dpaulb Posted July 8, 2023 Share Posted July 8, 2023 (edited) I purchased a WT-550 which has a constant hum. Nothing connected but my Bag End S15X-D. It isn't effected by the positions of the controls. I inserted a cable into the effects loop jacks with no change. I removed the lid found one wire from the D.I. circuit board not connected. I am wondering if it is to the ground/lift switch. Because it only has 1 wire connected. Could this be the reason for the hum? Edited July 23, 2023 by wateroftyne Quote Link to comment Share on other sites More sharing options...
DGBass Posted July 8, 2023 Share Posted July 8, 2023 Difficult to tell from the photo but it looks like that single dark green wire is floating in mid air? The schematic shows PIN1 on the DI out should be grounded via the ground lift swtich in normal operation. Can't think why someone would purposely remove a ground connection though and if it has fallen off a tag or solder connection due to wear and tear, where was it before? The other thing is I wouldn't expect a bad ground on PIN1 of the DI to make any difference with nothing plugged into the DI. Even if you disconnected the ground lift switch, it would be the same as if nothing was plugged into the DI. You didn't say whether you can hear a bass through the hum if you plug one in as normal or is it a constant hum on the speaker and no sound from you bass at all when plugged in? I see there is also a tube in the pre-amp stage. I'd always go for the obvious like a worn tube or dirty jack contacts or loose multi pin connectors etc before investigating a wiring issue, if anything just to rule out what can be easily checked. 1 Quote Link to comment Share on other sites More sharing options...
dpaulb Posted July 8, 2023 Author Share Posted July 8, 2023 The dark green wire is indeed floating in mid air. No problem hearing a bass. It sounds great other than the hum. Quote Link to comment Share on other sites More sharing options...
DGBass Posted July 8, 2023 Share Posted July 8, 2023 does it look like its fallen off a tag anywhere near its floating end and does turning the DI knob to zero with the switch at GRND make any difference? 1 Quote Link to comment Share on other sites More sharing options...
dpaulb Posted July 8, 2023 Author Share Posted July 8, 2023 I will check those things after I get some sleep. Quote Link to comment Share on other sites More sharing options...
Bill Fitzmaurice Posted July 8, 2023 Share Posted July 8, 2023 Green wires are almost always ground wires, and a disconnected ground wire is one of the usual reasons for hum. The trick will be finding where it's supposed to be connected. 1 Quote Link to comment Share on other sites More sharing options...
ahpook Posted July 8, 2023 Share Posted July 8, 2023 (edited) Given the position of the floating wire and - as far as I can make out - some solder residue on the Ground Lift Switch middle tag, I'd wager it does need to be reconnected there. But as to the hum, I suspect that you've just happened upon the DI wire issue and it's something else making the noise. I'd be with @DGBass and be checking the valve, connections and so on. Bit o'TLC might do the job. Fingers crossed for an easy fix ! Edited July 8, 2023 by ahpook 1 Quote Link to comment Share on other sites More sharing options...
Tdw Posted July 8, 2023 Share Posted July 8, 2023 I had a wt 400 which hummed constantly, the solution was to to turn around (rotate it around its central position) the toroidal transformer , apparently the change in the magnetic field ( I think) stopped the hum. The problem may well be something else but it's worth considering. 1 Quote Link to comment Share on other sites More sharing options...
Bill Fitzmaurice Posted July 8, 2023 Share Posted July 8, 2023 One of the advantages of toroidal transformers is they have very little EMI, and in theory rotating one should have no effect. I can't say why doing so worked for you. 1 Quote Link to comment Share on other sites More sharing options...
Tdw Posted July 8, 2023 Share Posted July 8, 2023 5 minutes ago, Bill Fitzmaurice said: One of the advantages of toroidal transformers is they have very little EMI, and in theory rotating one should have no effect. I can't say why doing so worked for you. I don't know why, but it did. The eden wt 400 and 550 amps are very compact for their power rating and type and all kind of components are packed in close together, perhaps this has something to do with it. Quote Link to comment Share on other sites More sharing options...
dpaulb Posted July 8, 2023 Author Share Posted July 8, 2023 12 hours ago, DGBass said: does it look like its fallen off a tag anywhere near its floating end and does turning the DI knob to zero with the switch at GRND make any difference? The middle tag on the ground/lift switch does have solder on it. The DI knob and switch to ground make no difference. Interesting that when first turned on the hum was only audible when close to the speaker. Since then it has gotten louder but not nearly as loud as yesterday. There is hiss when the master volume is half way or more. I don't understand why with the master up all the way and then turning the gain above halfway caused the input limiter light to stay on and a loud low frequency blurpy sound vibrating the entire room until I quickly turned it down. Quote Link to comment Share on other sites More sharing options...
Bill Fitzmaurice Posted July 8, 2023 Share Posted July 8, 2023 Since they have much lower EMI than standard transformers tightly packed components is one reason for using toroidals. One of their characteristics is they don't have stray magnetic fields caused by the ends of the cores, because the cores have no end. Whatever EMI they do radiate travels in all directions. They're also smaller and lighter, but are much more difficult to make, so they cost more. Why you had your result is puzzlement. 🫢 OP, you may find this of interest. Scroll to post # 33 https://www.talkbass.com/threads/eden-toroidal-transformer-buzz.391552/page-2 1 Quote Link to comment Share on other sites More sharing options...
dpaulb Posted July 8, 2023 Author Share Posted July 8, 2023 After leaving it powered on for a while the hum is barely audible. Without a bass plugged in and master at maximum, bass at maximum while turning the gain past 1:00 there was a loud oscillation coming from the speaker that shook the room. Of course I immediately turned it down. Just now I set the master at 12:00, tone controls flat and the gain was at 1:00 i turned the bass up just a bit from 12:00 and the low frequency oscillation started again. Is that because of the preamp tube? Noise not hum increases as I turn up the gain. Whilst playing a bass with the gain up where the red light comes on occasionally, the bass at maximum and the master at 1 or 2 the oscillation doesn't happen. Quote Link to comment Share on other sites More sharing options...
dpaulb Posted July 9, 2023 Author Share Posted July 9, 2023 Could the handwriting on this capacitor mean anything? 1 Quote Link to comment Share on other sites More sharing options...
BassmanPaul Posted July 14, 2023 Share Posted July 14, 2023 Does the centre terminal of the ground lift switch have any wiring to it? Do you have a multimeter? if yes, measure the resistance of that green wire to chassis. If the reading is zero ohms then it is a ground. Solder it back onto the switch terminal. I don't feel that that missing ground is going to change your hum level as the switch in the lift position disconnects the ground anyway. Are you using the DI to connect to a PA? Quote Link to comment Share on other sites More sharing options...
BassmanPaul Posted July 14, 2023 Share Posted July 14, 2023 Does the amp have an Effects Loop? If yes plug into the Return to see what difference it makes. 1 Quote Link to comment Share on other sites More sharing options...
ahpook Posted July 14, 2023 Share Posted July 14, 2023 (edited) On 09/07/2023 at 03:13, dpaulb said: Could the handwriting on this capacitor mean anything? Bad pad sounds like a fault on the board, hopefully a note to say it been fixed. Odd it only happens with no bass plugged in. Bit of a guess, but maybe the input jack isn't normalising properly - the input's not shorting to ground when nothing's plugged in. Bit of a check and clean there might be worthwhile. Not sure how that would cause the oscillation....just thinking out loud, really ! Edited July 14, 2023 by ahpook Quote Link to comment Share on other sites More sharing options...
BassmanPaul Posted July 21, 2023 Share Posted July 21, 2023 (edited) A faulty ground can cause all sorts of weird and wonderful effects. @dpaulb did you try plugging into the Return jack? If the hum stops then the problem lies within the pre-amp circuitry. Edited July 21, 2023 by BassmanPaul Quote Link to comment Share on other sites More sharing options...
dpaulb Posted July 21, 2023 Author Share Posted July 21, 2023 1 hour ago, BassmanPaul said: A faulty ground can cause all sorts of weird and wonderful effects. @dpaulb did you try plugging into the Return jack? If the hum stops then the problem lies within the pre-amp circuitry. I have an update. The hum has been barely audible for more than a week. I have no idea why. 1 Quote Link to comment Share on other sites More sharing options...
BassmanPaul Posted July 22, 2023 Share Posted July 22, 2023 If the input jack is board mounted you could try reflowing the connections to that board. Could be your fiddling about inside the chassis has jolted a bad connection to working again. Quote Link to comment Share on other sites More sharing options...
dpaulb Posted July 22, 2023 Author Share Posted July 22, 2023 52 minutes ago, BassmanPaul said: If the input jack is board mounted you could try reflowing the connections to that board. Could be your fiddling about inside the chassis has jolted a bad connection to working again. I understand. I did no fiddling though. I only removed the lid and took some photos. 1 Quote Link to comment Share on other sites More sharing options...
BassmanPaul Posted July 22, 2023 Share Posted July 22, 2023 16 minutes ago, dpaulb said: I understand. I did no fiddling though. I only removed the lid and took some photos. Maybe they were dirty photos!! LOL 1 Quote Link to comment Share on other sites More sharing options...
dpaulb Posted July 22, 2023 Author Share Posted July 22, 2023 1 hour ago, BassmanPaul said: Maybe they were dirty photos!! LOL Ha!!! Quote Link to comment Share on other sites More sharing options...
agedhorse Posted July 23, 2023 Share Posted July 23, 2023 (edited) After all the suggestions on TalkBass about "bad caps" being the cause (which for the most part is an absurd guess), it turns out that bad caps is unlikely the cause because bad caps don't "heal themselves", nor are they fixed by "ritualistic healing", or even burning at the stake. It may have been that the cause was unrelated to the amp itself, but was present at the input along with the signal. This is why we do troubleshooting rather than "guess-a-shooting". If the problem is gone (the noise floor of that amp wasn't particularly low to begin with), it may be best to leave well enough alone rather than create entirely new problems. If it ain't broke, don't break it... Edited July 23, 2023 by agedhorse 2 Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.