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Old 20th December 2013, 10:01 PM   #451
BigE is offline BigE  Canada
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The parts arrived, so I put them in immediately.

R4 = 275K ( 249K caddock + 1% metal film (mistake ordering)) was 330K
C2 = 0.0056 uF Relcap RTE (was 0.01)
C3 = 47uF Elna RBD

Results are terrific even without break in! Of course, since R4 is now below 300K a Vishay nude can also be installed. A Russian teflon is on the way for the Relcap.
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Old 20th December 2013, 10:57 PM   #452
ahaja is offline ahaja  Poland
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I'm not surprised.
You made 103.35Hz instead of 50Hz ...
5.6n + 33k gives you 861.23 Hz instead of 500Hz ...

You have to change all values in riaa not part of it.
Changing big R in second stage you also changing the gain (lower R lower gain).
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Old 21st December 2013, 05:04 AM   #453
BigE is offline BigE  Canada
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But the point of this is that given the design of a current to voltage convertor followed by a difference amp is not hard to model. The equations are closed form solutions. So is Riaa. Then, just take the results of the model, normalize to 1k, subtract normalized Riaa values, and square these errors.

This yields a sum of squared errors of 258 for the original design. The above changes lower the sum of squares of the errors to 12.5. I would think the changed implementation would be closer to Riaa regardless of whether or not specific time constants are met.

Using. 250K r4 gives an even closer sum of squared error = 8.34. How can this be a bad thing?
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Old 28th December 2013, 02:11 AM   #454
BigE is offline BigE  Canada
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After setting up the LTspice simulation, I have to agree.... the spreadsheet looks quite wrong..... I used an LT1677 for the op amp. Similar slew rate to the OP27.
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Old 28th December 2013, 03:08 AM   #455
BigE is offline BigE  Canada
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I found the error in my spreadsheet.

With my values, the sum of squares error is 145.

With the stock values, it is 1.9. With R1=1K596 it is 1.87.

The circuit values are correct and cannot be improved in any significant way.

R4 to 300K gives sum of squared error of 0.58! 310k gives 0.41!!!

Last edited by BigE; 28th December 2013 at 03:20 AM.
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Old 8th January 2014, 05:56 PM   #456
BigE is offline BigE  Canada
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The 0.01 cap is back in place... much better. 0.0056 sounded like hitting the "loudness" button.

According to my spreadsheet, 0.0098uF gives minimal error ( +/- 0.1 db from RIAA), but this is very close as well.

R4 is 300k, with no other changes from stock BOM values.
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Old 14th January 2014, 01:26 AM   #457
BigE is offline BigE  Canada
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After playing around, the best values I could generate from the spreadsheet were:

C3=10uF

R4=300000
R5 = 32600 ( 32570 == 33000 || 2M5 )
C2 = 0.0099uF

This is very very close to RIAA. Important frequencies are within 0.05db,with frequency extremes being 0.08db out.

This has not been tested.... parts are coming to try to build up the 0.0099 uF cap. The change of R4 and R5 will get closer... the 2M5 resistors are also on the way.,
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Old 15th February 2014, 06:16 PM   #458
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Can this phono stage be built in a balanced configuration? I was looking at the aqvox at first but I found this and it seems to be the more affordable alternative, I just don't know about the balanced option.
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Old 19th February 2014, 12:19 PM   #459
atupi is offline atupi  Romania
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I have a Hi output MC Denon DL110. Can it be used with this phono pre ?
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Old 5th May 2014, 01:33 AM   #460
BigE is offline BigE  Canada
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Yes.

Final values implemented:

All stock except:

R4 @ 300K (was 330K),
C2 @ 09.8 nF (was 10 nf) and
C3 @ 47 uF (was 10 uF)

Caps are now breaking in (FT-2 teflon).
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