Orban 111b noise..........jeeeez

[hyde maintenance]

Helloooo
I seem to have some hum from my orban spring reverb that is minimized when I cut at around 50 Hz.
Does anyone have experience with these things?
From what I've read it sounds like ground related hum, and I've tried playing with a few grounding solutions- single power outlet for the chain, grounding- lifting etc.- and nothing is working so far. Do I need a different grounding approach? Or could it be bad caps? Noisy op amps? I have the model without the transformer balanced output if that makes a difference.
I really want to use this thing on...well everything to be honest...but the noise is just too much.
Any suggestions?

[The Scum]

As old as it is, it could be dried up filter caps in the power supply.

Are you set up to measure for the presence of AC Voltage on the power rails?

[Kevin S]

Schematic is in the manual on Orbans web site.

I'd start looking at the usual suspects and check all the caps as said before.

Chopstick method may be helpful here.

[hyde maintenance]

Hey thanks Scum and Kevin for the responses so far. So it sounds like this 50Hz noise is not exclusive to ground hum then? I'll try the caps.

Would I need a scope to measure for AC on the power rails? Because all I have is a multimeter. Might be easiest (and about time anyhow) just to change out all the electrolytic caps and see if it helps.

I had to look up the 'chopstick method' with visions of karate kid and weight loss in my head. It seems oddly satisfying (poking things with a stick) and can't hurt, I'll give it a try first.

Thanks again

[Jim Williams]

Hum from these is from the reverb pickup coils. They are like single coil guitar pickups and are hum field sensitive.

You can do a few things to reduce it. First, replace all the electrolytic filter/power supply caps. Use bigger values, 105 degree rated Nichicon VZ are great as they last and are small. Double the values or more if they fit.

Next, unbolt the power transformer and rotate it for minimum hum, then drill new holes and mount it.

Mount the reverb box away from any hum emitting gear. Take it out of the rack and place it somewhere way from everything electric. Then rotate the box to find "mecca" on those reverb coils like you do with Fenders.

You could also obtain some "mu-metal" and wrap it around the pickup coils to reduce hum pickup.

To get fancy, order replacement reverb tanks from Accutronics. Get the type 9 three spring versions, better than your 2 spring models. You can order a pair of these with one the return coils magnets reversed polarity. Then you wire the two tank's return coils in series, that creates a humbucking pair of return coils that are dead quiet. Wire the drive coils also in series, but reverse one's polarity out of phase. That cancels the fundemental during drive that helps to eliminate the "sprong" sounds common from spring reverbs. The results are more like a good plate reverb.

The last thing would be to replace the 5532 opamps with something quieter. The AD 8599 is a great sub as it's 1/5th the noise so it will reduce hiss.

[hyde maintenance]

Hum from these is from the reverb pickup coils. They are like single coil guitar pickups and are hum field sensitive.

You can do a few things to reduce it. First, replace all the electrolytic filter/power supply caps. Use bigger values, 105 degree rated Nichicon VZ are great as they last and are small. Double the values or more if they fit.

Next, unbolt the power transformer and rotate it for minimum hum, then drill new holes and mount it.

Mount the reverb box away from any hum emitting gear. Take it out of the rack and place it somewhere way from everything electric. Then rotate the box to find "mecca" on those reverb coils like you do with Fenders.

You could also obtain some "mu-metal" and wrap it around the pickup coils to reduce hum pickup.

To get fancy, order replacement reverb tanks from Accutronics. Get the type 9 three spring versions, better than your 2 spring models. You can order a pair of these with one the return coils magnets reversed polarity. Then you wire the two tank's return coils in series, that creates a humbucking pair of return coils that are dead quiet. Wire the drive coils also in series, but reverse one's polarity out of phase. That cancels the fundemental during drive that helps to eliminate the "sprong" sounds common from spring reverbs. The results are more like a good plate reverb.

The last thing would be to replace the 5532 opamps with something quieter. The AD 8599 is a great sub as it's 1/5th the noise so it will reduce hiss.

Wow. Thank you for this awesome post Jim. I'm going to change the caps and try to 'find mecca' for the time being and see where that goes. Changing the chambers sounds cool, but I'm going to see how this thing sounds first as it was basically designed, 'sprong' and all. I'd be tempted to try a passive box made out of some of those type 9 chambers though.

Thanks again.
Cheers

[DrummerMan]

Out of curiosity, is the noise on both channels or just channel B?

Mine is pretty clean on Channel A, but B is a bit too much to use. I also know of a couple other 111B's that have the exact same issue: First channel good, second bad. I don't really need stereo reverb so I never worried about it, but this thread is making me curious.

[Jim Williams]

I would guess channel B's pickup coils are closer to the power transformer than A. If rotating that transfomer doesn't reduce hum, a torroid power transformer replacement may.

[hyde maintenance]

Mine is actually noisy on both channels, so I'm thinking the power supply caps may be a large part of my problem- although getting the unit away from other equipment did seem to help a bit.
I guess I was a little off track because the type of hum I have was referred to as ground specific in all my searches.
Hopefully I'll be able to pick up some new caps tomorrow and see what effect they have.

[hyde maintenance]

Hey Jim
A couple of greenhorn questions if you have a moment...

So I picked up a few replacement caps (of the same value but higher voltage) locally which just eyeballing them seemed like they would fit...nope. Looks like I'm going to just put an order together and be done with it. When you say I can double the value, do you mean voltage or uF? I assumed you meant voltage, but if it's uF what would changing this value do?

Also I'm going to get some new op amps as you suggested. My 111b has 4558s in it not 5532s. Are they still directly replaceable by the 8599s or will the new op amps want more current?

Thanks

[Freq_Band]

I had a lot of hiss and a tad of hum on my 111b. Both channels.

I replaced the old psu 470uf electrolytics with fresh 1000uf's (35v or higher).
Regulator's 15uf to 22uf (25v or higher).
This cut the hiss to a very reasonable level.

Removed the older RC4558 opamps, replaced with 8 pin sockets....and opamps of my choice. (opa2604, OPA2134, etc....)

Not mentioned so far.....as built, none of the opamp's power pins have bypass caps...whatsoever....nearly necessary if you replace the opamps with modern-fast replacements.
I soldered some small Wima 0.1uf's to the board's underside....from each power pin, to the nearest ground plane.

Also, one of the opamps was running very hot.....it was a bad (shorted) 47uf tantalum cap between the opamp output and the otuput transformer.....replaced with a 47uf electrolytic on both channels .

3-4 hours work.....and a different unit was born.

=FB=

[hyde maintenance]

Yeah I replaced those 470uF caps with 1000's too and it helped a bunch.
Thanks for the tip on the opamp replacements FB. Would pins 4 and 8 be the power pins that get the bypass caps?

[Freq_Band]

...... Would pins 4 and 8 be the power pins that get the bypass caps?

Yes, correct.

Glad it's working out for you.

=FB=

[Sean Sullivan]

Hey Jim
A couple of greenhorn questions if you have a moment...

So I picked up a few replacement caps (of the same value but higher voltage) locally which just eyeballing them seemed like they would fit...nope. Looks like I'm going to just put an order together and be done with it. When you say I can double the value, do you mean voltage or uF? I assumed you meant voltage, but if it's uF what would changing this value do?

Also I'm going to get some new op amps as you suggested. My 111b has 4558s in it not 5532s. Are they still directly replaceable by the 8599s or will the new op amps want more current?

Thanks

Hey friend. Order you capacitors from Digikey.com. Increase the value of the capacitors in uF, to a big as can fit. AD8599s can be used in place of 4558, but you are going to need to add phase compensation and power supply decoupling capacitor or you'll have oscillation. This is because you are using a high-speed op-amp, which the circuit wasn't designed to handle because, well, these types of op-amps didn't exist! This requires soldering a .1uF ceramic capacitor (I used Vishay Mono-Kap NPO capacitors) from pin 4 and 8 of the op-amp to ground. Then, you need to have a small cap across the feedback resistor of the opamps that have a 3 k ohm or larger feedback resistor. A 22 pf works well from 3 k to 25 k ohms, use a 10 pf if the resistor is larger than 25k ohms. Solder in parallel on the rear of the PCB.

Also, AD8599 are SO8 surface mount ICs so you need adapters to work as a replacement for the 4558. Those are available from Brown Dog.

It's a lot of work to do what Jim suggest and probably not a good first project if you don't have some help.

[hyde maintenance]

Thanks Sean.
I've never messed around with opamps so all the details are really appreciated.
I'll probably start nosing around in the Orban again after I finish recapping my PM1000.
Cheers.