Amp popping at startup? Get a new tube!

squirefan01 · Post by **squirefan01** » Thu Sep 13, 2007 2:06 pm

I asked a question months ago, about my Ampeg B200R amp "popping" very loudly at power up. It didn't matter if I had a bass plugged in or not. I read stories on the net about a relay circuit to prevent this type of thing, and thought it might be a relay. I wrote to Ampeg and they had not heard of this type of thing. Other than the pop it seemed to play great. The pop was so loud that I thought it could harm the speaker eventually. The only way to avoid it was to have the volume all the way down at power up (which some said is historically what you need to do anyways).

I was very close to driving it down to the nearest Ampeg service center today (47 miles away). On a whim, I decided to just get a new preamp tube (a common 12AU7 tube) and try it out first.

Well, I put it in tonight and the problem is gone! Now, instead of the pop, the amp just fades in as it warms up in the first 5-7 seconds, just like it did when I got it.

That was $17 well spent.

Just thought I'd share that as nobody anyplace gave me this very simple suggestion.

rictified · Post by **rictified** » Thu Sep 13, 2007 3:41 pm

That is not a common sign of a bad tube, usually they just get weaker and sound less clear after some years.

beatlefreak · Post by **beatlefreak** » Thu Sep 13, 2007 3:55 pm

FWIW, I always leave the volume at the lowest setting when powering up an amplifier. The more wattage you're pushing, the more important it becomes.

Sometimes popping in an electronic circuit can be caused by a faulty electrolytic cap, usually in the power supply. Evidently, not in this case, though.

squirefan01 · Post by **squirefan01** » Thu Sep 13, 2007 4:50 pm

Yes, from all I read about tubes it seemed that the bad tube would not cause the kind of buildup & arcing of electrons that would cause this popping.

johnallg · Post by **johnallg** » Thu Sep 13, 2007 5:54 pm

If it was gassy it could.

soundmasterg · Post by **soundmasterg** » Fri Sep 14, 2007 9:04 am

Any time you have a tube amp and you have a problem, the first thing to suspect is the tubes. Partly because they are a wear item and quality especially with today's stuff is sometimes hit or miss, and mostly because they are so easy to change you may as well eliminate them as a possible problem before moving on to more expensive troubleshooting. Glad it solved the problem.

squirefan01 · Post by **squirefan01** » Fri Sep 14, 2007 9:32 am

Me too! That's what I figured once I actually took the amp assembly out of the combo unit and saw that there was not much to it. It sure seemed more likely that the tube could go than any of the solid state components.

rob · Post by **rob** » Sat Sep 15, 2007 3:12 am

I used to have a solid state practice amp that did that. An SWR LA12, the first generation, to be exact. I'd turn it on to get a high pitched squeek that would shrill your bones. I had a headphone adaptor that I'd leave in the headphone jack to mute the speaker, then leave it in when the amp is not in use. Just pull it out after I turn it on, and I'm good to go.

squirefan01 · Post by **squirefan01** » Sat Sep 15, 2007 6:56 am

When I was researching my problem, SWR came up a few times. I guess that this pop would be normal in audio amp designs, but a relay circuit was designed to protect against it. Most amps have it but SWR does not. They say it's because they feel you lose some audio by incorporating this design into an amp.

This info started me on track to think that the relay circuit must be bad in my B200R. Not the case though.

rictified · Post by **rictified** » Sat Sep 15, 2007 9:16 am

"They say it's because they feel you lose some audio by incorporating this design into an amp. "

That's complete balony IMHO, they save a few bucks on each amp is more like it. That is stuff audiphools say about their 10,000.00 class A 5 Watts per channel tube amps with 24K gold point to point wiring and platinum connectors, some people have more money than sense.

soundmasterg · Post by **soundmasterg** » Mon Sep 17, 2007 9:56 am

Well there is something to be said for having extra components in the audio path and having that affect the sound Bob. Some of the best sounding guitar amps are some of the simplest. I work at a company that does audio design and almost all of the engineers here are into old tube stuff and audio designs and they always try to keep the designs as simple as possible and still get the job done, even with SS, because the more components in the audio path, the more phase shifts you have, which means the more you impact the sound.

I think price certainly played a part in their decision, but I think SWR's bit about the audio being affected is a consideration also. It doesn't sound too far-fetched to me.

johnallg · Post by **johnallg** » Mon Sep 17, 2007 11:59 am

What is the sound of one relay contact conducting in a forest if no one is there to hear it?

Sorry, I couldn't resist. I think SWR was justifying not having one in the amp. True, in a controlled listening room, with a no-holds-barred amp and speaker designs, you could hear one contact, but in a bass amp? Probably not. And I consider myself an audio purist.

Usually a relay is used in a SS push-pull amp design to decouple the speaker load until the circuit stabilizes so as to prevent DC through the speaker.

soundmasterg · Post by **soundmasterg** » Mon Sep 17, 2007 6:45 pm

I didn't catch the part that it was a relay. I doubt that a relay would change the sound any which way, but I know that other parts can and do.

squirefan01 · Post by **squirefan01** » Tue Sep 18, 2007 8:39 am

This is the blurb that I had seen about it. This is from the SWR 350x Bass Amp User's Guide:

"
Turning The Unit On

Remove the AC cable from the accessory pack and connect it from the amplifier to a standard wall outlet. Make sure that the both the Gain and Master Volume controls are set to the minimum position. Locate the power switch on the right side of the front panel and turn the amplifier on. The power switch should then illuminate in red. Upon powering up, don’t be surprised if you hear a small pop. This is absolutely normal.(Eliminating this “power on transient” would require a component called a relay. SWR chose not to incorporate this type of component due to the fact that relays degrade signal quality and often fail, causing the unit to have no output and requiring a trip to a local service center.)
"

rictified · Post by **rictified** » Tue Sep 18, 2007 2:42 pm

And maybe if it was still under warantee they'd have to pay for it?
My Marantz 2385 has a relay in it and it sounds great.