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Old 5th March 2011, 01:52 PM   #11
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Default C12 is really big...is this really needed?...say...so big one?

This uses to slow down the amplifier....and you see your square wave shows something less than perfect... well, very good job you have done..thank you as you are sharing with us.

regards,

Carlos
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Old 5th March 2011, 01:55 PM   #12
jgray is offline jgray  United States
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Bigun, I think your hunch is right regarding the cap on the phase splitter. I tried a capacitor in the 300pF range and I still had some ringing which I didn't like, but I bet there is an intermediate value that would be better. I may order a selection and do some further experimentation.
Joel
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Old 5th March 2011, 02:01 PM   #13
jgray is offline jgray  United States
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Jam, I calculated a value for R6 that was less (about half), but in simulation it showed minimum distortion at a higher level. I tried it with both and couldn't hear or see a difference so I went with the value from the simulation. Thanks, Joel
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Old 5th March 2011, 05:16 PM   #14
Bigun is offline Bigun  Canada
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Quote:
Originally Posted by jgray View Post
Bigun, I think your hunch is right regarding the cap on the phase splitter. I tried a capacitor in the 300pF range and I still had some ringing which I didn't like, but I bet there is an intermediate value that would be better. I may order a selection and do some further experimentation.
Joel
This issue with ringing can be a 'red herring'. I've looked at this recently and found some popular opinion that it's just a case of compensating the amp until it's smooth, as you've done, but I've seen some more considered thoughts on the internet pointing out the flaws in this approach which suggests that some ringing is 'OK' and preferable to over-damping.

For the kind of topology you have, with the LTP input, a compensation capacitor around 100pF should be much closer to the right value. In my own experiments I found the value had a subtle but repeatable impact on the sound. A value too high makes the sound a little dull, a value too low makes the high end too bright and somewhere in the middle you find the magic in the sound.

JLH was very wary of this kind of compensation too.

Keeping speaker cables reasonably short, and not using esoteric high capacitance speaker cables or speakers helps.
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Last edited by Bigun; 5th March 2011 at 05:19 PM.
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Old 5th March 2011, 06:13 PM   #15
jgray is offline jgray  United States
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That is very interesting. Now I want to try taking it down to a lower value and see what happens; both on the scope, and with my ears. Guess I am going to have to order some more parts
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Old 5th March 2011, 06:44 PM   #16
Bigun is offline Bigun  Canada
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It's all part of the fun for sure. A handful of values, and using some in parallel allows for quite a bit of experimentation. Modify one channel only and compare the two channels.

Be careful driving your amp with a square wave - I blew one up like that - square waves really stress the output devices. At full power it will blow it up before you have time to adjust your scope - at least it did for me !
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Last edited by Bigun; 5th March 2011 at 06:50 PM.
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Old 6th March 2011, 02:21 AM   #17
WuYit is offline WuYit  Sweden
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We deeply regretted that square wave event caused by an allegedly advanced, but in point of fact deficient compensation method.
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Old 6th March 2011, 02:42 AM   #18
Bigun is offline Bigun  Canada
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Indeed, may those poor silicon 3-legged friends rest in peace
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Old 6th March 2011, 03:06 PM   #19
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Quote:
Originally Posted by jgray View Post
my musician sons both said it sounded “Not Too Bad, ”
Joel, very impressive (first amp or not) I doubt any additional congrats compare with NTB. I really like the clean build, and clean square wave response (20V/us seems sufficiently fast to me for 10V rails). Your thought out responses reveal the care that went into this.
Interested in hearing what your final tweaked preferred listening values are.

Thanks
-Antonio
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Old 6th March 2011, 07:05 PM   #20
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Quote:
Originally Posted by destroyer X View Post
This uses to slow down the amplifier....and you see your square wave shows something less than perfect... well, very good job you have done..thank you as you are sharing with us.

regards,

Carlos
It is a 20 kHz square wave, and it is an audio amp, not a MW transmitter. For the second you need a better square wave indeed.
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