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Old 17th January 2012, 12:26 PM   #3531
soongsc is offline soongsc  Taiwan
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This is getting close to it. Truly amazing performance! Can't stop playing around with it. What I though was coloration of speakers turned out not to be the case. The power supply is as bit as important as the circuit, it's a make or break deal. I have never heard Placido Domingo sing with so much emotion. All the vocals seem to come so alive that I am moved by the emotion and skill each performer expresses. Violins seem so well presented that I think I could take lessons from the recording. Tomorrow some more people will be auditing this along with some other things. Got my fingers crossed to see how young people still in music school will think.
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Old 17th January 2012, 12:59 PM   #3532
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Soongsc- your path to your last post has been interesting and fun to watch. When you can, would/could you consolidate your actions into something like " I started here -- now I have this"? It appears some of your choices may differ from the published BOMs
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Old 17th January 2012, 01:59 PM   #3533
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I have not finalized yet, but the major difference would be the power supply. I have posted links to the modules I used, but yes, I think it would be a good idea to contribute a configuration to this thread, especially to thank all that made this possible.

The basis is the TP kit, but I took out the main DC power section keeping only the part that supplies the LM318 and the protection circuit.

R7 changed from 12K to 6K. C4 and C7 changed to X2 CAPS C4=0.068uF, C7=0.1uF. I have really not tried to see if other sizes are better, but just used what was available. 2.2uF X2 cap was added in parallel with C4. It can be put just across the large rectifying caps. I think it would be nice if someone would verify the sound of this using the standard power supply.
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Old 17th January 2012, 02:09 PM   #3534
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What have you changed regarding PSU?
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Old 17th January 2012, 02:35 PM   #3535
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Changed to switching power. If you look at the pic I posted a while back, the whole two channels are in that chassis.
My "audiophile" LM3886 approach
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Last edited by soongsc; 17th January 2012 at 02:39 PM.
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Old 17th January 2012, 02:40 PM   #3536
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Quote:
Originally Posted by soongsc View Post
.
R7 changed from 12K to 6K. C4 and C7 changed to X2 CAPS C4=0.068uF, C7=0.1uF. I have really not tried to see if other sizes are better, but just used what was available. 2.2uF X2 cap was added in parallel with C4.
Halving R7 doubles the loop gain - distortion will be lower, but so will stability. It's no longer a Rev C with this modification.

I'll however give the last mod a try - 2.2uF in parallel with C4. Finding one with higher than 63V rating and making it fit will be a challenge, but I'll do it in the next build. 1uF/100V may be an easier fit.
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Old 17th January 2012, 02:44 PM   #3537
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Halving R7 actually reduced the gain in my measurements. About 6db if I recall correctly. The bandwidth increased, and phase lag is reduced in the audio band.
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Old 17th January 2012, 02:49 PM   #3538
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Sure, it halves the closed-loop gain, by doubling the GNFB loop gain, both by ~6 dB. Bandwidth will increase, stability will decrease (lower phase margin at 0 dB loop gain), distortion will decrease, sonics will become more analytical.
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Old 17th January 2012, 02:52 PM   #3539
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Quote:
Originally Posted by soongsc View Post
I have not finalized yet, but the major difference would be the power supply. I have posted links to the modules I used, but yes, I think it would be a good idea to contribute a configuration to this thread, especially to thank all that made this possible.

The basis is the TP kit, but I took out the main DC power section keeping only the part that supplies the LM318 and the protection circuit.

R7 changed from 12K to 6K. C4 and C7 changed to X2 CAPS C4=0.068uF, C7=0.1uF. I have really not tried to see if other sizes are better, but just used what was available. 2.2uF X2 cap was added in parallel with C4. It can be put just across the large rectifying caps. I think it would be nice if someone would verify the sound of this using the standard power supply.
One more. Change R3 to a Caddock 30W rating film resistor. It was just an arbitrary decision to use the higher rating one when form factor is vary similar.
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Old 17th January 2012, 03:01 PM   #3540
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Quote:
Originally Posted by linuxguru View Post
Sure, it halves the closed-loop gain, by doubling the GNFB loop gain, both by ~6 dB. Bandwidth will increase, stability will decrease (lower phase margin at 0 dB loop gain), distortion will decrease, sonics will become more analytical.
It may seem analytical, but when the 2.2uF went in (which I was recommending C4 just be larger a while back), everything fell into place. Basically, the whole package is the deal. This is where critical listening plays an important role in decision making. Measurements might be possible, but setup of various measurement methods really takes lots of time.

So, what would I expect if I changed gm to 2 instead of 1?
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Last edited by soongsc; 17th January 2012 at 03:20 PM.
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