Current Source amplifier for low impedance loads - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

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 August 2011, 05:09 AM   #1
diyAudio Member
 
Join Date: Apr 2002
Default Current Source amplifier for low impedance loads

I have a very difficult speaker, Apogee Scintilla, impedance dropping to 0.7 ohms or so.
I'd like to DIY a CURRENT SOURCE amp, something like this:
http://apogee-acoustics.de/download/..._Apogee_EN.pdf

Any leads/ideas/schematics?
  Reply With Quote
Old 23rd August 2011, 09:06 AM   #2
AKSA is offline AKSA  Australia
diyAudio Member
 
Join Date: Sep 2001
Location: Melbourne, Australia
Dr. H,

You have no choice but to use voltage source amps - that is conventional designs - with an output stage capable of welding steel. This might require a minimum of 12 pairs of 125W power transistors per channel, and propels you inevitably to a Krell or large ML.

This is the downside of owning Apogees. Fine speakers, but limited by the amps that can drive them, and by and large, such large amps don't do detail all that well.

Hugh
__________________
Aspen Amplifiers P/L (Australia)
www.aksaonline.com
  Reply With Quote
Old 23rd August 2011, 09:50 AM   #3
Calvin is offline Calvin  Germany
diyAudio Member
 
Calvin's Avatar
 
Join Date: Nov 2004
Location: close to Basel
Hi,

You may want to have a look at Elektors ´The current Amp´ from Nov/Dec 1992 that specialized on driving low impedance loads below 1Ohm.
It later became the ´Ulti Amp´ that was designed for more loads in the typical 4-8 Ohms range.

jauu
Calvin
  Reply With Quote
Old 23rd August 2011, 11:42 AM   #4
diyAudio Member
 
Join Date: Apr 2002
Thanks guys.
Hugh I should just say that using the Krell KMA160 drives these speakers beautifully, but very low levels of detail (like the creak of a pianists chair) is a less audible than with normal 8R speakers with a good amp like the GB150.

Last edited by Dr.H; 23rd August 2011 at 11:48 AM.
  Reply With Quote
Old 23rd August 2011, 12:07 PM   #5
AKSA is offline AKSA  Australia
diyAudio Member
 
Join Date: Sep 2001
Location: Melbourne, Australia
Dr H,

An amp that I believe would be eminently suitable because of the speed of its feedback loop (which is responsible for retrieving fine detail you note) I would honestly think about Lazy Cat's design. MiiB (Michael Boresen) did a very good build out using lateral fets which I believe would be highly suited to this application - but you would need six pairs and about 70V rails.

Cheers,

Hugh
__________________
Aspen Amplifiers P/L (Australia)
www.aksaonline.com

Last edited by AKSA; 23rd August 2011 at 12:10 PM.
  Reply With Quote
Old 23rd August 2011, 12:39 PM   #6
diyAudio Member
 
Join Date: Apr 2002
Hi Hugh,

Funnily enough I posted the question about using Lazy Cats amp in that discussion but had no reponse.
  Reply With Quote
Old 23rd August 2011, 12:52 PM   #7
AKSA is offline AKSA  Australia
diyAudio Member
 
Join Date: Sep 2001
Location: Melbourne, Australia
Threads are funny; you cannot know who or what will happen, and the oddest things capture people's imagination.

For reasons of speed, the current feedback amp is best, and this configuration is well suited to massive output stages because the multiple switching of all those devices causes loss of resolution in slower feedback loops. You can also get dual die devices for latfets from Exicon, and maybe four of these would be best.

Furthermore, the electrostatic drive of a fet gives excellent immunity from back emf coming off the speaker; high damping factor should scotch this but galvanic isolation does the job very well. This means phase shifts in the speaker don't mess with the feedback loop and the amp maintains composure at all times.

Just today it was suggested to use the CFP high bias driver devised by Mihai Rauta (aka Roender) so capably used in his amp of a couple of years ago.

This too would be ideal for driving six pairs of lateral fets because to avoid switching in the drivers the CFP runs at 100mA, and this is current aplenty to drive a big output stage.

Alex_MM from Romania does beautiful pcbs, and very quickly too, and might be asked politely if he'd have a go. However, compactness is not really needed here; you must space all the output devices adequately to avoid too much thermal power concentration, say every 2 inches on a very large, say 24" long by 8" high heatsink.

Hope this helps,

Hugh
__________________
Aspen Amplifiers P/L (Australia)
www.aksaonline.com
  Reply With Quote
Old 23rd August 2011, 01:34 PM   #8
diyAudio Member
 
Join Date: Apr 2002
That really does, thanks Hugh.
  Reply With Quote
Old 23rd August 2011, 03:07 PM   #9
diyAudio Member
 
Lazy Cat's Avatar
 
Join Date: Sep 2007
Quote:
Originally Posted by Dr.H View Post
Hi Hugh,

Funnily enough I posted the question about using Lazy Cats amp in that discussion but had no reponse.
The answer for you prepared
  Reply With Quote
Old 23rd August 2011, 03:44 PM   #10
diyAudio Member
 
Join Date: Apr 2002
Thanks Lazy Cat!
  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
When driving low impedance loads, what is the killer? - Prevention? CBRworm Solid State 25 6th April 2009 01:09 PM
Class D and Very Low Impedance loads Bruno Putzeys Class D 30 3rd August 2005 08:38 AM
Driving Low Impedance Loads weinstro Solid State 14 8th May 2005 09:53 PM
LM3875s & low impedance loads - your thoughts? BlackDog Chip Amps 22 19th June 2004 12:18 PM


New To Site? Need Help?

All times are GMT. The time now is 11:17 PM.


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