Hi
I am currently working on this amp which had a bad bias drift problem. After inserting the Dr Tube bias mod, the bias is now stable, but the amp is buzzing (not hum).
I have confirmed that all the caps, resistors and diodes are OK. When powered on, at the beginning the amp is quite, but approx 15mins later, the buzz comes in and it gets louder and louder with time. I measured the voltage across the speaker terminals, there is 0V DC, but aprox 50mV AC and this voltage keeps increasing as the buzz increases. I have tried replacing the preamp tubes as well as the power tubes, but no change. Can it be that the leaking voltage on the main board is entering the preamp circuit. Please assist.
Thanks
I am currently working on this amp which had a bad bias drift problem. After inserting the Dr Tube bias mod, the bias is now stable, but the amp is buzzing (not hum).
I have confirmed that all the caps, resistors and diodes are OK. When powered on, at the beginning the amp is quite, but approx 15mins later, the buzz comes in and it gets louder and louder with time. I measured the voltage across the speaker terminals, there is 0V DC, but aprox 50mV AC and this voltage keeps increasing as the buzz increases. I have tried replacing the preamp tubes as well as the power tubes, but no change. Can it be that the leaking voltage on the main board is entering the preamp circuit. Please assist.
Thanks
It doesn't sound like a 50hz or 100hz hum, it is more of a constant mid frequency buzz, Sound like berrrrr, like if the grounding is removed.
Thanks
Thanks
I am plugging in a guitar with the guitar volume totally off, only the amp volume is on. If I unplug the jack then it is totally quite. It is not anything to do with the guitar, because it is OK if I plug the guitar into another TSL100.
Isn't it just wonderful those red pieces of junk Wima caps. Just as bad as the resistors used in the amp that are causing the drift.
Change out the Wima caps to Solen or just remove them.
If quiet with unplugged jack.
Maybe jack issue or if it has a switching jack
be the switch or circuit related to switch.
Maybe jack issue or if it has a switching jack
be the switch or circuit related to switch.
That is usually true but here Marshall adds a little trick: they use one of the extra Cliff jack switches to ground preamp output, so by unplugging the guitar it becomes magically silent.
So real noise test needs a shorted plug or a guitar with all pots set to 0
@Carlosraj : you need to scope speaker out and work backwards until you find where buzz starts.
Or start grounding different points along the path to find the offending stage.
As a side note, removing coupling caps will definitely remove buzz.
Wonder why nobody does that 🤔🤔🤔
So real noise test needs a shorted plug or a guitar with all pots set to 0
@Carlosraj : you need to scope speaker out and work backwards until you find where buzz starts.
Or start grounding different points along the path to find the offending stage.
Nice personal preference but is it related in any way to the OP's problem?
As a side note, removing coupling caps will definitely remove buzz.
Wonder why nobody does that 🤔🤔🤔
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I don't think they are coupling caps, The connector for the bias pot board (that gets 'upgraded" to fixed resistors) is after the coupling capacitors.
Besides all of this, the OP has a buzz. Which could be a transformer. I just haven't told him to tap the transformers yet with the handle of a screw driver when it starts buzzing after warming up.
It can be because I ban those caps in tube gear building long ago when I got my engineering samples of them when they were a new product and noticed most caused buzzing issues in tube circuits. Its definitely not a substitute for orange drops.
@Carlosraj and thisusername:
listen to the man who knows (JMFahey)
"you need to scope speaker out and work backwards until you find where buzz starts."
and leave the original components in it until you find the source of the "hum, buzz, noise, berrrrr ?"
Do it and comment each step you make.
btw:
Do you have a schematic?
Are you experienced with repairs?
Do you have test equipment like signal source, signal follower, scope?
And do not listen to those smart guys who tell you to change components without even knowing if they are bad.
listen to the man who knows (JMFahey)
"you need to scope speaker out and work backwards until you find where buzz starts."
and leave the original components in it until you find the source of the "hum, buzz, noise, berrrrr ?"
Do it and comment each step you make.
btw:
Do you have a schematic?
Are you experienced with repairs?
Do you have test equipment like signal source, signal follower, scope?
And do not listen to those smart guys who tell you to change components without even knowing if they are bad.
Not normally. Those do. But not a low frequency buzz. I would suspect a transformer first.
Junk Marshall amps, But a lot of Tube guitar amps are build terrible now these days. How long do you think those cheap amp/molex connectors are going to last in a piece of tube gear?
I'm assuming the OP is a technician who has sorted out the obvious.
I forget there is a 'mixed' audience and this is not a professional forum.
Of course I thought gearslutz, gearspace or whatever they want to call themselves this decade was a professional forum, until I noticed I was their answer guy surrounded by mostly other musicians that don't know how to connect gear, because they changed standards over time. Then of course there is the group of people I would call "gear pushers" that I assume is sponsored to advertise equipment in threads. It got really worse last 10 years with "sponsors" and musicians with bad attitudes.
Yes I do have a copy of all those Marshall schematics. Including the bias pot board that was replaced. f they used the correct bias pots this thread wouldn't exist.
Yes, I have a full electronics shop in one of my rooms and know how to use all of it.
"Caps do not cause buzzing."
post of thisusername and remarks:
Not normally.
When do they?
Those do.
How do you know?
But not a low frequency buzz.
What frequency?
I would suspect a transformer first.
Is it a cap or a transformer? Make up your mind without evidence.
Isn't it just wonderful those red pieces of junk Wima caps.
Have been in use since even before I got in touch with electronics more then 50 years ago and still used today. If they were bad, they have been removed from production a long time ago.
Just as bad as the resistors used in the amp that are causing the drift.
Wich brand of resistors and what drift are they causing?
Change out the Wima caps to Solen or just remove them.
Why change a non defective component with another one?
I'm assuming the OP is a technician who has sorted out the obvious.
Can be but a technician would isolate the preamp stage from the poweramp stage to find out where the "buzz" is coming from.
I forget there is a 'mixed' audience and this is not a professional forum.
So?
Of course I thought gearslutz, gearspace or whatever they want to call themselves this decade was a professional forum,
?
until I noticed I was their answer guy
Really?
surrounded by mostly other musicians that don't know how to connect gear,
There you have a point.
because they changed standards over time.
Explain
Then of course there is the group of people I would call "gear pushers" that I assume is sponsored to advertise equipment in threads.
Hm, like you do with replacing Wimas with Solen?
It got really worse last 10 years with "sponsors" and musicians with bad attitudes.
Oh, yes...
Yes I do have a copy of all those Marshall schematics. Including the bias pot board that was replaced.
There are thousands of TSL100 on the road and I never ever had to replace a bias pot board. Question is: Why the change is made in the first place.
If they used the correct bias pots this thread wouldn't exist.
Same remarks as the previous one. What is in your opinion a correct bias pot?
Yes, I have a full electronics shop in one of my rooms and know how to use all of it.
I do not mentioned you when I asked for experiance and test gear etc. But the OP.
My mistake.
Now, lets have the OP back in the discussion.
What is the situation of the "buzzing" amp?
post of thisusername and remarks:
Not normally.
When do they?
Those do.
How do you know?
But not a low frequency buzz.
What frequency?
I would suspect a transformer first.
Is it a cap or a transformer? Make up your mind without evidence.
Isn't it just wonderful those red pieces of junk Wima caps.
Have been in use since even before I got in touch with electronics more then 50 years ago and still used today. If they were bad, they have been removed from production a long time ago.
Just as bad as the resistors used in the amp that are causing the drift.
Wich brand of resistors and what drift are they causing?
Change out the Wima caps to Solen or just remove them.
Why change a non defective component with another one?
I'm assuming the OP is a technician who has sorted out the obvious.
Can be but a technician would isolate the preamp stage from the poweramp stage to find out where the "buzz" is coming from.
I forget there is a 'mixed' audience and this is not a professional forum.
So?
Of course I thought gearslutz, gearspace or whatever they want to call themselves this decade was a professional forum,
?
until I noticed I was their answer guy
Really?
surrounded by mostly other musicians that don't know how to connect gear,
There you have a point.
because they changed standards over time.
Explain
Then of course there is the group of people I would call "gear pushers" that I assume is sponsored to advertise equipment in threads.
Hm, like you do with replacing Wimas with Solen?
It got really worse last 10 years with "sponsors" and musicians with bad attitudes.
Oh, yes...
Yes I do have a copy of all those Marshall schematics. Including the bias pot board that was replaced.
There are thousands of TSL100 on the road and I never ever had to replace a bias pot board. Question is: Why the change is made in the first place.
If they used the correct bias pots this thread wouldn't exist.
Same remarks as the previous one. What is in your opinion a correct bias pot?
Yes, I have a full electronics shop in one of my rooms and know how to use all of it.
I do not mentioned you when I asked for experiance and test gear etc. But the OP.
My mistake.
Now, lets have the OP back in the discussion.
What is the situation of the "buzzing" amp?
Tarzan earns the ignore button.
Message to the OP:
Remove the caps, or put back in the original bias pot board and troubleshoot the amp. Because the caps in the "mod" are going to coverup and make it difficult to troubleshoot. Besides them being actually invalid in the circuit. But if the problem happen after plugging it in then I would suspect the caps. Because they don't belong in the circuit. Because you were not very clear if the buzzing was there before sticking in the fixed bias board.
Also, counterfeit Wima caps have infiltrated normal supply sources and they are terrible. So I avoid or replace them when ever I can. Because even the originals dulled the sound.
Message to the OP:
Remove the caps, or put back in the original bias pot board and troubleshoot the amp. Because the caps in the "mod" are going to coverup and make it difficult to troubleshoot. Besides them being actually invalid in the circuit. But if the problem happen after plugging it in then I would suspect the caps. Because they don't belong in the circuit. Because you were not very clear if the buzzing was there before sticking in the fixed bias board.
Also, counterfeit Wima caps have infiltrated normal supply sources and they are terrible. So I avoid or replace them when ever I can. Because even the originals dulled the sound.
How does a .022 Wima cap dull sound or cause buzz or give you bad breath or anything bad while an exact same value .022 made by Sola or any other MOJO brand does not?
Sounds like brand pushing or plain brand adoration to me.
Best case, naïve trust in what "boutique" sellers claim.
Unless backed by measurements, not accepted as Truth.
Sounds like brand pushing or plain brand adoration to me.
Best case, naïve trust in what "boutique" sellers claim.
Unless backed by measurements, not accepted as Truth.
I can't really explain it. I think its some sort of dielectric loss in those newer metallized polypropylene have and its quite noticeable going from the older style MKP series to these.
It can't really be a magnetic effect, but it could be loss in the way they join the plates, dielectric composition or even the metallurgy of the foil.
I can't really explain it.
Why trow it up then?
I think its some sort of dielectric loss in those newer metallized polypropylene have
No thinking without prove
and its quite noticeable going from the older style MKP series to these.
Give examples and measurements
It can't really be a magnetic effect, but it could be loss in the way they join the plates, dielectric composition or even the metallurgy of the foil.
Again, no prove.
The whole discussion about these caps looks more like snake oil to me... Unless there is physical prove.
In electronics, thinking is worthless. Measurements are the way to go.
Why trow it up then?
I think its some sort of dielectric loss in those newer metallized polypropylene have
No thinking without prove
and its quite noticeable going from the older style MKP series to these.
Give examples and measurements
It can't really be a magnetic effect, but it could be loss in the way they join the plates, dielectric composition or even the metallurgy of the foil.
Again, no prove.
The whole discussion about these caps looks more like snake oil to me... Unless there is physical prove.
In electronics, thinking is worthless. Measurements are the way to go.
Well you can definitely hear it.
Hear how cheap sounding the WIma cap sounds compared to others. Granted I this person in the video put it in a pedal, but this gets really worse in a tube circuit.
"Cheap" sound means nothing.
All 3 sound the same to me in that video clip and definitely can not be separated by ear in a blind test, even if there is a slight difference.
Attributable to value tolerance and not brand, construction, etc.
And that, because it is too small, on purpose, and is fed a variable duty cycle squarewave.
That is an extreme test ... and even so ....
Here in the HiFi domain, dealing with clean sound and with a crossover frequency chosen outside the Audio range (well below it, often a couple Hertz only) , nothing to hear.
All 3 sound the same to me in that video clip and definitely can not be separated by ear in a blind test, even if there is a slight difference.
Attributable to value tolerance and not brand, construction, etc.
And that, because it is too small, on purpose, and is fed a variable duty cycle squarewave.
That is an extreme test ... and even so ....
Here in the HiFi domain, dealing with clean sound and with a crossover frequency chosen outside the Audio range (well below it, often a couple Hertz only) , nothing to hear.