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Post subject: Vibrato Pop Pop Pop sound?
Posted: Sun Jul 28, 2013 11:08 am
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My 1965 Band Master makes a pop pop pop pop sound when the instrument is plugged into the Vibrato jack. Same on either Vibrato jack 1 or 2. the Amp is original, but new to me...photos in the other thread. I have never had a similar amp...but I have to assume this is neither to be expected or good.

Thanks in advance for any direction or advice.

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Post subject: Re: Vibrato Pop Pop Pop sound?
Posted: Sun Jul 28, 2013 11:31 am
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There could be any number of reasons for the audible popping and not all of them are directly related to the tremolo circuit. It sounds like the amp is ready for some professional-grade servicing -- find a competent tech and let him run a full set of diagnostics to isolate the problem(s).

Arjay

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Post subject: Re: Vibrato Pop Pop Pop sound?
Posted: Sun Jul 28, 2013 12:50 pm
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All these amp make some little pop pop, but too much is too much. Often it is the plate resistors

I fix mine with new plate resistor on V3 , 12AX7 pin 1, 220K resistor and pin 6 ,10M resistor.

By the way replace all plate resistor on your 12XX7 tubes. This will be done and silent the amp .

Those plate resistors come noisy when old.


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Post subject: Re: Vibrato Pop Pop Pop sound?
Posted: Mon Jul 29, 2013 4:35 am
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Thanks StratTele52. The popping is definitely too much. It's like a built-in metronome. I'll have it gone over more thoroughly as per Arjay, and ask the Technician to look specifically at those resistors.

The Normal channel is pretty quiet, but it also has a bit of snap crackle pop...so hopefully a little more bench time helps that as well. This is all part of the fun right? :wink:


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Post subject: Re: Vibrato Pop Pop Pop sound?
Posted: Mon Jul 29, 2013 5:00 am
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rflindall wrote:
Thanks StratTele52. The popping is definitely too much. It's like a built-in metronome. I'll have it gone over more thoroughly as per Arjay, and ask the Technician to look specifically at those resistors.

The Normal channel is pretty quiet, but it also has a bit of snap crackle pop...so hopefully a little more bench time helps that as well. This is all part of the fun right? :wink:



+1

Replace ALL filter caps too if you want to gig with , for home use you can wait

$150 job ?


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Post subject: Re: Vibrato Pop Pop Pop sound?
Posted: Mon Jul 29, 2013 10:58 am
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stratele52 wrote:
Replace ALL filter caps too if you want to gig with , for home use you can wait


Sacré bleu, mon amí!

An amp with bad filter caps can incinerate itself just as easily at home as it can onstage during a performance.

They should be inspected immediately and replaced at once if they look marginal. Fresh electrolytics are like life insurance.

Arjay

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Post subject: Re: Vibrato Pop Pop Pop sound?
Posted: Mon Jul 29, 2013 12:11 pm
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Retroverbial wrote:
stratele52 wrote:
Replace ALL filter caps too if you want to gig with , for home use you can wait


Sacré bleu, mon amí!

An amp with bad filter caps can incinerate itself just as easily at home as it can onstage during a performance.

They should be inspected immediately and replaced at once if they look marginal. Fresh electrolytics are like life insurance.

Arjay


Sure but at home , the show can stop any time ......
I have some Vintage amps with original filters caps , always play good. I use them at home only.


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Post subject: Re: Vibrato Pop Pop Pop sound?
Posted: Mon Jul 29, 2013 5:55 pm
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We each have our own servicing and maintenance protocols that we hope will keep these amps healthy for subsequent generations of owners to enjoy.

Arjay

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Post subject: Re: Vibrato Pop Pop Pop sound?
Posted: Tue Jul 30, 2013 1:42 am
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Retroverbial wrote:
We each have our own servicing and maintenance protocols that we hope will keep these amps healthy for subsequent generations of owners to enjoy.

Arjay


+1


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Post subject: Re: Vibrato Pop Pop Pop sound?
Posted: Wed Jul 31, 2013 12:33 am
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rflindall, the "pop-pop-pop" or maybe closer to "putt-putting" sounds like a classic motorboating issue. Nine times out of ten, replacing the main filter caps solves the problem. I'd replace ALL of them, including the bias filter cap. Then, you know the age of these caps.


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Post subject: Re: Vibrato Pop Pop Pop sound?
Posted: Wed Jul 31, 2013 5:56 am
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Thanks for the input BMW2002Ti. If the issue is the main filter caps or the bias cap...why is the putt-putt only noticable when I use the Vibrato inputs? Would it not be noticable on the Normal input as well? There is some hash on the Normal, but no pop...pop...pop

I did have the capacitors checked when I first bought the amp. The Technician (experienced....) suggested to leave them in place because they were in good shape and have "Aged" together with all of the other components. Replacing them would alter the tone and sag characteristics. I'll have the discussion again with him soon, pend the current round of investigation.


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Post subject: Re: Vibrato Pop Pop Pop sound?
Posted: Wed Jul 31, 2013 7:12 am
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It could be coupling between the vibrato and other stages. Due to a dried out cap that feeds the vibrato stage. When you disable the vibrato (via foot pedal), you ground out this stage. Thus, minimizing the coupling of this stage to others. For your Bandmaster, it would be cap B, of the power rail.

The vibrato output stage feeds into the bias supply. That is how the phase shift is controlled. So, it is also possible that the bias supply cap maybe dried out, too.

Electrolytic caps do not shape the tone of the amp, like coupling caps. The only time you "hear" an issue with them, is when they are old and dried out. Leading to inadequate filtering, de-coupling, and reserve power.

http://www.webphix.com/schematic%20heav ... _schem.pdf


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Post subject: Re: Vibrato Pop Pop Pop sound?
Posted: Wed Jul 31, 2013 7:07 pm
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BMW2002Ti wrote:
Leading to inadequate filtering, de-coupling, and reserve power.


......And quite possibly, catastrophic failure.

:shock:

Arjay

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Post subject: Re: Vibrato Pop Pop Pop sound?
Posted: Thu Aug 08, 2013 3:57 pm
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The fix is complete, and the pop pop pop is gone, and the amp is considerably quieter.

Replaced the 12AX7 in V3 with a Sovtek 12AX7-WA
Replaced the 25 microfarad, 25 Volt axial capacitor in the oscillator circuit (Sprague)
Replaced one of the 0.01 microfarad, 440v capacitors (went up to 630v, mylar)

Resoldered the sockets and the pots.

Seems good to my tone deaf ears.

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Post subject: Re: Vibrato Pop Pop Pop sound?
Posted: Thu Aug 08, 2013 4:18 pm
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Good news! Thanks, for the update.

:mrgreen:


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