DeltaBlues 210 loud pop when turned off

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rdoty
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DeltaBlues 210 loud pop when turned off

Post by rdoty » Mon Jun 29, 2020 4:39 pm

I've got a DeltaBlues 210 S/N 51072273 that gets very little use. When I turn it off there is a very loud pop in the speakers which I'm certain wasn't there when new. Is there a component gone bad and if so can you identify so I can change it.

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Enzo
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Re: DeltaBlues 210 loud pop when turned off

Post by Enzo » Mon Jun 29, 2020 9:13 pm

First, it won't hurt the amp, so it is merely an annoyance.

Try this, leave the power switch on, but turn the amp off by pulling the plug from the wall. Does it still pop?

In my mind, most likely the contacts inside the power switch are sparking a little, and the amp amplifies that as it fades away.

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Re: DeltaBlues 210 loud pop when turned off

Post by rdoty » Wed Jul 01, 2020 11:42 pm

Thanks for the reply.
When I unplug from wall it still has the loud pop.
You wouldn't happen to know where I could get a copy of the schematic. I'm a retired electronic engineer and I'm sure there is a faulty component.

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Re: DeltaBlues 210 loud pop when turned off

Post by rdoty » Thu Jul 02, 2020 12:03 am

I've tried turning both Pre and Normal switches to zero which makes no difference. I did notice that the control panel layout that I have shows a Standby switch but my amp doesn't have one. My experience with audio amplifiers is that there is usually a discharge resistor circuit off the power supply capacitor which is there to prevent this kind of loud pop.

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Enzo
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Re: DeltaBlues 210 loud pop when turned off

Post by Enzo » Thu Jul 02, 2020 12:16 pm

These amps don't need a standby switch, but so many consumers think all amps should have one, so later versions of this amp had a standby switch added.

I don't think your pop is big caps discharging. in fact the slower they discharge, the less likely a surge will happen.

Other than the tiny little trem circuit they stuck in it, the Delta Blues is identical to the CLassic 30.

You can get any Peavey schematic from customer service at the factory. But I stuck it on the bottom here for you, they are dealing with the virus stuff like everyone else.
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PV Delta Blues.pdf
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rdoty
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Re: DeltaBlues 210 loud pop when turned off

Post by rdoty » Thu Jul 02, 2020 2:07 pm

Thank you for the schematic.

This is not the subtle pop that we all experience when an amplifier is turned off. Those sometimes get loud enough to be annoying. This is an unnervingly loud pop – take a two-liter plastic jug and hit it as hard as you can with a bat. It draws attention. Which is why I believe there’s a component failure. A current surge like that can’t be good for my speakers.

The fact that my amplifier doesn’t have a standby switch suggests that Peavey made changes as a response to complaints, probably of the same issue I’m experiencing. Or it could just be that they wanted to have a competitive feature. Peavey is a large enough company to employ electronic engineers whose responsibility would be to address circuit design deficiencies. (They’re called Quality Engineers – I was one!) Companies don’t make changes to a good product unless it’s to correct a problem and maintain customer loyalty. I’m wondering if there is someone in the engineering I could communicate with that might help.

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Enzo
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Re: DeltaBlues 210 loud pop when turned off

Post by Enzo » Thu Jul 02, 2020 9:09 pm

Companies don’t make changes to a good product unless it’s to correct a problem and maintain customer loyalty. I’m wondering if there is someone in the engineering I could communicate with that might help.
Or for marketing. The Classic 30 and Delta Blues amps models came out around 1994-95. They have been extremely successful for the last 25 years. No particular circuit changes in that time. And as I was an authorized warranty station for the Peavey line - and many others - I am not aware of any change orders, service bulletins, and so forth involving this. If the model had any systematic design issues, I don't think it would have taken 20 years of problems before it was corrected.

Whatever is wrong with yours, they ALL don't do it. So I would resist altering the circuit instead of repairing it.

Isolate the problem. Plug a shorting plug into the FX return. Does it still pop? By doing that, we have disconnected any signal/noise from the preamp. And you can do it the other way too, run a cord from the FX send to the input of some other amp to see if the noise comes out of the preamp.

A common repair technique is to pull tubes individually to isolate noise. Unfortunately, the tube heaters on this amp are series wired, so pull one tube, the rest go dark as well.

You can scope the B+ nodes and see if there are glitches appearing there.

Just a thought, turn the reverb control to zero, any change? SOmething tickles in my brain that A DC offset in the IC driving the reverb could result in a pop. The reverb uses one 4558 IC that runs between -30v and ground, so the output sits at about -15v. ANy chance the wrong reverb pan connection could be grounding that drive? yes, I am grasping at straws.

You report that Pre and Normal controls to zero don't affect it. Does it matter which channel is selected? Probably not. The tone stack is a bit later in the signal path, does turning those controls all the way one side or the other change the tone of th pop?


Actually, the tube heaters are series wired, but in two groups. One is the four power tubes, and the other is the three small tubes. If we remove one of the small tubes, they all three will go off, but the four power tubes would continue to run. That might be a worthwhile test. To see if the power tubes alone can generate your noise.

You need to narrow the source down to a point, these are some techniques that come to my mind.

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Re: DeltaBlues 210 loud pop when turned off

Post by Pappy B » Fri Jul 03, 2020 10:03 am

For what it's worth, I have 7 Peavey amps. The noise generated when turning them on ranges from none to one that is quite loud. It has had all the electrolytic caps replaced. If I turn the Pre and Posts and the Reverb down it still pops but isn't near as loud.
The more I learn the more I realize how much I don't know.

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Re: DeltaBlues 210 loud pop when turned off

Post by rdoty » Fri Jul 03, 2020 12:25 pm

Thanks for the replies and info. I'll dig into it this weekend. Just remembered that I happen to have a scope in the closet (no skeletons!) so I'll drag that out and see if I can isolate the problem. Thanks again. Good forum!

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