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-   -   RIAA LCR Mythos (http://www.diyaudio.com/forums/tubes-valves/227736-riaa-lcr-mythos.html)

ClausD 13th January 2013 11:00 PM

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.

neskor 14th January 2013 07:13 AM

keep us posted ;)

oshifis 14th January 2013 10:38 AM

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.

PGDO 14th January 2013 11:03 AM

I'm interested, my next project will be a phono and I was thinking of an LCR with custom Tribute iron.

Kay Pirinha 14th January 2013 11:48 AM

I can't see any benefits compared to the well-proven RC designs. Is it just some more mythotology?

Best regards?

Vinylsavor 14th January 2013 12:12 PM

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.

Best regards

Thomas

ClausD 14th January 2013 09:34 PM

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.

revintage 14th January 2013 11:25 PM

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.

ClausD 15th January 2013 01:09 AM

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.

ClausD 15th January 2013 01:36 AM

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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