[sdiy] FETs for distortion

[Michael Ruberto]

Seb, Jim,

I have been wanting to build this circuit for a very long time but just 
never seem to find the time. I'm not sure if it will work well with synths 
but I'm sure some adjustments can be made.

http://www.geofex.com/Article_Folders/jfetdoub/jfetdoub.htm

Here is a nice page with JFET booster info. I've found it very helpful.

http://www.geofex.com/Article_Folders/foolwfets/foolwfets.htm

M. A. Ruberto


>From: Seb Francis <seb at burnit.co.uk>
>To: James Patchell <patchell at cox.net>
>CC: Synth DIY <synth-diy at dropmix.xs4all.nl>
>Subject: Re: [sdiy] FETs for distortion
>Date: Sat, 31 Dec 2005 14:00:10 +0000
>
>Hi Jim,
>
>Thanks for your reply.
>
>I have heard it said that FETs give a softer clipping than BJTs, hence 
>wanting to try them.  Since I will breadboard my ideas first, I will be 
>able to play around with biasing and driving levels to get a sound I like, 
>then use the same actual FETs when I build.  The temperature drift is 
>perhaps more tricky, so I will have to read the datasheet and see if I can 
>minimise the effects of temperature (or add some compensation).
>
>So far (from the various schematics I have seen) I'm going to buy some J201 
>and 2N5457.  Now you have said they may vary a lot, I will buy a few so I 
>can pick and choose.
>
>I think these two are JFETs.  I wonder if I would get a different sound 
>using MOSFETs?  I haven't seen them used in any schematics, and I've heard 
>they are damaged by static very easily, but someone on this list said 
>recently that they give a nice soft clipping (I'm not sure if this comment 
>also applied to JFETs, or was specific about MOSFETs).
>
>Seb
>
>
>
>James Patchell wrote:
>
>>One thing you should note about fets is that they have a tendency to 
>>"vary" a lot from unit to unit.  Depending on the circuit topology, you 
>>can pick a set of fets that will work perfectly, and if you then replace 
>>them with randomly selected parts...it will not work the way you expect.  
>>Plus, fet parameters drift with temperature in ways that you will 
>>definitely notice.  By comparison, BJT's are extremely well behaved.  I am 
>>not suggesting you use BJT's, just letting you know that you are going to 
>>be tackling.  Most people are pretty used to using BJTs.
>>
>>
>>
>>At 02:10 AM 12/31/2005 +0000, Seb Francis wrote:
>>
>>>Hi,
>>>
>>>I'm just playing around making a few distortion circuits (to be used for 
>>>electronic drums + synths, rather than guitars).
>>>
>>>I want to try out some distortions with MOSFETs and/or JFETs and I was 
>>>wondering if anyone had any recommendations of some part numbers to buy.  
>>>Preferably they need to be available in UK from Rapid or Farnell, but if 
>>>there's something particularly good I don't mind hunting around.
>>>
>>>I guess I'm asking whether one FET is going to be pretty much the same 
>>>sound as another (just a case of biasing and driving appropriately), or 
>>>are there some favourites for this type of app?  Or are there in fact 
>>>some particular specifications/attributes I should look for when choosing 
>>>a FET?
>>>
>>>I hope this is not too vague a question ;)
>>>
>>>Seb
>>>
>>>
>>
>>         -Jim
>>***************************************************************
>>http://www.oldcrows.net/~patchell
>>
>>***************************************************************
>>
>>
>>
>>
>