My "audiophile" LM3886 approach - Page 63 - diyAudio
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Old 25th August 2005, 11:20 PM   #621
needlz is offline needlz  United States
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Old 25th August 2005, 11:27 PM   #622
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Hi Erik,

So how is it working so far?

Cheers
Russ
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Old 25th August 2005, 11:37 PM   #623
needlz is offline needlz  United States
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Sounds pretty damn good. I am psyched to A/B it against the RevC blocks. I might etch those myself tomorrow.

I am going to let this burn in while I am out tonight. Not sure if the aluminum cover is enough. How hot should/can the chips get?
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Old 25th August 2005, 11:50 PM   #624
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Well that all depends on the efficiency of the HS. I don't think I would try leaving it unattended with what you have. Wait till you get a proper heatsink.

Glad to hear you like it!

Cheers!
Russ
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Old 26th August 2005, 02:02 AM   #625
GregGC is offline GregGC  Canada
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After reading almost everything in this thread and admiring the great work of Mauro I have a question. According to:

http://sound.westhost.com/z-effects.htm

Using current source with high output impedance does not always produce good results. Can you guys comment on that article.

How does a topology like the one in this thread sound different/better than the classic version of the chip amp? Are there a specific type of speakers that would benefit from this topology. Maybe the most benefit would have the single driver speakers with no crossover filters...?


Thanks in advance for your feedback.
Greg
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Old 26th August 2005, 07:05 AM   #626
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Hi Greg

i did some simulations and it seems that this arrangement is not to sensitive to various speaker loads.

the sound can only be compare in the following way. the classic arrangement sounds "stressed" compared to this one. the sound you are getting here compare much better to larger solid state amplifiers. I got them sounding very much like my JLH class A amps and that says alot.

there are several tweaks that you can do to tailer it to your taste. if you like much more laid back sound use a 470uf in the feedback and then even more so if you replace R 13 with a 1M resistor, instead of the 100k. then you are almost in the valve playing field

cheers
Rudi
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Old 26th August 2005, 08:25 AM   #627
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Hi all;

Greg,
I have explained all here:

MY_REF technical description

Analog_SA,
A lot of more good (than me) planners use the zener-shunt-reg. My test confirms what you say.

Dr_H,
I understand thing say, but LM318 has not " low noise " in any case, for which the effects of a low noise PS are limited.
I have prefered use the shunt simply because from more guarantees in a structure as mine.
Much little high quality SS power amp uses 3 pin reg. PS for the diff-pair.
I have noticed that even great experts of electronics don't know the difference among the problems of "high energy" and that of " low energy". If I has to plan an RIAA pre surely I uses a very accurate stabilization, with a " virtual GND" autonomous by all the other circuits. An pre-amp is always an autonomous unity.
In the case of a power amp, LM318 is not an pre-amp, but does the work of " floating diff-pair". More LM318 is an integral part of LM3886, more the circuit works better...
Naturally there are other systems to do this, but my is a "very low cost " circuit, & "very synthetic".

Ciao

Mauro
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Old 26th August 2005, 09:58 AM   #628
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Hi all,
little precise statement on 220uF elcap:

The criterions of choice that I have proposeded am not "absolute" and it is have to always do of the verification test.

Cyril Bateman has found of the little ameliorations among a polar and a bi-polar Elcap. And the solution that he recommends is a " series bi-polar pair", what has resulted very similar to the film PET cap.
The sizing that I have done limits much the effects of the Elcap-THD on the audio signal ( <-100dB), but if you prefer a "absolute" solution is able use 2 470uF bi-polar 35V in series + 0.1 to 1uF film cap (not-inductive) bypass.
This solution has to guarantee about <-115dB THD...

Ciao

Mauro
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Old 26th August 2005, 01:11 PM   #629
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Default Feedback cap

Just becuase it was all I had that fit, a 470 ufd 50V Panasonic FM was used in mine. I was wondering about the voltage rating here, it seems a 10 volt should work.
Do not know about actual tests on "back to back" polar caps versus a real non-polar cap. In several applications I tried, a real non-polar worked better as a coupling cap. This was good quality caps, Elna Silmic as the polar, and BG NH for the non-polar. The nonpolar won every time. The comparison was listening, not measuring.
Looking at the circuit, the voltage on this cap should be close to output swing. Seems a lower voltage will be fine. Think I have some 220 ufd 25V Nichicon Muse non-polar. The big problem here is size, the Muse series are all large.
From a safety standpoint, what is the minimum voltage rating needed here? Think there are some 220 ufd 6.3v BG NHX in my closet. These would be the cat meow, if they will not be overvoltaged.

George
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Old 26th August 2005, 01:55 PM   #630
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Default Re: Feedback cap

Quote:
Originally posted by Panelhead
Do not know about actual tests on "back to back" polar caps versus a real non-polar cap. In several applications I tried, a real non-polar worked better as a coupling cap. This was good quality caps, Elna Silmic as the polar, and BG NH for the non-polar. The nonpolar won every time. The comparison was listening, not measuring.
Looking at the circuit, the voltage on this cap should be close to output swing. Seems a lower voltage will be fine. Think I have some 220 ufd 25V Nichicon Muse non-polar. The big problem here is size, the Muse series are all large.
From a safety standpoint, what is the minimum voltage rating needed here? Think there are some 220 ufd 6.3v BG NHX in my closet.

Perhaps you are not understanding, or think as non-important, some of the points Mauro is raising for those caps.

He is talking about two non-polar caps in series, not back to back polar types. Those were found by Cyril Bateman as the best combination on the tests he made for his "Wireless World" article on capacitors. BTW a very good one.

Less 15dB in THD, as Mauro mentions for the two 470uF NP and 0.1uF film combo seems to me as a very interesting improvement and one that deserves listening to.

Such NP combination was also considered by Bateman as very good for input caps and feedback caps on power amplifiers, particularly the latter, where 'lytic caps are the most commonly used.

Perhaps Russ could find a way to provide for that option on Mauro's boards.


Carlos
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