Can I have some comments on this design? - 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 5th September 2009, 02:18 PM   #1
diyAudio Member
 
Join Date: Aug 2007
Default Can I have some comments on this design?

Hi there,

I'm about to get the ferric chloride out and make a few boards up, and before I do I'd appreciate any comments on the design and layout atached. in return they are placed in the public domain, for what they're worth

It's intended for 100W into 8R. The DC rails will be +/-50V

I think the design is fairly conservative - it's based on a dev board I made with the ability to try out a lot of different ideas; my conclusion was to keep it simple. It fits on a standard 100x160 eurocard and the only external components are the output power transistors (possibly some ballast resistors for them) and OP transistor d-caps (these will be wired- point-to-piont with their own ground).

I want to use low voltage-high performance transistors in some places, and I'd be really interested in any comments about start-up / fault etc conditions that might over-volt them. I'd like any suggestions for more suitable transistors for the LTP too...

Also If I've done anything silly

Cheers,
Attached Files
File Type: pdf Amp_schem.pdf (134.5 KB, 353 views)
File Type: pdf Amp_copper.pdf (55.2 KB, 69 views)
File Type: pdf PCB Amp_silk.pdf (34.0 KB, 59 views)
__________________
I am not an atomic playboy.
  Reply With Quote
Old 6th September 2009, 04:20 PM   #2
diyAudio Member
 
destroyer X's Avatar
 
Join Date: Feb 2004
Location: Recife - Brasil Northeast
Default Maybe transistor input capacitance will reduce your audio quality

But your circuit seems very interesting.

Have you built it?

I will be looking forward by your testings into the real thing.

regards,

Carlos
__________________
This Sunday assemble a toy amplifier....a good fun to your weekend; https://www.youtube.com/watch?v=yk0qvkwsAOY
  Reply With Quote
Old 6th September 2009, 04:57 PM   #3
tnsguy is offline tnsguy  United States
diyAudio Member
 
Join Date: Jul 2004
Location: San Diego
Default I think Q15 and Q17 should be PNP?

They are for cascode, right?

Tom
  Reply With Quote
Old 6th September 2009, 06:56 PM   #4
diyAudio Member
 
Join Date: Aug 2007
Hi,

Thanks Tom, yes you're right (I spotted that right after I submitted the post
Will work much better with PNP...
Also the bias adjust pot should be 1k, not 500R.

Cheers,
-- Ben
__________________
I am not an atomic playboy.
  Reply With Quote
Old 6th September 2009, 07:07 PM   #5
diyAudio Member
 
Join Date: Aug 2007
Hi Carlos,

The three transistors on each side of the LTP are after a mic amp I did with multiple supermatched pairs on the front end; depending on testing I may only fit one or two of them. It almost seems like something for nothing in terms of noise though.

I have built a fairly rough prototype of it (with PNP transistors in Q15/17...) and it works; step response and FFT looks good, but once I get the PCBs done I'll take it into work where I have an AP and let you know.
__________________
I am not an atomic playboy.
  Reply With Quote
Old 6th September 2009, 07:57 PM   #6
diyAudio Member
 
nigelwright7557's Avatar
 
Join Date: Apr 2008
Location: Carlisle, England
Why have you used multiple transistors in parallel ?

My amps work fine with one transistor where you have used 2 or 3.
__________________
PCBCAD50 software. http://www.murtonpikesystems.co.uk
  Reply With Quote
Old 6th September 2009, 09:05 PM   #7
diyAudio Member
 
Join Date: Aug 2007
Hi,
The reason for multiple transistors in the LTP is noise reduction.

Noise in this type of design is pretty much dominated by the input transistors; specifically by their base spreading resistance. Fitting three in parallel reduces this resistance by 2/3, and so noise should be reduced by 1/sqrt(3). Doesn't quite work that well in practice, but the reduction in noise is useful, given the cost.

The other places where there are two transistors in parallel are option fits - I was not sure whether I would want a TO92 or TO126 package in these positions so I've dual-pitched them to give me some options on transistor choice when I'm testing.

Cheers,
__________________
I am not an atomic playboy.
  Reply With Quote
Old 6th September 2009, 09:22 PM   #8
diyAudio Member
 
Join Date: Aug 2007
...specifically, if I need to increase the current from the Q20/Q26 source, I'm a bit concerned about running out of safe operating area with TO92 devices.
__________________
I am not an atomic playboy.
  Reply With Quote
Old 6th September 2009, 10:35 PM   #9
Pingrs is offline Pingrs  United Kingdom
diyAudio Member
 
Join Date: Jul 2005
Location: NW England
On a practical note. I'd make your pad drill marks much smaller (15 thou, say). You've almost no annulus to solder to, and they would easily lift with rework.

Cheers.
  Reply With Quote
Old 6th September 2009, 10:52 PM   #10
diyAudio Member
 
destroyer X's Avatar
 
Join Date: Feb 2004
Location: Recife - Brasil Northeast
Default I will be reading the thread... waiting you to do it real world

thank you Atomic

Carlos
__________________
This Sunday assemble a toy amplifier....a good fun to your weekend; https://www.youtube.com/watch?v=yk0qvkwsAOY
  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
Any comments on this design? icebear Tubes / Valves 23 19th May 2009 04:07 PM
Need comments on amp design mightydub Solid State 28 24th December 2008 01:01 AM
My first amp design - comments blueskynis Solid State 36 26th March 2008 03:38 PM
Comments on TL design, pls Jorge Multi-Way 2 9th June 2005 03:05 PM
Comments on this design? G Tubes / Valves 0 16th October 2003 05:09 PM


New To Site? Need Help?

All times are GMT. The time now is 01:45 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