GC Measurements

lgreen · 26th July 2004, 05:22 PM

I've started this thread to post some measurements of my Gainclone. This is an LM3886 inverting GC with buffer and 3300 uF per rail, 500 VA transformer.

We see a lot of gainclones here but very little in the way of performance data. If you have some data, add your own.

Here is a shot of the onset of clipping with a 40 Hz input signal into a 5 ohm load, about 45 watts. 5 v/div on channel 1.

lgreen · 26th July 2004, 05:26 PM

Here is the onset of clipping at 4 KHz into 5 ohms. Again, about 45 watts.

5 v/div on channel 1.

lgreen · 26th July 2004, 05:30 PM

Here is the power supply ripple when the chip is muted. The power supply gives about 35 v DC.

Channel 1- 50 mv/div (since probe was changed to 1x)

lgreen · 26th July 2004, 05:31 PM

Power supply ripple when the chip is operated and not clipping.

channel 1, .5v/div

It would be interesting to compare this to an implementation using 1000 uF per rail. I had one of these but added more caps due to the large amount of ripple. Now the ripple is not so bad, but still not great.

lgreen · 26th July 2004, 05:35 PM

Here is the positive power supply when the amp is clipping, and flattening the top peaks. This is a DC measurement at 5 v/div, and ground is the bottom line on the graticule. Thus you are seeing ripple at about 30-35 volts, much higher than the clipping point of about 12 volts in the first 2 posts.

moamps · 26th July 2004, 10:32 PM

Quote:

Originally posted by lgreen
Here is a shot of the onset of clipping with a 40 Hz input signal into a 5 ohm load, about 45 watts. 5 v/div on channel 1.

Hi,
Your scope reading doesn't look good. Did you check input waveform in GC? Clipping starts at 12V peak according to your picture, which is only ca 15Wrms/5ohm. How did you get 45W?

Regards
Milan

thomas997 · 27th July 2004, 01:46 AM

What scope is that?

Hopefully I will get one soon and will add some pictures to the list.

rdf · 27th July 2004, 02:08 AM

Why the asymetrical clipping? Is it typical of these chips? It almost implies a serious DC offset on the output, but that would be hard to miss.

lgreen · 27th July 2004, 01:51 PM

Yeah, the clipping is not symetrical, but DC offset is never more than 25 mv. I'll look at it again into different loads (maybe different results) but I would have no idea what's causing it, since it seems to be working fine. That's why I posted my data, wondering what everyone else's looks like on clipping?

Scope is a Tektronix 265M.

rdf · 27th July 2004, 02:37 PM

Are both PS rails the same voltage?

27th July 2004, 01:51 PM	#9
lgreen diyAudio Member Join Date: May 2003 Location: San Diego, USA	clipping Yeah, the clipping is not symetrical, but DC offset is never more than 25 mv. I'll look at it again into different loads (maybe different results) but I would have no idea what's causing it, since it seems to be working fine. That's why I posted my data, wondering what everyone else's looks like on clipping? Scope is a Tektronix 265M.

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
XAB Measurements	DarkOne	Pass Labs	12	16th April 2006 10:59 PM
New T-Amp measurements	Pano	Class D	12	14th March 2006 11:32 AM
SW measurements	Grandma´s_SUB	Everything Else	9	10th January 2005 01:34 PM
anyone have measurements of TB 871?	morbo	Multi-Way	5	27th November 2004 03:10 AM
Some CCS measurements	Jocko Homo	Solid State	10	29th May 2002 12:54 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	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

27th July 2004, 01:46 AM	#7
thomas997 diyAudio Member Join Date: Feb 2004 Location: Vancouver	What scope is that? Hopefully I will get one soon and will add some pictures to the list.

27th July 2004, 02:08 AM	#8
rdf diyAudio Member Join Date: Jun 2004 Location: big smoke	Why the asymetrical clipping? Is it typical of these chips? It almost implies a serious DC offset on the output, but that would be hard to miss.

27th July 2004, 02:37 PM	#10
rdf diyAudio Member Join Date: Jun 2004 Location: big smoke	Are both PS rails the same voltage?

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)