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Old 18th November 2010, 03:14 PM   #1881
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SY is on track, however, with the loading of the caps. This buffered output is not very realistic in the actual use of an audio cap. How often can we have 1 meg input impedance? Very rarely. Volume controls get noisy at 1 meg, filters too. If you want non-linear distortion measurement, you have to drop some voltage across the cap. This implies a realistic RC time constant, such as 10K-50K for realistic testing.
Linear error or DA will NOT completely go away, even with 1M loading, but it will not be as much in magnitude as it would be with a lower impedance load.
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Old 18th November 2010, 10:36 PM   #1882
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So a high impedance loading swampes cap diffences. Is that one reason that Mark Levinson used 1MOhm impedance in the Cello equipment and now at Daniel Hertz ?
I found out some time ago that high impedance buffered Opamp sound much better but i thought because of other reasons I will not expole that here at the moment. I will look at the Curl and Jung paper again, what kind of signal they used.
Smaler cap values may have also less probems with ESR, inductance, mechanical shock etc. Could that be one reason that high impedance tube equipment sounds better to some?
Anyway lets explore something i found. Feeding in a sine, triangle or square into the bypass and then into any of the 4 caps i installed i found a small jump in level athough the shape of the signal was not visually altered. I then checked the level difference with my tube meter and found that the bypass gave around 0.2dB more level. I checked that at 1kHz, 100kHz and 1MHz and it was always the same. I whould have understood that better at lower frequencies when the high pass action comes into play. So the straight bypass may not be a good refference because the ear has a tendency to prefer the louder signal. How well level has to be matched seems to have changed over the last 40 years. I learned in the 70th when i studied Telecomunications that 3dB is "just well audible" and 1dB is " barely detectable". When i now read for example the literature about the Heron Phonostage or trust what Siegfried Linkwitz is currently experiencing with his Orion 3.2, then the threshold is currently identified at better then 0.2dB. Where does that lead us ? Is that again the old argument about easy detection of small differences in LINEAR distortion ?
Anyway, here are the scope shots and the meter readings. Bypass, cap, from left to right.
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File Type: jpg 1 MHz squarewave bypass.jpg (81.4 KB, 238 views)
File Type: jpg 1 MHz squarewave with cap.jpg (89.6 KB, 237 views)
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Old 18th November 2010, 10:37 PM   #1883
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Here the meter.
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File Type: jpg 100kHz magnitute with bypass.jpg (64.2 KB, 236 views)
File Type: jpg 100kHz magnitute with any cap.jpg (73.2 KB, 237 views)
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Old 18th November 2010, 11:01 PM   #1884
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Quote:
Originally Posted by john curl View Post
SY is on track, however, with the loading of the caps. This buffered output is not very realistic in the actual use of an audio cap. How often can we have 1 meg input impedance?
With tubes or FETs, just about anytime we want.
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Old 18th November 2010, 11:21 PM   #1885
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I am moving to higher input impedance too recently at least at line level. This hole schebang is totally quiet, even with the 2Mohm i use.
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File Type: jpg Switchbox measurement setup.jpg (88.0 KB, 234 views)
File Type: jpg Switchbox and buffer.jpg (63.1 KB, 87 views)
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Old 18th November 2010, 11:29 PM   #1886
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John, as far as i can see you used a negative going step in the 1985 cap measurements.
Since the late 70th when i met Mr.Manger i do step response measurement on speakers too but usually with a positive going step. In the early days with an analog step generator and scope and later with impuls response measurement and convolution first with MLSSA and now with a log chirp in Praxis. The most basic way whould be just to connect a battery and then switch it of. It could be argued that a real step is more taxing then using a low crest factor signal and then postprocessing. Mathematically its all the same.
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Old 19th November 2010, 07:53 PM   #1887
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I build the input stage of the Simple Inductive Passive RIAA. I decided to do the mid-bass equalization right in the inverted input stage. The 1kHz gain is setup as 30dB and i will add a second inverted stage with 30dB of gain. Yes i know, it looks like Arte Powere in the High End Emergency Room but i did not have a fitting case for the rather big coils so i build it right in the open on a chip board plate. Heck, the ETF begins in less then a week and i whould like to show something unusual concerning phonostages. I measured it and it amplifies and i could squeze out a half decent squarewave at 1kHz. The level though is very small because i modified my invers RIAA to have an output impendance of 6.8Ohm. That way the input signal is very small and the aplification is only 30dB.
Lets see what happens when i add the second stage. If it works, i will publish a schematic.
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File Type: jpg Input Stage simple passive inductive RIAA.jpg (86.4 KB, 102 views)
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Old 19th November 2010, 08:12 PM   #1888
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Complete with mdf stuck layer pulled off from a speaker.
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Old 19th November 2010, 08:19 PM   #1889
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No, this is a super duper, fully organic, magic recipy damping compound !
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Old 19th November 2010, 08:49 PM   #1890
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But doing the mid-bass, which is handier, will not mitigate the +20dB HF cut on discs to enter the gain circuits, which would have been nice to evaluate its subjective impact as a technique...
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