Dx Blame MKIII-Hx - Builder's thread - Page 117 - 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 22nd April 2012, 12:02 PM   #1161
diyAudio Member
 
Join Date: May 2011
Location: Quebec
I won't argue on subjective topics. I did my homework and came with objective results.

Refer to the image below...

The offset test was made with the signal input leads shorted. I did it both with the real physical 42pounds heavy amplifier, and with the simulator. BOTH gave the same results...

There IS a DC offset voltage at the input transistor's base. The input cap DO block this from getting back in your source.

By removing the cap, that DC offset will leak to the ground and its amplitude be altered thus changing the stability of the speaker-out's offset.

Furthermore if, like me, you have an input pot to control the input sensitivity, turning it will change the resistance of the circuit (input DC offset to ground) and will alter greatly the DC offset at speaker-out. Turning that input pot makes the speaker go in and out like crazy, I guess the output varies by many volts .

Do your own tests my friend... and you will see.

I got to report this because other people may be tempted to remove the input cap and they risk breaking something. This amp cannot run directly coupled to a source
Attached Images
File Type: png Jump_Input_Cap.png (143.6 KB, 319 views)
  Reply With Quote
Old 22nd April 2012, 01:28 PM   #1162
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Canon,
well argued. Don't let them put you down when you have the evidence to support your conclusions and/or statements.

I would rather have music than broken equipment.

In my book "broken equipment" can never reproduce as well as working equipment.
__________________
regards Andrew T.
  Reply With Quote
Old 22nd April 2012, 01:31 PM   #1163
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
375mVdc of input offset across 47k indicates that a fairly high current is flowing from the base of the input transistor. It also indicates a low input impedance to the amplifier input stage.

That can be explained by the choice of 2n5401 as the input transistors.

Do you know the hFE of the input transistor/s that you used?
__________________
regards Andrew T.
  Reply With Quote
Old 22nd April 2012, 05:39 PM   #1164
a.wayne is offline a.wayne  United States
diyAudio Member
 
a.wayne's Avatar
 
Join Date: May 2008
Location: Front Row Center
Quote:
Originally Posted by canonnica View Post
I won't argue on subjective topics. I did my homework and came with objective results.

Refer to the image below...

The offset test was made with the signal input leads shorted. I did it both with the real physical 42pounds heavy amplifier, and with the simulator. BOTH gave the same results...

There IS a DC offset voltage at the input transistor's base. The input cap DO block this from getting back in your source.

By removing the cap, that DC offset will leak to the ground and its amplitude be altered thus changing the stability of the speaker-out's offset.

Furthermore if, like me, you have an input pot to control the input sensitivity, turning it will change the resistance of the circuit (input DC offset to ground) and will alter greatly the DC offset at speaker-out. Turning that input pot makes the speaker go in and out like crazy, I guess the output varies by many volts .

Do your own tests my friend... and you will see.

I got to report this because other people may be tempted to remove the input cap and they risk breaking something. This amp cannot run directly coupled to a source
Martin ,

Andrews rhetoric aside , there was no put down , my response was that of suprise and thanks for clarifying the results ...

Quote:
Originally Posted by AndrewT View Post
Canon,
well argued. Don't let them put you down when you have the evidence to support your conclusions and/or statements.

I would rather have music than broken equipment.

In my book "broken equipment" can never reproduce as well as working equipment.


I would rather you answer direct questions instead of flying in with your girlish retorts, Instead you take every chance you get for personal insults, even took time to hurl one at Carlos ...


Silly Rabbit ......
  Reply With Quote
Old 22nd April 2012, 05:42 PM   #1165
a.wayne is offline a.wayne  United States
diyAudio Member
 
a.wayne's Avatar
 
Join Date: May 2008
Location: Front Row Center
Quote:
Originally Posted by AndrewT View Post
Canon,
well argued. Don't let them put you down when you have the evidence to support your conclusions and/or statements.

I would rather have music than broken equipment.

In my book "broken equipment" can never reproduce as well as working equipment.
What about bad music ...?

Quote:
Originally Posted by AndrewT View Post
375mVdc of input offset across 47k indicates that a fairly high current is flowing from the base of the input transistor. It also indicates a low input impedance to the amplifier input stage.

That can be explained by the choice of 2n5401 as the input transistors.

Do you know the hFE of the input transistor/s that you used?
What would you change it to ..?
  Reply With Quote
Old 22nd April 2012, 06:09 PM   #1166
diyAudio Member
 
Join Date: May 2011
Location: Quebec
As per the specsheet, hFE is min 50-60 and max 240. (see pic)

Is there anything bad about these figures and this choice of transistor?

Mart.
Attached Images
File Type: png 2n5401_hfe.png (6.2 KB, 289 views)
  Reply With Quote
Old 22nd April 2012, 06:33 PM   #1167
a.wayne is offline a.wayne  United States
diyAudio Member
 
a.wayne's Avatar
 
Join Date: May 2008
Location: Front Row Center
What voltage are you operating the amp at Martin ....?
  Reply With Quote
Old 22nd April 2012, 08:13 PM   #1168
diyAudio Member
 
Join Date: May 2011
Location: Quebec
Quote:
Originally Posted by a.wayne View Post
What voltage are you operating the amp at Martin ....?
64VDC plus 64VDC
  Reply With Quote
Old 23rd April 2012, 08:53 AM   #1169
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Quote:
Originally Posted by a.wayne View Post
........... personal insults, even took time to hurl one at Carlos ...
I take exception to Carlos' claims.
I rubbish his behaviour.

I have done it in the past and where/when necessary, I will repeat my confirmation where there are mistakes or bad choices or downright lies.
__________________
regards Andrew T.
  Reply With Quote
Old 26th April 2012, 05:00 PM   #1170
diyAudio Member
 
Join Date: May 2011
Location: Quebec
Default Output stage bias

Back with more questions...

The output stage bias. Carlos mentioned a way to adjust it: measure the voltage drop across output resistor to obtain 1mV. However in the emitter-follower configuration like the HX, Dr. Self has determined that optimum is very far from that value.

Dr. Self suggest a voltage drop of about 27mV across those 0.47r resistors... Am I missing something, or based on this, Is my amp very underbiased with that 1mV drop??

Please see the pics below that are from Dr. Self's book...

Martin.
Attached Images
File Type: png Bias-Vq.png (16.7 KB, 216 views)
File Type: png Bias-Optimal_Values.png (22.4 KB, 212 views)
  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
Dx Blame ST - Builder's thread - post pictures, reviews and comments here please. destroyer X Solid State 1711 17th August 2014 01:37 AM
Dx Blame MKIII Supercharged will soon be released destroyer X Solid State 346 22nd April 2014 03:01 PM
group buy for DX Blame MKIII Hx PCBs ByronInPortland Group Buys 247 5th December 2012 12:05 AM
Group By: DX Blame MKIII Hx boards ByronInPortland Group Buys 9 19th July 2011 07:21 AM
Dx Blame MKII, an obvious evolution from the Dx Blame ES/ST destroyer X Solid State 4 25th September 2010 06:41 PM


New To Site? Need Help?

All times are GMT. The time now is 02:00 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