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Class D Switching Power Amplifiers and Power D/A conversion

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Old 27th March 2014, 02:38 PM   #71
udailey is offline udailey  United States
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Quote:
Originally Posted by danielwritesbac View Post
Udailey, Feel free to produce the ClipNipper and/or preferably the higher performing ClipNipper DA (higher fidelity, twice as many optos, no bridge rectifiers) for nonprofit and/or profit use.

I have always been convinced that volume controls *should* result in effective concert sound if turned to max.

P.S.
In other news, simple, dynamics promoting power supplies really do exist.
Thanks for that offer Daniel. I have no idea if I will do that or not right now but its very generous of you.
Whats this power supply you are talking about?
I have ordered 10 boards with two channels of noninverting LM3886 with the 1k noninverting input resistor replaced with an LDR and the inverting input to ground resistor (usually 680) replaced with an LDR. I wonder if you would like to have one of the boards? I was looking for a few people to assemble and test it. I think it would be pretty easy to also test it in bridged or parallel which is why I put two on one board, to mess around with different configurations. Of, course then we would have to add output resistors but thats not a big deal. Let me know with your address if you would like to try it. If it was to be commercial the two layers would be used to full advantage instead of mirroring my single layer design and the board would allow for better selection of parts in the zobel. Maybe single psu entry points rather than one for each amp. Other than that I'm pretty pleased with it.
Its not my intention to turn your thread to my advantage. This offer is for Danielwritesback only. Please dont pm me.
Uriah
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Old 27th March 2014, 07:42 PM   #72
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Thank you for your offer; however, the next round of LM3886/LM3876/LM3875/LM1876/LM4780 (any overture) will be inverting mode for me.
In regards to LDR as feedback-shunt-resistor, I have noticed that when I tried a Multi-Turn, CerMet, variable resistor, that it always worked better than an ordinary resistor--I have tried dialing in a just right value and then replacing the trimmer with same value fixed resistor, but the ordinary resistor Never works as well as the variable cermet, especially if they're the same value. When using an ordinary resistor instead, a given amp needs a little more gain, and that also means, a little more compensation. So, I end up leaving the cermet in-circuit.

As for power supplies, I did one for a good feature set despite a small 200VA transformer attempting 200W (statement speakers are 4 ohms). Optimizing TDA7294 Output. Per rail, it looks like BR, 3300u, MBR1645||0.28R, 5x3300u. That is a low loss crc whereby a bypass diode prevents excessive filter losses (especially bass impact). The diode forward voltage drop figure sets the limit on crc filter losses, whereby schottky is about 0.3v, fast silicon is about 0.5v and standard silicon is about 0.7v (see forward voltage drop in a diode's datasheet). On my personal supply, I only allowed 0.3v for the CRC filter (my R is bypassed with MBR1645), and that is just fine because I have an additional filter. . .

And, next for the amplifier board Virtual Dual Mono which has ordinary 6A05 (6a1, 10a05, 10a1, sturdy standard silicon) diodes series with the V+ and V- power connection to each channel of audio amplifier board (that is a monophonic parallel amp in the photo--it takes 4 diodes for stereo + split rail, which is 2 diodes per each channel, as shown in the photo). The stereo width of virtual dual mono is not the main benefit, but it is a rather good excuse for doing it.
Just a quick note: decoupling cap size is specific to a given amplifier--A non-inverting LM3886 would require significantly larger power decoupling caps directly at the chip, but the prospects are otherwise similar.

We might disagree on using better parts for the zobel, because the standard and expected capacitor is a rather high esr polyester dip cap (like the little green tracon from the radio shack--this type filter cap looks like green or red blob); however, if a high efficiency, low loss, box cap were used then you'd need to increase your resistor value, else RC value comes out not known to be useful with audio amplifiers. SO, when it comes to the zobel, don't zoot the capz.
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Last edited by danielwritesbac; 27th March 2014 at 08:06 PM.
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Old 29th March 2014, 08:16 AM   #73
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Oh, I had an idea! Since you've got an LDR for the feedback-shunt resistor, you could conceivably install a feedback resistor somewhere between 56k and 112k (much experimentation; but, somewhere in that range) and dial in a rather pretty tone with your LDR shunt, despite the tone difficulties with the non-inverting LM3886. I know the thing can image like a champ, however, practical tone often evades it. The adjustable variable control could be highly beneficial. Tone/Gain/Stability are very closely related and have a narrow range of perfect that is not usually hit on target by fixed resistor values.

The higher resistor values will also result in more audio being able to pass through the feedback coupling cap and thus less distortion.

P.S. I wonder why the LDR is more effective at base stopper locales?
I'm certainly not saying that it isn't, but rather, the fact that it is, is interesting.
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Last edited by danielwritesbac; 29th March 2014 at 08:18 AM.
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