Technics Class-AA / Sandman Bridge - 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 27th June 2004, 03:30 PM   #1
Did it Himself
diyAudio Member
 
richie00boy's Avatar
 
Join Date: Nov 2003
Location: Gloucestershire, England, UK
Question Technics Class-AA / Sandman Bridge

Does this type of amp/topology rely on driving a loudspeaker of impedance within a narrow range?

I am going to use one of these amps in a test setup to measure Thiele-Small parameters, but as I will be driving the load via a 2k resistor, I'm wondering if the amps output will be skewed in some way because it's not driving the proper amount of load.
  Reply With Quote
Old 27th June 2004, 03:49 PM   #2
diyAudio Member
 
jan.didden's Avatar
 
Join Date: May 2002
Location: Great City of Turnhout, Belgium
Blog Entries: 7
Rich,

If you want a 2k series resistance you don't really need the amp, just drive it from your audio oscillator, or if you use a test CD, from the preamp (if it's solid state; tube preamps generally can't handle that kind of load).

If you really need/want to use the amp, you can always load it with say 8 ohms in addition to the 2k + speaker test load. The amp won't notice the difference.

Jan Didden
__________________
If you don't change your beliefs, your life will be like this forever. Is that good news? - W S Maugham
Check out Linear Audio!
  Reply With Quote
Old 27th June 2004, 03:57 PM   #3
johnnyx is offline johnnyx  United Kingdom
diyAudio Member
 
Join Date: Jan 2004
Location: manchester
From what I understand of it, if the load impedence is 2k, then you just need the Class A stage. The high current Class C stage will not be turned on much by the load current. It works like a Wheatstone Bridge in series with the load, so that when the load current is sufficient to unbalance the bridge, the Class C stage supplies the load current while the Class A stage fills in the missing bits of the crossover region. At the same time, the Class C stage increases the effective load impedence of the Class A stage, reducing the distortion.
Why not use a Class A amp for such a load?
  Reply With Quote
Old 27th June 2004, 04:11 PM   #4
sreten is offline sreten  United Kingdom
diyAudio Member
 
Join Date: Nov 2003
Location: Brighton UK
Default Re: Technics Class-AA / Sandman Bridge

Quote:
Originally posted by richie00boy
Does this type of amp/topology rely on driving a loudspeaker of impedance within a narrow range?

I am going to use one of these amps in a test setup to measure Thiele-Small parameters, but as I will be driving the load via a 2k resistor, I'm wondering if the amps output will be skewed in some way because it's not driving the proper amount of load.
Simple answer is no it doesn't and no it won't.

FWIW technics class AA is not a sandman bridge, it uses a class
B power amplifier to drive the centre point of a 15-0-15V high
current class A amplifiers floating supplies.

sreten.
  Reply With Quote
Old 27th June 2004, 04:42 PM   #5
Did it Himself
diyAudio Member
 
richie00boy's Avatar
 
Join Date: Nov 2003
Location: Gloucestershire, England, UK
Thanks for all the great (and quick) replies.

Unfortunately my oscillator will only output up to 0dB and in order to generate 100mV across my loudspeaker (at 10 ohms impedance) then I need to swing 22V from my amp.

I would just use a class-A amp as the current requirement is very low, and I have thought about building one as I will be testing drivers a bit. I've also thought about bridging NE5532, run at 18V split this would just about give me enough swing. However, I would like to do some testing today so using my amp seemed like a good choice.

sreten, I thought that what you had described there is the Technics 'New Class-A' topology, not the Class-AA which I thought was based on Dr Sandman's circuit.
  Reply With Quote
Old 27th June 2004, 05:11 PM   #6
sreten is offline sreten  United Kingdom
diyAudio Member
 
Join Date: Nov 2003
Location: Brighton UK
Quote:
Originally posted by richie00boy
sreten, I thought that what you had described there is the Technics 'New Class-A' topology, not the Class-AA which I thought was based on Dr Sandman's circuit.
As fars as I'm aware "New class A" is "Super class A" is Technics "class AA".

You could always use an op-amp configured with currentfeedback for an output impedance
of 2kohm, current capability (NE5532 should be fine) would then be the only issue.

sreten.
  Reply With Quote
Old 27th June 2004, 05:26 PM   #7
Did it Himself
diyAudio Member
 
richie00boy's Avatar
 
Join Date: Nov 2003
Location: Gloucestershire, England, UK
When the amp was a current model, the lower ones in the range were badged New Class-A. I thought they were different from my Class-AA, maybe it was just a marketing trick.

As the 2k resistor is really only to mimic constant-current operation, I have also thought about just making a cc amp using an op-amp buffered by small-signal transistors. That way I would only need to swing less than a volt.
  Reply With Quote
Old 27th June 2004, 06:42 PM   #8
djk is offline djk
diyAudio Member
 
djk's Avatar
 
Join Date: Feb 2001
Location: USA
"I have also thought about just making a cc amp using an op-amp buffered by small-signal transistors. That way I would only need to swing less than a volt."

Best solution yet.
  Reply With Quote
Old 27th June 2004, 06:44 PM   #9
diyAudio Member
 
jan.didden's Avatar
 
Join Date: May 2002
Location: Great City of Turnhout, Belgium
Blog Entries: 7
Yes, there is a neat circuit to do this called a "Howland current pump", works with any standard opamp and a couple of resistors. Google should lead you to it.

Jan Didden
__________________
If you don't change your beliefs, your life will be like this forever. Is that good news? - W S Maugham
Check out Linear Audio!
  Reply With Quote
Old 27th June 2004, 06:47 PM   #10
diyAudio Member
 
jan.didden's Avatar
 
Join Date: May 2002
Location: Great City of Turnhout, Belgium
Blog Entries: 7
....http://eportal.apexmicrotech.com/mai...m_id=&f_page=5

Jan Didden
__________________
If you don't change your beliefs, your life will be like this forever. Is that good news? - W S Maugham
Check out Linear Audio!
  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
80s Amps: Technics New Class A, SU-V2X arki Chip Amps 7 31st October 2013 01:21 AM
Technics Class A Bias Circuits sdman Solid State 5 1st July 2010 05:58 PM
Technics Class A Biasing atiq19 Solid State 46 15th January 2009 09:31 AM
Technics new class-a amp (runs cold ?) Rixsta Solid State 2 17th March 2005 09:56 PM


New To Site? Need Help?

All times are GMT. The time now is 09:11 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