Biroids CMOS Aliaser/bitcrusher/ring mod help

[John Lyons]

I'm interested in building this but I was wondering if anyone could walk me through it a bit here.



Here's the schematic:



There are sound samples here: http://www.diystompboxes.com/smfforum/index.php?topic=48815.msg362504

Vcc connects to 9v and all the Vcc points tie together.
All the Analog grounds tie together and all the Digital ground tie together separately.
I'm a bit unsure how analong and digital grounds tie to each other though. I assume is a possible source of Bleedthrough...
It looks like both grounds tie to a .1uf cap to Vcc/ 9v as well.

Easy on me now...

Thanks

John

[The Tone God]

I'm a bit unsure how analong and digital grounds tie to each other though. I assume is a possible source of Bleedthrough...
It looks like both grounds tie to a .1uf cap to Vcc/ 9v as well.

You tie all the analog grounds to one point and all the digital grounds to another single point. Then you take both sets of grounds and tie them together at one point only. This prevent ground loops and other noise. The cap is there for decoupling purposes.

Andrew

[John Lyons]

So this is like "star" grounding as amps are done?
Is there any order to which the grounds connect or can I have my Digital grounds all together and my analog grounds all together, and just connect them with one trace anywhere?

Thanks, Just seems I was expecting there to be more to the layout issue.
John

[The Tone God]

So this is like "star" grounding as amps are done?
Is there any order to which the grounds connect or can I have my Digital grounds all together and my analog grounds all together, and just connect them with one trace anywhere?

Yep. You got it. There is no real. Just one spot for analog and one for digital sharing one common trace between the two. Its seems overkill and complex but it is playing it safe otherwise you could spend a HUGH amount of time debugging noise with a chance of never even eliminating the noise because it is cause by the layout.

Good luck.

Andrew

[birt]

i made a lay-out for this. it worked but was really noisy, probably because i didn't know i had to ground those things properly.
here it is: http://users.pandora.be/vandijckheffen/bert/CMOSnyquistperf.jpg

[bioroids]

Hi!

I did the circuit only on the breadboard. It still had some background whining but was perfectly tolerable. You may want to put a socket for the ICs as different brands of CD4016 behaved in different ways.

For some strange reason the decoupling cap may have a detrimental effect on noise, and I think there is a possibility of having lower noise without it. I also think it is important to have short wires and keep the input and outputs separated, to avoid coupling noises.

I also found it was important to use exactly the pins described on the schematic. There seems to be some coupling inside the ICs that makes the stages interact with each other when used as amplifiers.

Luck!

Miguel

[John Lyons]

I worked this up last night. Not the most elegant layout but it's correct as far as I can tell.
Does anyone see any problems or issues to address?

In the original the Digital ground and Analog grounds as well as the +9v  supply to both points were separated by 121R.
Do you think this is something I should build into the layout?

John

[bioroids]

I would join the analog and digital ground at a point very near to the GND pad. The way it is on the layout right now, the digital ground is connected just after the analog ground, this way all the noise coming from the digital part of the circuit goes also through the analog part.

I think of it this way: on a ground path you have all the electrons going back to the power supply after doing their job. The electrons from the digital circuit come all shaky and frenetic (because of the nature of the digital applications), so they shouldn't mix with the relaxed electrons coming from the analog part (they don't want to be disturbed, otherwise they cannot do their job well). So they have to return to the power supply home by a different route.

The power supply is normally where the negative part of the battery or DC jack is connected, and usually that is the place where you put a power supply decoupling cap.

The rest of the layout seems to be fine, with the digital and analog parts separated and the input and outputs away from the digital stuff.

Luck!

Miguel

[John Lyons]

Oh, ok, That makes sence!
How is this?



Should I put the .1 decoupling cap near the Gnd point and wrap the +9v over to the right side to connect the two?

Thanks Biroids

John

[bioroids]

That looks better! Yes, I think it would make more sense to put the decoupling cap and the +9v pad just next  to the GND cap.

I would put the 1K input resistor closer to IC1, away from IC2. You can move that track higher if you exchange its position with the track that joins the 1M resistor and the 10K resistor. Other than that, I think it would work fine.

But if you have a breadboard, it would be cool to try the circuit there first. As far as I know I'm the only one who ever made it work.

Regards!

Miguel

[John Lyons]

I'm not sure mocing the +9v pad will do much but I moved it anyway. ...

Here's how it looks now. I moved the input higher and re aranged the 1M/10K . Also moved the IC sections a little further apart.



Thanks for the Advice Miguel!!

[bioroids]

It looks like it's ready to etch!

Happy building!

Miguel

[John Lyons]

Thank you very much Miguel! I appreciate you help with this.
John

[calculating_infinity]

Wow great job guys, I was watching this post but had nothing intelligent to add.  "Thats f***ing teamwork!" -Tenacious D. 

[birt]

ehr, how did it work out for you Basicaudio?

[calculating_infinity]

http://www.diystompboxes.com/smfforum/index.php?topic=54135

It worked out well apparently!

-Jonathan