Brian GT Gainclone Watts/Ch & Power Supply - diyAudio
Go Back   Home > Forums > Amplifiers > Chip Amps
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

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
Thread Tools Search this Thread
Old 14th April 2005, 05:26 AM   #1
lgreen is offline lgreen  United States
diyAudio Member
lgreen's Avatar
Join Date: May 2003
Location: San Diego, USA
Default Brian GT Gainclone Watts/Ch & Power Supply

Well, I have to admit that I redid my differential-buffered-inverting gainclone that I had struggled to make with point-to-point wiring and a differential recieiver on my own PCB. I used the BrainGT snubberized LM3886 design. I'll post the cookie cutter pics of the modified version later, but for now, how about the performance?

I have not listened yet, but have measured. Attached is a screen shot of an oscilloscope display of the snubberized GC, output of a sine wave at 1 KHz. 4x10,000 uF Elna for Audio in the P.S. and a 500 VA transformer shared between channels, both channels driven into 5 ohms. 10V/div with the appropriate probe.

Unless I'm reading this wrong, I found that I could get about 25 volts (50 peak to peak) into 5 ohms from about 20 Hz to 20,000 Hz. Plus and minus 20 V is 50/8 ohms, and 100/4 ohms, right? So this little GC is giving me about 125 watts into 5 ohms, and this is with both channels driven simultaneously. I could not get the GC to clip with my iPod on SE input. Doubling the voltage (balanced line driver to balanced input) allowed me sufficient signal to drive the amp into clipping into 5 ohms.

The power supply is about + and - 36VDC, this does NOT drop below 30VDC even when the amp is driven into clipping at 20Hz.

I double checked my measurements with a Tek DMM.

Anyway, looks like really good performance from the Brian GT gainclone, which is at the limits of the data specified by National Semiconductor. It looks like anything in excess of 20,000 uF per channel is unnecessary as the limits of the chip cause the clipping, not the limits of the power supply.

Has anyone else who has built this actually measured the power output and power supply drop? Are your results consistent?
Attached Images
File Type: jpg 1khz_10v_div_clip_a.jpg (79.0 KB, 629 views)
  Reply With Quote
Old 14th April 2005, 02:56 PM   #2
diyAudio Member
Join Date: Apr 2005
Location: In the Wild, Wild West
I think your math might be wrong. One, because the LM3886 will not drive that much output power into a 5 ohm load without major heat sinking and probably a fan. Two because when you figure power you take the peak voltage dividied by Sq. Rt. of 2 and this gives you RMS voltage. Then figure (V^2)/R = Power. I would run the level down to just before the start of clipping and measure the voltage. If this was 20V peak then output power = 40W for 5 ohm load. Try to measure your supply voltage under this condition as well for some good information. Am I reading your post wrong?


Edit: I see now the rails don't drop below +/-30V. Running some numbers you are probably getting somewhere around 70 - 75W before the start of clipping. Check the datasheet and you will see that with a +/-30V supply and even a 4 ohm load the LM3886 never hits as much power as you originally calculated. Check the graph on page 14 and the output power with +/-30V for 4 ohms is around 85W and 6 ohms is 60W so 5 ohms is somewhere right in between.
  Reply With Quote
Old 14th April 2005, 03:55 PM   #3
breez is offline breez  Finland
diyAudio Member
Join Date: Jul 2004
Location: Finland
25V p-to-p = 25/1.41 Vrms

And into 5 ohms it would be 62.5W, just between the 60W and 85W figures for 6 and 4 ohms.
  Reply With Quote
Old 14th April 2005, 06:11 PM   #4
lgreen is offline lgreen  United States
diyAudio Member
lgreen's Avatar
Join Date: May 2003
Location: San Diego, USA
Default power calcs

One reason I posted this is that I kind of forgot the math involved in making power calculations. So help here is appreciated. I did not mean to imply an RMS calc, that's why I posted the actual measurement.

My measurements indicate this GC provides plus and minus 22 to 25 volts before clipping, total swing of 44-50 volts peak to peak into 5 ohms.

What's the equation for computing power?
  Reply With Quote
Old 14th April 2005, 06:59 PM   #5
AndrewT is offline AndrewT  Scotland
diyAudio Member
Join Date: Jul 2004
Location: Scottish Borders
peak power = Vpk * Vpk / r
rms power = Vpk * Vpk / 2/ r
so 25Vpk into 5ohms = 62.5w & 22Vpk =48.4w
regards Andrew T.
Sent from my desktop computer using a keyboard
  Reply With Quote
Old 14th April 2005, 07:04 PM   #6
lgreen is offline lgreen  United States
diyAudio Member
lgreen's Avatar
Join Date: May 2003
Location: San Diego, USA
Default thanks

Thanks for the info!

So it looks like this thing is working just like it should to the maximum specs graphed in the data sheet, or right around there. Not bad.
  Reply With Quote


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
Question about CT transformer and Brian's Rev C power supply board maurycy Chip Amps 9 8th December 2009 09:21 AM
Brian gt chip amp power supply? guycom Chip Amps 4 29th September 2008 09:57 PM
Beautiful power supply! Brian's danielwritesbac Chip Amps 34 28th January 2008 04:44 AM
Switching Power Supply 48v 150 watts lawbadman Swap Meet 1 13th February 2006 01:11 PM
Brian GT NIGC, Power supply voltage kanaddict Chip Amps 12 24th November 2004 02:28 AM

New To Site? Need Help?

All times are GMT. The time now is 02:12 AM.

vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright 1999-2017 diyAudio

Content Relevant URLs by vBSEO 3.3.2