LPB-1 whine with power supply, but not with battery

[FirstTimer007]

Been dabbling with pedal builds and some mods for only a short while (boxed up a Ge Rangemaster and a Ge Fuzz - which work a treat).
Just competed a LPB-1 type boost ( in beautifully hand painted case thanks to an artist friend of mine) which is the first I've made with a DC socket. Pedal tests fine with a battery, but with my (brand name) regulated isolated power supply it works and generates a whine about 900 Hz  (a sharp A at the 12th  fret 5th string.)
I used an electrolytic cap across the +9V input to ground, but did not include a diode across same. Have since tried with a diode as well now  (1N4002) but no difference!
This is the first pedal I have squeezed into a nice small case with no battery snap - or space left for a battery!
This puzzle has got me - I'm moving on to make some other pedals, but would like to avoid this in the future - can anybody shed some light please?
Have tried to attach an image of the schematic I used, but I'm not sure how to do that?

[GibsonGM]

Hi First timer...so, the power supply doesn't do this with other pedals?   Any possibility at all of a wiring error on your part?  Got the + wire running too close to other wires or the transistor??   

If no...then you can try adding a 100 ohm resistor in series with the "+" input, by the jack....and from its "farther than the power supply end", place a 100u cap to ground, see if that helps with the whine.   

Not seeing where a diode does anything to help filter (it is transparent if it is "on"), but if it is put in backwards across the power supply, it can help protect against reverse polarity plug ins...

Out of curiosity - what brand power supply?  It's ok to name it here.      Oh - is the LPB in the enclosure when it is whining, and does it do it if not in there?  And, is the encl. grounded by at least one of your jacks?   A grounded enclosure might help if the whine is actually 'environmental', as most switching supplies don't run on so low a freq....

[FirstTimer007]

Thanks for the reply GibsonGM 
It is whining when in the case, but if I connect a battery to the DC jack the whine is gone?

I think the in/out jacks are both grounded (paint may have compromised it - I will check that - ta!)

I will check the actual lie of the wiring inside also to ensure the power and signal lines are not too close to each other or the transistor .

I did include a 100uF electrolytic cap to ground, it is on the board right after where the power lead joins the board, maybe it would be better to place that straight across the DC jack?

My power supply seems to work faultlessly with any other pedals - it is a Decibel Eleven brand "Hot Stone".
Here is my schematic...I hope 

[GibsonGM]

Hi First - the schematic did not make it, ha ha.  I know the LPB-1...it is a basic transistor gain stage.   It shouldn't whine!   And your PS does not whine with other pedals??

Hmm...and switching power supplies are generally operated at much higher frequencies....kilohertz, not 900Hz +/-.   This now sounds like some kind of self-oscillation issue.  Something may be mis-wired with the transistor, perhaps - but that is reaching far.  See - if operation on battery is ok, we must rule out the DC adapter first!   

Do you have access to another power supply you can plug in, to be sure the pedal wiring is correct?  That would help us to eliminate your power supply.

After that, we'd have to find pathways for feedback to occur inside your circuit.   Rather rule out the easy things first!      But really, if it is not the power supply, then the wiring really is more suspect...if it's good with battery, the circuit is probably ok.

[FirstTimer007]

Oops! Thanks for the replies! I took the suspect pedal, to give it to my guitar set-up dude as was the plan, and after telling him it works only with battery power, it worked a treat with with his "Fuel Tank" PS!

Seems something isn't quite right with my power supply...maybe that's another project after these next two pedals - an Octavia and another Rangemaster?

Cheers!  Happy building   

[GibsonGM]

Awesome!  I thought there might be something with the PS, which is why we had to rule it out before ripping the circuit apart

Switching supplies (if it is one....) run on higher freq's, but COULD produce a sub harmonic down there, making noise.   I'd keep trying to filter it, just to see if I could...

Enjoy the Oct and RM, they're both fun.  I love the 60s RM dirt with a tube amp!

[induction]

Any gain stage that relies on the power rail to provide bias (like the LPB1, COT-50, Fuzz Face, lots of the older mojo circuits that were designed to work only with batteries, etc.) will very likely be noisy with a non-regulated adapter unless low-noise biasing is implemented in the circuit. (Possible, though uncommon, on the LPB1, but not possible on the Fuzz Face or COT-50 without changing the topology in a way that changes the sound.) This is because any noise on the power supply is fed to the gain stage, so the noise gets amplified along with the signal.

Since your power supply was regulated and still noisy, I think you're right, there's something wrong with it. Fortunately, it's very easy to make a regulator box that will convert any old cheap and crappy 12V DC adapter ($4 all day long at the Goodwill Computer Store; even cheaper at the bottom of a box full of old answering machines and christmas decorations in your favorite aunt's garage). The datasheet circuits on the 7809 and 78L09 regulators are very simple and work like a charm. I have several pedals that are absolutely unplayable with unregulated 9V adapters, but are quiet as a mouse with the world's noisiest 12V adapters and about $1 worth of caps, resistors, and a regulator.

[PRR]

Did you read this part?

try adding a 100 ohm resistor in series with the "+" input, by the jack....and from its "farther than the power supply end", place a 100u cap to ground

Big frikkin capacitor alone has no leverage. You need some slack between the crap and the cap. 100 Ohms seems a fine value here. Now the 100uFd can actually do some good.

[Transmogrifox]

Just to learn something about your power supply, does it change if you have other pedals connected onto the same power output?  More simply put, I'm talking about loading.  For a test you could put a 1k across the +9 to gnd on the DC input jack and see if that changes things.

It's not that a 1k does anything to suppress noise, but if it's a switching power supply there is potential for a "sour spot" particularly at light loads where it becomes somewhat unstable, or at least bistable with audio frequency patterns in its regulation characteristic.

On more extreme case is a converter that employs a light-load burst mode. Any "name brand" manufacturer for audio-purposed stuff should realize that light-load burst mode means audible whine.

Maybe the LPB-1 is such a light load on the supply that it operates in a funky mode and it's not a problem with other pedals because when adding the load it makes its noise inaudible.

Just an idea.  It's clear that if there is an audible whine, the power supply is to blame since it is highly unlikely a simple booster like this would go unstable at an audio frequency although there may be an interaction there between the LPB-1 and PS that makes the PS go unstable.

Either way I think +1 PRR & GibsonBM about adding 100 ohm series with 9V to 100uF.  Good chance that will silence it..

[GibsonGM]

Yes, Trans, it might silence it...not that I came up with it, LOL! Age-old "cures"...

Good idea, maybe the load is so light the thing's just 'lighting up' and doing all kinds of crap wanting to get in the ring, ha ha....good test anyway. We'll figure that thing out.

[finkaudio]

Hi,

I have the same problem with a EA-Tremolo, just working with transistors. I think what I get is some noise from the SMPS.....the simple transistor stage does not suppress anything that comes in via the power supply. A pedal with OpAmps may not show the problem. I tried a current compensated inductor with a small capacitor on the input and a fairly big (6800uF) on the output and the noise almost disappeared.

I know 6800uF is stupid, but my inductor is too small in value and I need to get a larger value first. I ordered one and will try it out as soon as it arrived and report about the progress (or non-progress  ) 

So I guess you have a similar problem, as your PS is also switch mode. BTW, with a linear PS, the problem does not show up.

Best regards

KH

[GibsonGM]

You too can try 100 ohm/100u cap instead of using an L, F - but if it's working for you and already built, maybe next time

Welcome to the forum!

[finkaudio]

Hi,

tried 100 Ohm with a 2200uF cap yesterday and it was dead quiet 

The inductors I need anyway, so no money lost

Best regards

KH

[GibsonGM]

Hi,

tried 100 Ohm with a 2200uF cap yesterday and it was dead quiet 

The inductors I need anyway, so no money lost

Best regards

KH

Good, Fink....See if you can lower the value of the cap to something like 100u....decrease the value until it is quiet.  Just curious if you NEED the big cap or if a smaller one would do - it usually does.  Huge cap = more time to charge and discharge.

There is a ripple voltage going on with the power supply, rising and falling very quickly, that we interpret as a "HUM".  The R an C form a filter that smooths that ripple, resulting in a clean(er) DC that makes no noise since it has no 'frequency'.    You'll learn more as you go along

[finkaudio]

...sure, I can try and report back.

Best regards

KH

[Topaz]

Big thanks for the cap resistor ti,  just built a five cats lpb1 and it had that exact squealing. your suggestion fixed it instantly.

Top Man...  cheers

Hi First timer...so, the power supply doesn't do this with other pedals?   Any possibility at all of a wiring error on your part?  Got the + wire running too close to other wires or the transistor??   

If no...then you can try adding a 100 ohm resistor in series with the "+" input, by the jack....and from its "farther than the power supply end", place a 100u cap to ground, see if that helps with the whine.   

Not seeing where a diode does anything to help filter (it is transparent if it is "on"), but if it is put in backwards across the power supply, it can help protect against reverse polarity plug ins...

Out of curiosity - what brand power supply?  It's ok to name it here.      Oh - is the LPB in the enclosure when it is whining, and does it do it if not in there?  And, is the encl. grounded by at least one of your jacks?   A grounded enclosure might help if the whine is actually 'environmental', as most switching supplies don't run on so low a freq....