Choke for RIAA

Design and use of Chokes for PS, anode and filament use.
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Ken S
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Joined: Sun Sep 18, 2005 9:10 am

Choke for RIAA

Post by Ken S »

I've seen some circuits that use a choke and cap/resistor combo for RIAA ccompensation. What are the benefits to having the choke there? Indeed, whey even the need for one? I've seen similar circuits without the choke.
dave slagle
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Post by dave slagle »

I have personally never built a LCR riaa, but for the most part the people whose tastes i trust swear by them.

Like most magnetic devices they are quirky and a PITA to implament, but for some reason when done right they just seem to sound better.

If you want to play with a design, we could banter about it here and get into some (slightly) uncharted waters or there are many existing circuits that use LCR and LR EQ's, but most of them are a bit complex for my tastes.

dave
Ken S
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Joined: Sun Sep 18, 2005 9:10 am

Post by Ken S »

Oh crap! I was hoping that you would've and that you could easily whip up a set.

I'm willing to try something out, but I'm a total novice when it comes to RIAA compensation (How it works, what to listen for etc.), so the chances of me running around in circles is pretty high.
dave slagle wrote:I have personally never built a LCR riaa, but for the most part the people whose tastes i trust swear by them.

Like most magnetic devices they are quirky and a PITA to implament, but for some reason when done right they just seem to sound better.

If you want to play with a design, we could banter about it here and get into some (slightly) uncharted waters or there are many existing circuits that use LCR and LR EQ's, but most of them are a bit complex for my tastes.

dave
dave slagle
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Post by dave slagle »

i said i have never built a RIAA phonostage. Inductors for the EQ are a different story altogether. Did you see Steve Bench's LRIAA preamp? I have also done the inductors for a few other people so that part is not the issue.

If you are going to embark on this journey, i'd make sure you have a signal generator, Scope and an inverse Riaa. http://www.hagtech.com/iriaa.html

then all you need to worry about is flat response to see if your EQ curve works.

What cartridge are you looking at?

dave
Ken S
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Joined: Sun Sep 18, 2005 9:10 am

Post by Ken S »

Wow, sounds like this would take more technical know-how & time than I have. Ermm... Perhaps it'll be better if I went commercial.

Thanks anyway Dave. :D
Raj Gupta
Posts: 37
Joined: Fri Feb 11, 2005 2:19 am

Rule #1: NEVER go commercial

Post by Raj Gupta »

Don't freak out . . .

Maybe you should, hmm . . . .

On the one hand:
The only commercial inductor-based RIAA units are long ago out of production.

On the other hand:
They were top-shelf studio gear, used in radio stations etc., or low-production semi-DIY products.

Anyway, doing an inductor-based RIAA is not a quick little hack-it-together DIY project (trust me, I know a little about being a hack.) However, as Dave says, it is one step closer to audio nirvana for some. I've heard one and it definitely put the technology onto my list of things to try when I have the time & focus.

Anyway, to try and answer your original question:
The "big idea" behind an inductive EQ circuit is that it presents a constant load impedance to whatever is driving the EQ circuit. Other implementations of RIAA equalization present a HUGELY varying load impedance to the driving circuit. So this is an advantage for the inductor based EQ circuit.

Unfortunately, this constant impedance is usually quite low - 600 ohms - in the classical implementation (based on the TANGO inductor which is itself based on a Pultec product from about 50 years ago.)

This presents a problem - hard to drive well - along with its advantage - constant load impedance.

Some of the egghead audio DIYers have thought about scaling the impedance up to say, 6K, or 10K, to try and get the best of both worlds. This has proven hard to implement in practice - the theory of the inductors has been tricky to match in reality.

Other attempts have been made to build more robust drivers that will not be compromised unduly by the 600 ohm load. I have heard one of these (Thomas Mayer's implementation of 2000, since upgraded I think?) and it was well worth the effort on his part since I didn't have to do it, I just had to listen :)

Sounded like pure sweetness. Very true, effortless, and rich.

Hope I haven't added any layers of confusion and even maybe stripped a few away. It's not a simple question by any means but the answer is worth pursuing for sure.

-j
Ed Sawyer

LCR RIAAs still being made

Post by Ed Sawyer »

"On the one hand:
The only commercial inductor-based RIAA units are long ago out of production. "


Actually, not quite so. S&B makes a couple different LCR RIAA packages, one designed for 600ohm, one for 10kohm. I have a pair of the 10K version but haven't yet gotten around to using them yet.

Just an FYI.

-Ed
Raj Gupta
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Joined: Fri Feb 11, 2005 2:19 am

Post by Raj Gupta »

clarifying: I meant built-up components, not DIY parts, basically I was referring to the Pultec unit.

-j
JeffreyJ
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hey you wookies...

Post by JeffreyJ »

I build one... and I of course use some of Dave's iron in it..

so don't forget to at least throw my name out there.... when I am selling gear, dave gets more money for winding cool iron.. and then we all get to the trickle down benefits...

I'd love to get dave to wind the inductor for a 6k LCR RIAA.... and then throw some fine triodes around... maybe even something outlandish like 417a > 45 > LCR > EML20.. that would be fun...

Peace,
Me
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