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Old 13th January 2013, 10:00 PM   #1
ClausD is offline ClausD  United States
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Default RIAA LCR Mythos

Is there any interest in the community to design a RIAA LCR network yourself with the freedom of choosing your favorite impedances, the complete theoretical background, the design calculation and the simulation?
I’m working on a white paper and will publish this article in a couple of weeks in the forum.
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Old 14th January 2013, 06:13 AM   #2
neskor is offline neskor  Serbia
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keep us posted
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Old 14th January 2013, 09:38 AM   #3
oshifis is offline oshifis  Hungary
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What would be the advantage over the RC EQ? Coils have lower Q due to DC resistance, they can pick up stray magnetic field (hum), are difficult to manufacture to tight tolerance, big and nasty... Non-air core inductors have some more problems, like hysteresis, nonlinearity, etc. I assume they are more sensitive to vibration (acoustic feedback) than capacitors.
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Old 14th January 2013, 10:03 AM   #4
PGDO is offline PGDO  Netherlands
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I'm interested, my next project will be a phono and I was thinking of an LCR with custom Tribute iron.
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Old 14th January 2013, 10:48 AM   #5
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I can't see any benefits compared to the well-proven RC designs. Is it just some more mythotology?

Best regards?
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Old 14th January 2013, 11:12 AM   #6
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Hi!

There is nothing mystical about LCR type filters. The greatest advantage is the constant input impedance these filters have, independent from frequency. When the driving tube ages it changes it's rp. This has no effect on the RIAA accuracy with LCR filters.

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Old 14th January 2013, 08:34 PM   #7
ClausD is offline ClausD  United States
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I like your comment on my question, and that is one of the mythos. What you posted is all correct and everybody knows it and it is published and copied several thousand times in the internet.
But what about if you want design your own LCR network, e.g. with an impedance of 2.2kOhm. Do you know how to calculate all the components? What is about the answer to add the 3.18us high frequency cut-off time constant. Do you have a reference for the design?
There are so many questions in the internet not answered. My intention is to clarify some of them and to help DIY people to design their own LCR network.
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Old 14th January 2013, 10:25 PM   #8
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Most of what one needs to know about LCRs is covered in the phono section of Dave Slagles :: Index. The subject is covered from almost every angle. May take a while go through it though.

In addition to the virtues Thomas mentiones I´d like to add the abscense off large series resistances found in all other passive networks.

I look forward to see your paper.

Last edited by revintage; 14th January 2013 at 10:33 PM.
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Old 15th January 2013, 12:09 AM   #9
ClausD is offline ClausD  United States
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I really thank you very much for the link. I think Dave has a lot of experience in designing tube amplifiers and gives a lot of contribution to the DIY community (also for me). Mostly, he's working with LTSpice which also is my favorite simulation solution (free of charge and unlimited).
I answer you spontaneously without reviewing all of Dave's details but it seems that his explanations relies on the “Tango solution” and does not consider the general generic design of an RIAA LCR filter.
My approach will be independent of any solution, where of course I also will discuss the accuracy of the “Tango Solution” but with the opportunity to choose the individual filter components based on the required (or chosen) impedance and the inductance limits without any relation to the “Tang Solution”.
Additionally, I try to explain the theoretical background, the evaluation of the formulas for calculation the component values, an Excel sheet for calculation, a LTSpice file for verification of my approach and a generic LRC RIAA tube preamplifier in LTSpice.
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Old 15th January 2013, 12:36 AM   #10
ClausD is offline ClausD  United States
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Hi oshifis
You are completely right regarding the LCR challenge design. My interest is not to judge the advantages or disadvantages of a LCR design. On the other hand there is a large community for exactly this solution and I want to contribute.
I'm working a couple of time on a symmetrical DC-coupled tube phone preamplifier where I really have no solution for an LCR filter (I use a traditional RC filter) but I saw so many many internet links, discussions, statements, wrong solutions and... unverified solutions. My decision was to analyze the theoretical background and write this paper give my contribution to the community.
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