Make it clear when the amp reaches the peak of clean amplification

[lingyueqing]

The title might be misleading/confusing. I'm building an amplifier with TDA2003(https://forums.prsguitars.com/forums/amplifiers.51/create-thread) IC's which could be both suitable as a guitar amplifier and as a music amp. Where diodes come into this circuit? As you might know most transistor based amplifiers clip really harshly and it's amplifiers way of telling you "stop asking more from me!".


The idea I have - putting soft clipping diodes (perhaps 1N4148? datasheet::https://www.vishay.com/docs/81857/1n4148.pdf) before the input of the amp and to manipulate it in a way that it starts softly clipping just before the amp could say "little more and I will be angry".



What's the point of that? You would start knowing when the amp starts to reach the peak of clean amplification and you would still get in comparison a nice more overdrive like tone rather than instant angry distortion. For me this is great as my amplifier is going to be used for both guitar and music so in (my) theory it should sound quite great both at low and high levels of amplification for both guitar and music!

Though I've came across a problem - how do you manipulate the diodes so they start clipping only at specific input level? Would it have to be resistors before diodes? And would this affect music audio listening quality when the signal is supposedly clean (and soft clipping diodes are on vacation until input is higher)__? P.S. perhaps you know any great diodes that clip softly besides popular 1N4148 ?

 

[elvis]

The problem with a soft limiter is it adds distortion all the time. You would want to look at max output before clip, divide by total amp gain and limit there. You can put a zener diode (or more than one) in series with your clip diode to raise the threshold.

I would avoid that altogether and put in a detector circuit that lights an LED near clip. Then keep the level below that.

SS hard clip is not a "problem", they give almost no distortion until you hit their absolute limit. Just stay below that limit. What really happens odd that you're clipping on the power supply. A tube amp on the same power supply would also hard clip on exactly the same way at the same level, but it will soft clip way before that.

You can always build in higher supplies to get more headroom.

 

[Dusty Chalk]

Could you use a silicon diode to keep the soft clipping diode out of the circuit until, say, 1/2 of the limit of the soft clipping diode?

 

[Deleted member 5962]

don't have time for detailed response yet. But if you want softer clipping, find a germanium diode that meets the voltage you want to clip at, or stack them to create clipping at the desired voltage. GEs should clip more to your liking than silicone

And, I'm with Elvis. Don't put clippers prior to input stage.
IMHO

 

[elvis]

Could you use a silicon diode to keep the soft clipping diode out of the circuit until, say, 1/2 of the limit of the soft clipping diode?

Yes, but the input range may be much more than a couple diodes. Pls diode voltage changes a lot with temp. That's why I recommended a Zener.