single and split power supply best practices?

Just Say Noise! · Joined: Nov 14, 2011 Posts: 17 Location: Portland, Oregon

I hope this is the right forum to post this question concerning powering my synth. If not, please advise.

I am currently building a Lunetta type synth. Most of the IC's are CMOS and run on a single +9v supply as would be expected with a lunetta. I am powering it with a simple 9v wall wart or battery. I want to add some envelope generators, VCA's and VCF's that are OPamp based to the circuit which require a split supply and virtual ground reference. Therefore, I am splitting the 9 volts into +4.5v/ 0v/-4.5v for these OPamp IC's. I know EG's VCA's and VCF's are not typical with Lunettas but I want to experiment anyway.

My question is this:
What is the best way to power multiple IC's that require single supply and split supply power?

Is it best to just buss the +9v and 0v to the circuit and then create a separate voltage divider for each IC that requires the +4.5/0/-4.5 split supply?

Can i use just one voltage divider and split the 9v supply first, then buss this +4.5/0/-4.5 to the circuit powering all the IC's that require the split supply AND THEN pull from the +4.5 and the -4.5 (which is 9v) for the IC's that require a single 9v supply?

Thanks for any suggestions!

Grumble · Posted: Sun Apr 10, 2016 2:49 pm Post subject:

There is a short answer and a long one...
The short answer is: it depends.
The long answer is: it all comes down to the amount of power you use on each voltage.
If you use the virtual ground just for reference, and draw very little current from it, I would go for a 4.5v reference voltage ic like a RF194 from analog devices or the like.
But if you plan to sink or source from this virtual ground you might be better of with two (or maybe three) power supplies.

Grumble · Posted: Sun Apr 10, 2016 3:03 pm Post subject:

There might might be another solution, one I have used in the past.
Once I needed a negative power supply of a few volts, and used a voltage inverter., but you can only use this if you draw very little current from the negative voltage.

PHOBoS

You've got several options depending a bit on what your plans for the future are.

The BEST way would be to create a dual supply with an actual ground. You could either use a center tapped transformer
for this but you can also get great results with a single AC wallwart. You can have a look at the MFOS wallwart supply
on how to do this. If you also want to use batteries you would have to use 2 batteries wired in series where the connection
between them will be your ground/0V. Most if not all CMOS chips will run on 18V but check the datasheet to be sure. You would
probably have to add a switch to choose between AC or battery power. You could also run the CMOS of 9V and add AC coupling
caps at inputs/outputs of circuits that need the dual supply.

Another option would be to create a fake ground but the succes rate of this depends a bit on the circuits you use.
To do this you can sometimes get away with just a simple voltage divider made with 2 resistors but you will get a more
stable 'ground' if you connect an opamp to it configured as a voltage follower. If you use multiple circuits that need a dual
supply I would advice you to create a fake ground for each circuit which you don't connect together but you will have to
add AC coupling caps to in/outputs of the circuit to remove any DC offset voltage.

Keep in mind that if you use a single 9V supply and create a fake ground your (dual supply) circuits will only have -4.5V/+4.5V which
doesn't leave a lot of headroom. So you might run into some problems if you connect the outputs of CMOS chips (9V) directly to it
without attenuation. On the other hand they are squarewaves so it might not matter very much.

Just Say Noise! · Joined: Nov 14, 2011 Posts: 17 Location: Portland, Oregon

Just Say Noise! · Joined: Nov 14, 2011 Posts: 17 Location: Portland, Oregon

Just Say Noise! · Joined: Nov 14, 2011 Posts: 17 Location: Portland, Oregon

Great feedback already! Love it! Let me give some more info on what I am trying to power.

Everything is on breadboards at the moment. I set a goal to try and get the most out of a 9 volt powered synth as I possibly can. I realize this goal has its limitations, but wanted to see how far I can push things within this restriction and master this level of building before advancing on to dual batteries or the MFOS wall wart supply (which I have built and played with a bit). So for the moment I am focusing on powering everything from 9 volts or less.

As far as how much power I will be drawing and if I will be sinking/sourcing from the virtual ground, or just using it as a reference, I do not know. Mostly due to my limited knowledge on such things and also because I'm still adding and removing "modules" as I breadboard/discover them. Hopefully if I list out what Im building it may give a better picture on how to solve my supply power question.

So far this is what I have. 9v powered IC's which make up a kind of sample/hold and melody/sequencer thingy:
4046's
4066
40106
4017
4051
4040
simple VCA's from 2N5457 tranny's

IC's running on 5 volts which is basically atari junk (would love to get this to just run off 9 volts so i can ditch the 5 volt regulator):
78L05 regulator
7555
74HC164
74HC86

Now for the OP amps:
LM324 envelope generator and a VCF (based on MFOS noise toaster)
I plan on using a couple of these chips as you can get an envelope and VCF out of the same chip (thanks Ray!). I am trying other OP amp VCF circuits, but with less luck.

So I have the 4000 series IC's all on one breadboard and the 74HC series IC's on another breadboard and the LM324 OPamp stuff on yet another breadboard. I want to power all the boards simultaneously so I'm using a TLE2426 "rail splitter" to send -4.5/0/+4.5 down the busses on the breadboards, mainly for the LM324. From those busses I just pull off what I need for each IC (most IC's are being powered from the +4.5v buss and -4.5v buss, which should appear as 9v to the IC, right?). However, problems seemed to arise when I tried tying each of these separate breadboard "modules" together. I can only imagine that it has something to with splitting the power and expecting some IC's to "see" it as split and other IC's to "see" it as single. Not sure.

Hope this gives a clearer picture of my set up/questions. I'll research the info in the responses I've received already and see where that gets me.

Grumble · Posted: Mon Apr 11, 2016 2:41 am Post subject:

synaesthesia · Posted: Mon Apr 18, 2016 9:43 am Post subject:

Just Say Noise! · Joined: Nov 14, 2011 Posts: 17 Location: Portland, Oregon

Just Say Noise! · Joined: Nov 14, 2011 Posts: 17 Location: Portland, Oregon

Just Say Noise! · Joined: Nov 14, 2011 Posts: 17 Location: Portland, Oregon

Grumble · Posted: Tue Apr 19, 2016 11:43 pm Post subject:

I didn't know how much power you need so I figured that the best you can do (when you need a lot of power) is to have a transformer with separate windings for 9V and 5volt pos and neg.
But looking at your power needs (prob. less than 100mA in the negative voltage) There is no need for separate power supplies and you could just as easy stick with your 78L05 and use a MAX660 for the negative supply. This little bugger will provide you with the negative voltage of the value you supply it with (in your case 5volt) and can output no less than 100mA which should suffice your negative voltage needs. .

MAX660.pdf

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PHOBoS

mike page · Joined: Sep 26, 2016 Posts: 134 Location: norwich, uk

Hi all,

Ive got the same situation. Ive got my lunetta running on +9v, 0 and some simple filter and such circuits running on +5, 0,-5.

Can I just run the lunetta on the -5, +5 of the dual supply?
Will everything be happy?

(sorry if the answer is in the above text and I missed it)

MP

PHOBoS · Posted: Thu Feb 09, 2017 1:53 pm Post subject:

Since you are using a symmetrical supply this should IMO work fine since it will cause the CMOS signals to be biased around 0V,
even though they aren't directly connected to it. If you would for example use a -6V, +9V supply than the CMOS signals would be
biased around 1.5V creating a DC offset voltage.

However it does depend a bit on the circuits you are using and how you connect them to eachother. Synth circuits that create a
gate signal often have a 0V..+5V output and connecting this to a CMOS chip that is powered by -5V/+5V will most likely not work
because the 0V is not low enough to be recognized as a low level.

JovianPyx · Posted: Thu Feb 09, 2017 7:32 pm Post subject:

Cfish · Joined: Feb 24, 2016 Posts: 477 Location: Indiana

Can't believe I had not noticed this thread.

I have a couple of questions.

When using the partial wave rectification used in the MFOS schematic link posted by PhoBos, is the noise level elevated from using a center tapped full wave rectified supply???

It's not lunetta, but center tapped +-15v transformers are getting hard to find.

I had been thinking of trying to calculate the capicitors to do exactly that. Especially for low consumption modules.

My initial quick calculations showed the capicitors would not be cheep to fill the dips in the rectification. And size would get pretty large for 1/2 amp supply

worth. However my curiosity is still aroused.

Edit. Also, what happens if you use to large of capicitors in a supply like this? I have a few 8800uf 370v capicitors lying around. I suspect they might cause a volt drop if the transformer is unable to charge the cap within a wavelength and might cook the transformer.

JovianPyx · Posted: Sat Feb 11, 2017 7:27 pm Post subject:

Cfish · Joined: Feb 24, 2016 Posts: 477 Location: Indiana

Thanks JovianPyx very helpful.

mike page · Joined: Sep 26, 2016 Posts: 134 Location: norwich, uk

Looks like the little +-5 I was using isnt up to running both the circuits it was intended for and my lunetta. (not for very long at least, it has a charge pump IC on it which got VERY hot, then stopped working until it cooled down).

I think I'm going to get this : http://www.ebay.co.uk/itm/PD-2505-Pwr-sup-unit-pulse-25W-120-370VDC-90-264VAC-Outputs2-5VDC-/192107938977?hash=item2cba8684a1:g:HpMAAOSwfVpYp74Z