I put together a BrianGT kit using mostly the parts supplied with the kit including the Ci cap for low DC offset. No input cap currently.
The amp works great but I felt the way it clips seems strange to me.
I'm using an Antek 300VA 20+20 transformer. My testing was done using a Tektronix 100MHz analog scope and a decent signal generator. load was two Dale 1% 250W 8 ohm resistors. I used two for 4 ohm tests.
The amplifier clips the bottom way before the top and it clips bad all of a sudden. The best way to describe what it does is the bottom of the sine becomes a UU with the right U being much higher. If I run it barely into clipping it alternates between a perfect sine wave and clipped bad, again bottom only.
My power output was 30W into 8 ohms and 54W into 4 ohms. temps were all fine during the tests. I can try and post some pics of the scope tonight if need be.
Perhaps this is just the nature of the chip and completely normal?
Will be neatening up the wires a bit more with sleeving and zipties.
The amp works great but I felt the way it clips seems strange to me.
I'm using an Antek 300VA 20+20 transformer. My testing was done using a Tektronix 100MHz analog scope and a decent signal generator. load was two Dale 1% 250W 8 ohm resistors. I used two for 4 ohm tests.
The amplifier clips the bottom way before the top and it clips bad all of a sudden. The best way to describe what it does is the bottom of the sine becomes a UU with the right U being much higher. If I run it barely into clipping it alternates between a perfect sine wave and clipped bad, again bottom only.
My power output was 30W into 8 ohms and 54W into 4 ohms. temps were all fine during the tests. I can try and post some pics of the scope tonight if need be.
Perhaps this is just the nature of the chip and completely normal?
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Will be neatening up the wires a bit more with sleeving and zipties.
Just took some pictures and did more testing. It doesn't seem as bad as I had originally thought.
top line is just the scope connected to the negative rail. The bottom of the sinewave clips just slightly before the top.
Wires are a bit neater now as well.
top line is just the scope connected to the negative rail. The bottom of the sinewave clips just slightly before the top.
An externally hosted image should be here but it was not working when we last tested it.
Wires are a bit neater now as well.
An externally hosted image should be here but it was not working when we last tested it.
Last edited:
What I see happens immediately as soon as the amp is turned on and remains the same unchanged. The chip is cool to the touch.
I am also under the impression that SPIKE effects both top and bottom of the wave but not the in this way according to National Semiconductors writeup on it.
http://www.national.com/an/AN/AN-898.pdf
I am also under the impression that SPIKE effects both top and bottom of the wave but not the in this way according to National Semiconductors writeup on it.
http://www.national.com/an/AN/AN-898.pdf
Hi TheTube 
I performed some clipping tests on my LM3886 P2P a few years back. Basically it is based on the BrianGT schematic, and I have an Antrim 20+20 300VA transformer so similar to you. Main difference is I only have 1000uF / rail / channel of capacitance in the PSU.
The clipping waveform was very ordinary see this post http://www.diyaudio.com/forums/chip-amps/66255-wintermutes-gainclone-3.html#post757137 Admittedly only a PC based scope but when the same test was run on my 100W mosfet amp I got perfectly flat tops and bottoms on the sinewave, so it's not the test that is at fault.
I had certainly read that once these chips clip it is pretty ugly! I guess the bottom line is don't over-drive them!! Certainly My setup at the moment with 4 ohm speakers which are around 92db efficiency I don't have a problem with it not going loud enough for my tastes
Tony.
I performed some clipping tests on my LM3886 P2P a few years back. Basically it is based on the BrianGT schematic, and I have an Antrim 20+20 300VA transformer so similar to you. Main difference is I only have 1000uF / rail / channel of capacitance in the PSU.
The clipping waveform was very ordinary see this post http://www.diyaudio.com/forums/chip-amps/66255-wintermutes-gainclone-3.html#post757137 Admittedly only a PC based scope but when the same test was run on my 100W mosfet amp I got perfectly flat tops and bottoms on the sinewave, so it's not the test that is at fault.
I had certainly read that once these chips clip it is pretty ugly! I guess the bottom line is don't over-drive them!! Certainly My setup at the moment with 4 ohm speakers which are around 92db efficiency I don't have a problem with it not going loud enough for my tastes
Tony.
wintermute : how do you like your amp with the 20+20 transformer?
Everything here seems to add up. I'm down to around 25V+- under full load which yields 30WPC into 8 ohms and around 54WPC into 4 ohms. Almost identical to what the datasheet claims. My mains measured 118V during the test.
I kinda wish I had gone with the 22+22 transformer for a bit more muscle, yet heat would've gone up substantially as well.
Everything here seems to add up. I'm down to around 25V+- under full load which yields 30WPC into 8 ohms and around 54WPC into 4 ohms. Almost identical to what the datasheet claims. My mains measured 118V during the test.
I kinda wish I had gone with the 22+22 transformer for a bit more muscle, yet heat would've gone up substantially as well.
I'm quite happy with it for the cost (it was less that $150AU to build) I think it would be hard to beat it! It was originally built as a test amp (for testing speakers) with the possibility to end up being the second amp in my planned BI-AMP setup (playing from 200-300HZ and up), but for the last few months it has been doing main duty as one of the channels on my main amp has stopped working and I haven't had the time to investigate.
I do notice it has a slightly more pronounced treble than my old amp (particularly noticeable hissed esses, not something I like...) interestingly on a FR analyses it is very slightly flatter (like 0.5db) in the higher frequencies, ie the mosfet amp starts showing a slight rollof from about 10Khz down by 0.5db by 20Khz whereas this amp is essentially flat. I don't think this is what is making what to me is a fairly pronounced difference though.
I still haven't really had a fair test though because I'm running it off my HT PC (no preamp) which is simply using the on board sound card, which I'm not certain about the quality!
I was actually very impressed at how well it works for HT use (stereo). Even without my 10" woofers running (my active crossover project has been stalled for a while), it is very good for sound effects, and the imaging is very good
Tony.
for the cost (it was less that $150AU to build) I think it would be hard to beat it! It was originally built as a test amp (for testing speakers) with the possibility to end up being the second amp in my planned BI-AMP setup (playing from 200-300HZ and up), but for the last few months it has been doing main duty as one of the channels on my main amp has stopped working and I haven't had the time to investigate. I do notice it has a slightly more pronounced treble than my old amp (particularly noticeable hissed esses, not something I like...) interestingly on a FR analyses it is very slightly flatter (like 0.5db) in the higher frequencies, ie the mosfet amp starts showing a slight rollof from about 10Khz down by 0.5db by 20Khz whereas this amp is essentially flat. I don't think this is what is making what to me is a fairly pronounced difference though.
I still haven't really had a fair test though because I'm running it off my HT PC (no preamp) which is simply using the on board sound card, which I'm not certain about the quality!
I was actually very impressed at how well it works for HT use (stereo). Even without my 10" woofers running (my active crossover project has been stalled for a while), it is very good for sound effects, and the imaging is very good
Tony.
Hi,
just because I have this transformer available for testing. It has two outputs per secondary: 18 VAC and 28VAC at rated load. I use the lower one for now. Since this is a 330 VA toroidal, under normal usage for single channel, the output voltage will be higher than the full load output.
No sir. They are built into the back of my powered advents, which have a nominal impedance of slightly less then 8 ohm. They run pretty hot with 35V rails into 8 ohms.
Its the BPA-200 with servos and a single LM3886 with a linkwitz-riley crossover. both woofer and tweeter are direct coupled to amplifiers. 500VA 25+25 transformer with two 22,000uf comp grade caps. They have been in service since fall of 08
One of two :
Its the BPA-200 with servos and a single LM3886 with a linkwitz-riley crossover. both woofer and tweeter are direct coupled to amplifiers. 500VA 25+25 transformer with two 22,000uf comp grade caps. They have been in service since fall of 08
One of two :
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Last edited:
one other, I have a small TDA7265 amp I built that runs off of two 19V SMPS bricks from samsung tablet pc's. Used it at work for a few months, nice little amp. I built it literally for $10 or so from parts laying around. Had to buy the chip and a few caps.
Both the large silver\white rackmount enclosure and this tiny silver one are ELMA aluminum enclosures that we had left over at work.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Both the large silver\white rackmount enclosure and this tiny silver one are ELMA aluminum enclosures that we had left over at work.
Well I finally did it. around 10 years ago I bought a pair of A/D/S L300E speakers. Ever since then I've been trying to find an amp that sounds good with them. The only one that ever had any bass driving them was my fisher KX-200. The speakers are 4 ohm and the things I had to use with them always sounded dead, thin, weak, no bass.
The LM3886 amp with 300VA supply is driving them with ease. Plenty of strong bass just like the fisher KX-200.
Last two things tried with the speakers were a pioneer sx-680 which was by far the worst sounding with them, and then an Advent 300 which was ok, but still didn't have the muscle needed.
The LM3886 amp with 300VA supply is driving them with ease. Plenty of strong bass just like the fisher KX-200.
Last two things tried with the speakers were a pioneer sx-680 which was by far the worst sounding with them, and then an Advent 300 which was ok, but still didn't have the muscle needed.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.