OPT at frequency extremes - 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 July 2005, 12:15 PM   #1
diyAudio Member
 
Join Date: Jun 2004
Location: Indiana
Default OPT at frequency extremes

If I understand correctly the difficulty in designing wide bandwidth OPTs is getting both high primary inductance and low shunt capacitance making it difficult to do both ends well.

In multi-amped systems where each amplifier will be limited to three or four octave range would it be theoretically possible to wind OPTs that reach the extremes of frequency seperately. That is to say would it be possible to come up with a transformer that goes down to say 10Hz as long as it only has to get up to 200-300Hz range and one that can go up to 30kHz as long as it only has to go down to about 2kHz?

mike
  Reply With Quote
Old 21st July 2005, 12:31 PM   #2
Fuling is offline Fuling  Sweden
diyAudio Member
 
Join Date: Aug 2001
Location: Sweden (Mora)
I had similar ideas a year or so ago (before I got into fullrange drivers and BL horns).
IIRC someone here at the forum has done something similar with custom made transformers from Sowter UK.
  Reply With Quote
Old 21st July 2005, 12:34 PM   #3
Fuling is offline Fuling  Sweden
diyAudio Member
 
Join Date: Aug 2001
Location: Sweden (Mora)
Good tube amp designs for Biamping?!?
  Reply With Quote
Old 21st July 2005, 01:14 PM   #4
EC8010 is offline EC8010  United Kingdom
diyAudio Moderator Emeritus
 
EC8010's Avatar
 
Join Date: Jan 2003
Location: Near London. UK
And if you look at the recent Motorola console thread, you'll see it was done commercially. The problem with a transformer is not getting one or other extreme, it's getting both simultaneously. It's easy to make a transformer with only a few octaves of bandwidth, but increasing that number of octaves is much harder. Where you place those octaves is a function of primary inductance. Lots of older amplifiers were distinctly stingy on core material and primary inductance, but their HF response is satisfactory, so they make great tweeter amplifiers. Am I allowed to suggest solid state for bass?
__________________
The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...
  Reply With Quote
Old 22nd July 2005, 03:56 AM   #5
diyAudio Member
 
Join Date: Jun 2004
Location: Indiana
Oh yes you can suggest SS for bass. You are not the first and there is a good possibility that it will start that way and even end that way. It just occured to me that getting the proper iron might be much easier in the multi-amp situation (I will eventually have tri-amp on each side plus sub).

The sub will handle 16-70Hz or so. Therefore the midbass amp will only have to handle down to 60Hz or so. It seems any respectable SE transformer should be able to handle 60-12K or so. Thus the first amp I build will probably be the one for the midbass. I could initially use it as a computer amp since my sound card can't do more than about 50-10k or so anyway.

mike
  Reply With Quote
Old 23rd July 2005, 10:54 PM   #6
diyAudio Member
 
Join Date: May 2005
Location: Pretoria, South Africa
The main h.f. problem is capacitance between primary and secondary; not so much primary interwinding, i.e. you can get a goodly h.f. response despite transformer size. Suitable C-cores will keep windings small (I assume here that you have a choice or can wind your own).

As a typical illustration (no fancy stuff involved) I am at present using a 130W output transformer with the following specs: Primary inductance = 120 H; leakage inductance = 6 mH (measured in the usual way); equivalent interwinding capacitance approximatelt 2 nF. Overall size using C-core = 10 x 11 x 12 cm. This will give in my application a l.f. (-3dB) point of 7 Hz and an h.f. (-3dB) point of 35 KHz, the latter mainly as a result of the pri/sec. capacitance. This is just the transformer, before application of negative feedback. I use 3 secondary sections which was probably overkill: the h.f. -3dB point because of leakage inductance alone would have been 400 KHz! (For the record the output tubes are 2 x 2 6L6GC in p.p./parallel.)

Bi-amping is of course advantageous for other reasons: Eliminating of loudspeaker cross-overs.
  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
tweeter extremes...which end of the spectrum to choose? thadman Multi-Way 2 7th December 2006 02:58 AM
Taking CFB to the extremes...? Fuling Tubes / Valves 17 15th September 2006 08:50 PM
Frequency CUT and a HOLE in frequency range... -_nando-_ Everything Else 0 28th December 2005 08:17 PM
What's my x-over frequency? hanskrj Multi-Way 0 5th February 2004 07:20 AM


New To Site? Need Help?

All times are GMT. The time now is 08:56 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