[sdiy] I have found that SSM2210 transistor arrays give better performance in my latest oscillator design.

[Ray Wilson]

The jitter seems most prevalent at lower frequencys when I use a value below 
330pF (integrator cap). So instead of getting a nice hollow sounding square 
wave I get a square with what seems to be a very very slight but audible 60 
Hz jitter. I believe it may be induced from the fluorescent lights above my 
bench (4 feet away). When I grounded the metal part of my work table (one of 
those folding table types with the particle board top, metal frame and 
folding legs) it was reduced to inaudibility. I haven't seen it with my 
scope. That was with 100pF. When I use 330pF or above I get the same level 
of inaudibility without grounding the metal parts of the table. I know that 
sounds weird but it's true. It is not a problem at higher frequencies (> 150 
Hz) I'll try some of your suggestions and see what happens. My bench power 
supply is capable of 1 Amp at +/-12V (and 1 Amp at +/-15V) and I'm only 
using 30 to 40 mA in the circuit. I use LM7812/LM7912 and LM7815/LM7915 
pairs with National's suggested bypassing.

Thank you.

Ray



----- Original Message ----- 
From: "Ian Fritz" <ijfritz at comcast.net>
To: "Ray Wilson" <raywilson at comcast.net>
Sent: Saturday, June 24, 2006 9:42 PM
Subject: Re: [sdiy] I have found that SSM2210 transistor arrays give better 
performance in my latest oscillator design.


> At 03:18 PM 6/24/2006, you wrote:
>
>>All I've done so far is remove one of the LM394s and replace it with an 
>>SSM-2210 and then adjust the scale pot while inputting 0 through 7 volts. 
>>If I try to use a smaller cap (and I assume lower the current at 10KHz) I 
>>tend to get a fair amount of jitter. Is there something you would suggest 
>>I try to lower the current other than reducing the integrator cap value? 
>>Or is there something that could reduce jitter at low cap values? I 
>>appreciate your input. I have observed that you are way more into the math 
>>and theory than I am. I'm more of a technician (try this and that until it 
>>works kind of guy) than an electronics engineer.
>
> Well, Ray, I've always leaned very heavily on the "Edisonian" approach 
> myself.  Especially in the rarified atmosphere of the fine points of VCO 
> tracking. The theory explanations tend to come after the data and the 
> bloody work of tweaking up the circuit.  And I very much appreciate the 
> high level of performance you are getting from relatively simple and 
> inexpensive designs.
>
> As far as jitter, I really don't have any ideas.  I haven't ever looked 
> too closely at that ... never seemed to be much of an issue.  I guess the 
> first thing I would look at is possible HF oscillations in the converter. 
> After that, maybe noise pickup on the supply lines to the converter. 
> Ferrite bead decoupling between the switching section and the converter 
> might be something to try.  Also be careful of switching spikes coupling 
> radiatively into the converter.  How bad is the jitter?  Is it audibly 
> annoying, or just something you see on a scope?
>
>   Ian