Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

Volume at the output of preamplifier matching transformer
Volume at the output of preamplifier matching transformer
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 23rd May 2020, 09:05 AM   #1
Glass_painter is offline Glass_painter  Israel
diyAudio Member
 
Join Date: Apr 2003
Location: Israel
Default Volume at the output of preamplifier matching transformer

Hi,

Please look at the schematic.
This is presented as a clone of REDDI DI box in a different forum.
The pot at the output will short the transformer at the extreme position.
Am I missing anything here?
Thank you
Glass painter
Tube DI REDDI.jpg
  Reply With Quote
Old 23rd May 2020, 09:29 AM   #2
JonSnell Electronic is offline JonSnell Electronic  United Kingdom
diyAudio Member
 
JonSnell Electronic's Avatar
 
Join Date: Dec 2012
Location: The Jurassic Coast, England. GB
Not a good idea to mismatch the transformer.
Fit any volume control to the input side of the valve in the recognised way; wiper to the grids or
Attached Images
File Type: png Screenshot 2020-05-23 at 10.53.57.png (21.1 KB, 113 views)
__________________
Support for Fender, Marshall and all Valve Equipment; Audio Innovations, Audiorama FU29, Quad and Leak. www.jonsnell.co.uk

Last edited by JonSnell Electronic; 23rd May 2020 at 09:55 AM. Reason: More info
  Reply With Quote
Old 23rd May 2020, 10:05 AM   #3
Schmitz77 is offline Schmitz77  Germany
diyAudio Member
 
Join Date: Apr 2015
A level adjustment pot has to be either on the input side of the pre or between the two tube stages.
This 1K pot is at the wrong place and wrong value in the schemo.
  Reply With Quote
Old 23rd May 2020, 11:08 AM   #4
JMFahey is offline JMFahey  Argentina
diyAudio Member
 
JMFahey's Avatar
 
Join Date: Mar 2009
Location: Buenos Aires - Argentina
Wrong as drawn
MIGHT work if shorting pot placed across the XLR pins, *after* the 300 ohm resistors R5 and R6 but still the proper way would be to wire it as a non shorting volume control.

Transformer secondary end to end, "ground" and wiper to pins 3 and 2 respectively.

1k pot value is fine there.
__________________
Design/make/service musical stuff in Buenos Aires, Argentina, since 1969.
  Reply With Quote
Old 23rd May 2020, 12:39 PM   #5
analog_sa is offline analog_sa  Europe
diyAudio Member
 
analog_sa's Avatar
 
Join Date: Aug 2002
Location: Cascais
Volume at the output of preamplifier matching transformer
It is a drawing error. With the pot on the right side of the 300ohm resistors it will work perfectly.

Last edited by analog_sa; 23rd May 2020 at 12:41 PM.
  Reply With Quote
Old 23rd May 2020, 12:52 PM   #6
analog_sa is offline analog_sa  Europe
diyAudio Member
 
analog_sa's Avatar
 
Join Date: Aug 2002
Location: Cascais
Volume at the output of preamplifier matching transformer
What kind of input voltage is anticipated? Without a level adjustment at input distortion may be higher.
  Reply With Quote
Old 23rd May 2020, 01:56 PM   #7
Schmitz77 is offline Schmitz77  Germany
diyAudio Member
 
Join Date: Apr 2015
Quote:
Originally Posted by analog_sa View Post
It is a drawing error. With the pot on the right side of the 300ohm resistors it will work perfectly.

No, its not. Its the complete wrong pot type in this application.

If you wish to adjust a symmetric 600 Ohm line then its necessary to put a symmetric 600 Ohm balanced attenuator into it, which reflects always on in- and output the constant 600 Ohm.

As this method is very oldfashioned and out of style, nowadays we put those kind of pots shown here with different values between the voltage amp tube stages.
Thats good design practise. Or maybe on the input of the circuits. But never on the outputs.
  Reply With Quote
Old 23rd May 2020, 03:07 PM   #8
analog_sa is offline analog_sa  Europe
diyAudio Member
 
analog_sa's Avatar
 
Join Date: Aug 2002
Location: Cascais
Volume at the output of preamplifier matching transformer
Quote:
Originally Posted by Schmitz77 View Post

If you wish to adjust a symmetric 600 Ohm line then its necessary to put a symmetric 600 Ohm balanced attenuator into it, which reflects always on in- and output the constant 600 Ohm.


The circuit provides a perfect balance, an acceptably low output impedance and does not overload the amplification stage.

It does not have a constant input impedance but does it really matter?
  Reply With Quote
Old 23rd May 2020, 03:36 PM   #9
Schmitz77 is offline Schmitz77  Germany
diyAudio Member
 
Join Date: Apr 2015
Its not any longer a balanced output

Last edited by Schmitz77; 23rd May 2020 at 03:44 PM.
  Reply With Quote
Old 23rd May 2020, 03:54 PM   #10
JMFahey is offline JMFahey  Argentina
diyAudio Member
 
JMFahey's Avatar
 
Join Date: Mar 2009
Location: Buenos Aires - Argentina
Sorry but you are wrong.
It stays a balanced output for the very good reason that itīs floating, completely unreferenced to ground, it comes from the secondary of a transformer.

If it drives a true balanced input, either active or best, a transformer, it works as intended.
__________________
Design/make/service musical stuff in Buenos Aires, Argentina, since 1969.
  Reply With Quote

Reply


Volume at the output of preamplifier matching transformerHide 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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Matching 16 ohm loudspeaker into 8 ohm output transformer: can i do any modification? ygg-it Tubes / Valves 6 10th December 2014 02:48 PM
Output transformer impedance matching cspirou Tubes / Valves 10 11th November 2014 02:06 AM
Newbie question about output transformer to speaker matching rss388 Tubes / Valves 5 15th May 2011 08:05 AM
Output transformer matching to active device driving it macrohenry Solid State 3 17th August 2007 06:51 AM
SE Output Transformer Matching ttan98 Tubes / Valves 2 27th April 2006 04:28 PM


New To Site? Need Help?

All times are GMT. The time now is 10:45 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
Copyright ©1999-2020 diyAudio
Wiki