Loud "pop" from preamp

[jakobz]

Hi there
I have build a powersupply, powering some old neumann preamps. Everything works fine, but im struggling with a rather loud POP from the speakers when the units are powered up. I have tried powering up the preamps with a Labsupply which has the voltage ramping up, and this results in significantly lower pop. So i was hoping i could find away to introduce a slow start to the powersupply. I have fooled around with some simple capacitor charging circuits to make the voltage ramp up, but i am not getting it right. Any ideas will be appreciated

 

[JohnRoberts]

Back in the 90s an engineer working for me developed a circuit that that would only allow the - supply to come up after the + supply was up and stable (or vice versa). This apparently made a difference for turn on noise in the mixers he was working on.

Can you power up these preamps first, and turn them off last?

JR

ps: it was also pretty common to incorporate fet output mutes, but I would advise redesigning your preamps.

 

[pucho812]

Seen this enough times that the simplest answer is to sequence when you power stuff on, power stuff off or if you can't do that, mute the feed to the speakers so that any powering on or off of equipment avoids the pop.
For example, at the studio we have all our circuit breakers numbered, the sequence to power all of them results in circuit #1 being the last on, and the first to shut off. This is because we have our speakers on there. It avoids any pop in the monitors.

 

[Bo Deadly]

As pucho812 says, usually you connect your speakers to a power conditioner that has a "sequencer" feature where some of the outlets on the back turn on some number of seconds after the others. This is generally a must-have feature for even a home "studio".

Otherwise, there might not be a lot you can do about it. It depends on the circuit. Post a schematic.

Slowing down the supply rails might help but I would be weary about making it too slow. If it's single supply, it's probably not a problem. But if it's bipolar and one rail comes up before the other, that's not ideal. Under some confluence of circumstances, you could damage something.

If it's a simple linear supply, you might get away with adding otherwise unnecessarily large filter caps.

Post a schem of your PS too.