Possible ground issue?

[SineHacker]

I am working on a basic drone instrument that is based around a CMOS 40106, I want to run it through a LM386 because I do some things to the gates/oscillators that makes them sound good but makes them quite quiet, and each oscillator has a separate volume pot

The problem is, if I power both chips from one battery everything sounds like battered shit, which I'm fairly sure is to do with the 40106 making the ground really noisey - If I use two batteries then it sounds fine

Another problem is that I am thinking of adding one of my crappy PT2399 based delay circuits to it as well which needs to run at 5v and 5v regulators eat 9v batteries for breakfast so I was hoping I could use a single power supply for everything from the wall.

Soooo, if I use a separate regulator for each part of the circuit would that by any chance give some separation of grounds? Actually even writing that down makes me think that will do nothing as I think the ground is linked up and unaffected by the regulator - any suggestions?

The current signal path is like this: 40106 oscillator to voltage divider (volume) x 6, so there are 6 oscillators that I sum to a 2n3819 and that goes into the lm386 - this currently goes straight to the output but I want to add the delay circuit here to try and add a crude chorus like quality to the sound. I would like to use a 7809 for the LM386 a 7805 for the PT2399 and a LM317 variable for the 40106 all powered from a 12v DC supply - I have never used multiple regulators so any tips on this would be good, I'm just going to run with it for now and experiment

Rather than trying to describe where the circuit is grounded at each point, I will draw a schematic tomorrow (at work till 9pm tonight!) and post it to help with the explanation if needed, but any thoughts on separating the ground or perhaps taming CMOS ground noise would be great!!

[elmegil]

Have you put bypass caps on all your chips power supply pins?

[SineHacker]

[bubzy]

how does it sound at the output of your summing transistor?

[elmegil]

Just checking

I've never seen 1uF or bigger caps used as bypasses though. Usually I see 1uF or 10uF on the main supply line in, and then .1uF or .01uF caps for bypasses.

Sorry I don't have anything more helpful to suggest....

[SineHacker]

@ Elmegil: ok I will try it that way cheers (should have brought it with me to work!)

[SineHacker]

Have you guys got any experience with rail splitters/virtual ground/virtual dual-supply

I'm not sure if this only really applies to op-amps that require a dual-supply, but there is some interesting info here: http://tangentsoft.net/elec/vgrounds.html

[SineHacker]

Hey again, yeah it was to do with choice of bypassing capacitors - I used 10uf across the supply and 0.1uf at the +v pin of each chip as elmegil suggested and that properly stabilised the circuit. So thanks!

I also checked the signal at the transistor and it is clear there but the lm386 gives it a nice boost anyway, I might try without the transistor next

thanks again

[bubzy]

[SineHacker]

[SineHacker]

Cool, I finished it last night! Works really well. Thanks for the help - I tried adding a pic but not sure my phone wants to...

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[bubzy]

what's it sound like?!

[SineHacker]

Like dis

Headphone drone jam from Ginko (Aidan Taylor) on Vimeo.

[bubzy]

sounds good man!

needs more wubs

[PHOBoS]

yeah, that was nice!

[SineHacker]

Yeah, I think I need to adjust the wub control... but really - I want the delay effect to be less subtle I think, you don't really hear it until the feedback is on the brink of self-oscilation, needs a mix control or some adjustment. I pretty much built the delay line from the PT2399 datasheet but switched out some of the capacitors to improve the sound quality (by trial and error!!). I am wondering if I can improve the volume by changing the resistor values between the lpf input and output - or what I presume is the main input but the pins are marked as LPF in and out. It's a great chip by any means!

[PHOBoS]

[SineHacker]

Neat, that's very helpful - I have a new project on the go now where I am going to revisit the pt2399 so I think I will start again from scratch

I am going to use a basic 4017 based 4 step sequencer to blink LED's and these will be used to opto-couple a single audio signal across 4 delays, the idea is to chop a signal in a sequence to each delay input. If it sounds as good as my brain is making out then it will be FUN

gonna put it in a vintage cornflakes tin