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Best inductors for RIAA?

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Posted on October 27, 2001 at 21:10:26
thinking of building RIAA eq with inductors but wonder what type of inductors would be best. Using the values of 1.8h and 45mh I could get air core speaker inductors, even foil inductors, but am unsure if this is the best Route. Because it is in a phono circuit I may have to pot them to avoid picking up stray elecromagnetic interference.
Because of the low current involved, 15 ga. speaker inductors would really be overkill. Any ideas on the best inductors for the job?

 

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Re: Best inductors for RIAA?, posted on October 28, 2001 at 08:10:16
DrM
Air core inductors, such as the ones you mention will work best I think. One question: what are the equalization equations for an inductive RIAA? I have a copy of the Lipschitz paper around here somewhere, all I can remember is a CR model.

Dan

 

Re: Best inductors for RIAA?, posted on October 28, 2001 at 12:39:46
Check out the RIAA curve link at : http://www.infomaniak.ch/~bonavolt/audioel.htm

This equation varies based on what year the RIAA put it out. I would really like to find the RIAA curve used by Columbia in the 50's and 60's because their recordings are always the best to my ears and the have the artists I like best.

I think I saw on another post that you have a 27 based preamp. Have any advice on operating this tube and any ideas where to get the 5pin sockets?

Thanks,
Charles

 

Re: Best inductors for RIAA?, posted on October 28, 2001 at 14:54:51
dave slagle


 
i think you will be best avoiding the air-cored inductors for the LCR riaa... the linearity of them is really desirable, but even a value of 45mh would be pretty big, and 1.8hy?? while possible, i think you may be looking at a 10 pound spool of 15 ga wire for starters :-)

like all riaa eq's its best to cut and try, and in this case its a wind and listen situation... i suspect if you really want to get into it, and follow through, you will have the best luck winding your own, or be prepared to pay for lots of different 1.8hy inductors... you cant simply call a winder and spec it and expect the best results... inductance values are very soft numbers... and the riaa requirements may or may not work well when you plug in a soft number...

the two values you state are quite similar to the tango eq-600 numbers... which they publish... if it were as easy as putting all those parts into a can... they wouldn't tell you whats in there... i have seen numerous people try to duplicate this circuit, and one of two things happens... they try it once, and it fails and they proclaim LCR EQ sucks, or they try it once, again it fails, but the see promise and spend another year on it and end up with something brilliant.

sadly very few people fall into the second category...

dave

 

Re: Best inductors for RIAA?, posted on October 28, 2001 at 15:00:50
dave slagle


 
This equation varies based on what year the RIAA put it out. I would really like to find the RIAA curve used by Columbia in the 50's and 60's because their recordings are always the best to my ears and the have the artists I like best.


not to be a smartass here, but if these recordings always sound so good, could it be because they are being played back through an improper (post 60's) filter??? and if you recreated their proper filter, suddenly all the 50-60's stuff would then suck, but everything else would sound like those awesome 50-60's recordings????

its at least something to think about... maybe we should look more into the differences of the filter through the years and see if there is a correalation, and see if we can learn something.

dave

 

Re: Best inductors for RIAA?, posted on October 28, 2001 at 16:14:38
Thorsten
Manufacturer

Posts: 4209
Location: Somewhere nice on planet dirt
Joined: September 25, 1999
Hi,

First, the Pultec RIAA Network (yup - Pulse Technology - an ex Bell/WE Subsidary orginally pioneered this network - don'tchahateit when you get another - invented by WE item) has a few peculiarities. First, it requires termination with 600 Ohm and 600 Ohm or less drive impedance. This effectively limits the use to transformer coupling and suitable low anode impedance, high gain Valves, which IMHO limits the usefullness. I should add that the late and great Nobu Shishido used Black Gate Caps for capacitively coupling the Tango RIAA Unit to a 6DJ8/6922 Mu-Stage.

I have thought about this myself long and hard and I am now in the process to develop with Stevens & Billington a pure RL RIAA (no f...ing capacitors here) using Inductors made exactly to this purpose, individually tuned, with defined and controlled leakage capacitances aimed at termiinating the Network in common high Gm, medium Mu Valves, build on big airgapped mumetal cores and shielded (shielding is needed for avoidance of hum pickup). The Values will be 31.8H and 7.5H....

Once fully developed these Inductors plus the whole schematic for the RL EQ after adding three resistors will be generally avaiable. The Network terminates into around 100k and requires a maximum source Impedance of around 6k rather than 600 Ohm.

Ciao T

 

Re: Best inductors for RIAA?, posted on October 28, 2001 at 18:42:55
DrM
I've done a lot of modeling of my RIAA design in spice, and have read and pondered the original Lipschitz paper. The thing I don't understand, is how to go from the RC model Lipschitz uses (for passive equalization) to an RL model. I couldn't find anything on that site explaining that.

> I think I saw on another post that you
> have a 27 based preamp. Have any advice
> on operating this tube and any ideas
> where to get the 5pin sockets?

The sockets are everywhere. China makes a nice Johnson replacement, and Angela (www.angela.com) has the cheapest prices I've found. I have a big collection of 27 tubes, and prefer the mesh plates, but only loaded by a C4S (see Doc B's site). I think I run 4 mA through them.

The globes are microphonic and prone to hum. I use massive filtering on the filaments, with a high current LM317 (IIRC) feeding the filaments.

Dan

 

Hey Dave you nutcase, posted on October 28, 2001 at 18:49:35
DrM
dya want 20 preamps, each for the right vintage recording!??! :) I've got an old, what is it, MC30 McIntosh preamp. It has 4 or 5 equalization schemes built in, for those pre-RIAA recordings. I'll check and see if it has a Columbia setting :)

Dan

 

Re: Hey Dave you nutcase, posted on October 28, 2001 at 19:45:00
dave slalge


 
its just this kind of history that can actually teach us something... multiple riaa schemes in a single phono pre??? never heard of that one... what i find interesting is that if indeed the cutterhead riaa of the most cherished recordings may be substantially different from the playback riaa of the folks who made them so cherished... talk about irony....

dave

 

There's only one RIAA equalization for phono, posted on October 28, 2001 at 20:20:17
"multiple riaa schemes in a single phono pre??? never heard of that one... "

RIAA standardized the equalization for phono. Before that every major recording company did its own equalization and sold the phonographs with their equalization scheme built in. All of these were mono records, mostly 78's. Later some preamps built "universal equalization", a switch to the one you needed. kind of like "universal digital players" today. RIAA stepped in and created the standard we live with today. There were no "multiple RIAA schemes." Early records will often be labelled with the RIAA logo on it to tell you it's equalization was for the new standard.

Kurt

 

Re: Best inductors for RIAA?, posted on October 29, 2001 at 02:42:28
Hi Dave, All,

I guess the reason why people failed to duplicate the Tango
RIAA is because of the DC resistances of the coils. I spent
quite some time on LCR RIAAs and carefully analyzed Tango's
design. They did a fine job of compensating the DCRs of
the coils. That's why they put in those parallel resistors
to the caps. And that's also the reason why they use 1.8Hy
instead of 1.9Hy which the calculation gives assuming 0 DCR.

Just dubbing the tango circuit with soem coils with different
DCr will of course yield a different result.

I tried to put the formula for a LCR EQ with DC resistances in
an Excel sheet. Anybody interested in this can email me. But
be warned, it requires at least some basic knowledge of the
subject, it's not foolproof and will give rubbish results if
the inputs are not ok.

To my ears LCR EQ is sonically the best. I havent' heard
a LR EQ yet. I'll probably give that a try some time.

Ciao ... Thomas

 

see SP #16, posted on October 29, 2001 at 06:28:26
Jim Dowdy
Manufacturer

Posts: 1518
Location: Atlanta, GA
Joined: July 22, 2000
Although I haven't tried it; Diego Nardi gifted us with a pretty cool mono phono stage with multiple eq settings.

 

well said, Dave!, posted on October 29, 2001 at 06:35:42
Jim Dowdy
Manufacturer

Posts: 1518
Location: Atlanta, GA
Joined: July 22, 2000
The Tango LCR RIAA box is indeed a frustratingly difficult thing to re-create without MUCH suffering and heartache.

After considerable anguish and penance, I'm going to an AV20 - Magnequest DS-050/600 - Tango LCR RIAA and try to have fun with phono again.

 

Perhaps?, posted on October 29, 2001 at 07:14:57
markmac


 
I think that you might be referring to the Mac C-8. It has multiple frequency eq switches on the front panel to select different settings as required by different record manufacturers back in the pre-stereo days. As it had no power supply of its own, the C-8 was frequently partnered with the MC-30 amp, from which power was drawn via an octal-socketed umbilical.
I would suspect that Roger Russell's McIntosh history website would have the definitive story, but I don't have the URL to pass along right now.
Mark

 

Re: There's only one RIAA equalization for phono, posted on October 29, 2001 at 07:41:16
J Epstein
Reviewer

Posts: 1041
Joined: April 6, 2000
When the LP was developed, there were still multiple standards but they were soon consolidated into RIAA and a European standard which was the same as RIAA but with a subsonic filter. Short-lived LP EQ curves included the Decca standard, RIAA, and I think maybe two or three more. There were different, non-standard playback EQ settings in the 78 era. More info can be found in one of the reprints from Wireless World published by Old Colony Sound Lab, which contains a full-function preamp designed during the transition era with built-in switchable EQ settings. The reprint is:

ITEM #BKAA27 $16.95 Mullard Tube Circuits For Audio Amplifiers

There is also more info in Morgan Jones, Valve Amplifiers.

I have a friend who transfers 78s for reissue projects and he has several variables to consider: playback speed (78s were not all cut at the nominal 78 RPM); stylus shape; stylus material; playback EQ. He has a table of EQ settings and speeds that MOSTLY work for each label but there are always exceptions.

In contrast, us LP-heads have it easy!

-j

 

Re: Perhaps?, posted on October 29, 2001 at 07:42:20
DrM
Actually it has its own power supply. I think it might be a C10 or C20, C10 probably. I've got it sitting in a box at home - too much other audio stuff to mess with at the moment :)

Dan

 

Re: There's only one RIAA equalization for phono, posted on October 29, 2001 at 09:26:48
dave slagle
Manufacturer

Posts: 5429
Location: NYC
Joined: April 27, 2001
i dunno??? i was going by the post above... is this accurate???

http://www.AudioAsylum.com/forums/tubediy/messages/465.html

dave

 

Re: Hey Dave you nutcase, posted on October 29, 2001 at 10:20:44
Tom Dawson
Audiophile

Posts: 1882
Joined: May 14, 2000
Columbia did once have their own eq curve which, as I recall, boosted the highs and lows relative to the mids compared to RIAA.

 

Re: Hey Dave you nutcase, posted on October 29, 2001 at 13:51:41
Lew
Audiophile

Posts: 10911
Location: Bethesda, Maryland
Joined: December 11, 2000
My folks had a Harmon-Kardon mono tube receiver that had a built-in phono section with at least three different equalization curves, switchable from the front panel. If memory serves, these equalization choices were RIAA, Columbia, and LP. (I am the least certain of the last one; there may have been another or 4th curve, beginning with the letter "E".) I own the "Ella and Louis" recordings on Verve, original cuts, English pressings. The tonal balance is all wrong, and I've wondered whether its because they were not made to the RIAA standard. There is at least one current production pre-amp, made in Switzerland but I cannot remember the company, that offers multiple equalization curves in phono, for about $20,000.

 

Can't wait to the schematic, sounds great (nt), posted on October 29, 2001 at 14:22:08

 

Re: Best inductors for RIAA?, posted on October 29, 2001 at 17:42:11
Have you built your own LCR RIAA preamp? If so, do you have a schematic with parts list? I would like to build one but the concerns about the dc resistance of the chokes and impedences as well as static resistances of interstage transformers leading to the stage has kept me away from trying. Thanks for any help.

Charles

 

Re: Best inductors for RIAA?, posted on October 30, 2001 at 00:49:00
Hi Charles,

So far I have built 5 Phonostages with LCR RIAA. I have no
schematic. They are so simple that's not necessary to draw
them. All of them are transformercoupled. Three use the
Tango RIAA and are based around the Telefunken EC8020.
Unfortunately this tube is very difficult to get. But there
are alternatives. One of the other two is an all DHT preamp
with 801As. For this one I built a 'discrete' LCR RIAA.
The last one was an experimental phonostage with 6HV5.
For this I built a RIAA with UTC variable inductors. This
one led me to the analysis of the Tango RIAA. Obviously
the DC resistance of the UTC coils is very high which for
example leads to a early bass roll off.

I will try my calculation scheme with those UTC coils to
see if it's valid.
Typically I drive the LCR with a step down transformer,
so that it's fed with a source impedance of 200 Ohms or
less. The DC resistance of the driving transformer is not
critical. It will only generate some loss, but it's not
frequency dependant.

To get enough gain I always place a 1:4 step up transformer
after the RIAA.

There is a schematic of a LCR phonostage in the latest
VALVE magazine. The article is from a friend of mine.
His Phonostage is very similar to my EC8020 based
one.

Regards ... Thomas

 

Kirchhoffs Laws are not that hard..., posted on October 30, 2001 at 05:49:52
lk4200
Audiophile

Posts: 85
Joined: February 28, 2001
Come on guys, dig out some theory and do your homeworks ;))

t

 

"E"= EMI, probably [nt], posted on October 30, 2001 at 11:45:27
J Epstein
Reviewer

Posts: 1041
Joined: April 6, 2000
/

 

Re: Best inductors for RIAA?, posted on October 30, 2001 at 12:19:03
Thanks for your response. I was considering building the RIAA in the latest "Valve" but was unsure whether the inductors used had a specific static resistance that was critical to the design. You note that in your own "discrete" design the high resistance of the inductors caused bass rolloff. Is there any guideline to use to determine what the total resistance of the circuit should be from input to output, or any simple way to compute the inductance as compared the resistance of the inductors and how resistor and capacitor values are dependant on the inductor values? Also, how do you find the TANGO Eq-600 works in your circuits? I tried to buy a pair a year or so ago and was put on temporary and then permanent hold when Hirata closed the company. Don't know where to look for them now so just trying to do it on my own.

Thanks again,
Charles

 

Re: Best inductors for RIAA?, posted on October 30, 2001 at 12:38:29
Hi Charles,

as mentioned in my previous post, I put the formulas
for the LCR RIAA into an excel sheet. You enter the
corner frequencies you want, the inductance and resistance
of the coils and the sheet calculates all the resistor
and capacitor values.

The inductance values need to be close to the nominal
values, otherwise the sheet will produce rubbish. This
technique to compensate the DCRs of the coil is an approximation.
I haven't tried for real high DCR coils yet.

With this sheet you can also calculate the LCR values
for other EQs than RIAA. You can also put in the 'secret'
4th timeconstant 3.18us a la Allen Wright.

The sheet generates values for two different kinds
of LCR network. One is the Tango-Version. The
other one has a slightly different resistor arrangement.

Email me if you want the sheet and I will send it. I'll
help you to come up with the right values.

Although I like the Tango units very much (I use them in
my main phonostage) I think they have been over-mystified.
There is nothing magic in them it's just solid engineering.

Ciao ... Thomas

 

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