Looking for Old Elector Tube Preamplifier article - Page 2 - diyAudio
Go Back   Home > Forums > Commercial Sector > Vendor Forums > Elektor

Elektor News and offers from Elektor Magazine

Reply
 
Thread Tools Search this Thread
Old 13th May 2005, 08:42 AM   #11
diyAudio Member
 
Join Date: May 2005
Location: Hong Kong
Smile Power Supply for Elektor Tube SRPP Preamplifier

Hi Docali,

just thinking about the power supply board of the elektor SRPP tube preamp today, I may decide to go with two seperate rectifier board strips, one for the RIAA and one for the Line Stage.

I'm thinking of having two seperate strips for the power supply board with individual heater outputs. The HV rectifier I'm thinking of is the 6Z4 rectifier tube.

Could do SS, but would like to try and have a valve ps if possible.

What do you think?

Regards,

Steve

P.S. Lite Electronics, China already have a TP-3 (6Z4 tube) ps kit or bare board available. I have the parts so just need to buy the bare boards.
  Reply With Quote
Old 13th May 2005, 10:40 AM   #12
docali is offline docali  Germany
diyAudio Member
 
Join Date: Oct 2004
Hi stevesebastianb,

I reduced the cathode resistors of the second stage (ECC81) from 1k to 560 Ohms and the third stage (ECC82) from 1k5 to 1k2. All bypass capacitors are 220uF BlackGate (no parallel foil capacitor). You may try leave the bypass capacitors away as many people say this will yield a better sound but will slightly reduce the amplification factor.

RIAA correction I use is 56k -> 47n - 6k8, 15.6n (orig 18n). Grid resistor of next stage is 470k (orig 220k).

You should shift the heater voltage to about 80-90V above ground (max cathode to heater voltage). This can be done with a voltage devider as shown in the original publication.

A tube rectifier would be worse to test but I can not advise you if a channel separated power supply would yield better results. To decouple the channels you may use clever RC combinations.

Best regards,
docali
  Reply With Quote
Old 14th May 2005, 06:33 AM   #13
diyAudio Member
 
Join Date: May 2005
Location: Hong Kong
Smile Power Supply For SRPP Preamplifier

Hi Docali.

Have looked at alternatvies, Lite electronics also have a TP2 HV power supply board which utilizes a IRF830 for the HV section and this could be used for the HV rectification. The heater supply is the usual LM317 supply.

I could run two of these strips seperately for the HV power supply without much problem.

Regards,

Steve

  Reply With Quote
Old 15th May 2005, 08:03 PM   #14
bucurb is online now bucurb  Romania
diyAudio Member
 
Join Date: Sep 2004
Location: Bucharest
Default New passive network

docali,

It's interesting your modification. I would ask if you considered a bigger value for the ECC81 grid resistor (e.g 1M), please? Increasing this resistor could be a positive feature for this phono preamplifier, isn't?

Thank you.
  Reply With Quote
Old 16th May 2005, 07:53 AM   #15
diyAudio Member
 
Join Date: Dec 2000
Location: Germany
The grid resistor is part of the RIAA, caution!
  Reply With Quote
Old 16th May 2005, 08:24 AM   #16
bucurb is online now bucurb  Romania
diyAudio Member
 
Join Date: Sep 2004
Location: Bucharest
Default grid resistor ...

reinhard,

Grid resistor is part of RIAA correction, absolutely! You are right, but I'm focussing on an other issue. If this grid resistor has greater value (keeping 56K and recalculating only capacitors and one resistor of RIAA network) one could obtain a bigger S/N !

Because Ri + 56K with the grid resitor are making a voltage divisor on the first tube ouput voltage ...
Ri is the internal resistence of the first ECC83 SRPP coupled tube (it seems be about 1K, if I remember correctly).
RIAA correction is applied after dividing first tube output signal tension IMHO.
I wait your opinion, please.

Thank you!
  Reply With Quote
Old 16th May 2005, 12:26 PM   #17
diyAudio Member
 
Join Date: Dec 2000
Location: Germany
hello,

first of all the RIAA in that article is wrong,

the math for the calculated values does not include the internal resistance of the first stage.

With an 83 or AX7 the Ri is near 13KOhms.


With a 1M grid resistor and recalculated RIAA parts you get 2 dB more gain.

Reinhard
  Reply With Quote
Old 16th May 2005, 12:56 PM   #18
bucurb is online now bucurb  Romania
diyAudio Member
 
Join Date: Sep 2004
Location: Bucharest
Default however ...

Reinhard,

However measured correction (using an anti-RIAA network) of this preamplifier did show closed RIAA curve ... as author wrote in the article.
An explanation may be that ECC83 is working with very low anodic tension (about 150V/0.8mA) being in SRPP, please.

Thanks!
  Reply With Quote
Old 17th May 2005, 06:03 AM   #19
docali is offline docali  Germany
diyAudio Member
 
Join Date: Oct 2004
Hi reinhard,

I would be with you that the RIAA in the original article is is not optimal. The theoretical values ca be obtained from:
http://www.kabusa.com/riaa.htm
R1=47k, R2=6k83, C1=46n5, C2=15n9
The grid resistor of the next stage is part of the RIAA effectively parallel to R1 and not to forget the output impedance of the first stage which is effectively in series with R1! Therefore, R1 has a value of about 56k. Another effect is that the Miller capacitance of the second stage is effectively parallel to C2.

My RIAA values were optimized with Spice using models developed by Norman Koren, thus giving the lowest error I could find with possible combination of standard values of resistors and capacitors.
  Reply With Quote
Old 17th May 2005, 06:51 AM   #20
diyAudio Member
 
Join Date: Dec 2000
Location: Germany
hello docal,

your values are correct, my B2-Spice tells me the same.

R 1 without first stage is 59,8 k minus the internal 12,8k I get
47K.

Bucurb, it is not that easy to measure here at the 50 Hz pole.


The goal is to hear music, have seen much RIAA´s which are not correct but sounding good.

Reinhard
  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 microphonics (article) tomchr Tubes / Valves 5 23rd August 2009 05:03 PM
"Designing tube preamplifier" article Zoran Tubes / Valves 16 9th May 2009 11:55 PM
Tube article in EDN FrankDIY Tubes / Valves 5 15th April 2003 09:58 PM
Tube article HarryHaller Tubes / Valves 13 5th April 2002 04:41 PM


New To Site? Need Help?

All times are GMT. The time now is 02:05 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