:: class a symetric power amplifier :: - 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 14th October 2002, 10:59 AM   #1
diyAudio Member
 
dhengkoel's Avatar
 
Join Date: Nov 2001
Location: CIA
Default :: class a symetric power amplifier ::

Dear all,

I've redesign an old schematic and I came up with this schematic ... Any comment or designs you can recommend is welcome.

Thanks:
ragil.hastomo
Attached Images
File Type: jpg sym_class_a_front.jpg (61.5 KB, 2537 views)
__________________
:: The last but not least ::
  Reply With Quote
Old 14th October 2002, 11:00 AM   #2
diyAudio Member
 
dhengkoel's Avatar
 
Join Date: Nov 2001
Location: CIA
Default :: the end stage ::

Here the end stage .....
Attached Images
File Type: jpg sym_class_a_end.jpg (37.8 KB, 2471 views)
__________________
:: The last but not least ::
  Reply With Quote
Old 14th October 2002, 12:23 PM   #3
AKSA is offline AKSA  Australia
diyAudio Member
 
Join Date: Sep 2001
Location: Melbourne, Australia
Hi Sdr Hastomo,

Amp anda cukup bagus - bunyinya jelas, murni......

I think it would be terrific, but can make one suggestion.

Each of the two drivers should have a 100R base stopper; and output devices should have a 10R base stopper. The 120R/100n should be connected between the two output device bases as shown, and you could delete the 270R resistors from driver base to emitter.

With these changes, it's a good design.........

Kapan anda membikinnya??

Cheers,

Hugh

www.aksaonline.com
  Reply With Quote
Old 14th October 2002, 12:25 PM   #4
AKSA is offline AKSA  Australia
diyAudio Member
 
Join Date: Sep 2001
Location: Melbourne, Australia
Oh,

I should add that R4 and R25 (both 1K5) are unnecessary. If the diff pairs use matched transistors, and if the input bias resistor matches the resistance from output to fb node, then balance in the diff pairs is automatic.

Cheers,

Hugh
  Reply With Quote
Old 14th October 2002, 01:14 PM   #5
diyAudio Member
 
Join Date: Sep 2002
Location: Sweden
Hugh,

I know it is common to omit these resistors in diff pairs, but is
it really true that it does not matter? From a theoretical point
of view I think it will make a difference. At the Q point, we will
have the same Icq through both transistors in the diff pair if
these are matched. However, if we omit the collecor resistor on
one of them we get different Vceq. This means the power
dissipation differs and, hence, the temperature, which will
make the transistors slightly unbalanced in practice. It will
probably not make much of a difference in this particular case,
but resistors are cheap. Probably 1k5 is not the optimal value
to achieve balance, though, since the other transistor has a
load in parallel with its collector resistor.
  Reply With Quote
Old 14th October 2002, 07:00 PM   #6
The one and only
 
Nelson Pass's Avatar
 
Join Date: Mar 2001
Or you can buy an old KSA50 on ebay....



Here's a tip: put the trim pot base-emitter so that
when it gets old and dirty the bias goes to 0 instead
of infinity.

  Reply With Quote
Old 15th October 2002, 12:34 PM   #7
diyAudio Member
 
Join Date: Feb 2002
Location: Germany
dhengkoel,

are you sure the connections on the feedback network are drawn right? There is two lines leaving the first picture but only one is continued in the second picture. Also, I am not sure that all the connection points are correct.

What is the function of R14 by the way?

Regards,

Eric
  Reply With Quote
Old 16th October 2002, 12:14 AM   #8
The one and only
 
Nelson Pass's Avatar
 
Join Date: Mar 2001
R14 is the actual feedback resistor. The other two in
series with capacitors are the compensation, one looking
at the output and the other nested to the output of the
voltage gain devices. The diagram should show R12, 14, and 18
attached together on the left, which I can't see.
  Reply With Quote
Old 16th October 2002, 12:36 AM   #9
diyAudio Member
 
Morello's Avatar
 
Join Date: Jan 2002
Location: Sweden
Send a message via ICQ to Morello
Hello Sirs,

I suggest that VR1 i sconnected between base and emiter.

If you connect it as shown in the schematic, the bias-voltage will increase to very high levels if the whiper of VR1 fails.

Otherwise, it look like a proper symmetric design

SE-amps are best avoided, or what do you think Mr. Nelsson?

best regards
__________________
"It was never supposed to be a hit, it was supposed to be a Joe Morello drum solo"- Paul Desmond
  Reply With Quote
Old 16th October 2002, 02:52 AM   #10
diyAudio Member
 
dhengkoel's Avatar
 
Join Date: Nov 2001
Location: CIA
Smile :: full schematic in one sheet ::

Quote:
Hugh: Each of the two drivers should have a 100R base stopper; and output devices should have a 10R base stopper.
Saya akan menyelesaikannya akhir bulan ini. [I will finished it at the end of this month.]
Quote:
Nelson Pass: Or you can buy an old KSA50 on ebay.... Here's a tip: put the trim pot base-emitter so that when it gets old and dirty the bias goes to 0 instead of infinity.
The diagram should show R12, 14, and 18 attached together on the left, which I can't see.
I can't buy the KSA-50, that's too much expensive for me [sorry for that].
Is this schematic too close with your design KSA-50? I don't see the KSA-50 schematic yet.
I found the PCB in an old shop. Actually it's for 100w class AB amplifier. So I redesign it and decrease the voltage rail to 25v, but increase the Iq to 1.1A .....
Is that ok if I change the Q4 to PNP? [Because the PCB is ready ...]

Anyway thanks all for the comment; Here the full schematic in one sheet ....

Regards:
ragil.hastomo
Attached Images
File Type: jpg sym_class_a_full.jpg (92.3 KB, 1993 views)
__________________
:: The last but not least ::
  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
High Power Class G amplifier digitoxin Solid State 29 27th October 2009 10:56 AM
DIY Low Power Class A (or AB) amplifier suggestions gareth Solid State 2 16th June 2009 03:46 PM
Class A diy power amplifier jmar Solid State 1 18th January 2004 07:10 PM
Chassis for low power class A amplifier ppereira Pass Labs 4 16th March 2003 03:52 PM
class a power amplifier janey Solid State 4 30th August 2001 11:48 PM


New To Site? Need Help?

All times are GMT. The time now is 05:57 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