[sdiy] General White Noise Question

[harry bissell]

 From my (sad) experience you can vary the resistor from 50K or so to
a couple Megs...  Each transistor will have an optimum point.

In this high gain circuit... no, a trimpot is a bad idea :^P

And btw... try finding an NPN with a reverse Vbe other than 5 or 6 volts

Like maybe 10 or 20V ???  :^P

(we have any voltage you want, as long as its 5 - 6V :^)

H^) harry

Ray Wilson wrote:
> I've been using a 1 meg since I bought my first PAIA Gnome (which used 
> 1 meg and a 2N2712). You can change the value to see what happens it's 
> definitely not in stone but this works. I have a drawer full of 
> 2N3904's and I tested 6 to 10 random picks and got decent noise from 
> all of them. The gain of the second stage may need tweaked to go a bit 
> higher or lower depending on the trannie. If you have any 2N2712's 
> they do produce a very nice noise signal in this configuration. Just 
> about any NPN trannie with BVebo of 5 or 6 volts should do.
>
> I'll try the 100K on mine to see how its sounds. Thanks
>
> I tried to keep the runs around the high gain section short to reduce 
> induced AC in the noise too. Thanks for the tip on the SMT ceramic.
>
> Ray
>
>
> ----- Original Message ----- From: "Grant Richter" <grichter at asapnet.net>
> To: "rdrake" <rdrake at data2action.com>
> Cc: <tavys.ashcroft at gmail.com>; <synth-diy at dropmix.xs4all.nl>
> Sent: Sunday, August 06, 2006 1:25 PM
> Subject: [sdiy] General White Noise Question
>
>
>> The White Noise Source looks similar to the Electronotes designs.
>> The Noise Ring noise source is also based on that, BUT
>> I have had real problems using a 1 megohm in the R2 position for 
>> production (as in some original Electronotes designs).
>> I used a 1 megohm in the R4 position with the same C1 value and non- 
>> inverting JFET amp.
>> I had to switch to 100K in the R2 position to get all units to pass  
>> test.
>> Also do not use a SMT ceramic part for C1 or it will be microphonic.
>>
>> It seems (from experience of building the 100 modules) that somewhat  
>> more current into the zener biased transistor produces a more uniform 
>> frequency distribution and output level.
>>
>> Any quantum scientists have a theory why that should be?
>>
>>>>> Hi All
>>>>>
>>>>> I have another offering called the "Noise
>>>> Cornucopia" which you may find
>>>>> interesting.
>>>>>
>>>>> Its here...
>>>>>
>>>> http://www.musicfromouterspace.com/analogsynth/NOISECORNUCOPIA/ 
>>>> NOISECORNUCOPIA.php
>>>>>
>>>>> Cheers all
>>>>>
>>>>> Ray
>>>>>
>>>>>
>>
>
>
>