Random static and pops

[pucho812]

Just thinking aloud and seeing if you all have some ideas here.

What can cause random static with crackle and pops in a desk? It’s an all analog signal path and the noise is intermittent. It sounds like a frying egg. It’s also varies in volume level. I’ve tracked it down to the stereo bus. Nothing has visibly failed.
I can mute everything else(channels, returns, etc) and it is in the speakers. But if I mute the stereo bus or monitor a different source it is not in the monitors.
Clearly something is amiss with my stereo bus, but being intermittent makes it harder to pinpoint.

 

[user 130681]

Probably a noisy component in the bus line.
Make and model may enable me to give more of a clue as my crystal ball is not working today

 

[Newmarket]

Does it make a difference depending on whether channels are assigned to the stereo bus ?

 

[JohnRoberts]

Look for solder bridge or inadvertent short between a VE bus to ground.

JR

 

[Ike Zimbel]

Just thinking aloud and seeing if you all have some ideas here.

What can cause random static with crackle and pops in a desk? It’s an all analog signal path and the noise is intermittent. It sounds like a frying egg. It’s also varies in volume level. I’ve tracked it down to the stereo bus. Nothing has visibly failed.
I can mute everything else(channels, returns, etc) and it is in the speakers. But if I mute the stereo bus or monitor a different source it is not in the monitors.
Clearly something is amiss with my stereo bus, but being intermittent makes it harder to pinpoint.

Most consoles that I have worked on have electronics AFTER the mute circuitry, so muting every channel will usually NOT rule out individual channel strips as the source. What make/model of desk is it?

 

[pucho812]

It’s our desk at the studio, our trident a-range. It’s well over 40 years old. Every now and then I get stumped with what’s it doing today, lol.

 

[sodderboy]

The usual suspects, cold solder joint, bad component, etc.
For me, the "sounds like frying bacon" issues have been statistically heavy towards semiconductor components.
And of course it disappears when you get close to the the room.
You have to swap sides if you can to isolate, but it's both sides of the bus?
If you can get to the bus amp circuit boards, chop stick poking, heat gun and de-flux spray are your friends.
You've been hound-dogging broken studio junk for decades, so follow your nose.
Mike

 

[JohnRoberts]

Frying noise is often associated with excessive gain, like a shorted - op amp input to ground.

JR

 

[blakeyboy]

You run a Trident A range and don't have a Tech just a phonecall away?

 

[FIX]

Frying can be from a short causing excessive gain, or an op-amp that has been zapped and is generating noise, popping is usually "shot noise" and can be from the same cause, where a transistor in one of the amps is popping.

Mute every channel and see if it continues.

if it stops:
Then it could be the mic pre, EQ or buffers before the mute switch.

if it continues:
Then remove each channel from the mix bus (that is usually after the mute sw)

If taking it off the MIX bus stops it, then you know it's after the mute and before the mix bus, then MIX off on half the console and MIX on the other half. The keep doing that until you locate it. (half of what left, then half that...) This is usually faster than individual channels if you have to wait for it to pop.

If muting makes it stop, unmute half the console and wait. If it stops, mute that half and unmute the other half. (half of what left, then half that...) The keep doing that until you locate it. This is usually faster than individual channels if you have to wait for it to pop.

If it's a constant noise, mute each channel. if that doesn't make it stop, then remove each channel from the MIX bus.

 

[Newmarket]

Yes. "Binary Search" is a good way to diagnose.

 

[Brian Roth]

I don't have complete/detailed info on the A Range (wish I did! lol), so I don't know the signal flow to the buses. However, I am quite familiar with the MCI JH-636 desks which a world apart from that Trident. BUT, in the MCI the channel mute is waaay upstream from the stereo bus, located at the channel fader. Hence, there are active stages in the path to the stereo buses.

If there is a failure downstream from the fader/mute section, then noise from those stages will still hit the stereo buses even if the errant channel is muted.

Fortunately, MCI had a 2 pole Schadow switch just before the panned channel signal hit the stereo buses which was a "hard mute". So, it was easy to track down noise feeding the stereo out.

Don't know how Trident did their routing, however.....

Bri

 

[pucho812]

You run a Trident A range and don't have a Tech just a phonecall away?

I am the tech just a phone call away. I have this thing by the short hairs. However a few mods here and there and once in a while I get thrown for a loop...

 

[pucho812]

I don't have complete/detailed info on the A Range (wish I did! lol), so I don't know the signal flow to the buses. However, I am quite familiar with the MCI JH-636 desks which a world apart from that Trident. BUT, in the MCI the channel mute is waaay upstream from the stereo bus, located at the channel fader. Hence, there are active stages in the path to the stereo buses.

If there is a failure downstream from the fader/mute section, then noise from those stages will still hit the stereo buses even if the errant channel is muted.

Fortunately, MCI had a 2 pole Schadow switch just before the panned channel signal hit the stereo buses which was a "hard mute". So, it was easy to track down noise feeding the stereo out.

Don't know how Trident did their routing, however.....

Bri

yes of course. I am narrowing it down further and further. Stereo bus insert returns are clean and no static. I would suspect a frying opamp.
The desk here was rebuilt so it's not a traditional a range. the channels are original(mic pre eq) the rest was all redone with Jensen 990's discrete pampas on all the summing sections(axes, busses, stereo bus) and monitor so whittling it down to the right card for fault checking and such,

 

[pucho812]

Frying can be from a short causing excessive gain, or an op-amp that has been zapped and is generating noise, popping is usually "shot noise" and can be from the same cause, where a transistor in one of the amps is popping.

Mute every channel and see if it continues.

if it stops:
Then it could be the mic pre, EQ or buffers before the mute switch.

if it continues:
Then remove each channel from the mix bus (that is usually after the mute sw)

If taking it off the MIX bus stops it, then you know it's after the mute and before the mix bus, then MIX off on half the console and MIX on the other half. The keep doing that until you locate it. (half of what left, then half that...) This is usually faster than individual channels if you have to wait for it to pop.

If muting makes it stop, unmute half the console and wait. If it stops, mute that half and unmute the other half. (half of what left, then half that...) The keep doing that until you locate it. This is usually faster than individual channels if you have to wait for it to pop.

If it's a constant noise, mute each channel. if that doesn't make it stop, then remove each channel from the MIX bus.

yes... Of course. Isolation is key. So far I have it between the stereo bus insert send and upstream because if I patch into the stereo bus return clean as a whistle. you know, perhaps this would be a good time to pitch a fix desk to the powers that be

 

[user 130681]

It is full of uA741 op amps that are prone to noise when they get old.
I would follow the signal path with my oscilloscope, from the output back into the mixer until I get to the point where the noise stops. There is where the noise is coming from. Then replace thenoisy component.
Could be a resistor or an op amp. Who knows, you are working on it.

 

[Brian Roth]

It is full of uA741 op amps that are prone to noise when they get old.

Hmmmmmm....I have a couple of copies of the A range input module schemos and everything in the signal path is discrete transistors. Did they suddenly "go on the dark side" and throw 741 opamps everywhere downstream??

Bri

 

[user 130681]

I must have the wrong manual then.
Here is a sample of what I have, changed to 5534s or 358s etc;

 

[mjrippe]

Hmmmmmm....I have a couple of copies of the A range input module schemos and everything in the signal path is discrete transistors. Did they suddenly "go on the dark side" and throw 741 opamps everywhere downstream??

Bri

That would be the Fleximix consoles

 

[mjrippe]

I must have the wrong manual then.
Here is a sample of what I have, changed to 5534s or 358s etc;

Your schematics are clearly labeled TSM series. Nothing like A Range.