+9V and -9V Rail Op Amp Supply Problem

[west portion]

Hey all!

In my overdrive circuit design I decided to create a -9V rail to be used with the +9V rail instead of creating a 4.5V virtual ground. I'm using OPA2134, but have run into a problem with a high pitched whine that occurs as soon as I turn the supply on. Each rail was tested with my dmm and supplies a steady +-9V, with an added filter and flyback diode at the supply entrance. I've read the datasheet and the op amp should be within its capabilities, but I have yet to find any solution or similar schematic to figure out why the whine is happening.

Forgetting the dual idea and just creating the 4.5V ground works just fine and the circuit sounds great. I've tried low pass filters at various parts of the circuit with no meaningful results and I've used multiple supplies and even a battery. Do I need to be referencing the other components to the -9V for this to work? Is this just the drawback of designing with a breadboard? Really any piece of advice/schematic/encouragement would be very helpful. This is my first time here so it's exciting af

Thanks if advance!

[PRR]

Welcome!

Where is this -9V coming from?? Another battery? Another wall-power rectifier? Some kind of switching converter??

> any piece of advice/schematic/encouragement would be very helpful.

We could come up with billions of possibilities. More interesting to know what YOU did. YOUR schematic, pictures, shopping list.

[antonis]

Apart from your schematic, power supply decoupling configuration should also be of major interest..

e.g. you have one 100nF cap from each supply to GND or a single cap between +/-9V..??

[Radical CJ]

... e.g. you have one 100nF cap from each supply to GND or a single cap between +/-9V..??

Is one way generally considered better than the other?

[antonis]

... e.g. you have one 100nF cap from each supply to GND or a single cap between +/-9V..??

Is one way generally considered better than the other?

Generally, yes..!! 
Late one (one cap between supply rails) is considered better 'due to GND "isolation" from power supply garbage..

[marcelomd]

One capacitor between rails vs one for each rail to ground.

Every time I read one way is better, someone points the other way is the True Way.

Last time I called a fellow engineer who really likes to nerd out on this stuff. He recommended to use THREE capacitors. +V to ground, +V to -V and ground to -V.

Now I follow the datasheet for the particular device.

Regarding squeals: Show us the schematic and pictures of the board. Some circuits, specially high gain, are designed too close to some oscillation threshold. Part tolerance and layout can tip it over.

[merlinb]

One capacitor between rails vs one for each rail to ground.
Every time I read one way is better, someone points the other way is the True Way.

I have never yet got any discenible benefit from rail-to-rail capacitors, but they sure have created problems for me.

[marcelomd]

Late one (one cap between supply rails) is considered better 'due to GND "isolation" from power supply garbage..

One capacitor between rails vs one for each rail to ground.
Every time I read one way is better, someone points the other way is the True Way.

I have never yet got any discenible benefit from rail-to-rail capacitors, but they sure have created problems for me.

See? I wasn't lying 

On topic: last time I built something with a dual PSU, I used two capacitors because it was recommended in the design guide for that module, a 500W power amp. Zero noise.

Can we assume a capacitor between a single supply, +9V and 0V, sits between rails? Shouldn't we have a capacitor between +9V and +4.5V and another between +4.5V and 0V?

Do opamps care if the power supply is single or dual?

[iainpunk]

welocme to the forum!

despite the interesting discussion above about power supply caps, i doubt it has much effect in solving the issue.
i suspect its oscillations of a feedback loop, but a full schematic might help us help you pinpoint the problem.
have you put together an audio probe yet? ist my favorite tool to debug both whining and dead circuits.

clip one side to ground and the other to a thin piece of wire and you can easily trace the audio through the circuit, see where it either stops putting through signal or where it picks up noise/whine

cheers, Iain

[west portion]

Damn y'all thanks so much for the replies! I've placed the cap between the two rails and it cuts down the hum tremendously so you've all been a great help.

As for the high pitched whine, I used the two unused inputs on my cmos NAND gate (from the tube-like gain in the circuit) as a clock to increase the frequency on my ICL7600 (supplies the negative voltage) past audible human hearing and it seems to have solved it!

Will I run into problems using this approach? That's such a general question, but if I need to address controlling frequency, I should use the decoupling technique again?

[west portion]

welocme to the forum!

despite the interesting discussion above about power supply caps, i doubt it has much effect in solving the issue.
i suspect its oscillations of a feedback loop, but a full schematic might help us help you pinpoint the problem.
have you put together an audio probe yet? ist my favorite tool to debug both whining and dead circuits.

clip one side to ground and the other to a thin piece of wire and you can easily trace the audio through the circuit, see where it either stops putting through signal or where it picks up noise/whine

cheers, Iain

This is some high level troubleshooting stuff, very pumped to know this now! The thought of troubleshooting used to take a ton of my drive out of working on projects, but over time learning techniques like this have started to take me a long way. Any more knowledge you want to drop?

[antonis]

Can we assume a capacitor between a single supply, +9V and 0V, sits between rails?

Of course, it does sit between rails..

Shouldn't we have a capacitor between +9V and +4.5V and another between +4.5V and 0V?

IMHO, no..

P.S.1
I make myself clear, again, by stating I was talking about 10-100 nF decoupling cap(s) and not about reservoir ones.. 

P.S.2
Just pasting here some points of view:

From Rod Elliot:
"High speed opamps must have good bypassing. Most of the time, this will be between the power supplies, avoiding the earth (ground) circuit completely. A normal opamp has no knowledge of earth, ground planes or anything else earth related. It is only interested in the voltages present at its two inputs, and when used in linear mode will attempt to make them the same voltage."

From Douglas Self:
"The essential requirement is that the positive and negative rails should be decoupled with a 100 nF capacitor between them, at a distance of not more than a few millimeters from the op-amp; normally one such capacitor is fitted per package as close to it as possible.
It is not necessary, and often not desirable, to have two capacitors going to ground; every capacitor between a supply rail and ground carries the risk of injecting rail noise into the ground."

[antonis]

I've placed the cap between the two rails and it cuts down the hum tremendously so you've all been a great help.

But you don't seem to be grateful enough by posting your particular PS schematic, do you..?? 

[west portion]

I've placed the cap between the two rails and it cuts down the hum tremendously so you've all been a great help.

But you don't seem to be grateful enough by posting your particular PS schematic, do you..?? 

haha insatiable! i just don't have it drawn out yet. when it comes time to I can post it here. that is if you're still interested a few days from now

[PRR]

....your particular PS schematic, do you..??

haha insatiable! ...................

There is a method to his meanness. Frequently a clue to your troubles can be found IN an accurately drawn schematic.

[iainpunk]

welocme to the forum!

despite the interesting discussion above about power supply caps, i doubt it has much effect in solving the issue.
i suspect its oscillations of a feedback loop, but a full schematic might help us help you pinpoint the problem.
have you put together an audio probe yet? ist my favorite tool to debug both whining and dead circuits.

clip one side to ground and the other to a thin piece of wire and you can easily trace the audio through the circuit, see where it either stops putting through signal or where it picks up noise/whine

cheers, Iain

This is some high level troubleshooting stuff, very pumped to know this now! The thought of troubleshooting used to take a ton of my drive out of working on projects, but over time learning techniques like this have started to take me a long way. Any more knowledge you want to drop?

an important skill would be guesstimating the voltages on pins of chips and transistors, but that comes with understanding the circuit and plain experience, combined.
just knowing about electronics as much as possible will make everything more understandable and logical.
another great skill is when to ask for help. some people, when they encounter a problem, they try and try a lot of weird and sometimes unrelated fixes and get super frustrated and then they ask the forum, but i strongly suggest asking the forum before you are getting frustrated, it gives both you and the forum members a happier and more enjoyable time. this also makes the trouble shooting generally quicker, so you do more projects in the same time, gain more experience and thus make less problems.

cheers

[ElectricDruid]

Just pasting here some points of view:
From Rod Elliot:
From Douglas Self:

Given that Antonis is a Greek (a Thessalonian, I believe), we can expect he has a high degree of familiarity with Philosophy, seeing as the Greeks invented the field while the rest of us Europeans were still hitting goats with sticks or some such nonsense. Hence he realises clearly that the position he has put forward is "an appeal to authority" and therefore not rhetorically valid in any way. Who cares who said it! The question is "Is it true?". However, given the calibre of the sources that Antonis is quoting, I'd be very inclined to defer to the argument from authority in this case unless I'd got a very good reason not to! Both Rod Elliot and Douglas Self know what they're talking about, so we might feel that despite the logical incoherence of the argument, practical considerations outweigh this and HE MIGHT BE RIGHT!!

[Jarno]

On a sidenote, I have used OPA2134 quite a lot, and found them to be quite gentle creatures, I always have at least 47uF from each rail to ground where the power comes onto the board, and 100nF SMT ceramic caps really close by each IC from rails to ground.
Where is your power coming from, off the shelf DCDC, a transformer, home made DCDC with a 555 etc etc?
Pictures of the layout?

[antonis]

The question is "Is it true?"

For such deterministic quests, the answer depends on what you wear during the discussion..