best amp PCB layout..1 vs 2 PCBs - 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 1st August 2004, 08:42 PM   #1
diyAudio Member
 
LineSource's Avatar
 
Join Date: Sep 2003
Location: SiliconValley
Default best amp PCB layout..1 vs 2 PCBs

Appreciate shared knowledge and test data or pictures from experienced amplifier PCB designers. Thanks...

Design target: 25-50 watt Class A low voltage, high current amplifier with 4+4 output transistors

What the best PCB layout?

1) A single PCB that takes advantage of high capacitance density of 10-16V caps.(attached)
a) create a star ground point on PCB
b) attach rectifier diodes above PCB star ground point with short copper bus bar
b) put input adjacent to PCB star ground. Put output close to input for short feedback path
c) many small caps on PCB for unregulated output power supplies. 0.3-0.5F total
d) modest power regulated supplies for driver circuitry on PCB
e) use 1" stand-offs to mount PCB to heatsink to reduce heat transfer


2) Two PCBs wired together
a) PCB for output transistors and output power supply filter caps mounted to heat sink
b) PCB for driver circuitry and regulated power supply
c) wire both boards to star ground point at rectifier diodes
d) wire feedback directly from output point to feedback point on driver PCB

3) Better alternative?...description...data...picture?
Attached Images
File Type: gif pcb1.gif (94.7 KB, 520 views)
  Reply With Quote
Old 1st August 2004, 09:10 PM   #2
diyAudio Member
 
Join Date: Aug 2003
Location: Prague,Czech Republic
What is real size of showed PCB ?
  Reply With Quote
Old 1st August 2004, 10:15 PM   #3
diyAudio Member
 
LineSource's Avatar
 
Join Date: Sep 2003
Location: SiliconValley
The example PCB layout is ~ 60 sq inches...9" x 6.6", $23 prototype quantities 2 layer, 2 oz copper.

Four output transistors are evenly spaced on each 9" edge, eight total, attached to the heat sink. 48 x 8,200uF @16V capacitors are on the PCB for the +/- 10V unregulated output power supply.
  Reply With Quote
Old 2nd August 2004, 04:17 PM   #4
diyAudio Member
 
Join Date: Feb 2001
Location: Mars
Default Re: best amp PCB layout..1 vs 2 PCBs

What the best PCB layout?

I think this book has a section on pcb layout recommendations.
http://www.amazon.com/exec/obidos/tg...glance&s=books

1 vs 2
From what I've noticed, most people here chose to make
the pcb's small to reduce cost, that seems to be #1 priority.
I did a layout of a 6.5" x 10.75" board, 4 layer and it cost alot.
qty 10 @ $1000.00
qty 20 @ $1200.00
+$250 NRE
  Reply With Quote
Old 2nd August 2004, 04:32 PM   #5
diyAudio Member
 
jan.didden's Avatar
 
Join Date: May 2002
Location: Great City of Turnhout, Belgium
Blog Entries: 7
Well, I don't know. If your total PCB area is the same, I'm pretty sure a single one would be cheaper than two parts, unless it gets so big that the manufacturer has to use special machines. That will rarely be the case in audio.

Your board is 1) pretty big, and 2) 4-layer. That's not your regular audio PCB, and the 4 layers really up the price.

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 2nd August 2004, 04:47 PM   #6
sam9 is offline sam9  United States
diyAudio Member
 
sam9's Avatar
 
Join Date: Jun 2002
Location: Left Coast
I can attest to two considerations that the origan poster inquired about.

Location of output relative to input -- keep them away from each other. An otherwise stable amp can become an oscillator just by putting the output circuitry in close proximity to the input! In fact, I'm moving toword the idea the best place for the zobel and output inductor (if you use them) is off the PCB and at the binding posts.

Power ground and signal ground (signal return?) should be separate and exit the PCB from different points. This implies the star point is off-board. There may be some ambiguities with some ground points as to whether they are power or signal related. I use the rule that if the purpose is to provide a low impedance path for unwanted signals "riding the rails", its a power ground. Treating the zobel as above moots what to do with that.
  Reply With Quote
Old 2nd August 2004, 05:13 PM   #7
1audio is offline 1audio  United States
diyAudio Member
 
Join Date: Mar 2004
Location: SF Bay Area
Blog Entries: 3
Default Challenges of a small board amp

I have always used smaller PCB's but not for cost. The benifits are short paths low inductances and and low stray caps to degrade performance. However the big challenge is keeping the magnetic fields at bay. There is a lot of current in the output section and it will couple into an trace parallel even if the trace is some distance away (by PCB standards). The biggest offenders are the leads around rectifiers and filter caps. Since these are dealing with line frequency the noise induced has nothing to do with audio and is very audible.

What I did in the Spectral amps was move the low level circuits into a small daugter board at right angle to the main board and orient it as best possible at right angle to the main current path.

I always kept the rectifiers and main supply caps away from the board. Smaller local caps (1000 uF) handled the HF currents and the remote (10" of #12 wire) 50,000 uF caps dealt with the high current low frequency requirements. It also kept the rectifier close to the transformer, reducing the radiating window in the supply leads.

I prefer bridge tied loads as the best way to keep unwanted currents out of the ground, however it greatly increases the complexity of the amp.

Ohter people have different philosophies here but these have always worked well for me.
Demian
__________________
Demian Martin
Product Design Services
  Reply With Quote
Old 2nd August 2004, 05:31 PM   #8
diyAudio Member
 
Join Date: Aug 2003
Location: Prague,Czech Republic
Are you working for Spectral ? Or was you ?
  Reply With Quote
Old 2nd August 2004, 06:30 PM   #9
1audio is offline 1audio  United States
diyAudio Member
 
Join Date: Mar 2004
Location: SF Bay Area
Blog Entries: 3
Default Spectral

I co-founded Spectral many years ago. I designed the amps and preamps through the late 80's. Keith Johnson has been doing the chores since using the same guidelines.
-Demian
__________________
Demian Martin
Product Design Services
  Reply With Quote
Old 2nd August 2004, 07:08 PM   #10
diyAudio Member
 
Join Date: Aug 2003
Location: Prague,Czech Republic
Spectral was one of my favored firms, 'cos was made very high speed amps, which I like too and had clear and logical prospect. But explain me, why this firm recomend for his product cables, which absolutely kills good parameters of this amps, 'cos this cables have inside high cut filters, which cut hearable in acoustic band ? Is it not somewhat contrast demand ? Or aren't this amps stable ? Or is it for, that here exist close relatives between both owners, how I heard somewhere ?
  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
Eagle vs. Sprint-Layout for PCB design/layout hollowman Parts 11 12th January 2014 10:01 PM
FS: Aleph-X PCBs , NIGC PCBs , OPA541AM OpAmps e.lectronick Swap Meet 25 6th March 2013 08:40 PM
Recommendations on Ono phono stage PCBs or layout files luvdunhill Pass Labs 2 17th February 2007 05:23 AM
Trade Aleph X PCBs for Aleph P 1.7 PCBs highbias Pass Labs 0 27th September 2004 06:59 PM
Where to get PCBs done in UK? Frisbee78 Parts 5 6th February 2004 07:02 AM


New To Site? Need Help?

All times are GMT. The time now is 06:34 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