Hi Guys,
I powered up my TWExpress this evening,
First thing I notice is the Power trans is humming, and its a mechanical hum, also the hum comes through the speakers. It was there before the tubes went in.
Regardless, I went ahead and measured voltages and set the bias at 41mv. They all seem to be within a few volts of recommended.
As it is after midnight here in Australia, I didnt plug my guitar in but there is hiss coming from the speakers .
If I can get rid of the hum, It will be very quiet.
Any thoughts, ideas as to the problem.
Regards Peter
Mechanical Hum
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WhopperPlate
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Re: Mechanical Hum
Easiest thing to suggest is to quadruple check all wiring for errors and continuity on all connections. Definitely sounds like a power supply issue if it hums with no tubes.
Pictures are always helpful.
Pictures are always helpful.
Charlie
Re: Mechanical Hum
If it hums with no power tubes then it's magnetic coupling between the PT and OT most likely.
Ken didn't put the transformers round the best way on the chassis and they're closer than they should be too, so it's always a challenge.
Ken didn't put the transformers round the best way on the chassis and they're closer than they should be too, so it's always a challenge.
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WhopperPlate
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Re: Mechanical Hum
could it be the dreaded lamination rattle?
Re: Mechanical Hum
Here are a few pics
Peter
Peter
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Re: Mechanical Hum
A simple check to perhaps eliminate the xformer locations as the cause, is to get a sheet of aluminum or steel, ground it then place it between the trannys. But I've never had a transformer that had internal audible hum, that just sound wrong.
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RJ Guitars
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Re: Mechanical Hum
Only time I've run across this was with a steel chassis and the power tranny was coupling to it extremely well... inspired me to start over with an aluminum chassis.
I agree with Ampdoc's method of sorting out what it might or might not be. I also agree with Paulster that the close proximity of these transformers is not ideal. However, there are plenty of wrecks on both sides of the pond that have steered past the proximity location hurdle.
If the aluminum shield silences the hum then it would indicate that the output tranny was magnetically coupling to the power tranny. You might solve that by shifting the locations of one or both transformers on the mounting slots - unless you like the idea of an aluminum fence between the transformers. That seems odd that you would have the only one out of hundreds that needs that extreme of a fix though.
I am quite curious to learn from this if you don't mind sharing the progress reports.
rj
I agree with Ampdoc's method of sorting out what it might or might not be. I also agree with Paulster that the close proximity of these transformers is not ideal. However, there are plenty of wrecks on both sides of the pond that have steered past the proximity location hurdle.
If the aluminum shield silences the hum then it would indicate that the output tranny was magnetically coupling to the power tranny. You might solve that by shifting the locations of one or both transformers on the mounting slots - unless you like the idea of an aluminum fence between the transformers. That seems odd that you would have the only one out of hundreds that needs that extreme of a fix though.
I am quite curious to learn from this if you don't mind sharing the progress reports.
rj
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Re: Mechanical Hum
Ok, tried the sheild, didnt work,
Also noticed when Its out of standby, the hum is louder and seems to climb with the volume, another thing is all the pots are very scratchy when turned.
Peter
Also noticed when Its out of standby, the hum is louder and seems to climb with the volume, another thing is all the pots are very scratchy when turned.
Peter
Re: Mechanical Hum
I susspected my multi meter to have flat batteries so i replaced them and had another look at the voltages, my power trans is set for 240v
I recently found out that the nominal voltage in my area is 230v
my voltages at the power supply for example 415 is concidered to be the right voltage ( pin3 EL34) and found them to be about 380v meaning all the voltages are quite lower than specified, is this a problem.
Peter
I recently found out that the nominal voltage in my area is 230v
my voltages at the power supply for example 415 is concidered to be the right voltage ( pin3 EL34) and found them to be about 380v meaning all the voltages are quite lower than specified, is this a problem.
Peter
Re: Mechanical Hum
Interesting problem. I had a Tiny Terror come across my bench that had suddenly developed really bad 120Hz hum. It hummed even without the power tubes. In this case, with the power tubes pulled, the only electrical connection to the OT is the center tap. So this means that either a. the noise is coupled to the OT magnetically, or, b. the OT is blown, and there's now an electrical connection between the primary, which is connected to the least filtered node of the power supply, and the secondary, which is passing that 120Hz hum to the speaker.
In the case of the Tiny Terror, the OT was blown. Yours may be, too, which would be very sad, it being brand new. I hope it's magnetic coupling. So try this: with the power tubes pulled, disconnect the center tap. If you hear no noise in the speaker, double check with headphones. If you still hear no noise in the headphones, I'd suspect the OT as bad. You could check continuity between primary and secondary with a meter.
Also, if you've got scratchy pots, you've got DC on them. This means bad coupling caps.
I have had PTs vibrate, but they generally didn't cause noise issues.
In the case of the Tiny Terror, the OT was blown. Yours may be, too, which would be very sad, it being brand new. I hope it's magnetic coupling. So try this: with the power tubes pulled, disconnect the center tap. If you hear no noise in the speaker, double check with headphones. If you still hear no noise in the headphones, I'd suspect the OT as bad. You could check continuity between primary and secondary with a meter.
Also, if you've got scratchy pots, you've got DC on them. This means bad coupling caps.
I have had PTs vibrate, but they generally didn't cause noise issues.
Rich Gordon
www.myspace.com/bigboyamplifiers
"The takers get the honey, the givers get the blues." --Robin Trower
www.myspace.com/bigboyamplifiers
"The takers get the honey, the givers get the blues." --Robin Trower
Re: Mechanical Hum
Never came across a new transformer that made the mechanical hum noise, but i guess it could happen.
I would remove any voltage to the PT, except the AC coming in, turn on the amp, and see if it still has the vibrating noise, if so, you most likely have a bad PT. If you put your hand on the PT you can feel the mecanical vibrations. When some of these are not too bad, you can try tightening the bolts, and things like that,but when you get one that is excesive, their is nothing i know of that can cure that but a new PT.
Things that can cause the PT to have similar problems, is usually something miswired, or bad componet, putting stress on the PT but the amp will usually blow a fuse. If you disconnect all but the incoming AC, and the PT still has the problem, that will tell you the PT itself has a problem. If it stops making the vibration and hum, then something after is causing the PT to have the problem. Work in sections.
And usually if not using tubes in the amp, i like to use a lower rated fuse, so if their is a problem, the lower rated fuse will blow much quicker.
One of the worst types of these problems i came across,was a new reisue vox AC-15, the PT in that amp, vibrated so bad, it sounded like you was running a vacuum cleaner.. and same thing as yours, the chassis vibrated, and picked up the noise,and carried through the amp.
A new PT and the amp was quiet again.. no buzz,hum or rattles..
I would remove any voltage to the PT, except the AC coming in, turn on the amp, and see if it still has the vibrating noise, if so, you most likely have a bad PT. If you put your hand on the PT you can feel the mecanical vibrations. When some of these are not too bad, you can try tightening the bolts, and things like that,but when you get one that is excesive, their is nothing i know of that can cure that but a new PT.
Things that can cause the PT to have similar problems, is usually something miswired, or bad componet, putting stress on the PT but the amp will usually blow a fuse. If you disconnect all but the incoming AC, and the PT still has the problem, that will tell you the PT itself has a problem. If it stops making the vibration and hum, then something after is causing the PT to have the problem. Work in sections.
And usually if not using tubes in the amp, i like to use a lower rated fuse, so if their is a problem, the lower rated fuse will blow much quicker.
One of the worst types of these problems i came across,was a new reisue vox AC-15, the PT in that amp, vibrated so bad, it sounded like you was running a vacuum cleaner.. and same thing as yours, the chassis vibrated, and picked up the noise,and carried through the amp.
A new PT and the amp was quiet again.. no buzz,hum or rattles..
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RJ Guitars
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Re: Mechanical Hum
I like what Richie is suggesting. If you disconnect and insulate every wire on the PT except the AC input and it still hums, you have isolated the problem so that it can only be in the power transformer.
You mentioned something about the standby switch and the hum climbing with the volume control. This is telling us something but I'd run Richies test first because it protects your other components from risk of damage or at least further damage.
Here is something else to check. If I recall correctly this is one of those multi-tap Euro voltage transformers. If you haven't already done this, make sure every one of those alternate voltage leads are isolated and insulated from each other. Those taps will all have voltage on them and they can't touch each other or go to ground... in case you didn't already know that. Most folks trim them off and insulate the ends, but however you have done things make sure they aren't causing you this grief. If you haven't trimmed them off and you have all of them coiled in loops it might do some weird stuff but I wouldn't have expected a major problem if the ends are insulated.
http://www.rjguitars.net/Digital_Images/HTS-5199EX.jpg
At any rate, give us an update after you look into these things.
rj
You mentioned something about the standby switch and the hum climbing with the volume control. This is telling us something but I'd run Richies test first because it protects your other components from risk of damage or at least further damage.
Here is something else to check. If I recall correctly this is one of those multi-tap Euro voltage transformers. If you haven't already done this, make sure every one of those alternate voltage leads are isolated and insulated from each other. Those taps will all have voltage on them and they can't touch each other or go to ground... in case you didn't already know that. Most folks trim them off and insulate the ends, but however you have done things make sure they aren't causing you this grief. If you haven't trimmed them off and you have all of them coiled in loops it might do some weird stuff but I wouldn't have expected a major problem if the ends are insulated.
http://www.rjguitars.net/Digital_Images/HTS-5199EX.jpg
At any rate, give us an update after you look into these things.
rj
Good, Fast, or Cheap -- Pick two...
http://www.rjguitars.net
http://www.rjaudioresearch.com/
http://diyguitaramps.prophpbb.com/
http://www.rjguitars.net
http://www.rjaudioresearch.com/
http://diyguitaramps.prophpbb.com/
Re: Mechanical Hum
Hi Guys,
I followed the info Richie and RJ have given me and sure enough the mechanical hum is still there. RJ is currently organizing a new PT for me. I will keep you guys informed when I install the new PT and double check the other components, If anyone has any more advice , please let me know.
Regards Peter
I followed the info Richie and RJ have given me and sure enough the mechanical hum is still there. RJ is currently organizing a new PT for me. I will keep you guys informed when I install the new PT and double check the other components, If anyone has any more advice , please let me know.
Regards Peter