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 Forum index » DIY Hardware and Software » Circuit Bending
FET crossfade / volume fade / pan
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SineHacker



Joined: Mar 09, 2010
Posts: 98
Location: United Kingdom

PostPosted: Thu Jun 28, 2012 10:47 am    Post subject: FET crossfade / volume fade / pan Reply with quote  Mark this post and the followings unread

** I updated the schematic because of the mistake in the original **

well I had some serious fun today

I had a play with some FET's today and I don't really know much about them, but through messing around I found this great way to volume fade / crossfade / pan. I was amazed at the simplicity of this, and it makes me feel like I have done something disgustingly wrong, or something that an engineer would spit on, that said if people can help me learn a bit more about them or improve the design, that would be great! You guys might know all this already but:

Posted Image, might have been reduced in size. Click Image to view fullscreen.

The FET's go down to perfect silence as far as I can tell, 10k seems like a good pot to use for mixing as I tried a 1k and everything was a lot quieter (thought the fade was very smooth) and a 100k pot cut signals in too hard. It makes a good volume fader if you just omit signal B and its FET from the diagram, and I'm sure it would be easy to implement it as a mono to stereo pan if you wanted (maybe with a 10k resistor between the signal input and the 2n3819). I'm not sure if the 10k resistors are needed before the output but I put them in just to be safe.

now I had some real fun today, I don't know if you have tried this but if you use small signal diodes to mix oscillators from something like a cmos 40106 then you get a cool unison effect between them, and this can be really interesting if you use oscillators running at super low or high frequencies - I was using the diodes after the 2n3819 pair to mix oscillators in and out (doesn't work if you place them before), it sounds freakin amazing! the unison effect creeps in really gently. I have basically sat mesmerised for quite some time this afternoon just fading between 2 oscillators

I have only tried this mixing with CMOS oscillators so far, but I presume it will work with other stuff as well, give it a go and I'll let you know if I find anything else if you like!

Aidan

Last edited by SineHacker on Thu Jun 28, 2012 11:46 am; edited 1 time in total
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SineHacker



Joined: Mar 09, 2010
Posts: 98
Location: United Kingdom

PostPosted: Thu Jun 28, 2012 11:33 am    Post subject: Reply with quote  Mark this post and the followings unread

I just realised I made a blunder, with the post, the pot is actually linked to GND, I messed it up because I was trying to work with a +9v signal in the first place which was making it do weird things (discovered the circuit above by accident)
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SineHacker



Joined: Mar 09, 2010
Posts: 98
Location: United Kingdom

PostPosted: Thu Jun 28, 2012 11:52 am    Post subject: Reply with quote  Mark this post and the followings unread

I'm not sure if this will work with signals other than CMOS squares but will test it out tomorrow afternoon hopefully. all signals carry voltage so maybe it will work right? Rolling Eyes
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SineHacker



Joined: Mar 09, 2010
Posts: 98
Location: United Kingdom

PostPosted: Thu Jun 28, 2012 1:05 pm    Post subject: Reply with quote  Mark this post and the followings unread

well I was bored and finished some other work I had to do so I tested the circuit with some other signals. It didn't work very well, I guess some kind of preamp circuit might sort it out but on it's own it is very quiet and wouldn't actually reach total silence as a volume fader.

if anyone is interested this is the circuit that I thought sounded really good:

Posted Image, might have been reduced in size. Click Image to view fullscreen.
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