Question for the One and Only. (Mr. Pass) - diyAudio
Go Back   Home > Forums > Amplifiers > Pass Labs

Pass Labs This forum is dedicated to Pass Labs discussion.

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 3rd February 2004, 01:35 AM   #1
K-amps is offline K-amps  United States
diyAudio Member
 
K-amps's Avatar
 
Join Date: Nov 2003
Location: Indiana
Question Question for the One and Only. (Mr. Pass)

Mr. Pass I have just come across a Forte Model 6a. I think it is 200wpc and uses IGBT's.

Can I reduce the rails by half (by rewiring the Toroids in series) and bias it to 50 watts class-A?

I have done it in the Forte Model 3 with good results but that uses BJT's, I am worried playing with these IGBT's.

If so, what idle bias do you recommend going to with rails of approx +/-38vdc?

Thanks much in advance,

K-amps.
  Reply With Quote
Old 3rd February 2004, 11:49 PM   #2
K-amps is offline K-amps  United States
diyAudio Member
 
K-amps's Avatar
 
Join Date: Nov 2003
Location: Indiana
Unhappy C'mon anyone?

Anyone with ideas?
  Reply With Quote
Old 3rd February 2004, 11:51 PM   #3
diyAudio Moderator
 
pinkmouse's Avatar
 
Join Date: Apr 2002
Location: Chatham, England
I'll move this to the Pass forum, you stand a better chance of getting a reply there.
__________________
Rick: Oh Cliff / Sometimes it must be difficult not to feel as if / You really are a cliff / when fascists keep trying to push you over it! / Are they the lemmings / Or are you, Cliff? / Or are you Cliff?
  Reply With Quote
Old 3rd February 2004, 11:53 PM   #4
K-amps is offline K-amps  United States
diyAudio Member
 
K-amps's Avatar
 
Join Date: Nov 2003
Location: Indiana
Thanks!!
  Reply With Quote
Old 4th February 2004, 01:02 AM   #5
diyAudio Member
 
Join Date: Jan 2001
Location: Scandinavia
Rule of thumb:

To stay in the same thermal envelope: When halving the PSU voltage, you can double the current.

The other alternative is to aim for a temperature which should not be more than 70 degC.

You might also want to do some reading up on IGBT's to evaluate their thermal stability. If I know NP, I suspect that the emitter resistors are large enough to offset any thermal runaway should the devices be so inclined.

Petter
  Reply With Quote
Old 4th February 2004, 01:08 AM   #6
K-amps is offline K-amps  United States
diyAudio Member
 
K-amps's Avatar
 
Join Date: Nov 2003
Location: Indiana
Thanks Petter,

Additionally I'd like more insights especially from NP. I suspect he knows something about this that I should know.

I just dont want to blow the IGBT's and have a worthless amp on my hands.

I agree with you on the value of NP's emitter resisters, probably a minimum of 0.47 ohms... right?
  Reply With Quote
Old 4th February 2004, 05:10 PM   #7
The one and only
 
Nelson Pass's Avatar
 
Join Date: Mar 2001
Default Re: Question for the One and Only. (Mr. Pass)

Quote:
Originally posted by K-amps
Mr. Pass I have just come across a Forte Model 6a. I think it is 200wpc and uses IGBT's.
Can I reduce the rails by half (by rewiring the Toroids in series) and bias it to 50 watts class-A?
I have done it in the Forte Model 3 with good results but that uses BJT's, I am worried playing with these IGBT's.
If so, what idle bias do you recommend going to with rails of approx +/-38vdc?K-amps.
Should work just fine, although I don't have a schematic on
it, as it was after my time. I would just crank up the bias until
the sinks reach a continuous 50 deg C (touchable for 5 seconds).

  Reply With Quote
Old 4th February 2004, 06:35 PM   #8
K-amps is offline K-amps  United States
diyAudio Member
 
K-amps's Avatar
 
Join Date: Nov 2003
Location: Indiana
Thanks all, especially Mr. Pass!
  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
To Low Pass Or Not To Lowpass...That Is The Question CarlosT Full Range 2 18th December 2006 11:45 AM
Question for Mr.Pass Metric Pass Labs 5 27th May 2005 09:17 PM
Question to Mr. Pass Metric Pass Labs 7 19th April 2005 10:13 PM
A75 question for Mr Pass demons_wing Pass Labs 13 25th April 2004 08:21 AM
A Question for Mr. Pass (and all..) W.O.L.F. Pass Labs 4 12th March 2003 12:59 AM


New To Site? Need Help?

All times are GMT. The time now is 03:01 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