Marshall Haze 40 frying bacon sound

[g1]

Just to be sure about those preamp tube voltages, can you measure and post DC voltages for pins 3 & 8 of V1,2,&3.

[hatecheapstuff]

Just to be sure about those preamp tube voltages, can you measure and post DC voltages for pins 3 & 8 of V1,2,&3.

Thanks for your input!

Here are some readings with power tubes installed, amp turned on and standby set in "playing" position:

V1:
pin 3: -2,06 mV
pin 8: -2,05 mV

V2:
pin 3: -2,08 mV
pin 8: -2,08 mV

V3:
pin 3: -2,08 mV
pin 8: -2,09 mV


I have noticed, that:
1) Without V1 it crackles
2) Without V2 it doesn't crackle
3) Without V3 it doesn't crackle

That's on turned on amp and standby set in "playing" position.

[g1]

It seems there is no current through any of those tubes (they are not turning on).
Are all their heaters lit?
If so, there may be a common grounding connection in the cathode circuits of those tubes that is not getting its connection.
You can do resistance checks from those socket pins to a main ground and see what you get for resistance readings.

[hatecheapstuff]

It seems there is no current through any of those tubes (they are not turning on).
Are all their heaters lit?
If so, there may be a common grounding connection in the cathode circuits of those tubes that is not getting its connection.
You can do resistance checks from those socket pins to a main ground and see what you get for resistance readings.

Yes, they are lit. I can take a picture of them too.

So you would like me to measure resistance to ground (chassis) from pin 3 and pin 8 on each preamp tube?

[R.G.]

Hi guys,
When I took it off standby it makes a frying bacon/crackling sound and I can't hear guitar at all. When I turn the volume/gain knobs all the way up I'm able to hear the guitar just a little bit.
First, I thought this must be worn tubes so I replaced both preamp and power amp tubes. Sadly, it didn't help.

Good choice for a first step. The first thing to suspect in a tube amp is that it's a problem with tubes. There is a reason that they are in sockets. But sometimes it's not the tubes - or not **just** the tube(s).

My next step was to replace most of the electrolytic caps, because I thought that filtering caps could be old. This also didn't help.

Not as good a guess. Electro caps do get old and sometimes will cause crackling and so on. But this is a rare thing.

I'm sure there are no broken/cold solder joints in this amp.

How did you determine this as a certainty?

I even tried removing the effects PCB but no luck with that.

That was actually a reasonable guess. Sometimes digital noise can be heard as hissing, crackling, or frying, but again, it's not that common.

I plugged the emulated line out with my other amp and I could hear the same stuff (crackling) on the other amp as same as form the speaker of the Haze.

And this is the second really good guess - split up where the noise is coming from so you focus on finding what is making the noise. Unfortunately, the amplifier only emulates a line out, it doesn't really produce one.

If it were my amp and I didn't have an oscilloscope, I would temporarily solder a 1K resistor across R101 and see if the noise quits.

R101 is a ground reference resistor at the input to the power amp. There is a muting relay that "shorts" a 1K across it when it's trying to mute the amp. Temporarily soldering in a resistor amounts to permanently muting the output of the preamp.

When you have done this, listen for whether the noise is gone. If it is, then the preamp circuit before the power amp is making the noise. If it is not gone, then either the power amp is making the noise, or it is being radiated into the power amp from some other source.

As a side note, I notice that Marshall has taken my advice that MOSFETs can be used in tube amps seriously and has sprinkled them everywhere. I hope they were careful. MOSFETs can self-oscillate at frequencies that can't even be seen on lower-end 10MHz and 20MHz scopes. When that happens, the RF jitter noise can sometimes be heard as an "angrier" type of hiss than thermal noise.

But hissing, crackling noises can also be created by bad solder joints and connectors.

[hatecheapstuff]

Here are the tubes lit:
https://www.dropbox.com/s/nv7mip61ei...13.52.jpg?dl=0

Notice how V1 glows poorly.

Here are the power tubes:
https://www.dropbox.com/s/jy37trcalv...14.50.jpg?dl=0
Notice blueish glow.

Here are resistance readings with power tubes installed and amp turned off
Resistance measured between each pin and ground (chassis).

V1:
pin 3 to GND: 0,8205 kOhms
pin 8 to GND: 0,8273 kOhms

V2:
pin 3 to GND: 0,8201 kOhms
pin 8 to GND: 6,768 kOhms

V3:
pin 3 to GND: 14,574 kOhms
pin 8 to GND: 14,574 kOhms


Now, I really hate Marshall for making such a junk...

[hatecheapstuff]

Good choice for a first step. The first thing to suspect in a tube amp is that it's a problem with tubes. There is a reason that they are in sockets. But sometimes it's not the tubes - or not **just** the tube(s).


Not as good a guess. Electro caps do get old and sometimes will cause crackling and so on. But this is a rare thing.


How did you determine this as a certainty?

That was actually a reasonable guess. Sometimes digital noise can be heard as hissing, crackling, or frying, but again, it's not that common.


And this is the second really good guess - split up where the noise is coming from so you focus on finding what is making the noise. Unfortunately, the amplifier only emulates a line out, it doesn't really produce one.

If it were my amp and I didn't have an oscilloscope, I would temporarily solder a 1K resistor across R101 and see if the noise quits.

R101 is a ground reference resistor at the input to the power amp. There is a muting relay that "shorts" a 1K across it when it's trying to mute the amp. Temporarily soldering in a resistor amounts to permanently muting the output of the preamp.

When you have done this, listen for whether the noise is gone. If it is, then the preamp circuit before the power amp is making the noise. If it is not gone, then either the power amp is making the noise, or it is being radiated into the power amp from some other source.

As a side note, I notice that Marshall has taken my advice that MOSFETs can be used in tube amps seriously and has sprinkled them everywhere. I hope they were careful. MOSFETs can self-oscillate at frequencies that can't even be seen on lower-end 10MHz and 20MHz scopes. When that happens, the RF jitter noise can sometimes be heard as an "angrier" type of hiss than thermal noise.

But hissing, crackling noises can also be created by bad solder joints and connectors.

Thanks for your input.

I have 3 complet tube sets. One is old, and the other two are brand new. I have exactly same results on each set.

I check solder joints with a magnyfing lenses - Optivisor and I do some checking with a continuity test on my DMM. It's hard to see a cracked joint with this Lead free solder crap but I add some flux and reflow the joint. I have checked the whole board couple of times, trust me - I could smell the PCB when doing that!
I cleaned all the connectors with IPA and I made myself sure they are all snug fit.

I may try your trick with adding 1K resistor. What wattage should it be?

[g1]

Your resistance readings from the cathode pins all seem good (I think V2 pin 8 is typo and should read 67,68Kohms).
You should be measuring DC voltages at pins 3 & 8 of V1,2,3 but you show only millivolts.
Can you double check plates and cathodes for the 3 preamp tubes? (pins 1,3,6,8)

[hatecheapstuff]

Your resistance readings from the cathode pins all seem good (I think V2 pin 8 is typo and should read 67.68Kohms).
You should be measuring DC voltages at pins 3 & 8 of V1,2,3 but you show only millivolts.
Can you double check plates and cathodes for the 3 preamp tubes? (pins 1,3,6,8)

I took resistance readings with the amp turned off and preamp tubes removed. There is NO typo. They are exactly rewritten as on my DMM.


I redid the measurements:

1) Amp powered on. standby in "playing" position. both preamp and power tubes installed.

V1:
Pin1: 90.1 VDC
Pin3: 0.4 VDC
Pin6: 127.4 VDC
Pin8: 1.25 VDC

V2
Pin1: 20.3 VDV
Pin3: 0.09 VDC
Pin6: 150 VDC
Pin8: 18.3 VDC

V3:
Pin1: 153.6 VDC
Pin3: 27.3 VDC
Pin6: 150 VDC
Pin8: 26.6 VDC

2) Amp powered on. standby in "playing" position. preamp tubes removed. poweramp tubes installed.

V1:
Pin1: 351.3 VDC
Pin3: -2.04 mVDC
Pin6: 353.16 VDC
Pin8: -2.07 mVDC

V2
Pin1: 353.8 VDV
Pin3: -2.1 mVDC
Pin6: 356.6 VDC
Pin8: -2.07 mVDC

V3:
Pin1: 354.2 VDC
Pin3: -2.1 mVDC
Pin6: 354.7 VDC
Pin8: -2.1 mVDC

3) Resistance. Amp powered off. all tubes installed.

V1:
pin 3 to GND: 0.82 kOhms
pin 8 to GND: 0.82 kOhms

V2:
pin 3 to GND: 0.82 kOhms
pin 8 to GND: 23.9 kOhms

V3:
pin 3 to GND: 14.57 kOhms
pin 8 to GND: 14.57 kOhms

3) Resistance. Amp powered off. preamp tubes removed. poweramp tubes installed.
DIFFERENT READING FROM BEFORE JUST FOR THE V2 Pin8

V1:
pin 3 to GND: 0.82 kOhms
pin 8 to GND: 0.82 kOhms

V2:
pin 3 to GND: 0.82 kOhms
pin 8 to GND: 6.1 kOhms

V3:
pin 3 to GND: 14.57 kOhms
pin 8 to GND: 14.57 kOhms



I'm happy to do more readings, but please specify exact conditions like amp turned on or off, which tubes installed etc.


Thanks!

[g1]

The voltages I'm concerned with are with the tubes installed, V1 and V2. V3 voltages look good.
For the V1 and V2, some of the readings I don't think you are getting good contact. You will need to really dig in with the probes.
V1 pins 6&8 look good.
Please redo V1 pins 1&3, V2 pins 1,3,6,8. (DC voltages with all tubes installed, standby in "play" mode.)

As far as R.G.'s suggestion about adding a 1K across R101 (post #20), any wattage will work, 1/2W or whatever you have. See if the noise stays or goes.

[hatecheapstuff]

The voltages I'm concerned with are with the tubes installed, V1 and V2. V3 voltages look good.
For the V1 and V2, some of the readings I don't think you are getting good contact. You will need to really dig in with the probes.
V1 pins 6&8 look good.
Please redo V1 pins 1&3, V2 pins 1,3,6,8. (DC voltages with all tubes installed, standby in "play" mode.)

As far as R.G.'s suggestion about adding a 1K across R101 (post #20), any wattage will work, 1/2W or whatever you have. See if the noise stays or goes.

I will redo the readings tomorrow.

I didn't have any 1K resistor, but I had 1.8K and I installed two in parallel so they made 0.9K so they make together 1K almost. I added them across R101 and the noise went away!
But I couldn't hear the guitar though... as I remember, the Presence pot was a bit scratchy and I still could hear it after I added those two resistors.

I guess my trouble is somewhere in preamp section then?


Thanks guys for your support.