LCR RIAA AND TUBES. - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 18th February 2003, 10:56 AM   #1
diyAudio Senior Member
 
fdegrove's Avatar
 
Join Date: Aug 2002
Location: Belgium
Default LCR RIAA AND TUBES.

Hi,

THOMAS MAYER

For a long time I've been tinkering with this type of RIAA correction for a tube preamp.

Since the LCR modules are again available I am looking for some input from others on how to best implement this.
More precisely, how to do this without using any stepdown xformers if possible.

Cheers,
__________________
Frank
  Reply With Quote
Old 18th February 2003, 11:17 AM   #2
GaryB is offline GaryB  United States
diyAudio Member
 
Join Date: Sep 2002
Location: Silicon Valley
Default LCR RIAA web links

Frank,
Any reason you want to stay away from transformers? They're not that expensive and can sound pretty good. I think a tube loaded with a lundahl 1660 could drive the LCR network pretty well.

Here are a few links to get people started:
http://digilander.libero.it/paeng/inductive_riaa.htm
http://www.rintelen.ch/pdf/Preamp.pdf
http://www.vt52.com/diy/myprojects/a...pre/exopre.htm

There was also a japanese web page where the gentleman used a 6922 SRPP to drive the LCR without transformer, but I can't find the link right now.

---Gary
  Reply With Quote
Old 18th February 2003, 11:39 AM   #3
diyAudio Senior Member
 
fdegrove's Avatar
 
Join Date: Aug 2002
Location: Belgium
Default RE:LCR RIAA AND TUBES.

Hi,

Quote:
Any reason you want to stay away from transformers?
Mainly because I don't want to take the "easy" way out...
Nothing is ever perfect of course but I feel I have a better chance of maintaining large bandwidth by using tubes.

There is also the possibility of a fully balanced preamp, you may of course say that this is easier to achieve by using xformers.
You're absolutely correct but I would love to try that with tubes as well.
If it turns out to be a delusion, than so be it.

Cheers,
__________________
Frank
  Reply With Quote
Old 18th February 2003, 12:18 PM   #4
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Default Re: LCR RIAA AND TUBES.

Hi,

Quote:
Since the LCR modules are again available I am looking for some input from others on how to best implement this.
More precisely, how to do this without using any stepdown xformers if possible.
I have been really struggeling on this myself. I am not per se against using transformers, but with most "normal" valves (eg. 6S45-PE) you end up wedging the RIAA between two Transformers, the stepdown one probably having to be used in parallel feed as well.

This means two transformers add their rolloff, which even with something like a pair of Stevens & Billington TX-103 per channel for matching the RIAA (and yes, I did consider that and even tried something similar clipleaded with an RC RIAA just to ***** the impact of the Transformers) means you have over 2db more loss at 10Hz (and less consequentially but audible) 100KHz than without the transformers.

As few transformers offer relaibly such wide bandwidth at the required levels (such transformers also cost less of course) things may be even worse. I like transformers but not just for their own sake.

One option that frees you totally from the question how to drive a low impedance LCR RIAA EQ is to make a high impedance one. Yet given the problems of making the relative low value inductors for the 600 Ohm Impedance RIAA I suspect a 10k LCR RIAA may prove very difficult to make reliably.

Secondly, you could of course simply use any old Valve stage with suitable gain, take a small value coupling cap and use a solid state unity gain buffer to drive the pubishing (for valves and even most Op-Amp's) 600R Load of the RIAA, but of course, that is "cheating" (I'd say inspired and competent engineering, but I know it's cheating in the end.

I ended up persuing a very different Tack. Using suitably high Gm Pentodes (E810F - 50mA/V) you get plenty of gain even into a 600 Ohm load and even better, as the Output impedance of the Pentode Valve stage is very high you can at least partially compensate the use of a much smaller value than conventionally required coupling capacitor. I have tried as small values as 2.2uF in my circuit.

The circuit I'm talking of is of course this one:

Phonostage Circuit

Click the image to open in full size.

Total gain of this Phonostage with a S&B TX-103 wired for 26db stepup is over 66db, output impedance is under 2k, just fine for a TVC with 6db stepup, which in total gives 72db gain.

With a typhical 0.25mV MC pickup this gives around 1V RMS out with around 14db headroom on top of this (the Max. Headroom on LP is around 14db above the reference 5cm/S at 300Hz), or up to 5V RMS on the highest peaks. Just right to feed an Ultracurve Digital EQ or low gain DHT Amplifiers.... ;-)

Assembled the whole thing with S&B TX-103 MC Stepups and Prototypes of the S&B RIAA-600 EQ Modules looks like this:

Phonostage piccie

Click the image to open in full size.

Using the same basic principle of driving the RIAA from a very high source impedance I could think of using three or four paralleled 2SK170 J-Fets in Cascode with a valve (say a 6N30?) to give 60 - 80/V into the 600R RIAA. This will give a gain of the first stage of around 36 or 48 aka 31 and 33db respectively. The output could then be the other halve of the 6N30 again, very low impedance to drive a TCV or the like well. Overall gain of such a circuit without MC Stepup could be around 33 to 35db due to the low gain of the second valve.

Of course, if you liked you could use another 3 - 4 2SK170 Cascode in the second stage with 600 Ohm anode load for low output impedance. Then you have a total gain of 42 - 46db without MC Stepup and up to 72db with a TX103....

Maybe all this gives you some ideas?

Sayonara
  Reply With Quote
Old 18th February 2003, 03:57 PM   #5
diyAudio Senior Member
 
fdegrove's Avatar
 
Join Date: Aug 2002
Location: Belgium
Default MISSING LINK.

Hi,

Gary B.,

Would this be link you're missing?

SHISHIDO

All,

EC8010 raised an interesting question regarding the input impedance of the RIAA network.

From the previous designs I've seen it was always stated as being 600 Ohm.

Is this information correct ? If so, shouldn't it than be drive form an even lower source impedance?

Cheers,
__________________
Frank
  Reply With Quote
Old 18th February 2003, 04:37 PM   #6
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Default Re: MISSING LINK.

Hi,

Quote:


Gary B.,

Would this be link you're missing?

Actually, there are plenty more. My HDD holds over a dozend RLC or RL equalised Phonostages....

Quote:

EC8010 raised an interesting question regarding the input impedance of the RIAA network.

From the previous designs I've seen it was always stated as being 600 Ohm.

Is this information correct ? If so, shouldn't it than be drive form an even lower source impedance?
To save me excessive typing I shall quote here from the Application note posted here:

S&B EQ-600 RIAA Module Application Notes

"The EQ-600 is designed to operate in a 600 Ohm matched impedance system, as provided in many broadcast and similar applications. Either the load provided to the RIAA Module must be 600 Ohm in which case the drive impedance is immaterial and the RIAA Module presents the driving circuit with a frequency independent 600 Ohm Load (+/-5% or closer tolerance) OR the impedance of the source (drive impedance) must be very accurately 600 Ohm in which case the load impedance is immaterial."

"The specifics of the amplification stages are really up to the designer using the RIAA Module, the degree of freedom in choice of topology, active device and so on is huge and even a most scant coverage would require a long article. The RIAA circuit will in any case of application cause around 20db attenuation at 1KHz. Possibilities include Operational Amplifiers set to give 30db gain, Mu-Follower stages using a 6SL7 or similar valves for the gain parts and suitable follower devices and many other Valve, hybrid, discrete solid state or monolithic integrated solutions. As a rule the output of the first amplification stage should either be of a matched impedance of 600 Ohm or of low source impedance and able to drive a 600 Ohm load to significant level."

"Typically, to maximise overload margins and such one would have for a typical "moving magnet" type phono stage Amplification stages with around equal gain of around 30db each and suitable output impedance's. In such a case a phono stage using the RIAA Module would have a total gain of around 40db allowing an IEC sensitivity of 5mV for Phono."

"If a TX103 is added ahead of the phono stage to match MC Cartridges the IEC sensitivity becomes 1mV, 0.5mV and 0.25mV respectively for the 1:5, 1:10 and 1:20 step-up ratio. If a TX-102 based passive controller is used following the phono stage and if the output stage gainblock offers a compatible output impedance the TX-102 can be connected in 6db "passive gain" mode, giving IEC sensitivities of 0.5mV, 0.25mV and 0.12mV for the complete phono stage."

"Other gain schemes are possible but will result in reduced overload margins."

I hope this clarifies.

Sayonara

PS, driving a 600 Ohm load from an infinite source impedance is no issue, the load simply is driven in pure current mode. Equally a Pentode has no problems at all to lineary drive a dead short at all (the same cannot be said of triodes though).
  Reply With Quote
Old 18th February 2003, 05:03 PM   #7
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Default Re: Re: MISSING LINK.

Hi,

Quote:


Actually, there are plenty more. My HDD holds over a dozend RLC or RL equalised Phonostages....

On second thought, I always believed the best way to enrich oneself is to freely give away what one has, so I have uploaded/am uploading a library of LR/LCR equalised Phonostages for the general entertainment of the distingue audience....

All schematics are deposited here:

LR/LRC RIAA EQ Schematics

Note that some schematics (especially those from the Sakuma inspired school) do not offer an overly accurate RIAA Response. How relevant this is everyone must decide for themselves.

Sayonara
  Reply With Quote
Old 18th February 2003, 06:43 PM   #8
diyAudio Member
 
Brett's Avatar
 
Join Date: Jan 2002
Hi Thorsten,

Cheers for all that.
Do you have an idea of the price for the S&B units? None of the distributors (like Brian) have them listed yet.
  Reply With Quote
Old 18th February 2003, 07:21 PM   #9
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
Frank, would you entertain a naive question from me? Since it's extremely easy to design a tube RIAA stage with arbitrarily low deviations from the standard, low noise and distortion, low source Z, and stable into the loads typical of cables and preamps (or 600 ohm lines, if it's for studio rather than home use), what's the point of using LCR circuits and transformers? What design advantages does one get for the expense and complication?
__________________
You might be screaming "No, no, no" and all they hear is "Who wants cake?" Let me tell you something: They all do. They all want cake.- Wilford Brimley
  Reply With Quote
Old 18th February 2003, 08:05 PM   #10
diyAudio Senior Member
 
fdegrove's Avatar
 
Join Date: Aug 2002
Location: Belgium
Default LCR.

Hi SY,

Quote:
Frank, would you entertain a naive question from me?
Sure.

From what I've read and tried to understand of it, this type of correction has the advantage of being impervious to ageing of the tubes.(Changes in operating parameters)

Another advantage is that you work into low impedances forcing current drive of the next stage.

Transformers have the added advantage of providing galvanic ( is that the correct Enlgish word?) isolation between groundplanes, so there is no interaction between them.
Personnally I do not use any, other people swear by them.

This is quite likely not the complete answer, so those who have actually built this kind of circuit may be better placed to answer any further questions.

Cheers,
__________________
Frank
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Tube Noob! need help with tubes lots of tubes therapy_fan Tubes / Valves 15 29th January 2009 09:01 PM
WTT: Various tubes for 6CA4/EZ81 rectifier tubes GordonW Swap Meet 4 27th August 2008 12:37 AM
CV428 tubes (Loktal 807) tubes FS mobyd Swap Meet 3 2nd January 2008 11:26 AM
Passive RIAA with tubes jackinnj Tubes / Valves 5 9th December 2005 09:07 PM
Active RIAA Eq for tubes- Brian Clark's article jackinnj Tubes / Valves 0 2nd November 2005 10:18 PM


New To Site? Need Help?

All times are GMT. The time now is 05:44 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2