Yet Another Phono Stage Suggestions Thread - Page 2 - 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 8th October 2008, 06:38 PM   #11
diyAudio Member
 
Join Date: Apr 2004
Location: Monroe Township, NJ
Guys,

I frankly have trouble mapping KAB's diagram onto a real world circuit, like this. AAMOF, R6 should be 255 KOhms, not 470 KOhms. The 20 MOhm value for R2, instead of 680 KOhms in a "stock" RCA circuit, forces that change. Clearly, interactions are present. Yet another issue is properly sizing the coupling cap. between the 1st gain block and the EQ network. Should the value remain 100 nF.?

Noise considerations make the use of a Caddock part in the 20 M position close to mandatory. If an assault on near SOTA performance is to be attempted, I can see using a Vishay bulk metal foil part for R1 in the KAB diagram.
__________________
Eli D.
  Reply With Quote
Old 8th October 2008, 07:07 PM   #12
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
Quote:
Originally posted by Eli Duttman
Guys,

I frankly have trouble mapping KAB's diagram onto a real world circuit, like this. AAMOF, R6 should be 255 KOhms, not 470 KOhms. The 20 MOhm value for R2, instead of 680 KOhms in a "stock" RCA circuit, forces that change. Clearly, interactions are present. Yet another issue is properly sizing the coupling cap. between the 1st gain block and the EQ network. Should the value remain 100 nF.?

Noise considerations make the use of a Caddock part in the 20 M position close to mandatory. If an assault on near SOTA performance is to be attempted, I can see using a Vishay bulk metal foil part for R1 in the KAB diagram.
That's understandable.. Not IMHO near the best implementation I've of this circuit that I have seen. I generally place the grid bias resistor for the following stage before R1, and choose network values that keep the overall effective bias resistance below that recommended for the type in question. Yes grid bias current does flow through R1 in this scenario, but so far I have not observed any noise related issues and placing the resistor ahead of the EQ network eliminates its effect on the network.

A 0.1uF coupling is a bit marginal once R1 drops below about 300K or so, the pole interacts with the lowest pole in the RIAA EQ and causes a premature roll-off in the low end and hence the accuracy of the LF EQ . Choose too small of a value and you can inadvertently get quite close to the IEC modified playback response and if you have a rumbly TT this might actually be useful. Otherwise make the -3dB corner at least a decade lower than the 50Hz RIAA turnover point.
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan
  Reply With Quote
Old 8th October 2008, 07:18 PM   #13
diyAudio Member
 
Wavebourn's Avatar
 
Join Date: Sep 2006
Location: Pleasant Hill, CA
Send a message via Skype™ to Wavebourn
Quote:
Originally posted by kevinkr

A 0.1uF coupling is a bit marginal once R1 drops below about 300K or so, the pole interacts with the lowest pole in the RIAA EQ and causes a premature roll-off in the low end and hence the accuracy of the LF EQ . Choose too small of a value and you can inadvertently get quite close to the IEC modified playback response and if you have a rumbly TT this might actually be useful. Otherwise make the -3dB corner at least a decade lower than the 50Hz RIAA turnover point.
Once my amp spit off a cone of a woofer with a piezoelectric crystal glued to it (feedback by acceleration) trying to follow output from a vinyl with a bit shifted center hole.
__________________
The Devil is not so terrible as his math model is!
  Reply With Quote
Old 8th October 2008, 07:29 PM   #14
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
Quote:
Originally posted by Wavebourn


Once my amp spit off a cone of a woofer with a piezoelectric crystal glued to it (feedback by acceleration) trying to follow output from a vinyl with a bit shifted center hole.
Literally wow...
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan
  Reply With Quote
Old 8th October 2008, 08:40 PM   #15
diyAudio Member
 
Wavebourn's Avatar
 
Join Date: Sep 2006
Location: Pleasant Hill, CA
Send a message via Skype™ to Wavebourn
Quote:
Originally posted by kevinkr


Literally wow...
That's why I implement HPF even in bass guitar amps.


__________________
The Devil is not so terrible as his math model is!
  Reply With Quote
Old 9th October 2008, 12:02 AM   #16
diyAudio Member
 
dsavitsk's Avatar
 
Join Date: Jan 2005
Location: Hartford
Here's a first go incorporating some of the ideas from the thread. I don't know what mosfet to use, or how to calculate the resistor under it, so that's the next thing to figure out. B+ probably will be ~120V or so, though as low as ~90V should be fine.

Thoughts?
Attached Images
File Type: jpg phono_stage.jpg (44.8 KB, 1102 views)
  Reply With Quote
Old 9th October 2008, 12:40 AM   #17
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
Use one with a lowish Cdg.

To figure the resistor, assume that the source voltage will be within a volt of two of the gate voltage. The gate voltage will be equal to the plate voltage of the 6T4. So the resistor will be that voltage divided by the desired operating current.
__________________
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 10th October 2008, 03:19 AM   #18
diyAudio Member
 
Join Date: Apr 2004
Location: Monroe Township, NJ
Quote:
Originally posted by dsavitsk
Here's a first go incorporating some of the ideas from the thread. I don't know what mosfet to use, or how to calculate the resistor under it, so that's the next thing to figure out. B+ probably will be ~120V or so, though as low as ~90V should be fine.

Thoughts?

Dude,

Assuming you get close to full mu gain from the CCS loads, you come up (IMO) a bit short in the net gain dept., using the 6T4 in the 2nd gain position. Expect somewhat less than 40 dB. net, in the real world.

The IRFBC20 I previously mentioned will be fine in the source follower role. A FET with a low and stable reverse transfer capacitance is required. Check the IRFBC20 data sheet out.
__________________
Eli D.
  Reply With Quote
Old 10th October 2008, 04:33 AM   #19
diyAudio Member
 
dsavitsk's Avatar
 
Join Date: Jan 2005
Location: Hartford
Quote:
Originally posted by Eli Duttman
Assuming you get close to full mu gain from the CCS loads, you come up (IMO) a bit short in the net gain dept., using the 6T4 in the 2nd gain position. Expect somewhat less than 40 dB. net, in the real world.
Input sensitivity on my power amps is about 1.5V, and I never listen anywhere near that level. So, I think I should be fine. But, the 6Gk5 and 6t4 have the same pin out, so I can just dial back the current in the second tube and drop in a 6GK5 if necessary.

Here's a slightly more complete schematic.
Attached Images
File Type: jpg phono_stage.jpg (53.4 KB, 968 views)
  Reply With Quote
Old 11th October 2008, 02:14 AM   #20
Sheldon is offline Sheldon  United States
diyAudio Member
 
Join Date: Dec 2003
Location: San Diego
This calculator is nice if you want to split stages: http://www.hagtech.com/equalization.html

Sheldon
  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
Phono stage for 12B4 amp [from previous thread] coffeedj Tubes / Valves 1 2nd April 2009 09:26 PM
DIY phono to replace roksan phono stage seroxatmad Analog Line Level 6 14th December 2008 05:46 PM
new phono stage or old preamp with phono? flohmann Analog Line Level 2 2nd October 2008 09:51 PM
Should I replace Scott 222C phono stage with Claret phono stage? Bing Yang Analogue Source 0 22nd August 2005 06:41 AM


New To Site? Need Help?

All times are GMT. The time now is 03:58 AM.


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