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Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

Bob Cordell's VinylTrak
Bob Cordell's VinylTrak
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Old 2nd July 2018, 01:41 PM   #101
Adams_Leo is offline Adams_Leo  China
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Quote:
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Finally....

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Very nice JOB!!!!

Leo
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Old 2nd July 2018, 02:04 PM   #102
Edmond Stuart is offline Edmond Stuart  Netherlands
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Chapeau !!!
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Old 11th July 2018, 06:41 PM   #103
Black Jack is offline Black Jack  Ukraine
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Some measurements

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(SRP-MC my version of Bob Cordell`s VinylTrak)

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To be cont.

Last edited by Black Jack; 11th July 2018 at 07:00 PM.
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Old 11th July 2018, 07:21 PM   #104
Bob Cordell is offline Bob Cordell  United States
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Quote:
Originally Posted by Black Jack View Post
Some measurements

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(SRP-MC my version of Bob Cordell`s VinylTrak)

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To be cont.
Looks good!

Cheers,
Bob
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Old 11th July 2018, 08:25 PM   #105
Black Jack is offline Black Jack  Ukraine
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It is interesting that in the right channel there is a delta 0.35 dB with the left channel.
Probably because some mismatch in DC-Servo components values.
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Old 11th July 2018, 08:29 PM   #106
Bob Cordell is offline Bob Cordell  United States
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Quote:
Originally Posted by Black Jack View Post
It is interesting that in the right channel there is a delta 0.35 dB with the left channel.
Probably because some mismatch in DC-Servo components values.
Yes, I noticed that. The delta begins to exceed 0.1 dB at 30 Hz. You are probably right about it being the DC servo.

Cheers,
Bob
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Old 18th October 2018, 03:19 PM   #107
Dontsov is offline Dontsov  Russian Federation
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I have a question regarding Wilson current mirror. Do I have to match Q10 and Q11 (Q29 and Q30 as well) for better performance?
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Old 17th December 2018, 08:14 PM   #108
JasonB299 is offline JasonB299
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Default Matching not needed :)

Hey Dontsov,

Since none of the experienced builder here has answered you yet, I'll give it a try. It is better than nothing, right?

In general, matching in audio will *always* give you a better performance. However, there is a point of diminishing returns. If I would build the VinylTrak, I would not match Q10/11 resp. Q29/Q30. My reasoning is as follows:
I assume you would match beta of the BJTs. I am very sure that the performance of the VinylTrak is mainly limited by the matching of (the Idss of) the input JFETs. That is why Bob uses dual JFETS (sry, can't find the thread righ now). Compared to the variation between the individual FETs, the input/output current variation in the current mirror due to unmatched beta of the BJTs will typically be negligable, especially since beta is already very high for the 2N5089. Therefore, I would rather spend my time listening to the preamp than matching transistors.
BUT, if you already have matched the transistors, of course use them. There is nothing to loose here.

By the way, Bob found later that a 3-transistor current mirror gave better noise performance, see http://www.cordellaudio.com/preampli...inyltrak.shtml. I added the picture below.

I hope it helps
JB

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Old 15th February 2019, 08:00 PM   #109
Dontsov is offline Dontsov  Russian Federation
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JB,
Thanks for your comments! I've finally decided to play it safe and put in a matched dual transistor in the current mirror. But what you are saying absolutely makes sence.

P. S. Haven't got an answer notification, although I'm pretty sure I subscribed to this thread....
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