Go Back   Home > Forums > Amplifiers > Chip Amps

Chip Amps Amplifiers based on integrated circuits

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 15th August 2006, 11:08 PM   #1
diyAudio Member
 
enzedone's Avatar
 
Join Date: Nov 2004
Location: New Zealand
Default Pushing the limit of supply voltage

I have a tranny that'll give me 42.4VDC (+/-) unloaded. I think this is right on the limit for a LM3785?

But I got the thing free out of an old amp.
__________________
I realized that a major part of my job was to figure out how to use technology control to create economic force, or leverage, such that money and business flowed in Microsoft's direction” — Alex St.John, father of DirectX.
  Reply With Quote
Old 15th August 2006, 11:13 PM   #2
Sherman is offline Sherman  United States
diyAudio Member
 
Join Date: Feb 2004
Location: Chicago area
The spec sheet says 84 volts max so you are .8 V over the limit.

However since the 42.4 is unloaded you can count on a few volts dropping when you connect it to your amp. You will be under the limit.

Build it!
__________________
--Sherman
  Reply With Quote
Old 16th August 2006, 12:00 AM   #3
diyAudio Member
 
enzedone's Avatar
 
Join Date: Nov 2004
Location: New Zealand
Default Build and check

Yeah, I'll build the power supply up and then check again, just to make sure it's not too far out.
__________________
I realized that a major part of my job was to figure out how to use technology control to create economic force, or leverage, such that money and business flowed in Microsoft's direction” — Alex St.John, father of DirectX.
  Reply With Quote
Old 16th August 2006, 12:07 AM   #4
diyAudio Moderator
 
pinkmouse's Avatar
 
Join Date: Apr 2002
Location: Chatham, England
You will need big heatsinks though...
__________________
Al
I conceive of nothing, in religion, science or philosophy, that is more than the proper thing to wear, for a while. Charles Fort
  Reply With Quote
Old 16th August 2006, 12:13 AM   #5
diyAudio Member
 
enzedone's Avatar
 
Join Date: Nov 2004
Location: New Zealand
Lightbulb Heatsink

Well, I have a 3 metre length of heatsink sitting in the garage, so I think that should cover it




Brett
__________________
I realized that a major part of my job was to figure out how to use technology control to create economic force, or leverage, such that money and business flowed in Microsoft's direction” — Alex St.John, father of DirectX.
  Reply With Quote
Old 16th August 2006, 05:27 AM   #6
pwan is offline pwan  United Kingdom
diyAudio Member
 
Join Date: Apr 2006
Location: Earth
Quote:
Originally posted by Sherman
The spec sheet says 84 volts max so you are .8 V over the limit.

However since the 42.4 is unloaded you can count on a few volts dropping when you connect it to your amp. You will be under the limit.

Build it!
just wonder if using resistor ( one or more "1 Ohm 10 W" per rial) in series will help more voltage dropping and a bit lower ripple?
  Reply With Quote
Old 16th August 2006, 05:53 AM   #7
diyAudio Member
 
Join Date: Apr 2003
Location: Portland,Oregon
Blog Entries: 4
Send a message via AIM to DigitalJunkie
Or perhaps some chokes with a bit of DCR?
  Reply With Quote
Old 16th August 2006, 08:02 AM   #8
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Hi,
using the higher supply voltages has the consequence of demanding you use the higher load impedances as well.

Effectively 4 to 8ohm and 6ohm speakers are out the window.
Some demanding 8ohm may also overstress the chips.

12ohm or 16ohm speakers become your ideal match. Headphones?
__________________
regards Andrew T.
  Reply With Quote
Old 16th August 2006, 01:16 PM   #9
macboy is offline macboy  Canada
diyAudio Member
 
Join Date: Oct 2003
Location: Ottawa, Canada
The LM3886 will tolerate extreme supply voltages better than the LM3875. The LM3875 doesn't have a lot of wiggle room (its safe operating area is more limited than the LM3886).

If you parallel two LM3875s and drive no less than 8 ohms, you may get decent results.

You could also try lowering the voltage using a capacitor multiplier or a regulator. Either one will help clean up the power supply in addition to lowering the voltage to a more ideal point.
  Reply With Quote
Old 16th August 2006, 04:17 PM   #10
rabbitz is offline rabbitz  Australia
diyAudio Member
 
rabbitz's Avatar
 
Join Date: Jul 2003
Location: Newcastle, Australia
Throwing a larger heatsink at it will work to a certain limit and you can forget about it for a TF package but the TA package is on the limit with a 6R load.

Reducing the voltage is a better way to go and have a look around for the Overture Design Guide spreadsheet at National Semi Conductor. That will give you a guide at what you can and can't do.
__________________
No longer DIY active
  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
Power supply current limit for testing kubeek Solid State 1 12th February 2009 09:57 AM
Preamp output voltage limit ashlar Car Audio 2 2nd December 2008 11:41 AM
Pushing OnSemi transistors to the limit EWorkshop1708 Solid State 23 15th March 2008 12:44 AM
Variable 6922 heater to cathode voltage limit...? ashok Tubes / Valves 2 13th April 2007 08:16 AM
How to make current limit for PC supply? luka Power Supplies 10 27th February 2007 03:31 PM


New To Site? Need Help?

All times are GMT. The time now is 12:55 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