Will the correct Doug Self Wireless World RIAA please stand up? - diyAudio
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Old 2nd February 2006, 12:19 AM   #1
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Default Will the correct Doug Self Wireless World RIAA please stand up?

I was trying to find a "best" RIAA eq for my preamp in this thread: Would this work (simple OPA1632 phono preamp)? and the Doug Self circuit from 1996 is mentioned often. In Rod Elliott's Project 25 http://sound.westhost.com/project25.htm he does show a schematic and points out that 1 cap is likely the wrong value and if you change it you do get the 3180 us constant. However I found another project http://www.mhennessy.f9.co.uk/preamp/schematics.htm (click Phono stage schematic) where the designer also claims to use the Self eq but has other components with different values. Does anyone have the original Self article or know enough about the subject to verify what is correct?
The whole problem with the world is that fools and fanatics are always so certain of themselves, and wiser people so full of doubts. Bertrand Russell
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Old 2nd February 2006, 12:51 AM   #2
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you might want to read Nelson Pass' article on the Pearl (I believe that's the one) -- www.passdiy.com
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Old 2nd February 2006, 01:22 AM   #3
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I think 'cos it's still available from http://www.softcopy.co.uk/mag/defaul...070540&count=1 (watch out, this adds it to a 'shopping basket') for 4 pounds, it might not be readily available on the net.

As it's not on his own site (http://www.dself.dsl.pipex.com/ampins/ampins.htm) you might end up having to get a copy for yourself to verify what is correct.

"It is impossible to build a fool proof system; because fools are so ingenious."
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Old 2nd February 2006, 01:06 PM   #4
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I'm prepared to be wrong on this but I think the mhennesey value
for the big resistor isa conseqence of misreading the schematic in 'Self on Audio'.

I think 5220 Ohms in parallel with 14.32n and 63500 in parallel with 50n gives the right numbers.

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Old 2nd February 2006, 01:31 PM   #5
sreten is offline sreten  United Kingdom
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I have the book at home so I can check tonight.

However D.Self categorically states that the time constants interact
and you cannot get accurate EQ by using the time constants for each
section. Consequently for the proper values a simple R||C time constant
calculation should yield "incorrect" time constants.

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Old 2nd February 2006, 01:32 PM   #6
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If I remember I'll check his book when I get home.
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Old 2nd February 2006, 03:36 PM   #7
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I have one of Doug Selfs Wireless World design articles at work and can check tomorrow.

The best thing is to use a simulator like Simetrix and simulate against the ideal mathematical model. It's quite easy to get very close to ideal.

I have seen a few discrete preamps that are off at the 3180us point because they run out of gain
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Old 2nd February 2006, 04:59 PM   #8
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I recall an article by Reg Williamson in Audio Amateur about 15 years ago on this subject. He had 4 different topologies for the RIAA network and the correct time constants for each topology to provide the proper RIAA break frequencies.

Finding the article may take some time.
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Old 2nd February 2006, 05:44 PM   #9
jcx is offline jcx  United States
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you might want to look at jung's Op Amp Applications book

section 6 has a dozen pages on riaa circuits

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Old 3rd February 2006, 01:29 AM   #10
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Doug Selfs Wireless World February 1979 RIAA preamp
This was a single supply bipolar transistor design.
I have modeled it here with opamps for simplicity but the results are similar. Note that the gain is low from 50Hz to 1KHz, as much as 1.6dB so the 3180 us pole is wrong.
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