Solid State Testing- Tug of war - 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 12th February 2010, 11:05 AM   #1
diyAudio Member
 
sumaudioguy's Avatar
 
Join Date: Jan 2010
Location: Midwest U.S.A.
Default Solid State Testing- Tug of war

We actually test amps this way. Amps that seem like they will take it anyway and wondered if anyone has a valuable opinion for this test.

Take channel 1 of a stereo amp and hook it to channel 2 of the same amp with a resistor. This would be red to red binding post with the resistor in between. We start with a 4 ohm power resistor. Drive channel 1 and read all your favorite measurements on channel 1. Next look at the signal on channel 2 which is used as the virtual ground when driving channel 1 with your favorite test signals. This residual signal seems to speak volumes about the amplifier or in many cases the ampli-fire. Many amps do not like this test but the amps that do well here seem to usually sound pretty good in general and are often the most reliable. Of course this is if all normal testing goes well also.

I like this test as driving a speaker is kind of like pulling a trailer with a truck, robust is better.

Anyone have a thought about this? I really like this test!
  Reply With Quote
Old 12th February 2010, 03:47 PM   #2
diyAudio Member
 
Jan Dupont's Avatar
 
Join Date: Apr 2003
Location: Copenhagen, Denmark
Send a message via MSN to Jan Dupont
This test doesn't say anything about how the amp handles inductive and capacative loads like real speakers though.....
__________________
Free Schematic and Service Manual downloads www.audio-circuit.dk, Company: www.dupont-audio.com, Joint venture: www.DupontMantra.com
  Reply With Quote
Old 12th February 2010, 05:34 PM   #3
diyAudio Member
 
sumaudioguy's Avatar
 
Join Date: Jan 2010
Location: Midwest U.S.A.
Quote:
Originally Posted by Jan Dupont View Post
This test doesn't say anything about how the amp handles inductive and capacative loads like real speakers though.....
Yes you are correct.

We go on to add complex circuits there and resonators- L C in series with various resistors as a standard test method using a repeatable procedure. It is a virtual ground so in theory if it were perfect there would be no signal on channel 2. Always far from that in reality.

The straight resistor is very useful and valid for determining real damping factor at any frequency.

Speakers may be placed where the resistor goes. Does not get any more real than that.

For horrible load simulation a brush type low voltage AC motor is placed where the resistor goes.

I hope some of you try this with your favorite amps! Let us know what you find. This is also a great way to hook two amps together and learn which is the master... I mean for testing.- tug-o-war.
  Reply With Quote
Old 12th February 2010, 07:03 PM   #4
llwhtt is offline llwhtt  United States
diyAudio Member
 
Join Date: Jun 2008
Location: SoCal
Sounds similar to a method explained by Nelson Pass back in the early '80s. He used it in the Citation 12 mod. article for Audio Amateur. Go to PassDIY and find the Citation article.

Craig
  Reply With Quote
Old 23rd November 2011, 01:40 AM   #5
diyAudio Member
 
unclejed613's Avatar
 
Join Date: Dec 2006
actually this is a good way to measure output impedance (or inversely damping factor). if the output of amp A is 10Vpeak (20Vp-p), and the resistor is 10 ohms, then you are feeding 1Apeak into amp B's output. so a measurement with an oscope on amp B's output will show a relationship of 1mV/milliohm. this will also reveal if the amp is underbiased, because you will see spikes at the zero crossing due to the changes in output impedance as the transistors move through the crossover region. this may be an effective way to correctly set the bias on an amp without a distortion analyzer (i really need to experiment with this a bit more before i recommend it). i'm not yet sure what the effects of amp A being underbiased or overbiased would be, which is another reason i need to explore this a bit more
__________________
Vintage Audio and Pro-Audio repair ampz(removethis)@sohonet.net
spammer trap: spammers must die
  Reply With Quote
Old 23rd November 2011, 10:04 AM   #6
ontoaba is offline ontoaba  Indonesia
diyAudio Member
 
ontoaba's Avatar
 
Join Date: Nov 2009
Location: Kudus, Malang, Dieng
Good idea, change the resistor with real loudspeaker too they are reactive.
My test is little different, using sweep AC current source connected to amp output.
  Reply With Quote
Old 23rd November 2011, 10:13 AM   #7
ontoaba is offline ontoaba  Indonesia
diyAudio Member
 
ontoaba's Avatar
 
Join Date: Nov 2009
Location: Kudus, Malang, Dieng
Quote:
Originally Posted by unclejed613 View Post
this will also reveal if the amp is underbiased, because you will see spikes at the zero crossing due to the changes in output impedance as the transistors move through the crossover region. this may be an effective way to correctly set the bias on an amp without a distortion analyzer (i really need to experiment with this a bit more before i recommend it). i'm not yet sure what the effects of amp A being underbiased or overbiased would be, which is another reason i need to explore this a bit more

Not only underbiased, but bad combination of output filter and feedback loop in classB or small bias classAB creates some noise when crossing, while most classA is free.
  Reply With Quote
Old 23rd November 2011, 12:37 PM   #8
diyAudio Member
 
unclejed613's Avatar
 
Join Date: Dec 2006
i have done some investigation of this. the best method is to use a "power" version of a Howland current source instead of an amp and resistor. if the amp output impedance is more than 100 milliohms, the measurement begins to show a bit of error. about 1% per 100 milliohm. a howland current source would also be useful for charting the impedance vs frequency curves of speakers, crossover networks, etc... and the current is set with a simple scaling resistor. the one i built to test the idea has switchable scaling for 1A, 100mA, 10mA, 1mA.... i just have to experiment with it more to find out if there are other sources of error i'm overlooking. i also want to try using it as an ESR meter (or even better a curve tracer for in-circuit testing of components).
__________________
Vintage Audio and Pro-Audio repair ampz(removethis)@sohonet.net
spammer trap: spammers must die

Last edited by unclejed613; 23rd November 2011 at 12:40 PM.
  Reply With Quote
Old 23rd November 2011, 01:12 PM   #9
jez is offline jez  United Kingdom
diyAudio Member
 
Join Date: Jan 2004
Location: n.e england
It's an old idea. IIRC Tim De Paravicini described this method for testing damping factor many years ago.
__________________
Repairs and mods to Real Hi-Fi, guitar amps and P.A. in North East England. http://www.arklesselectronics.com
  Reply With Quote
Old 23rd November 2011, 03:08 PM   #10
diyAudio Member
 
dirkwright's Avatar
 
Join Date: May 2011
Location: Virginia
Anyone build a DIY version of the Power Cube by Audiograph?
  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
Solid Solid State Power Amplifier PMA Solid State 265 30th August 2011 09:04 PM
solid state just isn't doing it for me!! bonsai171 Tubes / Valves 9 13th July 2004 12:25 PM
The Solid State Wiki - Your solid state reference guide Jason Solid State 0 25th June 2002 06:26 PM


New To Site? Need Help?

All times are GMT. The time now is 08:14 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