Will the correct Doug Self Wireless World RIAA please stand up? - Page 2 - diyAudio
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Old 3rd February 2006, 11:16 AM   #11
EC8010 is offline EC8010  United Kingdom
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That's unfortunate. Self spent all that time getting the HF bit right and allowing for the problem of the non-inverting amplifier just to get the LF wrong instead!
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Old 3rd February 2006, 12:49 PM   #12
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I wonder if it was intentional, a small lift above 1 KHz but without excess HF peaking can sound good. Plenty of well regarded commercial phono stages are not flat.
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Old 3rd February 2006, 06:46 PM   #13
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Hi,
I converted the Williamson formulae into a spreadsheet at the time. BUT it was before Lotus 123. First I need to find it, if at all possible, then try to get it to run or extract the formulae. Don't wait around!
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Old 4th February 2006, 11:02 AM   #14
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Well here is the Doug Self Precision Preamp '96 as printed in Electronics World/Wireless World:

Click the image to open in full size.
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Old 4th February 2006, 11:43 AM   #15
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Doug liked his rumble filters.

Living in a tropical climate I have a lot of trouble with fungus on vinyl, but at least my lps don't seem to warp anymore
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Old 4th February 2006, 12:03 PM   #16
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Quote:
Originally posted by davidsrsb
Living in a tropical climate I have a lot of trouble with fungus on vinyl...
If you have fungus, it must be living off something. Do you suppose it might be the mould release agent? (Pun unintentional.) If so, perhaps running the records through a record cleaning machine might help.
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Old 4th February 2006, 12:48 PM   #17
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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:

Quote:
Also, when comparing my schematic to the published version, you'll note some resistor value changes in the RIAA feedback network - R22 and R23 are [or should be] 52K and 1K5 respectively. However, 52K is not an E24 preferred value - I queried this with Douglas Self, and he was surprised that no-one, including himself, had noticed this before. As the correct target value for this series combination is 53.5K, I got close to it with 51K and 2K7.
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
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Old 4th February 2006, 01:01 PM   #18
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Quote:
Originally posted by EC8010


If you have fungus, it must be living off something. Do you suppose it might be the mould release agent? (Pun unintentional.) If so, perhaps running the records through a record cleaning machine might help.
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.co...lasticizer.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.
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Old 4th February 2006, 01:02 PM   #19
Bobken is offline Bobken  United Kingdom
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Default 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.
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Old 4th February 2006, 02:32 PM   #20
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Quote:
Originally posted by mhennessy
Also, when comparing my schematic to the published version, you'll note some resistor value changes in the RIAA feedback network - R22 and R23 are [or should be] 52K and 1K5 respectively. However, 52K is not an E24 preferred value - I queried this with Douglas Self, and he was surprised that no-one, including himself, had noticed this before. As the correct target value for this series combination is 53.5K, I got close to it with 51K and 2K7.
Well, I am still confused, since you refer to a 52K resistor, but in richie00boy's schematic we see a 68K resistor combined with the 1.5K.
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