I was trying to find a "best" RIAA eq for my preamp in this thread: http://www.diyaudio.com/forums/showthread.php?s=&threadid=73110 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?
you might want to read Nelson Pass' article on the Pearl (I believe that's the one) -- www.passdiy.com
I think 'cos it's still available from http://www.softcopy.co.uk/mag/default.asp?dir=ew&p=shopping&action=add&item=096070540&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.
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.
Hi,
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.
/sreten.
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.
/sreten.
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
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
you might want to look at jung's Op Amp Applications book
section 6 has a dozen pages on riaa circuits
http://www.analog.com/library/analogDialogue/archives/39-05/op_amp_applications_handbook.html
section 6 has a dozen pages on riaa circuits
http://www.analog.com/library/analogDialogue/archives/39-05/op_amp_applications_handbook.html
Well here is the Doug Self Precision Preamp '96 as printed in Electronics World/Wireless World:
An externally hosted image should be here but it was not working when we last tested it.
I had an email conversation with Doug Self about this when I was building it. My circuit is as close as intended to the original design, give or take 200 ohms. Allow me to quote from my site:
The circuit performs very well in my opinion, and has been shown (by simulation) to be extremely accurate RIAA correction - naturally, I recommend it.
If anyone wants more info, I'll have access to the old emails and simulation results when I'm back at work on Monday
Mark
The circuit performs very well in my opinion, and has been shown (by simulation) to be extremely accurate RIAA correction - naturally, I recommend it.
If anyone wants more info, I'll have access to the old emails and simulation results when I'm back at work on Monday
Mark
EC8010 said:
Much more likely to be the vinyl's plasticizer. They tend to be fatty esters (sebacates, adipates, or phthalates) at relatively high concentrations. Perfect food.
http://www.chemicalfabricsandfilm.com/pdfs_researchSection/techSupport/plasticizer.pdf
This also speaks to the issue of why one might be cautious about having vinyl contact solvent-sensitive materials like polystyrene.
There may also be viscosity modifiers added to the formulation which also provide excellent nutrition for growing molds and fungi.
RIAA
Wilfred Harms wrote a very informative, and apparently authoritative, article on RIAA equalisation, which explained why most designs are wrong due to the interactions between the different stages needed to make up the required curve (IIRC).
Unfortunately I have not (yet!) recalled where I read this article, or I would post a reference to it.
I just did a Google search, and the reference showed "RIAA Network Limitations" which is bound to be the same article, and this apparently appears in the book "The LP is back" which I believe is an AudioXpress publication.
I don't have this book, but if any poster does, maybe he could glean some valuable information from this.
Wilfred Harms wrote a very informative, and apparently authoritative, article on RIAA equalisation, which explained why most designs are wrong due to the interactions between the different stages needed to make up the required curve (IIRC).
Unfortunately I have not (yet!) recalled where I read this article, or I would post a reference to it.
I just did a Google search, and the reference showed "RIAA Network Limitations" which is bound to be the same article, and this apparently appears in the book "The LP is back" which I believe is an AudioXpress publication.
I don't have this book, but if any poster does, maybe he could glean some valuable information from this.
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