JVM1 head line out question - only 1 channel

Discussion in 'Marshall Amps' started by turbo, Oct 29, 2020.

  1. turbo

    turbo New Member

    Joined:
    Oct 29, 2020
    Messages:
    7
    Likes Received:
    7
    I just bought a used JVM1 head, the 50th anniversary one, and when I plugged my headphones into the emulated output, I'm only getting sound on one channel. I tried the same headphones with a few DSL Combos (DSL5 C old, DSL5 C reissue, DSL20 C), and I always got sound in both channels. Is my JVM faulty, or does it have a different output setup to the DSLs?
     
    SkyMonkey likes this.
  2. SkyMonkey

    SkyMonkey Well-Known Member

    Joined:
    Oct 28, 2018
    Messages:
    2,826
    Likes Received:
    3,638
    Location:
    Location:Location
    From reading around some forums I am not seeing any reference to your experience.
    This suggests that your JVM1 is faulty.
    I've included a schematic that shows the JVM1 Line Out appears to have all 3 connections needed to make stereo headphones work in dual Mono.

    A check list:
    Have you tried a different pair of headphones.
    If your headphones use a 1/4" adapter, have you tried a different one.
    Have you tried using the Line Out into any other mixing equipment.

    BTW The general consensus (in other forums) is that using the Line Out with headphones sounds like ass.
    I know the Emulated Out on my DSL40CR sounds like ass, so I never use it.

    If I need to use headphones I run them from the Headphone socket on the Boss GT-100 I use in 4CM with my DSL40CR.
    It sounds far superior to the onboard Emulated Out.

    Oh, and welcome to the MF @turbo :welcome:
     

    Attached Files:

    Jethro Rocker likes this.
  3. turbo

    turbo New Member

    Joined:
    Oct 29, 2020
    Messages:
    7
    Likes Received:
    7
    Thanks for you response, SkyMonkey.
    I have tried two sets of headphones with two 1/4" jack adapters. I also tried a stereo cable (one that I use for PC -> speakers) directly to monitor speakers. All same thing - only one channel/speaker works.
    Even though it might not be useful, do you think this can be fixed by a technician without the risk of damaging anything?

    Thanks for the schematic, by the way!
     
    SkyMonkey likes this.
  4. SkyMonkey

    SkyMonkey Well-Known Member

    Joined:
    Oct 28, 2018
    Messages:
    2,826
    Likes Received:
    3,638
    Location:
    Location:Location
    I would think a good tech could fix it if you aren't confident at having a look yourself.
    There are stored voltages in the amp capacitors that can do serious harm, even when unplugged.
    I tend not to do any amp work beyond re-tube and re-bias.
     
    tce63 likes this.
  5. turbo

    turbo New Member

    Joined:
    Oct 29, 2020
    Messages:
    7
    Likes Received:
    7
    One more thing. I noticed that it has a pretty loud transformer noise, louder than my DSL5C (in the same location, same power socket, same power chord). It comes from the back of the head, not the speaker, and regardless of whether it's in 1 or 0.1 watt mode.
    The weird thing is that it goes away if I tilt the thing a few degrees clock-wise horizontally. So if I were to tilt it 90 degrees and put it on the right side, it's fine.
    Is this technically considered a fault in the transformer? Can this be fixed without much expense?
     
    Last edited: Oct 30, 2020
  6. SkyMonkey

    SkyMonkey Well-Known Member

    Joined:
    Oct 28, 2018
    Messages:
    2,826
    Likes Received:
    3,638
    Location:
    Location:Location
    That could be electrical interference from the house wiring or another piece of equipment.
    A bit like adjusting an old-style analogue TV aerial (if you remember such an ancient practice!).
    To rule it out try moving the amp to a different position in the room to see if it changes.
     
  7. SkyMonkey

    SkyMonkey Well-Known Member

    Joined:
    Oct 28, 2018
    Messages:
    2,826
    Likes Received:
    3,638
    Location:
    Location:Location
    Sorry @turbo. It must seem like I am the only one in the whole MF that gives a f#ck at the moment.
    But others may chime in with more technical solutions.

    :thumbs:
     
  8. Biff Maloy

    Biff Maloy Well-Known Member

    Joined:
    Mar 13, 2019
    Messages:
    795
    Likes Received:
    1,808
    I have the JVM1. I will check this evening to see if i get the same response from using the line out with headphones. I've never used that feature.
     
    SkyMonkey likes this.
  9. turbo

    turbo New Member

    Joined:
    Oct 29, 2020
    Messages:
    7
    Likes Received:
    7
    I have tried that, actually. No difference. And I also have a DSL5 C - I tried it in the same places in my home, with the same power chord, and it didn't have that. I'd assume that if were are any interferences like that in my home, they'd affect both amps?

    It's actually a buzz, not a hum. And it comes from around the area where the power cable goes in.
     
    Last edited: Oct 30, 2020
    SkyMonkey likes this.
  10. RLW59

    RLW59 Well-Known Member

    Joined:
    Nov 30, 2017
    Messages:
    881
    Likes Received:
    823
    Power transformers actually expand and contract in pulse with the swinging line voltage. (60Hz or 50Hz depending on your location.) Magnetostriction. All do it to some degree, some more than others.

    I'm not sure if an excessively buzzy one can be fixed other than replacing it. But the normal buzz can make other things buzz. Loose mounting bolts can amplify it.

    Since you say that tipping the amp reduces it, and it seems to be mostly coming from the power cable jack area, maybe the jack receptacle is loose? Or the internal wires from the jack to transformer or switch are laid out so the transformer vibrations cause the wires to buzz against something, and gravity pulls them a little away when you tip the amp?

    I had a similar mechanical buzz that I discovered went away if I simply pressed the power transformer. So I stuffed a piece of high temperature foam between the head shell and the side of the transformer and that stopped the buzzing.
     
  11. Dogs of Doom

    Dogs of Doom Moderator Staff Member

    Joined:
    Aug 2, 2012
    Messages:
    22,268
    Likes Received:
    24,781
    Location:
    Los Angeles
    I've never tried headphones on mine, so IDK... :shrug:

    IIRC, the simulated out is not balanced, so, it would be mono, which would only come out of one side...
     
    tce63 and Biff Maloy like this.
  12. Biff Maloy

    Biff Maloy Well-Known Member

    Joined:
    Mar 13, 2019
    Messages:
    795
    Likes Received:
    1,808
    Same here. Never used mine. When i saw the OP's issue with headphones i thought the same thing. It's a line out which should be just a mono signal.

    I finally got around to checking mine this morning. I could barely tell if i was getting anything at all through headphones. It was only when i turned the amp off i heard the dying signal through one side.

    As far as the line output into headphones, your amp is normal. I don't think this connection was ever intended for that use.
     
    tce63 and Dogs of Doom like this.
  13. spacerocker

    spacerocker Well-Known Member

    Joined:
    Feb 6, 2009
    Messages:
    1,641
    Likes Received:
    1,177
    Location:
    UK
    As others have said - it is a "line out" not a headphone socket - therefore it will be a mono signal on a mono Jack socket! It is not intended to be a stereo output! No fault here.....
     
    SkyMonkey and tce63 like this.
  14. SkyMonkey

    SkyMonkey Well-Known Member

    Joined:
    Oct 28, 2018
    Messages:
    2,826
    Likes Received:
    3,638
    Location:
    Location:Location
    What would be the reason for the Line Out jack being an (apparently) fully connected TRS?
    Are the JS4 'ring' connector and the 'sleeve' (vertical rectangle) just connected to the same GND?

    JVM1 line out.JPG
     
    tce63 likes this.
  15. marshallmellowed

    marshallmellowed Well-Known Member

    Joined:
    Jun 26, 2009
    Messages:
    4,128
    Likes Received:
    5,554
    As stated, it's a line level out, not designed for headphones. If you're getting enough signal to be heard through headphones, it's probably borderline. The output impedance of the line out connector is matched to feed into a mixer, audio interface... You could feed your line out into an audio interface or mixer that has a headphone monitoring jack, which would work.

    As for the transformer buzz, sounds mechanical to me. I'd try tightening the screws holding the transformer together. I had to add nylon washers under the screw heads of one transformer to get rid of the buzz.
     
    Last edited: Nov 8, 2020
  16. turbo

    turbo New Member

    Joined:
    Oct 29, 2020
    Messages:
    7
    Likes Received:
    7
    Thank you for all of your comments, guys.
    Ok, so the line output is mono. The manual leaves a lot to be desired.
    I just got a JCM1 h and it doesn't have the buzz. So this means there's definitely something up with my JVM.
     

Share This Page