Selecting Output Transformers for My WOT Line Preamp - 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 June 2005, 01:06 AM   #1
diyAudio Member
 
Join Date: Dec 2003
Location: Hong Kong
Default Selecting Output Transformers for My WOT Line Preamp

I want to upgrade my WE437a WOT preamp (running at 25ma). I want wide frequency response and low output impedence as well as balanced outputs. I have considered the following Lundahl transformers:
(1) LL1671/30ma (Alt Q connection, L=35H, 4:1, no freq. spec.);
(2) LL1689/18ma (Alt P connection, L=90H, 18:4, no freq. spec.) to be gapped at 25 or 30 ma; or
(3) LL1660/18ma (Alt Q connection, L=100H, 4.5:1, freq. 11Hz-35kHz +-1db) to be gapped at 25 or 30 ma.
Grateful if anybody advise which of the above is the best for me? Or is there any more suitable counterpart? For options (2) and (3), should I specify the gap at 25 ma or 30 ma? What's the difference?

Any advice or information is appreciated. Thanks in advance.
  Reply With Quote
Old 28th June 2005, 03:02 AM   #2
diyAudio Member
 
Brett's Avatar
 
Join Date: Jan 2002
If it were me, I'd whack a CCS on top of it and run it parafeed. I reckon it sounds better.
If running the Tx on the anode, use the smallest gap you can get away with for the anode current. It'll increase the inductance. There's probably not going to be a lot of difference between the Lundahls once they're gapped to a similar spec. Turns ratio will likely be the major difference and choose that depending on what you need.
  Reply With Quote
Old 28th June 2005, 05:45 AM   #3
diyAudio Member
 
Join Date: Dec 2003
Location: Hong Kong
Hi Brett,

Thank you for your advice. Could you elaborate the difference between parafeed and normal (i.e. with DC current) design in terms of sound quality and technical performance?

What's the suitable candidate (brand and model) for the parafeed output transformer? Will it be permalloy or amorphous ones? How to calculate the value of the coupling capacitor?

Thanks
  Reply With Quote
Old 28th June 2005, 05:54 AM   #4
diyAudio Member
 
Brett's Avatar
 
Join Date: Jan 2002
Much cleaner sounding to me, less wooly and (not) vaguely distorted.
Any of the Lundahls will be fine, with no gap and whatever turns ratio you're after.

http://www.nutshellhifi.com/gary/index.html
  Reply With Quote
Old 28th June 2005, 06:32 AM   #5
diyAudio Member
 
analog_sa's Avatar
 
Join Date: Aug 2002
Location: Sofia
I have used a 1660/18mA as 4.5:1 and really liked the sound.

Parafeed will certainly sound different and would greatly increase the possible choices of transformers with better cores. If i were to go the parafeed route i would make sure i have a nice plate choke at hand - just in case i can't swallow the CCS. And a VERY decent cap. OMG, this parafeed adventure may get expensive
  Reply With Quote
Old 28th June 2005, 04:08 PM   #6
diyAudio Member
 
Join Date: Dec 2003
Location: Hong Kong
Quote:
Originally posted by analog_sa
I have used a 1660/18mA as 4.5:1 and really liked the sound.


What tubes that you are using and at what current? Thanks.
  Reply With Quote
Old 28th June 2005, 04:11 PM   #7
diyAudio Member
 
analog_sa's Avatar
 
Join Date: Aug 2002
Location: Sofia
6S45PE but i really can't recall the current. Very possibly 15-17mA.
  Reply With Quote
Old 28th June 2005, 07:36 PM   #8
diyAudio Member
 
Join Date: Mar 2003
Location: NYC
Quote:
Originally posted by Brett
use the smallest gap you can get away with for the anode current. It'll increase the inductance.
it will also decrease the linearity and place you in a very nonlinear part of the BH loop.

I'd suggest just the opposite. Determine how much inductance you really need and use the largest gap possible that will still give you that value.

dave
  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
Hashimoto HL-20K-6 Line Output Transformers nuhor68 Tubes / Valves 15 28th December 2008 08:20 PM
Locating Preamp Output Transformers dsavitsk Tubes / Valves 2 8th August 2006 12:08 AM
Preamp with line level output linuxenthusiast Analog Line Level 5 30th July 2006 11:42 AM
Output Transformers for WE-437a WOT Line Preamp snoopyma Tubes / Valves 4 28th January 2005 01:47 PM
My Loudspeaker Project: a 2 way transmission line. Phase 1: selecting drivers Bricolo Multi-Way 58 17th June 2003 08:13 AM


New To Site? Need Help?

All times are GMT. The time now is 06:14 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