Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Chip Amps Amplifiers based on integrated circuits

Specific Power Supply Question...
Specific Power Supply Question...
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
Thread Tools Search this Thread
Old 26th July 2011, 01:11 AM   #1
Ben78 is offline Ben78
diyAudio Member
Join Date: Sep 2010
Default Specific Power Supply Question...

Hi All!

I have been putting together a 2.1 chip amp system together. I have the 2 channels sorted but am now working on the .1 for sub.

The 2 channels are LM3876 and kit calls for 25-0-25 secondaries at 80VA per channel (I am using a 22-0-22 160VA currently)

I am looking at a ebay BTL LM3886 or TDA7293 prepopulated board for the sub channel. Most of these are asking for 24-28V CT AC at 300VA with one dual TDA7293 asking for a 700VA 35-0-35 supply

I have found some 30-0-30 300VA toroids at prices too good to pass up and was wondering if this would be suitable to power chimpamp kits. According to datasheets LM3876/86 can handle +/- 42v DC as a max so I accept that this toroid would be pushing the limit. TDA7293 is +/- 60V. Load will be strictly 8ohm so am ignoring the lower voltage requirements of 4 ohm loads.

I can change my 2 channels to TDA7293 based amps if required due to the increased voltage.

Is my train of thought heading in the right direction?

  Reply With Quote
Old 26th July 2011, 01:24 AM   #2
Ben78 is offline Ben78
diyAudio Member
Join Date: Sep 2010
I didn't realise I could run a regulated psu for amps, this makes it a bit easier!

LM338 regulated snubberized PSU for audio amplifiers
  Reply With Quote
Old 26th July 2011, 06:02 PM   #3
pacificblue is offline pacificblue  Germany
diyAudio Member
Join Date: May 2008
Using a regulated power supply for a power amp is like buying a car with 500 HP and then filling it with weight to avoid passing the speed limit. And it doesn't make it easier. On the contrary it adds more complexity, more heat to be sunk away and is a waste of power.

The transformers you quote for the kits are recommendations, not requirements.

30-0-30 is pushing the LM to the limits, although AN-1192 describes such a setup, too. The biggest issue will be heatsinking. The 60 V for the TDA are only valid with no signal and correspond to 47 V for the LM. The 42 V with signal of the LM correspond to 50 V for the TDA. The TDA has a current limiter with lower threshold than the LM. Both ICs have the same heatsinking area, so you should expect a similar performance.

Why don't you just connect the subwoofer amp to the power supply you already have? Check, if that setup satisfies you and if not, you can still add another power supply for the sub.
If you've always done it like that, then it's probably wrong. (Henry Ford)
  Reply With Quote
Old 27th July 2011, 02:14 AM   #4
! is offline !  United States
diyAudio Member
Join Date: Jun 2005
Location: Midwest
I built a regulated +-35V PSU for a pair of LM3886 with a 28.5-0-28.5 transformer, yes it uses a little more power than an unregulated setup would, but on the other hand I so often see people using several thousand uF of capacitance instead raising the cost and size about as much without reducing the ripple as much, though as PB mentioned, it's up to you which path to take with overbuilding a PSU or trusting the good PSRR figures for these chipamps.

Some say there is a sound difference. The only way you'll know for sure with your build would be to try it both ways. I think mine built that way sounds less lively but more accurate, like it's a much more powerful amp than it is even at middling output power if that makes any sense.

Another idea is whether you can unwrap the transformer and take some windings off to reduce voltage if it isn't potted. On a tight budget I'd consider PB's suggestion to share the existing PSU with all three channels, BUT with it only a 160VA transformer, it seems like you're cutting it close unless the L&R channels are just satellites not needing much power or you don't much listen to loud music.

Regarding heatsinking, something about the size of a CPU, early socket 370 heatsink should suffice, I used something about like this except without a fan, choosing one with a thick enough base that I could tap holes into the side of the base to screw it onto the PSU PCB:

Click the image to open in full size.
  Reply With Quote


Specific Power Supply Question...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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Specific Transformer Question Dags Chip Amps 7 30th April 2011 02:46 PM
Question about different gnd's on a specific amp Ermac Solid State 12 14th July 2009 08:43 AM
Specific 2-way crossover question (long) aabill Multi-Way 5 19th October 2005 01:16 AM
Highly application specific Resistor question ThorstenL Digital Source 3 14th June 2003 05:22 PM
Specific heat sink mounting question jag Pass Labs 1 27th September 2002 09:03 PM

New To Site? Need Help?

All times are GMT. The time now is 02:34 PM.

Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.79%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright ©1999-2017 diyAudio