NOISY NeoVibe?

[BubbaKahuna]

Finished up my GGG Neovibe and the effect works fine but the hum is almost as loud as the signal going through it.

When I first built it the noise was even louder and when I went through it I found the input jack was wired backward.
Reversing that fixed the super loud (like touching your guitar cable tip with your finger) noise, but the background hum is still there.

Polarity on both in & out jacks is (now) correct, I'm using an 18VAC wall wart to power it (polarity on that shouldn't matter - right?).

Under magnification there are no sloppy solder joint bridges, all very small shiny pyramids.
All wires are 24AWG data grade wiring rated at 300v.

All leads are as short as possible while allowing offboard components to be mounted and still be attached to the board.
18VAC power line in wire pair is twisted tightly like heater wires in a tube amp to reject noise. Wrapping this in foil doesn't help.

My light shield is made of an old radio tuner coil cover (aluminum) with teflon pipe tape along the bottom to insulate it from shorting out on the PCB.

One other thing to note if it helps ::
You can hear some noise leaking through that cycles with the light's oscillations even when bypassed (it's true bypass).

Any other ideas to quiet this thing down?
It's not just a little hum, it's REALLY LOUD. 

Any help is appreciated.

Cheers,
- JJ

[plankspank]

Does sound like a grounding issue. double check the circuit ground, the input & output jack ground, and the enclosure ground with a meter-they should all be the same. Also try powering it with a DC source.

[R.G.]

Is your AC input jack isolated from the chassis (and signal ground)?

I think that about half the people who build this simply buy a non-isolated DC jack for the power to come in on, causing precisely this condition.

'Course, you could be part of the half that get it right. But it's worth a check.

[BubbaKahuna]

My PS is an old US Robotics modem PS with a DIN connector.
I'm using an old MIDI jack to get the juice into the box and there is no connection between the chassis and any of the DIN pins.
Why a MIDI type power plug? No chance of plugging in the wrong PS to this. 
After reading the instructions again for about the 50th time that was the first thing I checked. 
There should be no power ground at all in the Neovibe if I'm reading it right.

The surround on the power socket is metal and is bolted directly to the chassis, but there is no continuity between the barrel of the plug/jack and the pins in the jack itself.

I was just going to go back to the schematic for this to look for circuit grounds to check not only them, but whatever is physically near them to see if I spaced out and have a pair of wires backwards.

I'll be back! 

[BubbaKahuna]

OK jack is isolated, all grounds are where they should be.

I'm thinking it's my PS.
If it's a switching PS, would that make noise?
It was for a modem so if that's the problem, I'll need to find something else to power this.

I have an 18vdc 50mA PS, is that even enough to power the NeoVibe?
Seems a little low for light bulbs + all that circuitry.

[Papa_lazerous]

My money is on the power supply.........ok thats me spent my £0.02 

[plankspank]

18VDC is fine. The 50 ma. is on the low side. you will need at least 100ma...

[BubbaKahuna]

OK, it works on the 50mA 18VDC wall wart - but still has noise.
I didn't run it very long maybe a minute to check it out - I didn't want the PS to get hot or anything.

The noise isn't really constantly there, but is there when the bulb is at the top of the sweep and on the bright side (if that makes any sense). 
Another thing I tried was to adjust the lamp bias trimpot. When I turn it full counter-clockwise, the noise is minimized and more treble heavy.
When I crank the trimpot clockwise, the tone (of the noise) turns much more bass heavy and a lot louder.

Maybe that can point to something in particular ... I sure hope so.
Cheers,
- JJ

[plankspank]

Hmmm, so you are only getting the noise when the bulb flashes on- is that correct?. If so measure the output of the voltage regulator when the bulb is on and make sure you have 15 VDC here. Like I said, 50 ma is a bit low for this circuit; the current draw is around 70 ma. You may be starving the regulator.

[R.G.]

OK jack is isolated, all grounds are where they should be.

OK, that's not it. It's just so common that it's always the first thing to check.

The noise isn't really constantly there, but is there when the bulb is at the top of the sweep and on the bright side (if that makes any sense). 

Hmmm, so you are only getting the noise when the bulb flashes on- is that correct?. If so measure the output of the voltage regulator when the bulb is on and make sure you have 15 VDC here. Like I said, 50 ma is a bit low for this circuit; the current draw is around 70 ma. You may be starving the regulator.

Good one plank. I'd go there next. Starving the regulator is a possible for the same symptoms.

[BubbaKahuna]

I'll need to buy another PS for it at this point.
I was hoping the original one I had would work, but no cigar.
It's rated at 18VAC @ 20VA. Not sure how that figures to mA.

What kind of PS do everyone else use with thier NVs?
Radio Shack doesn't seem to have much in the 18~24v range.
Next PS I get for this will be my third one, so this is getting expensive @ about $15 each.
Any good sources of known good PSs for these units?

Cheers,
- JJ

[R.G.]

It's rated at 18VAC @ 20VA. Not sure how that figures to mA.

"VA" stands for "Volts times amperes", so 20VA is the product of 18V and the ampere rating. That puts it at over 1A, which is plenty.

If that doesn't work, it's either defective or you have other internal issues, things like power supply caps backward or regulator backward.

[plankspank]

For a quick and dirty test you can try 2 9V batteries in series.
For a more permanent solution, I used this 18VDC switching mode supply on my neovibe, and it works great:
http://www.circuitspecialists.com/prod.itml/icOid/8371
They shipping costs are kind of high, though...

[SteveB]

While I can't help you with the hum issue, this is the tried & true AC adapter I have used with mine for years. Available from Peavey.

http://www.peavey.com/products/browse.cfm/action/detail/item/8575/16.5%20Volt%20AC%20Power%20Supply.cfm

Steve

[BubbaKahuna]

I'm pretty sure my caps, regulator and rectifier are all in correct.
I've even moved wires near the power input to the other side of the board with no improvement.

Maybe I'm missing something obvious and need a different pair of eyes:
http://s233.photobucket.com/albums/ee255/BubbaKahuna/stomps/NeoVibe/

Anything jump right out?

Cheers,
- JJ

[BubbaKahuna]

1. NeoVibe worked when assembled, but had lots of noise.

2. As suggested, tried a pair of 9v batteries in series to get 18v of clean power.
Tried it out with guts hanging out because I'm getting tired of remounting everything.
NEOVIBE WORKS & IS QUIET! YEAH BABY!

3. Put Vibe back together in the box making SUER nothing is shorted out or not where it belongs.
Even went so far as to test every single part of the power jack (plastic body) to make SURE.
Put rubber feet on the back of all pots and switch to make SURE nothing is touching.

Now NeoVibe doesn't even work. 
Sound passes both bypassed and when on, but sweep is only heard for about 1 second when first powered up, then sweep fades to nothing.
Tried all 3 ways of powering NV including my original PSs and batteries with exactly the same results.

I tested the power both before and after the rectifier on the board, getting 18vDC all day long.
Vibe only Vibes when first plugged in and (get this) if I disconnect the power for about 1 second before everything discharges and the sound cuts out.



Duh-whuh-HUH?!

[plankspank]

I tested the power both before and after the rectifier on the board, getting 18vDC all day long.

This doesn't seem right- you should be reading 15 VDC after the regulator.

Put Vibe back together in the box making SUER nothing is shorted out or not where it belongs.
Even went so far as to test every single part of the power jack (plastic body) to make SURE.
Put rubber feet on the back of all pots and switch to make SURE nothing is touching.

Now NeoVibe doesn't even work. 

Are you sure you're not shorting out the ckt board on the mounting standoffs? You said everything works when you had the guts out of the enclosure. Try pulling the guts out again....

[BubbaKahuna]

I tested the power both before and after the rectifier on the board, getting 18vDC all day long.

This doesn't seem right- you should be reading 15 VDC after the regulator.

No what I said was I'm getting 18v after the rectifier, not the regulator.
I'm getting 18vac before the rectifier, 18vdc after the rectfier & 15vdc after the regulator.

Are you sure you're not shorting out the ckt board on the mounting standoffs? You said everything works when you had the guts out of the enclosure. Try pulling the guts out again....

I'm not using standoffs, I'm using rubber feet on all the metal parts inside the box (pots and switch) and they're not conductive. They're rubber.
There is about 1/4" between the circuit board and anything else in the box when assumbled.
I've tried it both in and out of the enclosure and get the same results.

There is no longer any 'Vibing' going on in any mode or with any setting.
There is only vibe effect for about 1 second if I have the effect unpowered, run signal through it, and plug in the power.
Then and only then I get signal and effect for about one second.
After the first second of what sounds normal, the effect fades out and I get only the guitar signal with no 'Vibe'.
When I pull the power plug out with signal going through it, I regain the effect sound for about 1/2 second, then dead silence (which makes sense since there is then no power to the unit and it would store power in the caps for about 1/2 second or so).

I can also see the bulb flashing ONLY when I first plug in or unplug the power.
Otherwise, the bulb does not light up under any setting or whether the PCB and controls are in the box or laying on a non-conductive cardbaord sheet on my desk.

Does thes sound like a possibly fried bulb power transistor?

[R.G.]

You're well past "does it sound like", "do you think it's", and "could it be".

Put it into your box, power it up with your power supply then provide the suggested information as per "Debugging thread: What to do when it doesn't work."

I know it's tempting to keep easter egging and chasing possibilities, but go measure it all and we can actually tell what's happening.

[BubbaKahuna]

First thing I did was check continuity of every single wire in this thing and found one of my wires wasn't passing any juice to my speed pot. This probably happened from all the in & out I've done trying to chase the noise issue. I replaced the wire (on my speed pot) and I could see the light running again. So far so good.

I then reflowed ALL my solder joints again and it tested good with a pair of batteries chained together.

Put everything back together again and Ta-Da! I have a working NeoVibe. I'm still not wild about the speed and depth limitations, but maybe I'm just expecting too much. I thought with everything cranked and through tweaking the bulb bias and output resistor mix I could get nearly useless amounts of sweep, but it's only capable of about 180 BMP sweep speeds with what I would call a decent amount of 'vibe' in vibe mode, but not really a lot of chorus no matter what the controls are set at. That's not to say there's no chorus, I was just expecting more to it I guess.

Overall, I'm pleased with it and really didn't build it for a chorus since I already have one of those and prefer a separate stomp for more control over the two without twiddling knobs anyway.

Thanks for the help chasing my ghosts in this. I really appreciate it - cheers and beers (or whatever) all around!

My 2 power supplies both make noise that the batteries don't so it looks like I'm going to drop some more $$ on another PS.

Cheers,
- JJ