Fender '68 Custom Vibro Champ Reverb gut shot / idle hum

Discussion in 'Amp Tech Center' started by tillamook, May 11, 2021.

  1. tillamook

    tillamook TDPRI Member

    Posts:
    26
    Joined:
    Nov 18, 2005
    D4A3D842-D21A-4AAE-8C88-428B3412E31C_1_105_c.jpeg Hello Everyone:

    I'd like to reduce the idle hum in my new Vibro Champ. Would twisting some wires help? If
    so, could someone tell me which ones to twist (by color and location, not function) ?

    If it would help and there's a fair chance of success, I can snip the zip ties, spread the wires a bit, and take another photo, making it easier to identify the proper wires.

    If this would likely be a waste of time, I'll probably make the long drive to another store that has
    one of these amps and, if it's more quiet, return this one. I'd like to avoid the drive though, it's pretty much an all day endeavor.

    The hum isn't terrible, but I play at low volume in a very quiet environment.....

    Thanks in advance,

    Bill
    Astoria, Or



    View attachment 855552
     
  2. Boreas

    Boreas Friend of Leo's Silver Supporter

    Age:
    66
    Posts:
    4,719
    Joined:
    Nov 3, 2019
    Location:
    Adirondack Coast, NY
    Wiggle anything you want, but change nothing. You don't want to void the warranty. Tried a couple different outlets in different rooms/circuits?

    Fill the tank and take the drive if it doesn't please you. There are worse places in the country than the Oregon coast to take a day-long drive.
     
    Sidney Vicious likes this.
  3. tillamook

    tillamook TDPRI Member

    Posts:
    26
    Joined:
    Nov 18, 2005
    Thanks for the reply. It's definitely not house wiring or room location, just the typical single-ended hum. I've observed in all the single-ended hand-wired amps I've owned the heater wires are tightly twisted together. I'm not
    sure if that practice translates over to PCB amps.
    It is a nice drive over the mountains, I will admit.
     
    Boreas likes this.
  4. J. Bonkosky

    J. Bonkosky Tele-Holic Silver Supporter

    Posts:
    690
    Joined:
    Sep 7, 2014
    Location:
    Seattle Washington
    Welcome to the wonderful world of single ended amps. The all have idle him. Give another output tube a try. That may slightly reduce the hum, but you will never be able to completely eliminate it.
     
    W.L.Weller likes this.
  5. tillamook

    tillamook TDPRI Member

    Posts:
    26
    Joined:
    Nov 18, 2005
    Thanks, Bonkosky.

    I've had a Mojotone Champ (I believe wired up by Mojotone) and a couple Swart 6v6se amps that were close to dead silent. I've also owned a bunch of other single-ended amps, both vintage and boutiquey hand-wired, and yes,
    all were pretty hummy, a couple of the them obnoxiously so.

    I love this amp so I'm more than willing to put up with it, but if there's an easy way to reduce the hum, that would be great.

    I'm going to get a set of tung-sols in there and see what happens.
     
  6. J. Bonkosky

    J. Bonkosky Tele-Holic Silver Supporter

    Posts:
    690
    Joined:
    Sep 7, 2014
    Location:
    Seattle Washington
    See if you can get hold of a GE 6V6GT. I have had great luck with those tubes. They sound great with little hum in my silver face champs and last forever.
     
  7. tillamook

    tillamook TDPRI Member

    Posts:
    26
    Joined:
    Nov 18, 2005
    Thanks for the tip.
     
  8. Jon Snell

    Jon Snell Tele-Holic

    Posts:
    892
    Joined:
    Aug 31, 2015
    Location:
    Jurassic Coast. Great Britian.
    Do I see a swollen capacitor, centre of picture or is it an optical illusion?
    Swollen caps usually cause issues as they tend to be low value and have a high ESR;
    Screenshot 2021-05-11 at 19.56.39.png
     
    Jowes_84 likes this.
  9. homesick345

    homesick345 Poster Extraordinaire

    Posts:
    6,942
    Joined:
    Jan 20, 2012
    Location:
    Beirut, Lebanon
    Single ended class a will hum. There's nothing you can do about it.
     
  10. jimgchord

    jimgchord Tele-Afflicted

    Age:
    48
    Posts:
    1,624
    Joined:
    Apr 3, 2018
    Location:
    victor,ny
    These not much youll accomplish , its the layout of the board most likely.
     
  11. tillamook

    tillamook TDPRI Member

    Posts:
    26
    Joined:
    Nov 18, 2005
    Sharp eye you have there, thanks!

    I've decided to make the drive today and try the other one of these amps at a different store. If it's more quiet, problem solved, I can return this one. If it's hum level is the same, I'll pull the chassis again and take a look at the cap, and order some tubes. Fortunately, the store with the other amp has a little soundproof room where I can make an accurate assessment, unlike the store where I bought the current amp.
     
    Boreas and Sidney Vicious like this.
  12. tillamook

    tillamook TDPRI Member

    Posts:
    26
    Joined:
    Nov 18, 2005
    jmgchord and homesick345:

    I'm not trying to eliminate hum, it's not a Swart, just reduce it. I have to admit I'm also a little bit driven, perhaps foolishly, by some post on a thread somewhere by an owner of one of these amps who declared "it's dead quiet" or something close to that. I realize one person's dead quiet may be another person's irritating cacophony, but it wouldn't be the first time I embarked on a Quixotic journey!

    Not that I'm discounting your input, I will keep your advice in mind before going too far down the path. I thank you both.
     
    T-Bone likes this.
  13. Fretting out

    Fretting out Poster Extraordinaire

    Age:
    29
    Posts:
    9,182
    Joined:
    Jun 13, 2019
    Location:
    Land of Mary

    What is this single ended amp thing I keep hearing?
     
  14. Jon Snell

    Jon Snell Tele-Holic

    Posts:
    892
    Joined:
    Aug 31, 2015
    Location:
    Jurassic Coast. Great Britian.
    Single valve output is commonly known as Single Ended as opposed to Push Pull, which is tollerant to HT hum because it uses a pair of output valves that push or pull in class AB or even B (if you like a cold sound) and has better hum or noise rejection. Single Ended uses one valve that is set in class A, (1/2 to 2/3rds of the valve is on all the time, so it only pulls (on the transformer winding) and if the HT has ripple or hum, so will the speakers ... hum.
     
    Fretting out likes this.
  15. tillamook

    tillamook TDPRI Member

    Posts:
    26
    Joined:
    Nov 18, 2005
    OK, I'm back from the big city where I tested another CVCR in a room that I described in a previous post as soundproof but today had some sort of Air Conditioning thing happening. Regardless, I found that the amp had
    about as much hum as mine. So, unless someone tells me there's a good chance twisting the heater wire pairs
    together has a good chance of knocking the hum down considerably (warranty be damned I say), I'll get a set of tubes, maybe take a closer look at the suspect capacitor, and, even if nothing comes of those two activities, enjoy
    my new amp.

    Call me crazy but I traded a PRRI for this amp and couldn't be happier with my decision, hum and all. There's something about single-ended......

    One last thing; I've noticed that in my little music room (9x11) the hum's perceived loudness varies considerably
    by where in the room my ears are, soundwave nodes everywhere!

    Thanks to everyone for your input.
     
    Fretting out and Drew617 like this.
  16. Tenderfoot

    Tenderfoot Tele-Holic

    Age:
    74
    Posts:
    947
    Joined:
    May 8, 2014
    Location:
    Katy, TX
    tillamook, I feel your pain. I returned a 31 day old Blackstar Studio 10 6L6 today due to the hum (some expected) being too loud when compared to the one I played at the store or amps demonstrated on YouTube.

    FYI, replacing the Tube Amp Doctor 12AX7WA Select with a Tung Sol 12AX7/ECC803S and the Ruby 6L6GC-M-STR with a Tung Sol 6L6CG-STR didn't change the hum level.

    The replacement amp will arrive by next Monday and I will post if the hum level has improved to an acceptable level.

    Good Luck!
     
  17. tillamook

    tillamook TDPRI Member

    Posts:
    26
    Joined:
    Nov 18, 2005
    Thanks, good luck with your replacement.
     
  18. Mike M

    Mike M Tele-Afflicted

    Posts:
    1,016
    Joined:
    Dec 20, 2019
    Location:
    07040
    I had one for a week, and returned it.

    I loved the sound, but every time I would turn up the Reverb knob I would get a static or hissing sound. Since the Reverb is digital, I wasn't expecting that.

    I was hoping it was just an issue with the one I had, and am going to try a different one when my local store gets them in soon.

    Is that normal for this amp, a hissing that increases with the Reverb knob being turned up, even with nothing plugged in? Just curious
     
  19. Wally

    Wally Telefied Ad Free Member

    Posts:
    39,680
    Joined:
    Mar 17, 2003
    Location:
    Lubbock, TX
    First...step away from the amp! (;^) I find that with these little amps people like to get too close to them because these little bitty amps do not bite..hard, anyway!!! Eeehaw....
    Find the pitch of the hum....then play a rhythm in an appropriate key and sing along!!!
    One at a time, try different tubes in the preamp. No luck? You can TYR another 6V6 if you’d like. I doubt if it changes things.
    My 1954 5D4 Princeton with a 5Y3, a 12AX7, and a 6V6 has the obligatory and ime non-intrusive hum. The old ones had one end of the heater filament at ground where one side of the heaters were also taken... with the other end to the tube heaters. That can introduce noise. It doesn’t bother me...I never notice it.
    As one of our friends here notes...let’s all ‘play music’!

    and...if you can’t stand the hum by all means take that thing apart and do a better job than Fender did.
    I am subscribed.
     
    SnidelyWhiplash and Mike M like this.
  20. tillamook

    tillamook TDPRI Member

    Posts:
    26
    Joined:
    Nov 18, 2005
    There's a slight white noise starting around 4 1/2 and it increases a bit as you go up from there. However, I can't remember any amp I've owned, and that's a lot of amps, that did not exhibit this characteristic. This one is actually a lot quieter than most in that regard, probably because it is digital, I guess. On my amp the idle hum outweighs the reverb noise easily.
     
    Mike M likes this.
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.