[sdiy] keeping signals seperate..avoiding noise

Laurie Biddulph elby_designs at ozemail.com.au
Fri Nov 14 20:13:52 CET 2008


As a matter of good construction, the power supplies for each board should 
be run direct to the main power supply in what is sometimes referred to as 
`star' fashion. Daisy-chaining from one board to the next will allow noise 
induced on to the lines from one board to be radiated to the others.

The sense lines will not fix noise problems. There purpose is to improve the 
regulation and stability of the power rail by addressing for losses in the 
power cable.

Make sure your chassis has a GOOD and PROPER EARTH connection. As a minimum 
the earth pin from the inlet socket should be connected IMMEDIATELY to the 
chassis using heavy-duty wire, sturdy nut and bolt and star washers. The 
immediate area around the fixing (the area immediately under the star 
washers) should be clean of paint i.e. bare metal. This should be a 
mandatory step for equipment housing mains power supplies.

Best Regards

(Mr) Laurie Biddulph
Phone: +61 (0)2 4340 0938
Mobile: 0400 257 645

Elby Designs
ABN: 70 022 727 605
http://www.elby-designs.com

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----- Original Message ----- 
From: "Dan Snazelle" <subjectivity at hotmail.com>
To: <madhun2001 at yahoo.com>; "sdiy" <synth-diy at dropmix.xs4all.nl>
Sent: Saturday, November 15, 2008 5:05 AM
Subject: RE: [sdiy] keeping signals seperate..avoiding noise


>
> ok
>
> since there are actually 4 pcb's in this project, and ALL the digital 
> chips are on ONE board...i think i will run seperate lines all the way to 
> the PSU for JUST that board.
>
> i was even thinking of powering JUST that circuit off of a 9v battery but 
> then i figured it would be a hassle to always have to make sure a battery 
> was in the box. and since there will be a back panel...it would have to be 
> unscrewed,etc to change the battery
>
> and then i thought about a regulator for the digital board. BUT that STILL 
> wouldnt solve the dirty ground issue.
>
> SO....i think running all the way back to the PSU is the best bet.
>
>
> someone had mentioned sensing (on my psu) and i think i have it hooked up 
> properly....(to bypass it) but i am wondering if that could help at all 
> ( turning it on...anyone here actually USE the sensing within the context 
> of SYNTH DIY?_
>
>
> it's funny how you can spend months building something, it all works fine 
> (as separate elements) and then once you hook it
> all TOGETHER at the end, all kinds of NEW problems arise.
>
> i still am not quite sure why this didnt show up until NOW as i had tested 
> these boards many many times. the only difference i can find
> is that this time i am not using a battery and this time i have the boards 
> screwed into the case (on metal standoffs)
>
> i am going to try plastic spacers just for the hell of it too.
>
> i will test this all out this weekend and report back
>
> ANYWAY...thanks so much for the clarification.
>
>
>
> --------------------------------------------
> check out various dan music at:
>
> http://www.myspace.com/lossnyc
>
>
> http://www.soundclick.com/lossnyc.htm
>
>
> http://www.indie911.com/dan-snazelle
> (or for techno) http://www.myspace.com/snazelle
>
>
>
>
>> Date: Fri, 14 Nov 2008 07:39:56 -0800
>> From: madhun2001 at yahoo.com
>> Subject: Re: [sdiy] keeping signals seperate..avoiding noise
>> To: synth-diy at dropmix.xs4all.nl; subjectivity at hotmail.com
>>
>> Dan,
>>
>> There are 3 possibilities: noise in the grounds, noise coupling through 
>> adjacent wires, and noise coupling through shared power wires. The first 
>> two have been covered, so lets look at the third. Your noise problem is 
>> classic: digital circuits with their sharp little spikes of current 
>> during switching share power lines with analog circuits. Now wires are 
>> resistors, and when you pass spikey current through them you get spikey 
>> voltage drops. The opamps should in theory not care because they have 
>> what is called power supply rejection. But nothing is perfect and noise 
>> can still slip in. The first thing I would do is slap some tantalum caps 
>> across the power supplies. 10uF from +12 to gnd and -12 to gnd should do. 
>> These should be placed where the power comes into the board.
>>
>> Keeping analog and digital separate is an art. I've been known to run 
>> separate power and ground wires all the way back to the power supply to 
>> keep the digital spikes away from the analog power.
>>
>> --TimR
>>
>>
>> --- On Thu, 11/13/08, Dan Snazelle  wrote:
>>
>>> From: Dan Snazelle
>>> Subject: [sdiy] keeping signals seperate..avoiding noise
>>> To: synth-diy at dropmix.xs4all.nl
>>> Date: Thursday, November 13, 2008, 8:29 PM
>>> a few questions
>>>
>>> if i have a clean source going through a buffer and then
>>> that splits into one half going into a PLL and a divider and
>>> the other half getting boosted by a x10
>>> opamp stage...WHY would i be hearing the divider sounds in
>>> the background of the clean stage?
>>>
>>> this is very different than my lfo bleedthrough of the
>>> other night (into the vco) but it is similarly noisy.
>>>
>>> i have all pcbs on metal standoffs going into a metal
>>> box....could this cause the high frequencys of the PLL
>>> signal (and octave down) to bleed into the clean opamp?
>>> (though none of the standoffs touch traces)
>>>
>>> maybe i should put a regulator JUST on the divider board?
>>>
>>> i have bypass caps.
>>> pretty good ground planes.
>>> and seperate lines for digital and clean grnd.
>>>
>>> what about a bunch of wires laying all over each other or
>>> being bundled...can this cause signals to mix?
>>>
>>> i think i really need to understand noise better.
>>>
>>> any good books on this?
>>>
>>> thanks
>>>
>>>
>>> --------------------------------------------
>>> check out various dan music at:
>>>
>>> http://www.myspace.com/lossnyc
>>>
>>>
>>> http://www.soundclick.com/lossnyc.htm
>>>
>>>
>>> http://www.indie911.com/dan-snazelle
>>> (or for techno) http://www.myspace.com/snazelle
>>>
>>>
>>>
>>> _______________________________________________
>>> Synth-diy mailing list
>>> Synth-diy at dropmix.xs4all.nl
>>> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>>
>
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