6au6 line stage a bad idea? - 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 28th December 2011, 07:41 PM   #1
ryuji is offline ryuji  United States
diyAudio Member
 
Join Date: Feb 2011
Location: massachusetts
Default 6au6 line stage a bad idea?

Ill be rebuilding my amplifier getting rid of all of my 12au7's and 12at7's. I have addressed my gain stages for my main 5 audio channels however my LFE channel still remains to be thought out/designed.

Since im using an silicon style amplifier for my LFE channel i do not need large amounts of gain but i do need a way to balance the magnitude of the channel with my others. Im considering a cathode follower arrangement but have not found many documented cases of using a pentode as an cathode follower. Is there a reason why its not frequently done?

I intend to tune my channels such that 100% at my source is just barely touching clipping on main channels, thus with a matched subwoofer preamp i would only need to adjust master volume on my sound card and not have to fiddle with sub volume level like i do now(nonlinear at the moment with current topology)

Expectations for the b+ is 450 not 500 volts, compensated by different anode resistor choice. This circuit was tested as a single channel and shown to be superior to previous solution:
http://ryujiwarui.com/upload/Pentode-Rev4B.png
  Reply With Quote
Old 28th December 2011, 07:47 PM   #2
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
I can't see a cathode follower; the 6AU6 stage is a degenerated grounded cathode circuit.

You can use a pentode as CF, just think about g2 AC grounding. It is probably not often done because twin triodes are so convenient.
  Reply With Quote
Old 28th December 2011, 07:49 PM   #3
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
Quote:
Originally Posted by ryuji View Post
Im considering a cathode follower arrangement but have not found many documented cases of using a pentode as an cathode follower. Is there a reason why its not frequently done?
Generally, the pentode offers a gain closer to unity, but do you really care if it's 0.99 instead of 0.97? Other than that, there's no real performance advantage.
__________________
The more you pay for it, the less inclined you are to doubt it.- George Smiley
  Reply With Quote
Old 28th December 2011, 07:54 PM   #4
diyAudio Member
 
Join Date: Apr 2004
Location: Monroe Township, NJ
There's nothing wrong with a pentode cathode follower. The tricky part is that g2 must be tied by a cap. to the cathode.

Read Kimmel's μ stage dissertation. A μ stage is a μ follower with a pentode CF "upstairs".
__________________
Eli D.
  Reply With Quote
Old 28th December 2011, 08:19 PM   #5
ryuji is offline ryuji  United States
diyAudio Member
 
Join Date: Feb 2011
Location: massachusetts
Sorry for any confusion but I linked my complete circuit for high frequency channels only for background Information. I have not designed my subwoofer preamp circuit yet. My idea was that with identical tubes matching the channels would become easier.
  Reply With Quote
Old 28th December 2011, 08:53 PM   #6
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
As any CF has a gain just below 1, any CF will be a reasonable gain match to any other CF whatever valve is used.
  Reply With Quote
Old 28th December 2011, 09:06 PM   #7
diyAudio Member
 
Join Date: Nov 2002
There is an Aikido 6au6/5687 line stage. I made one and it sounds nice.
  Reply With Quote
Old 29th December 2011, 03:39 PM   #8
ryuji is offline ryuji  United States
diyAudio Member
 
Join Date: Feb 2011
Location: massachusetts
Quote:
Originally Posted by DF96 View Post
As any CF has a gain just below 1, any CF will be a reasonable gain match to any other CF whatever valve is used.
I did not plan on using a cathode follower on my other channels, however i do still intend/need the preamp on my LFE channel.

Using the same grounded cathode topology and then attenuating it back down to line voltage is a poor choice, So a cathode follower in theory would accomplish my goals?

From a implentation point of view is it as simple as taking my 28~33k resistor in the anode of my other preamp design and bringing it down to after the cathode bias resistor, and changing the 1 meg to join in after the cathode bias resistor? or is that a poor way to design my cathode follower?

As such i would think any nonlinearities would match up with my other tubes, just need an log taper on the input to adjust the balance to where i want (the power amp will not have any kind of volume controls after the preamp)

i would have to also elevate my heaters about 100v to compensate

Last edited by ryuji; 29th December 2011 at 03:41 PM.
  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
Aikido line stage - plus phono line stage cjkpkg Tubes / Valves 1 22nd November 2008 09:50 PM
Line stage preamp, based on SY's "Heretical Unity gain line stage" Danko Tubes / Valves 23 18th July 2005 04:07 AM
Double Line Arrays Good or Bad Idea? ralph-bway Multi-Way 2 26th January 2004 01:54 AM
Is this a bad idea? Jimmy154 Multi-Way 3 24th November 2002 12:18 AM
is this a bad idea? ChesterFuzzin' Multi-Way 2 28th June 2002 05:15 PM


New To Site? Need Help?

All times are GMT. The time now is 11:59 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