Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com
Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com
Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com

5G9 Tremolux Trouble Shooting

Discussion in 'Shock Brother's DIY Amps' started by jmp81sc, Dec 4, 2017.

  1. jmp81sc

    jmp81sc Tele-Meister

    166
    Feb 6, 2015
    Orange County
    Hi Everyone,
    I have a loud buzz that I can not track down in a homebrew 5G9 build.

    The amp works fine except for the buzz. I can play my guitar through it and get normal sounds.

    The volume and tone controls change the buzz, gets louder with the volume up and the tone control changes the pitch of the buzz.

    Pulling V1 has minimal effect, if I pull V2 the phase inverter, it is dead silent. If I short the bright cap to ground the buzz goes away.

    I have checked every solder joint, I have checked build against the layout and schematic countless times.

    I have checked all grounds with a ground probe, and replaced the coupling caps in the input and phase inverter sections. I have chopsticked every wire and joint, and checked every resister value.

    I have used a good known 12AX7 in all of the slots with no change.

    I unsoldered the volume and tone pots out of the circuit and the sound persisted.

    I used the stock fender layout and all of my voltages are close to the originals. The only strange thing is that V1 has higher DC on the plates than V2. It is reading around 200v vs 175v on the fender layout.

    I am guessing that I am getting DC voltage in the signal chain, but I cant figure out how.

    Hopefully you guys can help.
    Thanks
    John
     

  2. D'tar

    D'tar Tele-Afflicted

    Jan 11, 2013
    WNY
    Buzz present on both channels all inputs? Maybe post some pictures.
     
    tubeswell likes this.

  3. nasdak

    nasdak TDPRI Member

    41
    Mar 22, 2013
    france
    what sort of buzz? maybe a sound sample would help ?
    Do you use a regular chassis ?
     

  4. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City
    I'm not smart enough to diagnose, but those sound like good clues. In case it helps somebody zero in, I do have a schematic...

    Fender 5G9 schematic copy.png
     

  5. jmp81sc

    jmp81sc Tele-Meister

    166
    Feb 6, 2015
    Orange County


    Here is a quick video using the iPhone microphone.

    I am using a chassis I bought from ubuy guitars.

    Noise as shown in video is without an instrument plugged in. It persists with a guitar plugged in any channel.

    My guess was the .02-400 coupling cap between V1 and V2, but i clipped in a new cap with no change, then I removed it and soldered a new one with still no change.

    Thanks everyone
    John
     

  6. D'tar

    D'tar Tele-Afflicted

    Jan 11, 2013
    WNY
    Havent watched the video yet. I would like to see, imo, the heater wires moved to the other side of the sockets tucked into the corner of the chassis
     
    tubeswell and King Fan like this.

  7. rocksmoot

    rocksmoot Tele-Meister

    159
    May 6, 2012
    Rogers, Arkansas
    I've had buzzing that was caused by a bad solder joint and once a bad cap that was presumably arcing internally.
     

  8. clintj

    clintj Friend of Leo's

    Apr 4, 2015
    Idaho
    1. Make sure the shorting contact is actually shorting to ground on each input jack. A resistance check from the tip contact to chassis with no cable inserted, verifying zero ohms, is the test for that.

    2. Lay a cookie sheet over the open chassis or flip the chassis open end down and see what it does. You're missing some needed shielding with the chassis open like that.
     
    King Fan likes this.

  9. jmp81sc

    jmp81sc Tele-Meister

    166
    Feb 6, 2015
    Orange County
    Thank you all for your suggestions so far, unfortunately, no change.

    I flipped the chassis over same result, tried the cookie sheet not change. Resistance from tip of input jack to ground is 0.2ohms for all jacks.

    Chop sticking the heater wires has no effect on buzz/hum, or any other wires either.

    Grounding the .1uf cap on the instrument channel and the .02uf cap on the phase inverter makes the buzz stop completely. I checked for DC voltage leak on the coupling caps, no DC there.

    Just for background, this is my third amp build. I did an 5F6A kit and 5F2a partial kit from Boothill. Both builds were successful with very little tweaking.

    thanks again
    John
     

  10. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City
    Hmm. Wondering about things I don't know. A large topic... :D

    Pros, do you think that's hum, 60hz or ???
    Does the fact it varies with the volume mean it enters the circuit early on? Does that narrow the hunt or just say the amp is noisy? :)
    What does it mean that the hum disappears when bright cap is shorted to ground? Is that just dumping (noisy) signal, or does it imply something in the vol/tone wiring, or ???
     

  11. corliss1

    corliss1 Tele-Afflicted Gold Supporter

    Sep 13, 2008
    Lansing, MI
    Sounds like 120Hz to me, though I think those are sometimes hard to tell without being in person.

    Yes, that would indicate the problem happens before the control that you're turning. If it is the power supply, that touches each tube.

    Shorting the bright cap to ground completely cuts off all audio signal before that point in the circuit. That would tell us that it's entering the circuit at or before the bright cap.
     
    King Fan likes this.

  12. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City
    Thanks. That gets at what I was wondering about. As I learn more about building amps, I start to see the real challenge is troubleshooting.

    At this stage, I'm mostly Elvis Costello, 'Watching the Detectives.' But I'm watching closely. :D
     

  13. clintj

    clintj Friend of Leo's

    Apr 4, 2015
    Idaho
    Need some pics. Whole chassis from both sides, showing the control/jack wiring, and the socket wiring. Some close ups of the jack/controls would be awesome, too.

    That sounds like the 60/120Hz buzzsaw you get from either an open shorting contact or bad grounding/bad lead dress. We already ruled out the contacts, so my next stop would be wiring arrangement and ground scheme.

    Edit: if you want to hear that noise raw, open up two browser tabs to YouTube and pull up 2 videos at once: a 60Hz test tone and a 120Hz test tone. The overlapping frequencies makes that characteristic raspy buzz.
     
    King Fan and D'tar like this.

  14. Snfoilhat

    Snfoilhat Tele-Meister

    Age:
    36
    312
    Apr 8, 2016
    Oakland, CA
    Misread a post, deleted.
     

  15. jmp81sc

    jmp81sc Tele-Meister

    166
    Feb 6, 2015
    Orange County
    Ok here are some photos. After looking at these photos I may just rewire the whole thing more cleanly. The way that my board fit into this chassis I was able to fly the socket leads directly to the board with good separation, should I have tucked them next to the chassis instead?

    I have chopsticked every wire with no changes in the buzz. IMG_0593.JPG IMG_0594.JPG IMG_0595.JPG IMG_0596.JPG IMG_0597.JPG IMG_0598.JPG IMG_0599.JPG IMG_0600.JPG IMG_0601.JPG IMG_0602.JPG
     

  16. jmp81sc

    jmp81sc Tele-Meister

    166
    Feb 6, 2015
    Orange County

  17. clintj

    clintj Friend of Leo's

    Apr 4, 2015
    Idaho
    Ok, if I read this right you have all the filter caps grouped, with a common ground for them bonded to chassis at the PT bolt. Everything on the main board is grounded to the bus wire, and that is attached to the input jack.

    Ok, you've got a large ground current flowing through the chassis, and a lot of noise from the rectifier/reservoir circuit flowing back into the audio path. Separation of those is key to quiet grounding.

    Good news is the fix should be pretty easy. One of your filter caps is fed directly from the rectifier, and should then directly feed the output transformer. Ground only that one cap to the PT bolt. For the other three filter caps, run a short lead over to your main board ground bus and connect them to that, then cut the connection between their grounds and the reservoir cap.

    To recap: first filter cap only grounded at PT. Other caps grounded only to the main bus. This should drastically cut your noise level.
     

  18. jmp81sc

    jmp81sc Tele-Meister

    166
    Feb 6, 2015
    Orange County
    Thanks Clint,
    That is correct on my grounding. I will wire it as you have suggested 5F6A_Bassman_Amp_Layout.png . 1960-Fender-Tremolux-5G9-JA-028-159x212.jpg

    I used the 5F6a layout for the filter caps from Rob Robinette's site. The original 5G9 had a cap can like the 5F6a, with the grounds going to the can. I just thought that this was a pretty common way of grounding the filter caps.

    Here are some photos.
     

    Attached Files:


  19. clintj

    clintj Friend of Leo's

    Apr 4, 2015
    Idaho
    Oh, yeah. That's got a 2 cap reservoir. They should go first two to the PT bolt, and 2nd two to the main bus.

    My take, learned from Merlin, is that the rectifier/reservoir loop should be separated. It's more important for the screen node to be away from that hash noise than to have a perfect closed loop on the power tube.
     

  20. jmp81sc

    jmp81sc Tele-Meister

    166
    Feb 6, 2015
    Orange County
    Ok made the changes to the grounding per Clint's suggestion, no change to the buzz.

    I know my build is a little sloppy but if lead dress was the issue wouldn't chop sticking the wires change the tone or intensity of the buzz?

    My gut feeling is that I have a bad component somewhere in the input or phase inverter section. I replaced the coupling caps, but maybe there is a bad one.
     

IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.