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Some LME49600 implementations
May 20, 2012 at 3:23 PM Post #91 of 292
Quote:
wakibaki said:
Thanks Sebastian, I was beginning to feel that I was talking to myself. 
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I took your intermediate status updates as just that. :)
 
Odd that there's so little apparent interest, this is potentially a very high-performance design at a very reasonable cost.
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Yeah, you should at least give it a uniquely fancy name, hire someone who advocates your design and then spread it virally across all platforms... :wink:
 

<1mV is good
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<1mV is very good. :)
 
We had this little argument earlier about DC of servo-controlled vs. servo-less amps. My offset is no biggy, but below 1 mV is certainly zip even in a headphone amp.
 
I can hear a very quiet 100Hz hum from the fullwave voltage doubler with nothing playing [...] and if conventional rectifiers don't do the trick I can try strapping a cap across them.
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Is that normal for the type of regulators you chose? I hadn't noticed any audible mains buzz with my [you know what] amp. Could be increased by the supply you use (i.e. variac). I found that in my house for toroids I need a mains DC filter in order to get a PSU buzz free... 
 
I have a couple of jumpers in there which double the gain, they can be removed.
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Ah, okay, I hadn't paid attention, sorry. All the better. :)
 
May 20, 2012 at 8:04 PM Post #92 of 292
I thought I might call it Wakibaki's Smokin'.
 
The hum is a little puzzling since I have a very similar design in my TPA6120 desktop/portable, I've built 2 of those and there's no hum audible, although it has so much gain (>30dB) that you can turn it up to the point where the noise floor is audible.
 
Maybe these chips don't have as good PSRR, or maybe it's a quirk of the layout, despite the fact that the layout is more relaxed in this one (more room). I'll fiddle around with it over the next couple of days, try some different wallwarts, see if I can pick it up on another amp, things like that. It's only running 14V rails at the moment, I can turn that up a bit as well and fiddle with the CRCRC values.
 
Avro_Arrow, sek@, Kevin Gilmore, thanks for your support, if you want a board PM me your mailing address, I'll send you one FOC.  
 
Test results follow...
 
w
 
May 20, 2012 at 8:13 PM Post #93 of 292
Initial RMAA test results using M-Audio Delta AP 2496
 
Showing representative levels (soundcard straight thru):-
 

 
1st. column shows amplifier-soundcard without additional loading, 2nd. column amplifier loaded with 16 ohms resistive, 3rd. column, soundcard-soundcard straight thru.
 

 
The 3rd. column actually shows the soundcard alone with FR flatness 0.01dB worse than with the amplifier, but I think that just shows the limits of RMAA testing under these conditions.
 
w
 
May 20, 2012 at 9:51 PM Post #94 of 292
Why thank you, that is very generous.
PM sent.
 
Quote:
wakibaki said:
I thought I might call it Wakibaki's Smokin'.
 
The hum is a little puzzling since I have a very similar design in my TPA6120 desktop/portable, I've built 2 of those and there's no hum audible, although it has so much gain (>30dB) that you can turn it up to the point where the noise floor is audible.
 
Maybe these chips don't have as good PSRR, or maybe it's a quirk of the layout, despite the fact that the layout is more relaxed in this one (more room). I'll fiddle around with it over the next couple of days, try some different wallwarts, see if I can pick it up on another amp, things like that. It's only running 14V rails at the moment, I can turn that up a bit as well and fiddle with the CRCRC values.
 
Avro_Arrow, sek@, Kevin Gilmore, thanks for your support, if you want a board PM me your mailing address, I'll send you one FOC.  
 
Test results follow...
 
w
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May 21, 2012 at 12:58 PM Post #98 of 292
wakibaki,could you post results at 16/44.1 or 24/44.1 ?I want to compare my amp to yours.
smily_headphones1.gif

 
May 22, 2012 at 5:13 PM Post #100 of 292
Sebastian, board in the post. I'll post a detailed final schematic when I figure out how, the editor says 'You don't have permission to create attachments'. Maybe I'll just put a .zip file on my website for download.
 
w
 
May 22, 2012 at 5:50 PM Post #102 of 292
OK, if you right-click on the image and choose 'save image as...', you should be able to save an image with sufficient detail to read.
 

 
Here's the layout:-
 

 
Q3 has to be mounted upside down and rotated to make B,C & E line up correctly, or perhaps I can find an alternate txistor with the right footprint. Anyway, I'm sure you guys can make it work, I did.
 
w
 
May 25, 2012 at 10:34 PM Post #103 of 292
OK, I found the cure for the hum.
 
It was necessary to attack the ground planes with a Dremel with cutting disk.
 
Here's what had to be done, top:-
 

 
You can see the 2 cuts near the input jack, J3.
 
And the bottom:-
 

 
3 cuts here, with the long vertical one interrupted by tracks. The top 2 parts of the cut are probably unnecessary, but I really wanted to force the current up into the area above the regulators.
 
And that's got rid of the hum. Whoopee! It's a nice amplifier. Shame about the cuts, but that's what prototypes are for... I should have worked out this issue earlier, but as usual I was impatient to get some results.
 
w
 
May 25, 2012 at 11:03 PM Post #104 of 292
At least we are brave enough to try even if we make a few mistakes along the way.
Good job finding the source of the hum.
 
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