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Old 27th March 2014, 02:38 PM   #71
udailey is offline udailey  United States
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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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Old 25th April 2015, 05:02 PM   #74
panos1 is offline panos1  Greece
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HI...
i tried the limiter with the ldr but i can;t make it work...
i have less volume and when i turn the volume up the amp keeps cliping...
my ldr goes down to 800ohm with the led i used...
i did'n use extra bright led...
i added the limiter before the volume potensiometer...
what can i do to solve this problem?
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Old 26th April 2015, 01:14 PM   #75
udailey is offline udailey  United States
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It needs to be implemented like Daniel's schematic. If you dont have series resistance before it then it wont do a very good job. I also wonder the resistance range of the ldr you are using. What is its value when the circuit is off? It needs to be very high when off. Maybe 100k+. Assuming the ldr fits the bill I think your problem is positioning. Put it after the pot. Really this is the first thing you should do and it should have that ~1k resistor in series with signal right before it.
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Last edited by udailey; 26th April 2015 at 01:22 PM.
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Old 30th April 2015, 06:41 AM   #76
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Quote:
Originally Posted by panos1 View Post
HI...
i tried the limiter with the ldr but i can;t make it work...
i have less volume and when i turn the volume up the amp keeps cliping...
my ldr goes down to 800ohm with the led i used...
i did'n use extra bright led...
i added the limiter before the volume potensiometer...
what can i do to solve this problem?
First, move the limiter to a position between the potentiometer and amplifier.

Secondly, observe the series LED's to find out when the engagement happens--they ought to turn on solid when the amp has reached max, but not before then.

If the LDR used is not reactive enough (I accidentally bought a few like that and those don't work at all), you'd need several in parallel to get enough loading action from them. Really unfortunate LDR's do exist.

It would be better to use only LDR's that are compatible with the LightSpeed Attenuator project. Each has a broad capacity that ranges from a few ohms to greater than 100k. That wide range is vital.
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Last edited by danielwritesbac; 30th April 2015 at 06:47 AM.
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Old 12th February 2016, 07:29 PM   #77
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I know this thread is ancient, but it is still appreciated. Funny it should appear in the Class D forum, as I have in fact been looking to add a limiter like this, as the final piece of the puzzle, in a small battery powered Class-D practice guitar amplifier I've been working on for a long time. The final problem I encountered was that a guitar, by nature, has an extremely wide dynamic range, and as you may be aware, distortion caused by clipping in a class-D amplifier is neither pretty nor useful. The problem though is that if the amplifier is turned up to offer more volume when played quietly, it may be subject to some of this ugly distortion if the player starts strumming loud. The ideal solution would be a compressor/limiter, but as a simple practice amp, the added parts, costs, and controls needed for a complete "high-end" compressor circuit are just not justified. So, recently finding plenty of LDRs at places like electronicgoldmine, cheap even if not very well matched, I'm very hopeful I'll be able to concoct a simple and adequate LDR circuit like this.

Since I'll be dealing with a low power 20W class D amplifier, I'm a little concerned about driving the LDR directly from the loudspeaker, as I don't want to cause additional distortion at the point where the series zener starts conducting. But then maybe I'll get lucky and this won't be a problem.

Anyway, thanks for sharing this.

Last edited by Peter Pan; 12th February 2016 at 07:56 PM.
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Old 26th April 2016, 12:52 PM   #78
jfetter is offline jfetter  United States
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i like limiters but maybe put light bulb and led "in parallel" so there is some thermal memory.
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Old 26th April 2016, 04:31 PM   #79
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Originally Posted by jfetter View Post
i like limiters but maybe put light bulb and led "in parallel" so there is some thermal memory.
Well, it isn't 1927, so perhaps we ought to explore a little jfet.
Exploring a little jfet has been a goal, even though the 1970's LDR tech has been working well enough. The Achilles's heel of the LDR is repeat-ability when it comes to effectiveness. If the range isn't vast enough, then it will dull dynamics instead of working as expected. Yeah, they do make the right parts, but the shopping is a hazard!!!
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Old 26th April 2016, 05:55 PM   #80
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why not make trigger for this to start to work only over certain adjustable power treshold?
no dull dynamics?
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