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Old 3rd August 2012, 08:37 AM   #6541
hesener is offline hesener  Germany
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Quote:
Originally Posted by beetle View Post
What do you use to measure such tight tollerances? Or do you just match the chanels?
I used a LCR meter, some older device from HP whose number escapes me right now. I bought it at the ETF 2011, an it works just beautifully. I measured the capacitors that went in there, and combined them with additional small caps to achieve the exact value from the schematic. Yes, I rely on this LCR meter to claim the 0.1%, which is only true if that meter is that precise. But the two channels do match to each other that well. (And I calibrated my meter with another meter that just went through calibration....)

RIAA precision is a different thing. The caps and resistors need to be precise (what I tried to achieve), but as Joachim pointed out the other impedances in the circuit do play a role as well. The Paradise circuit tries to minimize these as much as possible, and as we have seen from Stefanoo's simulations the results are very close. What we are still missing is an actual measurement, using a anti-RIAA circuit, to find out if that is true.

But that raises the question, how precise can that be, when your components are 0.1% or so? This can be calculated (don'T forget the precision of the signal generator), only I haven't done it.... I think Joachim made that estimation in his FPS article....
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Old 3rd August 2012, 09:02 AM   #6542
Salas is offline Salas  Greece
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Its the outcome that counts. So most practical is to measure curves since this circuit responds to impedance division against the filtering components. Without an inverse Riaa feed-through for flat, we can always take the filtered curve and then compare it against the textbook Riaa curve. Here is one FFT of a tube phono that way. And there is no anti-Riaa circuit tolerance creeping in.
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File Type: gif ValveItchRiaaCurve.gif (19.8 KB, 305 views)
File Type: jpg Riaa.jpg (30.6 KB, 304 views)
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Old 3rd August 2012, 12:07 PM   #6543
Joachim Gerhard is offline Joachim Gerhard  Germany
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I have measured the new Pardise with an Anti RIIA and have posted the results. With the value that MiiB has chosen we get 0.75dB plus at 20Hz and 0.25dB plus at 20kHz. In a broad range between 300Hz and 10kHz the response is flat so we have a very slight loudness character. With Stefanos and Ricardos values the response will be flatter.
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Old 3rd August 2012, 12:20 PM   #6544
Salas is offline Salas  Greece
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Will the impedance of the mirrors vary somewhat due to various parameters in every each one of them built?
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Old 3rd August 2012, 12:27 PM   #6545
Joachim Gerhard is offline Joachim Gerhard  Germany
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Not much but 0.1% is optimistic. 1% gives a precision of slightly worse then plus-minus 0.1dB. For me that is good enough provided that the channels match.
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Old 3rd August 2012, 01:05 PM   #6546
jacco vermeulen is offline jacco vermeulen  Netherlands
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Quote:
Originally Posted by Joachim Gerhard View Post
For me that is good enough provided that the channels match.
By 0.2dB ? (0.172)
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Old 3rd August 2012, 01:27 PM   #6547
Joachim Gerhard is offline Joachim Gerhard  Germany
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With a scope that has two channels and a mathematics function it is quite easy to check if the channels are similar-
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Old 3rd August 2012, 01:57 PM   #6548
Stefanoo is offline Stefanoo  Italy
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Quote:
Originally Posted by Joachim Gerhard View Post
With a scope that has two channels and a mathematics function it is quite easy to check if the channels are similar-
Scope usually has a vertical accuracy of 5%.
What I have is a precision 5 1/2 digit Fluke meter and created a reference file with the RIAA using top level HP Meter I had access to for a couple of months.
Then I play the file and measure the output with my Fluke and record the variation and plot it vs. Frequency.
That as proven to be accurate to 0.05dB.

When I get the board I will be able to make reference measurements for all the community here and I will share the results with all of you.
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Old 3rd August 2012, 02:32 PM   #6549
jacco vermeulen is offline jacco vermeulen  Netherlands
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Quote:
Originally Posted by Stefanoo View Post
What I have is a precision 5 1/2 digit Fluke meter
A 5 1/2 digit LCR meter doesn't automatically have a 0.05% accuracy.
Basic accuracy of 0.05% doesn't automatically mean the measurement will be 0.05% accurate.

Capacitors have three parameters, i'd advise you to read an introduction to precise LCR meters, e.g. from Agilent, Wayne Kerr.

(me have a Philips 6340C with 0.05% basic accuracy, took me a course to manage to measure to that level)
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Old 3rd August 2012, 03:28 PM   #6550
Stefanoo is offline Stefanoo  Italy
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I meant the reference file I have created has an accuracy under 0.05%.
I created with the topo of the line Agilent meter.

I play the file at a level that will set a good spot for the meter thus allowing it to go down to 0.1% or better.
I got the idea of creating the reference file after going through a lot of pain in trying to measure the RIAA for another project I was developing and I was using an excel spreadsheet with a lot of formula to calculate the accuracy.
The process was really elaborate and I had to come out with a better and faster way but yet precise and that is when I got this idea.

Obviously playing the file also works if you have a flat soundcard to play with and my EMU 0204 is very good for this purpose and that is why I specifically choose this model sa it has a very flat frequency response.

I would recommend this method, it will be very straightforward to plot the frequency response.


Edit: I will definitely read the material you outlined
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