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Old 7th May 2012, 06:50 PM   #41
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Quote:
Originally Posted by keantoken View Post
What do you mean by "soft"? I thought you meant "not abrupt", in a timing sense, as an abrupt clip will be crunchy.
Hard clipper and Soft clipper are different, because instead of shorting out the signal, we "trip" a voltage divider very quickly for a softer effect with no square corners.

Soft clipper (sensor is at amp input)--must be blazin fast. Function = cut the corners off the square

Limiter (sensor is at amp output)--must be slowed down via timer cap (makes great treble but there will be some bass disturbances if the amp is run three times more than its normal means).

All must be constrained so that their effects aren't obvious to the ear.

Transparent (polite, secret): The engagement point is completely ineffective. It is standby. At the point of engagement, the effect is so mild that it doesn't even work. As need increases, effect increases gently. Transparent = not obvious. Nebulous knee voltage of schottky and LED helps a lot.

No cpu needed--InGan LED based detector lights brighter on dirty dc (clipping signal) but stays dim on ac (music). That feature is horribly dangerous for room lighting but works great for detector.

At some point of abusing the amplifier, transparency starts to fail, and in this case go for "pretty" since the option of increasing the power supply voltage doesn't work with the TA2020.

Abrupt (rude) = a Zener, or stepping on the garden rake. They're not soft, fluffy and sloppy. They're very noticeable. Specifically engineered for sudden engagement. They're not suitable. There's an abrupt device for bathroom doors and we should avoid this abrupt effect, since abrupt is not suitable--see attachment:
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Old 7th May 2012, 07:01 PM   #42
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Originally Posted by keantoken View Post
Another schematic. This illustrates the benefits of a high-order LP filter. High order harmonics are much lower. This is the result of an input voltage that is a combination of 500Hz and 490Hz, which produces a sine wave modulated at 10Hz, perfect for exploring limiter behavior.
That's really cool. Did you build some?
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Old 7th May 2012, 07:13 PM   #43
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Nope, haven't built anything. This circuit must be adusted in reality since you have to listen to it and choose a configuration that works best. The LDR model I used was for the Silonex NSL-32SR2.
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Old 7th May 2012, 07:29 PM   #44
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Wait, I didn't do that simulation right, try this one. I didn't equalize the levels...

Harmonics are higher before 650Hz, but this is because of the improved speed of the LP filter at low frequencies. The 1KHz intermodulation is lowered considerably with the better LP, which is the point. Better speed, as well as better filtering.
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Old 7th May 2012, 07:44 PM   #45
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Here it is more evident. The 3rd-order LP limits sooner and makes less noise.
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Old 7th May 2012, 08:03 PM   #46
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Arg, I keep contradicting myself. Let's see if I can get it right... Or if I'm even right at all...
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Old 8th May 2012, 12:30 AM   #47
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Originally Posted by keantoken View Post
Arg, I keep contradicting myself. Let's see if I can get it right... Or if I'm even right at all...
You're right, of course. I might be right too. Of course, Eva is right as well. It just depends on what frequencies you'd like to limit primarily.

The digital allows one to run multiple programs (multiple curve) on a single set of parts. When we use analog, that same feat requires multiple independent circuits--That is fast soft clipper with input side sensor run along with slow limiter with output side sensor. To limit the complexity, I hope we can do it in analog without making the analog circuit more complex than the digital circuit.

I think that since TA2020 clips badly well before its datasheet claims then ear sensitivity 1k~8k need to be limited primarily. I think it takes added circuits to either clean up or constrain the rest.

I'd like to see what you can do with 4n25 and dropping the internal led voltage to avoid heat. I used additional led's for that but you can use whatever you like although I do suggest at least one added led and at least one added 1N5819 (high voltage low amperage fast silicon diode or a similar Rectifier schottky) set in series to the 4n25's internal led.

We could have input monitor as a small op-amp driving the 4n25, and in this case, the output of the op-amp is not used for music--we can clip the op-amp, not the power amp. I'd also like to see a convenient dial for fine tuning extent (amplitude of the automated voltage divider) and another dial for fine tuning engagement (voltage to light the 4n25).

You can build this more easily, since 4n25's and op amps are inexpensive and everywhere.
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Old 8th May 2012, 12:44 AM   #48
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Well, there are some reasons a better LP filter will help, others it may hinder. Because of the nonlinear nature of the LDR, gain increases dramatically with input which is why it will motorboat if too high input is given. For this reason I switched to current-drive mode.

This new schematic allows for the use of much smaller film caps for the filtering, and is in many ways better. Thoughts:

I suppose you want immediate suppression of spontaneous transients, rather than a lingering drop in gain after a transient. The "lingering" is adjusted with R1. It could even be a knob.

R12 controls the threshold, it could be a knob too. I haven't looked into how I should reconcile the two redundant threshold controls, R12 and D5. Maybe delete D5? But then Q5's tempco would affect the threshold quite a bit.

The current drive buffer is convenient in that it allows us to shape the filtering without anomalous effects from the LED impedance. We can also use small film caps, so the circuit is more reliable.

This is how it operates at 2x overload, adjusted for 13V threshold.

I was thinking, why not try to use a thermistor-based coupler? A heater+thermistor combination chip would be extremely configurable and useful, just by changing things like heatsink size, thermal resistance to PCB and such, and if the heater was close enough to the resistor it may be capable of reasonable response times. Dunno if such things exist though.
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Last edited by keantoken; 8th May 2012 at 12:56 AM.
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Old 8th May 2012, 06:33 AM   #49
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Did you try the 4n25?
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Old 8th May 2012, 05:05 PM   #50
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The 4N25 is a transistor optocoupler, if you used it you would still need the LDR anyways. It could be helpful, or not. I'm not sure what you want to use the 4N25 for?
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