The buzz is KILLING ME!

This is the oddest grounding (?) problem I have ever encountered.

I built a GSSL for a friend few months back, he runs it through the patchbay, typically used in unbalanced inserts.

There is always a constant buzz present, and it's not even 50hz buzz, I think the fundamental is 150hz. We have now tried pretty much everything:

1) Pin 1 connected at one end only (both input and output have been tried)
2) Pin 2 connected at both ends
3) An 1:1 isolation transformer tested at both input and output, grounds referenced @ the GSSL end
4) My own, loaned unit at the same physical place in the rack = the problem doesn't go away. Both units measure and work fine at my place! My version is also very different from the stock version by the I/O and PSU.
5) Shutting down ALL the gear at the same rack - no help (and none of them do the buzzing, and they come through the same cabling and patchbay.).
6) Lifting ground from the power cord (don't kill me! I did it just to see if the problem is at this area - situation legal now )
7) Using other cabling (including running the unit to the console individually, balanced) - no help

This is really odd. Nothing helps and it's clearly not the units fault since my own version does the same thing too. None of the other equipment does the same thing, including an inner SSL limiter I built inside the consoles mix buss, the Neve-ish preamp and a stereo 1176 (the same I posted pictures of a while back) so it can't be my construction techniques either.

It's almost like it just doesn't like being in the studio. Everything from galvanic isolation to shield/pin 1 manipulations have been done. Oh, the racks are made of wood too, so the gear doesn't get a chassis-chassic contact through it either.



Is a big hammer the fix?

is the unit star ground? I'm sure it is but that helps.

Also try moving the power trafo around maybe even use it external it might help...

Same problem on one of my unit when connectet to an unbalanced environment... (have you tried that unit using balanced connections ?)

I used a good toroidal transformer, star ground, (I tried also different grounding schemes) without luck... :sad:

[quote author="pucho812"]is the unit star ground? I'm sure it is but that helps. Also try moving the power trafo around maybe even use it external it might help...[/quote]

It is, as is my own unit. Power transformers tweaked to maximum. And they both measure fine at my system..

patchbay system is part of a ground loop..?

[quote author="Svart"]patchbay system is part of a ground loop..?[/quote]

I dunno. To my sense, the possible loops should have been cut off with the pin 1 tricks, or at least with the 1:1 xformer. The mains are at the same phase/earth with the console, as far as I know.

hmmm. Have you tried Balanced I/O on the comp but having it unbalanced in the other end?

and it's not even 50hz buzz, I think the fundamental is 150hz

Click to expand...

Computer CRT monitor or switched PSU? I had that problem. It appeared only in some units. I had two identical patchbays, one picked up the hum from the monitor, the other didn't and a third unit picked up the hum from a PSU in a fourth unit... I solved it by moving stuff around for a day or two until I found where they wanted to be in the studio...

Good luck!

/Anders

I've had something similar with a SCSI drive connected to a particular socket in the ring main. Moving to another socket further away stopped it dead.

I made my patchbay part of a star ground with the console being the center and each patch jack getting it's ground from only the console and not a ground strap to the rack itself. that has worked very well so far.

I had also the strangest effects with my N*utrik patchbay when putting balanced and unbalanced cables together. Also such buzz in the 150Hz area although I've watched out for grounding loops, etc.
Upper row: Outputs
Lower row: Inputs

Strange enough, the buzz disappeared as I used the patchbay only for outputs and connected the balanced channel strip directly into the front outgoing jacks without a patch cord from output to patchbay input (as it is meant to be).
:?

Hey Jakko ! (I really hope you have NOT used the hammer fix tool yet !)
I think I've found a "solution" for my buzzing unit...
Yesterday i opened it again, and i tried to fix the buzz problem.

First thing i measured the buzz frequency, the foundamental was around 150Hz, exactly like yours...

For first I've tried a different toroidal transformer -> nothing changed
I tried to unplug the GND from the IEC -> nothing changed
At last tentative, I've built a Keith PSU (God bless gustav to send a PSU with each 9k board :grin: ) I've removed all the psu parts from the GSSL board, I've connected + and -15V and.... voilà !

THE BUZZ IS GONE !
Finally also my "unbalanced" GSSL is dead quiet !

Try this by yourself and, please, let me know if it works also for you !

Cheeeeeeeeeeeers ! :guinness:

must be a bouncing ground issue.. ?

Hi Svart !
What do you mean with "bouncing" ground ?

[quote author="Neeno"]I think I've found a "solution" for my buzzing unit[/quote]

Cool!

I do suspect it won't help in this case - we tested my unit too and it does the same buzzing. It has a monster 317/337 PSU and zero original PSU components..

My friend did some testing and he managed to kill the buzz at one point: when he tried connecting the compressor directly to insert jack of the console and the buzz was there, he managed to kill it buy shutting down his AD/DA which has a switching supply. Unfortunately, it doesn't help when the compressor is taken back to the rack.

He said btw that the fundamental is 50hz, but the harmonics are high enough to fool you..

[quote author="Neeno"]Hey Jakko ! (I really hope you have NOT used the hammer fix tool yet !)
I think I've found a "solution" for my buzzing unit...
Yesterday i opened it again, and i tried to fix the buzz problem.

First thing i measured the buzz frequency, the foundamental was around 150Hz, exactly like yours...

For first I've tried a different toroidal transformer -> nothing changed
I tried to unplug the GND from the IEC -> nothing changed
At last tentative, I've built a Keith PSU (God bless gustav to send a PSU with each 9k board :grin: ) I've removed all the psu parts from the GSSL board, I've connected + and -15V and.... voilà !

THE BUZZ IS GONE !
Finally also my "unbalanced" GSSL is dead quiet !

Try this by yourself and, please, let me know if it works also for you !

Cheeeeeeeeeeeers ! :guinness:[/quote]

Hey Neeno..
The solution to your problem was to build a new power supply for the SSl clone... ???? I think I have the same problem..

some time insufficient ripple smoothing (i guess there are other words for that) in the psu cause 120Hz noise (pulsating current after rectifier), enlarging the psu caps might help, actually i plan to do so in my gssl since it's a bit noisy at high gain.
how ever i don't see direct relation to grounding problems.

HI,

I exactly have the same noise problem :

see :

http://www.groupdiy.com/FORUM/viewtopic.php?t=14013&sid=96122d77d50e8a4193f1bf5764e1fb35

SO take higher voltage for the Capacitor fix the problem??

What is the Keith PSU?

150Hz usually indicates transformer pulsed saturation and radiation into other nearby pickup loops (for 50Hz mains countries; 180 Hz for 60Hz mains). The solution is to reorient the power trafo and/or move it away, and/or minimize the pickup loop areas. If you have enough voltage margin you can also put some dropping resistance in series with the winding to reduce the peak currents and avoid saturation.

Toroids are not immune BTW: if the cores saturate on diode charging peaks the trafo is no longer self-shielding.

pwr trans not working hard in this circuit?

anybody got a scope?

pwr supply ripple easy to trace back towrads front of multiple pies.

but, remember to observe your scope and probe ratings.

we always used a .47 on the end of our leads in school, just in case.
teacher got tired of us forgeting to turn the ac/dc heathswitch on the probe.

i believe those early heath's were taking a stab at
fet technology, and guess where the fame seeking engineer
put them? At the front end!

i guess the fets are better nowdays. plus protection circuits.
you can't always trust a zener or MOV to be quick enough. There is always going to be a little that sneaks by these devices. They need something to work on in order to activate their overload mechanisms, and this means a little overshoot. There are devices especially for protection, they are quicker than your normal diodes, and not as primitive as MOVs's.

They go under part numbers like P6KE18A, Clamps. Thats what they are. And they work real well and take a beating. I have never seen a unit come back with a bad PK device. Over a 12 year period and about 5,000 units a month. Most zeners will pop pretty easily if you really slam them. They are usually used in the 1/2 to 1 watt range. These PK things take about 3 wattts I believe.
Give them a try.
What was the question? :?