Popping from standby switch

[Normster]

I'm at my wits end trying to fix a popping noise from the standby switch. The circuit is a straight up hrm/bluesmaster clone w/precision power supply. The noise seems to be coming from the power amp side since it's there with preamp tubes pulled but goes away with PI tube pulled. Tried pulling inner/outer output tube pairs to isolate any problem with screens, but it's there with either pair pulled. In desperation, I replaced all power supply caps...no change.

I've tightened all grounds, rechecked (and resoldered) every connection I could think of, replaced the standby switch and suppressor cap. I'm kinda running out of ideas.

Has anyone tried using a scope to check HT DC? My scope has a 400V label warning so I'm not sure if the probe caps will fry.

Any and all ideas welcome. The amp works fine, but I'd really like to get rid of that pesky popping noise.

[talbany]

I think I posted this recently but will throw it out to you..An Easy Fix..... A Nice fix here is to wire the amp up hot all the time and use the STBY switch to lift the center tap of the HT B+ on the power transformer...This eliminates the high voltage surge and stress on the switch and caps is totally quiet...Ampeg has done this on quite a few amps and really wonder why more don't do it.. The only thing I see with this is when you turn the Stby on the caps remain charged so if you bang on the guitar it will spit at you until the caps discharge a minute or so..
The cure.... Don't play the guitar in STBY ..Good Luck!!


Tony VVT

[ayan]

I'm at my wits end trying to fix a popping noise from the standby switch. The circuit is a straight up hrm/bluesmaster clone w/precision power supply. The noise seems to be coming from the power amp side since it's there with preamp tubes pulled but goes away with PI tube pulled. Tried pulling inner/outer output tube pairs to isolate any problem with screens, but it's there with either pair pulled. In desperation, I replaced all power supply caps...no change.

I've tightened all grounds, rechecked (and resoldered) every connection I could think of, replaced the standby switch and suppressor cap. I'm kinda running out of ideas.

Has anyone tried using a scope to check HT DC? My scope has a 400V label warning so I'm not sure if the probe caps will fry.

Any and all ideas welcome. The amp works fine, but I'd really like to get rid of that pesky popping noise.

Consider replacing the screen grid resistors. When those start to go, you will get a pop/fizzling sound after switching from standyby to on.

Gil

[Normster]

I'm willing to try the center tap fix, but the problem is recent so I don't want to mask a failing component. (I guess I should have stated that in the beginning.)

Would it help to increase the screen resistors to 1K? (Currently 470R.)

[Structo]

Do you have the first filter caps wired so they are charged when you flip the power switch?
If so, try a .01 - .02uf 1Kv ceramic across the standby switch terminals.

[Normster]

Do you have the first filter caps wired so they are charged when you flip the power switch?
If so, try a .01 - .02uf 1Kv ceramic across the standby switch terminals.

Yes, and already have the cap in place. I'm going to try 1K screen resistors per Gil. I'll report back.

[jhaas]

I just went thru this on an 18W Lite build. I thought it was the standby switch too, but then realized it happened when powering down from the power switch too. In my case it was a pop followed by a trailing fizzing type sound.

With my amp it ended up being one of the blocking caps between the LTPI plates and the power tube grid resistors. Probably just one was bad, but I replaced both and was good to go.

I had other symptoms too - reduced headroom and slightly reduced overall volume.

[Structo]

Yesterday I re-wired my D'Lite to the Dumble way of having the standby switch after the first filter caps, before the choke resistor.
I put a nice .01uf 1kv ceramic across the standby switch, no pop or noise when I switch it.
So the problem is probably as suggested by the others.

[greiswig]

I'd rewired my standby some time ago with a cap across it to prevent popping, but it still popped a little. For grins, I decided to try what was discussed in http://ampgarage.com/forum/viewtopic.php?t=9790 this thread, and put a 100k resistor across it, too. Standby is totally muted, and switching it out of standby is silent.

[Structo]

That's great that worked for you.
That does seem like a good thing too as it would slowly charge the other caps while you wait for the tubes to heat.

I currently have 200uf on the first filter network, I just wanted to see what it would do.

When I changed all the E caps for F & T electrolytics, I took the 100uf I had from before and piggy backed them on top of the 100uf F & T caps.

I thought it would really tighten up the bass but I really didn't notice any effect.

[Normster]

The problem with my amp turned out to be a bad power connection to the relay board. (cold solder joint) It caused both the relay and the diode to fail so as the symtoms became worse, the problem was easier to find. Replaced the relay and diode and standby switching is dead quiet.

[Structo]

Wow, I would never of thought to check that.

That's kind of a freak incident that would leave a lot of people scratching their heads.

Did you put a scope on it to find it or what was your method to troubleshoot that?

[jelle]

Chopsticks?