Page 1 of 3 123 LastLast
Results 1 to 35 of 74
Like Tree6Likes

Thread: Marshall VS100R hum problem

  1. #1
    Member
    Join Date
    Nov 2017
    Location
    Madrid, Spain
    Posts
    32

    Marshall VS100R hum problem

    Hello guys, Im new here in the forum. I bought a Marshall Valvastate VS100R with reverb for a few bucks that has a hum issue and I need some help/advise. EVERYTHING ON THE AMP WORKS PERFECTLY the only issue the hum. Here are the symptoms:

    1) When I turn it on there is a pop and hum noise follows right after. The hum is there with all the pots on zero and no guitar plugged in.
    2) The hum gets a little bit louder when I crank up the volume. This happens on any channel
    3) The amp was off since yesterday, when I turn it on today I noticed that at the hum volume increases a tiny bit in time.
    4) When Im on the overdrive channel I noticed the treble pot make noises (like the ones you get on a dirty pot) every time you turn it, specially when you turn it from zero to a quarter turn.
    5) The frequency of the hum is the same as the vibration of the transformer when current is flowing through it.


    These are the things I´ve done with no positive results:
    1) I tried 5 different tubes
    2) I checked all the joints and resoldered a bunch of them.
    3) I replaced the electrolytic filter caps on the preamp section and the ones on the power section as well.

    PLEASE HELP LOL!!!

    Thanks guys

  2. #2
    Supporting Member The Dude's Avatar
    Join Date
    May 2010
    Location
    Sioux Falls, SD
    Posts
    4,451
    The pot noise could be as simple as a dirty or bad pot. Or, there could be DC on the pot. Check with your meter to see if there is DC there.

    On the hum, since you've already changed electrolytics and tubes, start on one end or the other and remove tubes to see if you can isolate the hum to a particular stage. In other words, pull V1. Still have hum? Pull V2. Still have hum? Etc.
    “Yeah, well, you know, that’s just, like, your opinion, man.”

  3. #3
    Member
    Join Date
    Nov 2017
    Location
    Madrid, Spain
    Posts
    32
    I will check the DC on the pot. This amp has one tube in the preamp and transistors on the power section. This week I will isolate each section of the circuit in order to find which is the faulty one and check every component there.

    Thanks for the advise!!!



    Quote Originally Posted by The Dude View Post
    The pot noise could be as simple as a dirty or bad pot. Or, there could be DC on the pot. Check with your meter to see if there is DC there.

    On the hum, since you've already changed electrolytics and tubes, start on one end or the other and remove tubes to see if you can isolate the hum to a particular stage. In other words, pull V1. Still have hum? Pull V2. Still have hum? Etc.

  4. #4
    Member
    Join Date
    Nov 2017
    Location
    Madrid, Spain
    Posts
    32
    I found like 10 caps that were bad (22uF most of them) replaced them all and the hum continues. I removed the tube and the hum remains. The first triode of the tube is a normal gain stage and the second one is a cathode follower that drives the tone stack of the overdrive channel only. This way I'm sure the hum doesn't come from the tube. Everything looks that something is happening on the transistor power section.

    Where should I start looking?? Thank you very much

  5. #5
    "Thermionic Apocalypse" -JT nickb's Avatar
    Join Date
    Dec 2009
    Location
    Devon, UK
    Posts
    2,412
    Quote Originally Posted by avoverdu View Post
    I found like 10 caps that were bad (22uF most of them) replaced them all and the hum continues. I removed the tube and the hum remains. The first triode of the tube is a normal gain stage and the second one is a cathode follower that drives the tone stack of the overdrive channel only. This way I'm sure the hum doesn't come from the tube. Everything looks that something is happening on the transistor power section.

    Where should I start looking?? Thank you very much
    1) Unplug CON1 on the power amp PCB. What happens to the hum?
    2) With all the controls turned down so that you hear the hum only, measure the ACV across the speaker terminals.
    Experience is something you get, just after you really needed it.

  6. #6
    Supporting Member The Dude's Avatar
    Join Date
    May 2010
    Location
    Sioux Falls, SD
    Posts
    4,451
    Oh boy. I just realized this is a valvestate amp, so my post #2 makes little sense. (Insert dunce cap emoticon here)

    http://www.thetubestore.com/lib/thet...-Schematic.pdf

    Start by checking for ripple/AC content on your power supply lines. Look at +LT, -LT, +15V, -15V, etc. Also check that DC levels are what they should be.
    “Yeah, well, you know, that’s just, like, your opinion, man.”

  7. #7
    Old Timer J M Fahey's Avatar
    Join Date
    Oct 2007
    Location
    Buenos Aires, Argentina
    Posts
    9,324
    Just to check where hum gets in, please do these 3 simple tests:

    1) at the power amp board short the Net R1-C2-J111d to ground ... any change in hum?

    2) at the preamp board, short across R49 ... any change in hum?

    3) at the preamp board, short across R77 ... any change in hum?
    Juan Manuel Fahey

  8. #8
    Member
    Join Date
    Nov 2017
    Location
    Madrid, Spain
    Posts
    32
    Thanks Nickb. I have the amp ready, everything on zero, clean channel, no guitar plugged in:

    1) I removed CON1 on the power PCB: The hum is reduced a lot but it is still there.

    2) -AC voltage across the speaker (8ohm) with the CON1 connected= 0.2VAC
    - AC voltage across the speaker (8ohm) with the CON1 disconnected= 0.0003VAC

    If it works here are the VDC readings too: with the CON1 connected= -0.015VAC
    with the CON1 disconnected= -0.015VAC




    Quote Originally Posted by nickb View Post
    1) Unplug CON1 on the power amp PCB. What happens to the hum?
    2) With all the controls turned down so that you hear the hum only, measure the ACV across the speaker terminals.

  9. #9
    "Thermionic Apocalypse" -JT nickb's Avatar
    Join Date
    Dec 2009
    Location
    Devon, UK
    Posts
    2,412
    Quote Originally Posted by avoverdu View Post
    Thanks Nickb. I have the amp ready, everything on zero, clean channel, no guitar plugged in:

    1) I removed CON1 on the power PCB: The hum is reduced a lot but it is still there.

    2) -AC voltage across the speaker (8ohm) with the CON1 connected= 0.2VAC
    - AC voltage across the speaker (8ohm) with the CON1 disconnected= 0.0003VAC

    If it works here are the VDC readings too: with the CON1 connected= -0.015VAC
    with the CON1 disconnected= -0.015VAC
    Good job! So it's coming from the preamp. Now we do what Juan suggested and see which part of the the preamp it's coming from. This is what he said:

    2) at the preamp board, short across R49 ... any change in hum?

    3) at the preamp board, short across R77 ... any change in hum?
    Experience is something you get, just after you really needed it.

  10. #10
    Member
    Join Date
    Nov 2017
    Location
    Madrid, Spain
    Posts
    32
    OK, these are the results:

    1) at power amp, if short at the point that connects R1 with J111 (R16 in the schematic) at the pin d, which according to my tester is the center pin= the hum is reduced a lot but still there.

    2) at the preamp board if I short R49= hum is reduced but is still there

    3) at the preamp board, if I short R77 hum is reduced even more. I think the reduction on 1 and 2 are about the same but number 3 is almost dead quiet BUT THIS BEHAVIOR IS JUST FOR THE OVERDRIVE CHANNEL, ON THE CLEAN CHANNEL THIS DOESN'T DO ANYTHING TO THE HUM


    Thanks in advance



    Quote Originally Posted by J M Fahey View Post
    Just to check where hum gets in, please do these 3 simple tests:

    1) at the power amp board short the Net R1-C2-J111d to ground ... any change in hum?

    2) at the preamp board, short across R49 ... any change in hum?

    3) at the preamp board, short across R77 ... any change in hum?
    Last edited by avoverdu; 12-01-2017 at 08:14 PM.

  11. #11
    "Thermionic Apocalypse" -JT nickb's Avatar
    Join Date
    Dec 2009
    Location
    Devon, UK
    Posts
    2,412
    It seems like it coming in around the OD tone stack as when you pulled the tube earlier the hum was still there.

    Pull the tube and short out R23. What happens to the hum?

    Also check the ACV on pins 4 and 8 of IC3. Hint: you will, unless you have a really good meter, need to use a small capacitor 0.01uf to 0.1uF in series with one of the meter leads to do this.
    Experience is something you get, just after you really needed it.

  12. #12
    Member
    Join Date
    Nov 2017
    Location
    Madrid, Spain
    Posts
    32
    Here we go, I pulled the tube, clean channel, R23 shorted= it sounds like the low octave of the hum is filtered out.

    About the ACV I have a 0.1uF cap, do you want me to read between pin 4 and 8, or between 4 to ground and 8 to ground??? Let me know

    Quote Originally Posted by nickb View Post
    It seems like it coming in around the OD tone stack as when you pulled the tube earlier the hum was still there.

    Pull the tube and short out R23. What happens to the hum?

    Also check the ACV on pins 4 and 8 of IC3. Hint: you will, unless you have a really good meter, need to use a small capacitor 0.01uf to 0.1uF in series with one of the meter leads to do this.

  13. #13
    "Thermionic Apocalypse" -JT nickb's Avatar
    Join Date
    Dec 2009
    Location
    Devon, UK
    Posts
    2,412
    Always with respect to ground unless stated otherwise. There was actually a slight problem with the R49/R77 measurement in that only one was valid as it depends on the which channel is selected. Since R77 made the big difference ( i assume about the same as when we pulled CON1) I'm looking at that path and assuming that channel was selected.
    Experience is something you get, just after you really needed it.

  14. #14
    Member
    Join Date
    Nov 2017
    Location
    Madrid, Spain
    Posts
    32
    Ok in that case:

    R77 shorted on clean channel: it does nothing
    R77 shorted on overdrive channel: reduces the hum

    R49 shorted on clean channel: it does nothing
    R49 shorted on overdrive channel: reduces the hum

    let me know, as soon as I measure the voltages on IC3 ill let you know. Thanks man I appreciate it

    Quote Originally Posted by nickb View Post
    Always with respect to ground unless stated otherwise. There was actually a slight problem with the R49/R77 measurement in that only one was valid as it depends on the which channel is selected. Since R77 made the big difference ( i assume about the same as when we pulled CON1) I'm looking at that path and assuming that channel was selected.

  15. #15
    "Thermionic Apocalypse" -JT nickb's Avatar
    Join Date
    Dec 2009
    Location
    Devon, UK
    Posts
    2,412
    Please go ahead and measure the ACV on IC3 pins 4 & 8.

    PS: Measure the DCV at the same time ( don't use the series cap)
    Last edited by nickb; 12-02-2017 at 09:51 AM.
    Experience is something you get, just after you really needed it.

  16. #16
    Member
    Join Date
    Nov 2017
    Location
    Madrid, Spain
    Posts
    32
    Quote Originally Posted by nickb View Post
    Please go ahead and measure the ACV on IC3 pins 4 & 8.

    PS: Measure the DCV at the same time ( don't use the series cap)
    OK: pins of IC3 to ground NO 0.1uF cap

    Pin 4: ACV: jumps a little bit then 0.000 after a couple seconds of turning it up. DCV:-12.07

    Pin 8: ACV: 0.000 DCV: 12.05

    I did read those voltages with the cap in series but the values were the same

  17. #17
    "Thermionic Apocalypse" -JT nickb's Avatar
    Join Date
    Dec 2009
    Location
    Devon, UK
    Posts
    2,412
    Well, it's not coming on the power supply. We have reached an apparent dead end as the pulling CON1 says it's before power amp, the shorting R77/R49 test says it at or before IC3's power supply, the ACV test says it not the IC3 power supply yet earlier when the 12AX7 was pulled that didn't help either. The 12AX7 is right before IC3. I therefore wonder if the reduction of hum is less than when pulling CON1 so misleading us.

    Measure the ACV on the speaker with R77/R48 shorted and then again with the 12AX7 pulled. If the hum reduction is much less then the 0.2VAC we got when pulling CON1 then we need to start looking at the daughter PCB. Ir would not do any harm to apply some switch cleaner to all the multipin connectors and plug/unplug a few times. You might get lucky and save some time.
    Experience is something you get, just after you really needed it.

  18. #18
    Old Timer J M Fahey's Avatar
    Join Date
    Oct 2007
    Location
    Buenos Aires, Argentina
    Posts
    9,324
    Adding a suspect: it might be not some hummy stage (or it could be *one* part but not the full story) but a grounding problem.
    Pulling Con1 not only removes preamp signal but also disconnects power amp gtround from preamp one.

    So I would pull Con1 but solder a wire copying what Con 1 ground contact + wire do.
    Or IF you have the means (single wire + proper connectors + crimping tool or long nose pliers) build a new "Con 1 wire" which just connects grounds as it does.

    Important: join same pads at the connectors base as would be joined by Con 1 , we want to reproduce the exact same path, in grounding problems grounding " here" or "just 1 inch away" is NOT the same.
    Juan Manuel Fahey

  19. #19
    Member
    Join Date
    Nov 2017
    Location
    Madrid, Spain
    Posts
    32
    Quote Originally Posted by nickb View Post
    Well, it's not coming on the power supply. We have reached an apparent dead end as the pulling CON1 says it's before power amp, the shorting R77/R49 test says it at or before IC3's power supply, the ACV test says it not the IC3 power supply yet earlier when the 12AX7 was pulled that didn't help either. The 12AX7 is right before IC3. I therefore wonder if the reduction of hum is less than when pulling CON1 so misleading us.

    Measure the ACV on the speaker with R77/R48 shorted and then again with the 12AX7 pulled. If the hum reduction is much less then the 0.2VAC we got when pulling CON1 then we need to start looking at the daughter PCB. Ir would not do any harm to apply some switch cleaner to all the multipin connectors and plug/unplug a few times. You might get lucky and save some time.
    OK. I cleaned the switches with deox and ran the tests:

    - Overdrive channel:
    ACV across the speaker with R48 shorted, without the tube: 0.002
    ACV across the speaker with R48 shorted, with the tube: it starts on zero and increases slowly, after a couple minutes reaches up to 0.213 or so.
    Same test on the Clean Channel is 0.000 to 0.002v

    ACV across the speaker with R77 shorted, without the tube: 0.000
    ACV across the speaker with R77 shorted, with the tube: 0.000
    Same test on the clean channel i got without the tube: 0.001 and with the tube increases slowly up to 0.25-0.27

    Now that you mentioned the daughter pbc, I found the hum increases (like adding a higher octave) when I push the power dimension button.

    I did this test: Overdrive channel, with the tube, no shorts, power dimension button OFF, ac voltage across the speaker = increases slowly up to 0.2 or so
    Same test but with power dimension button ON: 0.106 or so but the hum increases like I said, louder with a higher octave

    I repeated it without the tube: Power dimension button OFF: 0.002
    Power dimension button ON: around 0.050 and the hum gets louder and the pitch slightly changes. Its more like two octaves sounding at the same time, the lower octave is always there and the higher octave sometimes cutts off.

    Let me know of this could help.

  20. #20
    Member
    Join Date
    Nov 2017
    Location
    Madrid, Spain
    Posts
    32
    Quote Originally Posted by J M Fahey View Post
    Adding a suspect: it might be not some hummy stage (or it could be *one* part but not the full story) but a grounding problem.
    Pulling Con1 not only removes preamp signal but also disconnects power amp gtround from preamp one.

    So I would pull Con1 but solder a wire copying what Con 1 ground contact + wire do.
    Or IF you have the means (single wire + proper connectors + crimping tool or long nose pliers) build a new "Con 1 wire" which just connects grounds as it does.

    Important: join same pads at the connectors base as would be joined by Con 1 , we want to reproduce the exact same path, in grounding problems grounding " here" or "just 1 inch away" is NOT the same.
    All right. I looked the schematics and I saw the ground cable between the two PCBs goes from pin 1 of the CON1 of the preamp PCB to the pin 1 of the CON1 the power PCB so I placed a cable with alligator clips between those pins, I covered the next pins with tape to avoid the alligator clip to touch the other pins just in case.

    With this done, I read the AC voltage across the speaker with the tube in place= 0.003 on the overdrive channel and reads the same on the clean channel. Also the hum remains the same either if is connected this cable or not.

    I left the ground cable connected between the PCBs and disconnect the main ground wire which is connected from power PCB to the chassis through a green wire. I turned the amp on and touched this cable end on different parts of the chassis. The hum doesn't change if I touch the chassis here or 1 inch away. Let me know if I did this right LOL

    Thanks
    J M Fahey likes this.

  21. #21
    "Thermionic Apocalypse" -JT nickb's Avatar
    Join Date
    Dec 2009
    Location
    Devon, UK
    Posts
    2,412
    Well that wasn't quite what I intended you to do but it's an interesting result nevertheless. It would seem that, since the signal path is shorted out, that some part of the current in the tube is apparently flowing along the ground which has resistance and leads to the hum. I assume that the hum is increasing as the tube heats up.

    The dimension control will increase the bass and therefore the hum. I'd consider than normal.

    Hmmm... how did 'clean the multipin connectors' get translated into 'clean the switches'? The reason for asking you so do that is because of the grounds in each connector. A bad contact means high resistance and that it turn means a bigger signal from and hum currents.

    There might be bad ground solder joint on the preamp board that is associated with tube currents.

    You should probably check the ACV on the supply to tube at the junction of R22 to R19 just to eliminate that although I don't really think it's the cause.

    I just read your result on power amp ground test. The eliminates that ground.
    Experience is something you get, just after you really needed it.

  22. #22
    Supporting Member Jazz P Bass's Avatar
    Join Date
    Dec 2008
    Location
    Wernersville, PA
    Posts
    11,860
    Quote:" With this done, I read the AC voltage across the speaker with the tube in place= 0.003"

    Just my 2 cents worth: 3 mv's ac on the speaker to me is outstanding!

    It's not hum, it's normal. It's a tube amp.

    I don't fret until I see 9 mv's or so.

  23. #23
    "Thermionic Apocalypse" -JT nickb's Avatar
    Join Date
    Dec 2009
    Location
    Devon, UK
    Posts
    2,412
    Quote Originally Posted by Jazz P Bass View Post
    Quote:" With this done, I read the AC voltage across the speaker with the tube in place= 0.003"

    Just my 2 cents worth: 3 mv's ac on the speaker to me is outstanding!

    It's not hum, it's normal. It's a tube amp.

    I don't fret until I see 9 mv's or so.
    Except he's got 250mV
    Experience is something you get, just after you really needed it.

  24. #24
    Supporting Member Jazz P Bass's Avatar
    Join Date
    Dec 2008
    Location
    Wernersville, PA
    Posts
    11,860
    OOPS.

    That is cause for concern.
    Yup.

  25. #25
    Member
    Join Date
    Nov 2017
    Location
    Madrid, Spain
    Posts
    32
    Quote Originally Posted by nickb View Post
    Well that wasn't quite what I intended you to do but it's an interesting result nevertheless. It would seem that, since the signal path is shorted out, that some part of the current in the tube is apparently flowing along the ground which has resistance and leads to the hum. I assume that the hum is increasing as the tube heats up.

    The dimension control will increase the bass and therefore the hum. I'd consider than normal.

    Hmmm... how did 'clean the multipin connectors' get translated into 'clean the switches'? The reason for asking you so do that is because of the grounds in each connector. A bad contact means high resistance and that it turn means a bigger signal from and hum currents.

    There might be bad ground solder joint on the preamp board that is associated with tube currents.

    You should probably check the ACV on the supply to tube at the junction of R22 to R19 just to eliminate that although I don't really think it's the cause.

    I just read your result on power amp ground test. The eliminates that ground.
    Sorry, you mean to clean the tube socket? I will do it when I get home and check all the ground connections around the tube

  26. #26
    "Thermionic Apocalypse" -JT nickb's Avatar
    Join Date
    Dec 2009
    Location
    Devon, UK
    Posts
    2,412
    Quote Originally Posted by avoverdu View Post
    Sorry, you mean to clean the tube socket? I will do it when I get home and check all the ground connections around the tube
    No,not the tube socket (but it wont do any harm) The single row multipin connectors like CON1 etc.
    Experience is something you get, just after you really needed it.

  27. #27
    Member
    Join Date
    Nov 2017
    Location
    Madrid, Spain
    Posts
    32
    Quote Originally Posted by nickb View Post
    No,not the tube socket (but it wont do any harm) The single row multipin connectors like CON1 etc.
    Got it, I will!!

  28. #28
    Member
    Join Date
    Nov 2017
    Location
    Madrid, Spain
    Posts
    32
    Quote Originally Posted by avoverdu View Post
    Sorry, you mean to clean the tube socket? I will do it when I get home and check all the ground connections around the tube
    AC voltage on that R22 to ground= 000

    AC voltaje between the leads of the filament heaters supply = 13.64

    I also cleaned the tube socket, all the multipin connectors and re-solder all the components around the tube that are connected to ground. Hum is still there of course

  29. #29
    "Thermionic Apocalypse" -JT nickb's Avatar
    Join Date
    Dec 2009
    Location
    Devon, UK
    Posts
    2,412
    It was worth a try. Have you checked C21 and C19? These to caps are critical in establishing the signal ground AC level. The easy was is just to tack a new cap across the cap to be tested.
    Experience is something you get, just after you really needed it.

  30. #30
    Member
    Join Date
    Nov 2017
    Location
    Madrid, Spain
    Posts
    32
    Quote Originally Posted by nickb View Post
    It was worth a try. Have you checked C21 and C19? These to caps are critical in establishing the signal ground AC level. The easy was is just to tack a new cap across the cap to be tested.
    C21 and C19 on the preamp PCB?? I checked those days ago with the multimeter and they seemed fine

  31. #31
    g1
    g1 is offline
    don't forget the joker g1's Avatar
    Join Date
    Feb 2010
    Location
    Canada, somewhere north of Fargo
    Posts
    8,956
    I just want to point out something that could really screw up the testing and troubleshooting here, in case anyone is unaware.
    The muting circuit in this amp is a real strange one.
    For any kind of noise tracking, you should probably use a dummy plug in the input jack (and short tip to sleeve). Otherwise the grid of V1A is grounded via LK12 100n cap.
    Even the power amp input will not work by itself without a dummy plug in the gtr input jack. The point above V1A labelled "FXLPOUT" is coming from the Fx return.
    Certified Dotard

  32. #32
    Member
    Join Date
    Nov 2017
    Location
    Madrid, Spain
    Posts
    32
    Quote Originally Posted by g1 View Post
    I just want to point out something that could really screw up the testing and troubleshooting here, in case anyone is unaware.
    The muting circuit in this amp is a real strange one.
    For any kind of noise tracking, you should probably use a dummy plug in the input jack (and short tip to sleeve). Otherwise the grid of V1A is grounded via LK12 100n cap.
    Even the power amp input will not work by itself without a dummy plug in the gtr input jack. The point above V1A labelled "FXLPOUT" is coming from the Fx return.
    I noticed that too. I just did a test, I disconnected CON1 and connected the tip of my guitar jack cable to R1 of the power PCB and the sleeve to ground and it sounds with almost no noise. My common sense tells me that the power amp is full blast and is normal to have some noise. What else do you suggest???

  33. #33
    "Thermionic Apocalypse" -JT nickb's Avatar
    Join Date
    Dec 2009
    Location
    Devon, UK
    Posts
    2,412
    Quote Originally Posted by avoverdu View Post
    C21 and C19 on the preamp PCB?? I checked those days ago with the multimeter and they seemed fine
    A multimeter is of very limited value in testing caps. Tack a known good one on there.

    G1: Thx- I was aware of the input muting. The problem in this case is well after that, although I have to admit I am just about out of ideas on how to narrow it down further.
    Last edited by nickb; 12-04-2017 at 10:21 PM.
    g1 likes this.
    Experience is something you get, just after you really needed it.

  34. #34
    Member
    Join Date
    Nov 2017
    Location
    Madrid, Spain
    Posts
    32
    Quote Originally Posted by nickb View Post
    A multimeter is of very limited value in testing caps. Tack a known good one on there.

    G1: Thx- I was aware of the input muting. The problem in this case is well after that, although I have to admit I just about out of ideas on how to narrow it down further.
    Ill get a couple of those tomorrow and put them in just to be sure. Please let me know if you have any ideas, I appreciate it mate

  35. #35
    Member
    Join Date
    Nov 2017
    Location
    Madrid, Spain
    Posts
    32
    I have an update:

    On the preamp board I changed C21 and C19 on the supply and also changed C26, C27. On the rest of the preamp board I changed C45, and C2.

    This are the results: Everything on zero, no guitar plugged in, no dummy jack

    a) Clean channel,: when I turn it on is silent for a second, then a tiny pop and hum appears and increases. It takes around 30 seconds to get to its maximum volume. If I crank the volume the hum increases a little bit. If I crank the treble, as soon as I move it away from zero the higher octave of the hum disappears.

    b) Overdrive channel: silent, then I tiny pop and hum appears. The volume is about the same as the clean channel.

    NOW EVERYTHING THE SAME BUT WITH THE GUITAR PLUGGED IN:

    a) Clean Channel: everything on zero and the hum is louder compared to the previous test. sometimes gets a little louder and comes back to the original. If I crank the volume the hum increases a little bit when I put my hand closer to the chassis or if I move around the guitar it gets the volume of the hum changes. If i set the volume like 9 o´clock the hum is as loud as the guitar signal but if i crank the treble or the mids the hum is reduced as soon as im not on zero.

    b) Overdrive: pretty much the same but when I turn up the volume more than zero the hum disappears almost completely. The treble pot make noises the you turn it more than zero but it doesn't affect the hum.

    Any ideas or theories will be appreciated. Thank you guys

Page 1 of 3 123 LastLast

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. Marshall ValveState VS100R white noise / buzz problems
    By MarshallMallow in forum Maintenance, Troubleshooting & Repair
    Replies: 14
    Last Post: 11-10-2015, 02:36 AM
  2. Marshall Vasvestate VS100R Head
    By JohnnyVieira in forum Maintenance, Troubleshooting & Repair
    Replies: 12
    Last Post: 07-15-2013, 06:56 PM
  3. 117 volt transformer for a Marshall Valvestate VS100R
    By Sethkomar01 in forum Maintenance, Troubleshooting & Repair
    Replies: 12
    Last Post: 02-01-2013, 04:55 AM
  4. Marshall VS100R Schematic Mixup?
    By ConnorW in forum Schematic Requests
    Replies: 3
    Last Post: 09-28-2011, 03:46 AM
  5. Marshall Valvestate VS100R Transistors Blowing
    By neilm in forum Maintenance, Troubleshooting & Repair
    Replies: 10
    Last Post: 06-23-2009, 01:00 AM

Tags for this Thread

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •