New Schematic Linestage Tube Preamp using EF86 & 12AX7 - Page 3 - 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 20th January 2012, 05:48 PM   #21
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
I agree, try Lar's fix - it will work quite a bit better than the current implementation.
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan
  Reply With Quote
Old 21st January 2012, 08:07 AM   #22
Edwind is offline Edwind  Indonesia
diyAudio Member
 
Join Date: Jan 2012
Hello everybody.
Sorry for waiting.
I finished buils Lar's solution.
Also try using NFB.
All works well.
But I cannot described better in electrical because I don't have any instruments.
Just LCR + Multimeter.
  Reply With Quote
Old 22nd January 2012, 05:51 AM   #23
Edwind is offline Edwind  Indonesia
diyAudio Member
 
Join Date: Jan 2012
I'll describe the result.
By adding NFB, sound reproduction becoming a little bit "dull" and very sensitive to NFB's resistors materials.

By using Lars solution, the result totally different from original.
Bass becoming poor, boomy, loose, more like using very-very bad sub-woofer.
Treble also poor, very dull, seems already roll-off in 15kHz.
Midrange frequency very dominant, more like midrange booster.
All musical instrument loss it's timbre, for ex: differentiation between pianos brand and type becoming blur or sound same.
Sound stage becoming narrow.
All sound reproduction like "record sound" not real.
It seem odd-order harmonics becoming greater.
Last, it's degrading all my system performance.

Any other ideas?
  Reply With Quote
Old 22nd January 2012, 11:17 AM   #24
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
Could you post the schematic of what you actually built following Lars's suggestion? Also, please measure the voltages at each tube's plate and cathode. That will help us troubleshoot your problem.
__________________
And while they may not be as strong as apes, don't lock eyes with 'em, don't do it. Puts 'em on edge. They might go into berzerker mode; come at you like a whirling dervish, all fists and elbows.
  Reply With Quote
Old 22nd January 2012, 01:18 PM   #25
diyAudio Member
 
Join Date: May 2007
Edwind, you have probably made some mistakes but this is an easy fix. The schematics shows the topology of the correct one. Of course there need to be a few more components to make it complete.
Attached Images
File Type: png edwind.png (49.4 KB, 204 views)
  Reply With Quote
Old 22nd January 2012, 01:44 PM   #26
diyAudio Member
 
Join Date: May 2007
A quick sim shows this amp will clip at over 70V ptp and will have a distortion well below 0,1%(sim says 0,01%) at 2Vrms out. -3dB is over 0,5MHz.
  Reply With Quote
Old 22nd January 2012, 02:22 PM   #27
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
Quote:
Originally Posted by revintage View Post
Edwind, you have probably made some mistakes but this is an easy fix. The schematics shows the topology of the correct one. Of course there need to be a few more components to make it complete.
That should work very well (though gain still too high for most modern applications). It's important to bias up the cathode follower's heater ~75V so as not to challenge the heater-to-cathode voltage rating- I'm sure you know that, but Edwind may not, and we'd hate to hear about sparks and flames.
__________________
And while they may not be as strong as apes, don't lock eyes with 'em, don't do it. Puts 'em on edge. They might go into berzerker mode; come at you like a whirling dervish, all fists and elbows.
  Reply With Quote
Old 22nd January 2012, 02:24 PM   #28
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
The volume pot appears to be the wrong way round in that skeleton circuit.
  Reply With Quote
Old 22nd January 2012, 02:44 PM   #29
GoranB is offline GoranB  Poland
diyAudio Member
 
GoranB's Avatar
 
Join Date: Mar 2010
Location: Poland
Quote:
Originally Posted by Edwind View Post
I'll describe the result.
By adding NFB, sound reproduction becoming a little bit "dull" and very sensitive to NFB's resistors materials.

By using Lars solution, the result totally different from original.
Bass becoming poor, boomy, loose, more like using very-very bad sub-woofer.
Treble also poor, very dull, seems already roll-off in 15kHz.
Midrange frequency very dominant, more like midrange booster.
All musical instrument loss it's timbre, for ex: differentiation between pianos brand and type becoming blur or sound same.
Sound stage becoming narrow.
All sound reproduction like "record sound" not real.
It seem odd-order harmonics becoming greater.
Last, it's degrading all my system performance.

Any other ideas?
Try this
Attached Images
File Type: gif ciuff_nc2.gif (6.4 KB, 187 views)
  Reply With Quote
Old 22nd January 2012, 03:47 PM   #30
Edwind is offline Edwind  Indonesia
diyAudio Member
 
Join Date: Jan 2012
I already lift up the heaters to nearly 80V (from GE 12AU7 datasheet, 100V is maximum rating for DC component and 200V for DC component + peak).
Ah I forget to wrote before, that all components that I used to build my 1st post and Lar's are same quality (all low grade components), and all tubes that I used all are NOS tube, matched pair Mullard (1960) EF86 and Siemens ECC81 ( 1960). Using ECC82 became more terrible, very loud midrange, bad bass quality, treble more dull than using ECC81.
I'll draw the Lar's schematic including it's voltage values and post soon.
Please wait!
  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
Cascode Tube Mic Preamp: 12AX7/12AU7 Schematic 88man Tubes / Valves 13 4th August 2012 01:08 AM
converting EF86 to take 12AX7 vintage_dog Tubes / Valves 25 5th May 2011 05:36 PM
EF86 tube preamp gaborbela Tubes / Valves 2 10th February 2010 08:00 PM
12AX7/12BH7 Hammond Tube Preamp Project jordankersten Tubes / Valves 4 5th April 2009 03:49 AM
suitable preamp for a tube amp (kt88+12ax7) kevinkuang Tubes / Valves 6 17th March 2005 03:22 PM


New To Site? Need Help?

All times are GMT. The time now is 07:13 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