Tonepad's Filter/Sample&Hold troubles (not only).

[Eb7+9]

Looking at the schematic and think about what Eb+7 said, providing I understand it, it looks like the power supply feeds the LFO first from the 9V supply, and the Filter is fed second form the 8V supply. This sounds opposite to what Eb+7 is describing.

right, IMO best to supply clean +/-9v to the filter first - use a large cap like 2200uF or 3300uF (25v) between this first set of rails ... then supplying the LFO on the "in-side" of the diodes and also have a large filter cap there across those rails ... the caps go between +/- supply rails only and not to ground - this helps the ground stay clean and you're only using half as many caps ... see if that works for ya 

[ovnifx]

Hi Eb7+9,
I have to admit I'm still pretty confused about exactly which parts are being swapped out.  The way you describe running those large caps from rail to rail, not to ground, I wonder what relation they have to the cap and ground connections in that charge pump assembly in the schema?  Thanks very much for your help!

[soggybag]

I'm trying to put together the the PS filtering idea outlined JC in the posts above. Here is a drawing that I came up with. I'm not sure if this is what he was describing. Give me some opinions.

[Eb7+9]

the diodes replace the filter/drop resistors ... ie., the one going between +9v and +8v and the other going between -9v and -8v ...

there's two diodes and two caps in all, no other resistances ... one big ass cap going between +9 and -9 and another big ass cap between +8 and -8 ...

lemme know if this isn't clear and I'll draw something up later ...

[soggybag]

Thanks for the reply. I have changed the drawing above. Let me know if this is what your are describing.

Here the +-9V goes to the digital/LFO/Envelope circuits. It seems to me that you would want these to come after diodes? Would the filter and audio circuits need to come before?

If not what does this accomplish?

[ovnifx]

Soggy, it looks like in your current drawing the +9 and -9 from the max chip go straight to the +9 and -9 terminals (on the outside).  While that does seem to match what Eb7+9 is suggesting, will the cap between the junction points there provide a good filter for those voltages?  And does that matter?

[Eb7+9]

Would the filter and audio circuits need to come before?

the goal is to have a most steady supply for the audio circuit ... through passive means alone there's two "series" hookup versions (audio first LFO after, and vice versa) and a third "parallel" (both with resistive feeds) but only one will provide maximal drive (improved immunity) to the audio - that's the case when the audio supply is coming from the battery or source directly ... the LFO is then fed by the Downside of the diode circuit, we're calling it +/-8v ...

the diodes drop voltage as the exponential LFO trigger spike draws current from its supply lines - in turn this reduces the driving force behind the current - providing NFB action in the local LFO supply ... the downside cap needs to be large enough in value (guessing at least 1000 times larger than the main charging cap value in the LFO) to ensure that charge can be provided locally from a large enough reserve - same with the +/-9v filter cap ... btw, the so-called +/-8v is not static in the same sense as we want the main +/-9v to be - turns out the LFO is fine with that ...

[soggybag]

Thanks for the all the help, I have been determined to get this thing working, can I get you to confirm two things:

1) From your last post it sounds like the Audio should be fed from the +-9V side in my drawing, while the LFO/Envelope should be fed from the +-8V. This opposite of the marking on the drawing.

2) The drawing I've made is correct, except for the note above.

The orignal is set up with the LFO/Envelope connected to the power supply first followed by two resistors, two caps and these feed the Audio side.

[Eb7+9]

you got it Soggy ...

[soggybag]

thanks again, I'll give this a try when I have some free time this weekend. It will take a little work to cut a few traces and arrange things so the audio circuit is powered directly from the power supply and then set up the diode caps after to power the LFO/Envelope.

I have a few larger caps, but I don't have any in the 2200 - 3300 range. I think I test with a few 470uf caps in parrallel.

[Fp-www.Tonepad.com]

I just had a chance to update the layout trying to minimize the issues described in this thread.

You may look at it here:
http://www.tonepad.com/project.asp?id=50

Hopefully it won't have the problems the previous revision had.

[chemosis]

Is there anyway to change the frequency of the entire sound on the envelope filter side. want to achieve a lower lowpass sound. i thought someone said C5 and C3?? i love the envelope filter side but wish it had more controlls.