12au7 valve preamp (again?) - 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 21st December 2012, 01:57 PM   #1
ctcorp is offline ctcorp  Brazil
diyAudio Member
 
Join Date: Nov 2007
Default 12au7 valve preamp (again?)

I found this (and built if later) when googling around, BUT it seems to lack a lot of response on treble, can anyone give me a hint on what to do?

I have build it without that tone control of the schematic.
Attached Images
File Type: png 12AU7-Tube-Preamplifier-Schematic.png (10.2 KB, 330 views)
  Reply With Quote
Old 21st December 2012, 03:33 PM   #2
diyAudio Member
 
artosalo's Avatar
 
Join Date: Feb 2010
Quote:
Originally Posted by ctcorp View Post
....it seems to lack a lot of response on treble, can anyone give me a hint on what to do?
How did you verify that the high frequency response is declined ?
Do you have long cable at the output ?

Actually there is a chance to have poor low frequency response because the capacitor at the output is just 20 nF.
It should be minimum 10 x bigger (220 nF...470 nF).

Last edited by artosalo; 21st December 2012 at 03:35 PM.
  Reply With Quote
Old 21st December 2012, 03:49 PM   #3
ctcorp is offline ctcorp  Brazil
diyAudio Member
 
Join Date: Nov 2007
hi there

Big OOPS here, wrong schematic, new one attached (its from the same person that designed the first one, he made a few changes).

about wiring: short as possible (<1m shielded)
how i finded out? bypassing the preamp there is a lot of treble being played thru it: almost none.

tubes are matsushita.
Attached Images
File Type: png 12AX7-12AU7-Tube-Preamp-Schematic.png (6.8 KB, 303 views)
  Reply With Quote
Old 21st December 2012, 04:20 PM   #4
diyAudio Member
 
artosalo's Avatar
 
Join Date: Feb 2010
According to the circuit diagram, the high frequency response should exceed 100 kHz.

Edit: what is the output impedance the device where you take the audio signal to this amplifier ?

Last edited by artosalo; 21st December 2012 at 04:22 PM.
  Reply With Quote
Old 21st December 2012, 04:21 PM   #5
ctcorp is offline ctcorp  Brazil
diyAudio Member
 
Join Date: Nov 2007
interesting

is there a program to use the pc sound card to do some testing?
  Reply With Quote
Old 21st December 2012, 04:42 PM   #6
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
I assume this is some sort of guitar preamp/FX box? That would explain why the designer believes that any twin triodes with the right pinout can substitute for each other.

Does the amp you are driving have an input RF filter? If so, its capacitance combined with the fairly high output impedance of this preamp will reduce treble.
  Reply With Quote
Old 21st December 2012, 04:54 PM   #7
ctcorp is offline ctcorp  Brazil
diyAudio Member
 
Join Date: Nov 2007
Quote:
Originally Posted by artosalo View Post
According to the circuit diagram, the high frequency response should exceed 100 kHz.

Edit: what is the output impedance the device where you take the audio signal to this amplifier ?
good question, is a Realtek codec based onboard audio, I have no idea of the impedance of it

Last edited by ctcorp; 21st December 2012 at 05:14 PM.
  Reply With Quote
Old 21st December 2012, 07:05 PM   #8
diyAudio Member
 
jerluwoo's Avatar
 
Join Date: Feb 2006
Location: Ashland,Ky U.S
I'm with DF96 on this. The high output impedance and parasitic+input capacitance of the load is most likely the culprit.
  Reply With Quote
Old 21st December 2012, 08:02 PM   #9
ctcorp is offline ctcorp  Brazil
diyAudio Member
 
Join Date: Nov 2007
ok, I will check the amp foi input filters, and tweak things alittle
  Reply With Quote
Old 22nd December 2012, 08:30 PM   #10
diyAudio Member
 
ruffrecords's Avatar
 
Join Date: Jun 2007
Location: Holt, Norfolk
The loss in hf response is most likely due to the miller effect at the grid of the second triode.

Cheers

Ian
  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
12ax7 12au7 preamp Bengali Tubes / Valves 17 8th January 2012 08:46 PM
Preamp tube SRPP 12AU7 VS preamp tube Aikido 12AU7 = all use rec 6X5GT spiritm2r Tubes / Valves 1 6th March 2011 03:53 PM
3 - 12AU7 Preamp. Is there such an animal? cbj591 Tubes / Valves 12 25th October 2010 11:03 PM
12au7 preamp will not work prorms Tubes / Valves 8 11th November 2007 04:57 AM
Look for 12AU7 Preamp Circuit . RCA245 Tubes / Valves 2 2nd June 2006 03:02 PM


New To Site? Need Help?

All times are GMT. The time now is 09:40 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