Cacophonator question

R_Gol · Joined: Oct 17, 2019 Posts: 34 Location: World

Hi all
I'm about to build this lovely synthbox called Cacophonator: https://theremin.us/Circuit_Library/cacophonator.html

I have few questions regarding the components:

1. Can I replace cr1 diode (MUR210G) ? if so with what other diode ?
2. is the 2200uf polarized capacitor ( c7) can be 16v or should be 50v? is that true for all polarised capacitors? 16v is enough ?
3. all the frequency potentiometers should be A type or B type ?

Thanks for helping!

Steveg · Joined: Apr 23, 2015 Posts: 184 Location: Perth, Australia

Hi R_Gol,

Welcome to the Lunetta forum.
The MUR210G is a fast recovery diode with a 2A rating ... check for fast recovery diodes in your preferred suppliers catalogue. the purpose of the diode is to short the power supply if the battery is inserted backwards. R10 limits the current to .4 A so a 1A diode would probably be happy. Whether it actually needs a Fast recovery diode here is another matter which I am not qualified to judge. If you were constructing the kit connected to a power supply the I would just leave it out.

16V should be fine for a 9V supply.

Linear pots would be usual but putting a log pot in there would not be a huge problem. It isn't like you have precision control.

Enjoy,
Steve

PHOBoS · Posted: Thu Apr 23, 2020 6:37 am Post subject:

note that A/B labels for potentiometers can differ per manufacturer. The pots I used to use had A for linear and B for logarithmic.
Now that I use alpha pots most of the time it is the other way around. For this circuit (and other circuits with the same oscillators)
I would actually recommend using antilog pots. Except for maybe RV5.

R_Gol · Joined: Oct 17, 2019 Posts: 34 Location: World

Steveg · Joined: Apr 23, 2015 Posts: 184 Location: Perth, Australia

Well, 0.3A is less than 0.4A so no. The rule of thumb is that you would want it to exceed the predicted current by at least 50%.

But if you doubled the value of R10 then the current would be safe for your 1N4148.

Now if you have a cheap stock of 40106 chips and you are using a socket so the chip can easily be replaced then you may not need that diode at all unless you think you are prone to inserting batteries backwards. The circuit will function identically without it.

PHOBoS · Posted: Thu Apr 23, 2020 6:15 pm Post subject:

hmm 22ohm @ 0.4A. If you do reverse the power that resistor has to dissipate about 3.5W!
A better idea would be to use a (schottky) diode in series with the battery. You'll lose a bit
of the voltage but that's not really a problem for this circuit.

Steveg · Joined: Apr 23, 2015 Posts: 184 Location: Perth, Australia

D'Oh! Thanks Phobos, I totally forgot to calculate power dissapation.

R_Gol · Joined: Oct 17, 2019 Posts: 34 Location: World

got another question on another circuit and I didn't want to open another topic for that -

I created this cmos cowbell circuit https://hackaday.com/2015/04/10/logic-noise-more-cmos-cowbell/

instead of using two 40106 osc I changed it for two 4046 osc - the rest is the same.

My problem is that the envelop seems to sound good in its attack but as you can hear there is addition quieter sound accompany the cowbell sound that should not be there.

here is the sound example: https://www.dropbox.com/s/gcvwegxzxtn1jlf/example%20cmos%20cowbell%20issue.mp3?dl=0

I wondering if its because the circuit still on two breadboard and the moment I will solder it the problem will be gone or its something in the circuit ?

Thanks!

blue hell · Posted: Sat Apr 25, 2020 1:31 am Post subject:

R_Gol · Joined: Oct 17, 2019 Posts: 34 Location: World

blue hell · Posted: Sat Apr 25, 2020 2:35 am Post subject:

That would filter off some highs .. so yes that would help .. does it not become too dull overall now?

R_Gol · Joined: Oct 17, 2019 Posts: 34 Location: World