th October 2011, 08:30 AM   #1004
nar is offline nar
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Very nice and useful measurements. Thank you very much

Best,

nAr
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Old 26th October 2011, 07:43 PM   #1005
philbyx is offline philbyx  France
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Ouahouh!!!!

Many thanks Dsdjoy for these nice measures!
Cmrr is finaly not so bad!!!
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Old 28th October 2011, 09:17 PM   #1006
dsdjoy is offline dsdjoy  Germany
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Quote:
Originally Posted by philbyx View Post
Ouahouh!!!!

Many thanks Dsdjoy for these nice measures!
Cmrr is finaly not so bad!!!
I am getting convinced too, that this preamp measures (and it also sounds) better than many (and most) commercial preamps. Thanks a lot here to CheffDeGaar, 'Flat' from HCFR forum and last but not least Nelson Pass for this great preamp !

BTW: Now my speakers are the limiting factor....more DIY things to do....

Last edited by dsdjoy; 28th October 2011 at 09:32 PM.
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Old 9th November 2011, 09:58 PM   #1007
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Default 2SJ109, 2SK389

want to build UGS modules where can I buy jfet 2SK389 and SJ109?
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Old 9th November 2011, 10:40 PM   #1008
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Use matched substitutes, K170bl /j74bl
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Old 10th November 2011, 09:15 AM   #1009
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Quote:
Originally Posted by nar View Post
Use matched substitutes, K170bl /j74bl


Thank
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Old 10th November 2011, 10:33 PM   #1010
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Default k170bl/j74bl

Quote:
Originally Posted by nar View Post
Use matched substitutes, K170bl /j74bl

where can I buy K170bl/j74bl original Toshiba ?
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