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Post subject: Popping/Crackling Hot Rod DeVille, worse from tone knobs
Posted: Tue Jun 16, 2015 5:19 pm
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I stopped using my DeVille years ago because of this problem, but figured I'd try to get it working and swap it for something smaller. I get the dreaded fizz, crackle, pop even with nothing plugged in, and it's worse when I twist any of the knobs between (and including) Master and Drive. Treble makes it completely crap out for a few seconds. The drive channel is basically unusable (very low volume, constant fizz). The clean channel is also affected but not as drastically (occasional volume boost/drop). I've read the fix if it's the common phase inverter problem in V3, would this be what's causing the issues?
I've tried six different preamp tubes, and four different power tubes in various configs, and the problem is consistent, so it's not the tubes themselves. Any ideas what might specifically affect the tone/master/and drive controls this way? If I can fix what drives the tone (phase inverter?), it might fix the other issues.

Thanks.


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Post subject: Re: Popping/Crackling Hot Rod DeVille, worse from tone knobs
Posted: Tue Jun 16, 2015 5:26 pm
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Hi MoShaw,

It might be the Plate resistors, specifically those on the PI tube. :idea:

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Post subject: Re: Popping/Crackling Hot Rod DeVille, worse from tone knobs
Posted: Tue Jun 16, 2015 8:03 pm
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You can check the phase inverter circuit by plugging a guitar and boost pedal into the Power Amp In jack. It will be low, but if it is clean, it is upstream of the phase inverter, back towards the preamp.

It would be unusual for this problem to have a common cause except from the power supply. After discharging, try pulling gently on the positive lead of the filter caps to see if the lead is broken internally.

The Drive, tone and Master circuits are separate and one bad component wouldn't affect them all when they are turned
The amp should be resoldered completely if it hasn't been done already. This will eliminate the possibility of bad connections.

The controls should be cleaned to see if that has an effect on the symptom. If it does, you might consider replacing the noisy ones.


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Post subject: Re: Popping/Crackling Hot Rod DeVille, worse from tone knobs
Posted: Tue Jun 16, 2015 8:26 pm
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TimsAudio wrote:
You can check the phase inverter circuit by plugging a guitar and boost pedal into the Power Amp In jack. It will be low, but if it is clean, it is upstream of the phase inverter, back towards the preamp.


I actually played this way for a few years after the problem started, and until I got better amps. I just plugged a GNX4 into the Power Amp In, and avoided the crackle completely. I know it's a dumb question, but just to clarify, does "it is upstream of the phase inverter" mean that this is evidence of a phase inverter problem or evidence against it?

It's looking like a total re-solder is inevitable. If I tap on certain solder points with a chopstick, I hear similar crackles and pops. Especially on a couple of the V2 connections and on some resistors on the main PCB.

Thanks


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Post subject: Re: Popping/Crackling Hot Rod DeVille, worse from tone knobs
Posted: Wed Jun 17, 2015 12:34 am
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The best thing you could do for yourself is to leave that amp in an unlocked car and pray that somebody steals it.

:lol: :lol: :lol:

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Post subject: Re: Popping/Crackling Hot Rod DeVille, worse from tone knobs
Posted: Wed Jun 17, 2015 1:41 am
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Your amp just need a qualified tech .


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Post subject: Re: Popping/Crackling Hot Rod DeVille, worse from tone knobs
Posted: Wed Jun 17, 2015 2:54 pm
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And make sure you have ,"Contents" covered on your insurance policy.....

Until then, you have found your phase inverter to be innocent.
The power amp input jack puts signal through the phase inverter, so if it sounds OK, then it's not the phase inverter.
When we talk about upstream, we are referring to the signal flow through the amp. It's a daisy chain of circuits from the input jack to the speaker.
The HRDX is actually a single channel amp with extra volume controls and a gain stage switched in for the Drive channel, so most symptoms will occur on both channels.
The signal path goes from the input jack to a V1a gain stage, then to the volume controls, then to another V1b gain stage, then to the Tone controls, then to the V2a gain stage. In the normal channel, this signal is fed to the phase inverter, then the main power stage, then to the OT then the speaker.
The drive channel switches in the V2b gain stage and the Master volume between V2a and the PI. It also switches in the Drive control.

You can use this daisy chain to help troubleshoot the problems by pulling tubes and changing volumes one stage at a time. You can do this without removing the covers.
First step is to turn the volume all the way down. If the crackling goes away, then the problem is upstream, towards the first gain stage V1a or the input jack.
Next, pull the v1 tube. If the problem goes away, then it could be in the K1a relay or V1b plate resistor.
Next, turn down all the tone controls. If this makes much of a change, then there could be a bad cap in the tone stack.

Switch to the drive channel. If the problem is present in drive, but not in Normal, then look at V2b.
Then pull V2. In the normal channel, if the problem is gone then its in the V2a circuit.

I hope this helps you localize the problem. Still, a general resolder is the best approach, before trying to find a bad component. These amps all need a resolder if they are more than five years old


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Post subject: Re: Popping/Crackling Hot Rod DeVille, worse from tone knobs
Posted: Thu Jun 18, 2015 12:40 pm
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Well... this is embarrassing. After years of letting the amp collect dust, because I assumed it needed major repairs, I sprayed some contact cleaner in the pots and.... problem solved! Just seemed weird that the tone knobs would make it completely short out like that, even if they were dirty. Fizz, and crackle, yes, but complete temporary sound loss? Weird. I also sprayed the tube sockets, which could have also been the problem, or at least part of it.

Thanks for your help, TimsAudio! Ruling out the phase inverter saved me a lot of unnecessary work!


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