I'm making a crossfader to mix and fade between control voltages for an audio synthesiser. The crossfader fades evenly between two signals, when it is at either extreme, either one of two input signals is a gain of 1. I've used a two vca elements in a linear gain mode to fade the two signals and chosen the component values so +5 volts gives a gain of 1.

I am having a slight problem with processing the voltage from a pot, as limiting the voltage with a 5.1 zener diode is a somewhat soft clip - the control voltage needs to be preserved exactly until it reaches 5 volts (or thereabouts) then stopped, hard.

Is there a way I can look at to achieve a harder clip than just a zener diode?

 

What's the pot's resistance?
What supply voltages do you have available?
What is the control voltage range?

 

Any chance of a circuit of what your working with, voltage limits,?

 

pot resistance is 10K

+/- 12V power rails

cv is 0 - 5V

 

A TL431 precision variable zener will work from 2.5V to 30V, you could feed your voltage into an op amp to lower it to zero.

Or use your preset across the zener for zero to 5V.

 

ah, well the problem there is that the crossfader curve is not linear, so i can't just take a voltage and scale it down.

the pot is connected between 0 and +12V. as i turn the pot up, the cv rises linearly as the voltage on the wiper goes from 0 - 6V, rising from 0-5V then as the pot is turned from 6 to 12V the cv needs to stay at 5v. There is another cv which does the opposite - 0-6v produces 5V cv out, 6-12v produces 5v linearly decreasing to 0v.

see the different crossfader curves here - https://www.virtualdj.com/image/53066/181624/cf2.png the 'full' curve is what im after

 

I'm making a crossfader to mix and fade between control voltages for an audio synthesiser. The crossfader fades evenly between two signals, when it is at either extreme, either one of two input signals is a gain of 1. I've used a two vca elements in a linear gain mode to fade the two signals and chosen the component values so +5 volts gives a gain of 1.

I am having a slight problem with processing the voltage from a pot, as limiting the voltage with a 5.1 zener diode is a somewhat soft clip - the control voltage needs to be preserved exactly until it reaches 5 volts (or thereabouts) then stopped, hard.

Is there a way I can look at to achieve a harder clip than just a zener diode?

The TL431 has a sharper knee than most Zeners - but there's a few gotcha's in the implementation.

Its a comparator with built in 2.4V reference that needs a Vcc and a minimum operating current of about 1mA.

You could probably set a couple of them up with standing bias and strap the signal to them with diodes - the diodes still have dynamic resistance, but it might be better than Zeners.

 

Here's a clamp circuit using a quad op amp package (LM324), that should do what you want:
It sharply clamps the Out voltage from the pot at the Ref voltage.

If the +12V is sufficiently stable you could replace the zener with a 7.15kΩ resistor to generate the 5V Ref voltage.

 

Here's a clamp circuit using a quad op amp package (LM324), that should do what you want:
It sharply clamps the Out voltage from the pot at the Ref voltage.

If the +12V is sufficiently stable you could replace the zener with a 7.15kΩ resistor to generate the 5V Ref voltage.

View attachment 126143

thankyou! that is exactly what I was looking for and it works perfectly. A nifty design too, is it your design or from somewhere else?

 

thankyou! that is exactly what I was looking for and it works perfectly. A nifty design too, is it your design or from somewhere else?

Not sure whether I ran into it somewhere else in the past or not.
I've had it in my bag of tricks for quite some time.
Here's a short article I wrote on the circuit and its variations.

 

Hello,

If the pot is fed from a voltage that is too high, a series resistor limits the upper end range.
For example if the pot was 1k and connected directly to 10v, the pot arm would swing from 0 to 10v, but with a 1k series resistance the arm would swing from 0 to 5v.
If the pot arm is loaded then it's a little different but not much, just make the series resistor lower.
I dont see a schematic for your actual current circuit.