Metropoulos Forum

Hi everyone, I have a couple questions about my 100watt plexi.
I have built the 100watt plexi as well as the jtm 45, and all have gone flawlessly. However there is a weird hum coming form the 100watt. It sounds like its coming from one of the tranformers or maybe one of the caps. I also have another amp here that has a bad output tranformer (An old traynor), that makes the same noise. Could the ot or the caps be the problem, or could it be that the ot is weird wrong (i.e. out of phase, e.tc...) I should also mention that I have recently put on the lar/mar mv mod on it on the 100watt.
Thanks in advance
Tyler

Remove the PPIMV and see if the hum goes away, if it does not, then take pictures and post.

-Ty- wrote:Hi everyone, I have a couple questions about my 100watt plexi.
I have built the 100watt plexi as well as the jtm 45, and all have gone flawlessly. However there is a weird hum coming form the 100watt. It sounds like its coming from one of the tranformers or maybe one of the caps. I also have another amp here that has a bad output tranformer (An old traynor), that makes the same noise. Could the ot or the caps be the problem, or could it be that the ot is weird wrong (i.e. out of phase, e.tc...) I should also mention that I have recently put on the lar/mar mv mod on it on the 100watt.
Thanks in advance
Tyler

I get a hum from mine too. Never could figure it out. Seems the closer I am with the guitar to the amp, the louder it gets.

do you have fluorescent lights where you are playing? If you move around in a circle while holding the guitar does it get louder and softer? If so, its probably not the amp... are you running single coils or humbuckers? I'd rule out non amp related issues before sparking up the soldering iron!!

Good Luck!
Mike

axeman wrote:Remove the PPIMV and see if the hum goes away, if it does not, then take pictures and post.

Whoa, slow down! Seriously, did the hum only start after adding the PPIMV?

Also, always rule out tubes early in the troubleshooting process. Swap preamp tubes with your 45. If that doesn't fix it, try running the 100 with only the inner or outer power tube pair and swap the tubes around to see if one is bad (remember to set your impedance switch one click lower when doing this). Did the power tubes bias up close to each other (within 10mA)?

I doubt the OT is wired wrong. If the primaries were reversed you would definitely know it and the amp wouldn't be usable.

Your rite Toner, replace v3 preamp tube with v2 or v1, if that does work great, if not make sure chassis is in the box when you test it. Stay away from florescent light they make guitar, cords and amp hum like fn bees. If that doesn’t work send it to Toner so he can fix it or just remove the PPIMV and do it over again.

Good Luck

Art

I just tried switching my preamp tubes and no luck there, and I also had this buzz problem before I installed the PPIMV. I discovered though that the amp doesnt buzz when I have my jumper on the 2 channels in, could I need to rewire the grounds on the input jack? I opened it up and currently have the jacks grounded to the pot buss (The circuit board is also ground to the buss). The amp still makes a loud humming noise though when the standby switch is on.
Thanks
Tyler

Send pictures.

I have solved my problem, I opened it up and re-grounded the pots to SDM's specs and also took all of the preamp tube connections that were near any heater lines and put up in the air as much as possible (Also did some other ground mods). Also dressed up some soldering and shortens a couple of leads. All in all it still hums but no where near as bad, and when I put in my jumper to run both channels there is hardly no hum. The only that would it better would be a power conditioner.
Thanks to everyone for your help,
Tyler

I once had a mic in my studio that actually started humming and eventually picking up a radio station!
Turned out to be caused not only by a ground issue but also by the way the cord was ran to it. Make sure that cords from other devices you have nearby are not intersecting with your amp wiring if at all possible. This maybe eliminate the remainder of the hum. I have heard that power conditioners are not always beneficial and can end up being a waste of money.