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[Pitchfork]

...soldered a chip in the wrong way round

I feel such a pillock, but in my defence, it was artificial light, and the writing was small  

Just got it - you are AKA 'King Midas'
Must be a reference to the Hollies 'King Midas in reverse' hence that's why you soldered it on backwards!!!

BTW what causes a mains transformer to buzz loudly (both with & without a load) and also stick  50Hz hum on the output of an amp??
Any ideas anyone?

[TheBoy]

...soldered a chip in the wrong way round

I feel such a pillock, but in my defence, it was artificial light, and the writing was small  

Just got it - you are AKA 'King Midas'
Must be a reference to the Hollies 'King Midas in reverse' hence that's why you soldered it on backwards!!!

BTW what causes a mains transformer to buzz loudly (both with & without a load) and also stick  50Hz hum on the output of an amp??
Any ideas anyone?

Cheap transformers.  Can put out the electrical noise either due to insufficent shielding or insufficient smoothing.

Those cleverer than me will go in to details...

[Kevin Wood]

...soldered a chip in the wrong way round

I feel such a pillock, but in my defence, it was artificial light, and the writing was small  

Just got it - you are AKA 'King Midas'
Must be a reference to the Hollies 'King Midas in reverse' hence that's why you soldered it on backwards!!!

BTW what causes a mains transformer to buzz loudly (both with & without a load) and also stick  50Hz hum on the output of an amp??
Any ideas anyone?

Does the transformer buzz when the secondaries are disconnected and it's just powered up from the mains?

I'd hazard a guess at a failing reservoir cap or rectifier. Could be something further into the circuit overloading the DC rails and causing excess ripple on the supply.

Alternatively, if it's the transformer on its' own could be the chassis is loose around it and vibrating or the transformer needs a soak in varnish, or has a shorted turn and is fubar. Feel free to bring it over if you like. My window cleaner spotted the array of elecronic test gear in my bedroom when I was about 16 and started dropping off his valve amps for repair.  

Kevin

[Debs.]

....and also stick  50Hz hum on the output of an amp?....

'Earth loops' can do a good job of that too.  

[Entwood]

...soldered a chip in the wrong way round

I feel such a pillock, but in my defence, it was artificial light, and the writing was small  

http://www.specsavers.co.uk/cgi-bin/strudwick.sh/s?langid=1&pfmt=1&siteid=39&pname=glasses.html

[Pitchfork]

...soldered a chip in the wrong way round

I feel such a pillock, but in my defence, it was artificial light, and the writing was small  

Just got it - you are AKA 'King Midas'
Must be a reference to the Hollies 'King Midas in reverse' hence that's why you soldered it on backwards!!!

BTW what causes a mains transformer to buzz loudly (both with & without a load) and also stick  50Hz hum on the output of an amp??
Any ideas anyone?

Does the transformer buzz when the secondaries are disconnected and it's just powered up from the mains?

I'd hazard a guess at a failing reservoir cap or rectifier. Could be something further into the circuit overloading the DC rails and causing excess ripple on the supply.

Alternatively, if it's the transformer on its' own could be the chassis is loose around it and vibrating or the transformer needs a soak in varnish, or has a shorted turn and is fubar. Feel free to bring it over if you like. My window cleaner spotted the array of elecronic test gear in my bedroom when I was about 16 and started dropping off his valve amps for repair.  

Kevin

It buzzes when open circuit (no rectifier or caps connected) & in-circuit too
Nothing wrong electrically correct o/p voltages (centre tapped secondary)
It's well bolted to the case but the level of buzz changes when the cables in/out are 'wiggled' so it must be a mechanical problem
The laminations are bolted up tight, it's a shrouded transformer in a Peavey solid state mixer-amp
My guess is that it has had a knock at some point & the laminations are off-centre, unfortunately it's a US build amp!
Ian

[Pitchfork]

....and also stick  50Hz hum on the output of an amp?....

'Earth loops' can do a good job of that too.  

It's stand alone so no earth-loops (I know all about those  how to avoid them when on stage with a 5KW PA rig etc)

[Debs.]

It's stand alone so no earth-loops (I know all about those  how to avoid them when on stage with a 5KW PA rig etc)

No offence meant!   `Twas just a thought.    

[Kevin Wood]

If the buzz is present on the output as well there must be something funny going on though.  :-/ Maybe an internal insulation problem.

Are the outputs relatively common voltages? I might be inclined to change it for a decent toroidal transformer if so.

Kevin

[Ken T]

Hot Air, makes it sooo easy to get the little b*gg*rs off, you can even solder them back on using it, if you are lucky and don't blow them off the PCB. You can use a hot air Paint stripper, a bit vicious but will work.

Ken

Bl00dy-Hell A paint stripper!
Surely this cooks everything around the device & even burns the pcb?

Not if you are fast enough. Its a balancing act. Proper Tin-Lead solder melts at 183deg., fibreglass PCB start to decompose at about 150deg. But if you are quick enough, you can solder the joint before significant heat enters the pcb. That BGA fitting course I was on, you can only cook the BGA at 235deg for about 5 secs.  I used to use a paint stripper to get lots of IC's off boards. You used to pick up scrap boards for not a lot, warm them up and shake downwards, and all the IC's would come flying off. So much quicker than desoldering each pin one at a time. Only problem was as well as the IC's, the solder would come off as well, and molten solder sticks to carpet and wouldn't come off.

Ken

[Ken T]

...soldered a chip in the wrong way round

I feel such a pillock, but in my defence, it was artificial light, and the writing was small  

Just got it - you are AKA 'King Midas'
Must be a reference to the Hollies 'King Midas in reverse' hence that's why you soldered it on backwards!!!

BTW what causes a mains transformer to buzz loudly (both with & without a load) and also stick  50Hz hum on the output of an amp??
Any ideas anyone?

Does the transformer buzz when the secondaries are disconnected and it's just powered up from the mains?

I'd hazard a guess at a failing reservoir cap or rectifier. Could be something further into the circuit overloading the DC rails and causing excess ripple on the supply.

Alternatively, if it's the transformer on its' own could be the chassis is loose around it and vibrating or the transformer needs a soak in varnish, or has a shorted turn and is fubar. Feel free to bring it over if you like. My window cleaner spotted the array of elecronic test gear in my bedroom when I was about 16 and started dropping off his valve amps for repair.  

Kevin

It buzzes when open circuit (no rectifier or caps connected) & in-circuit too
Nothing wrong electrically correct o/p voltages (centre tapped secondary)
It's well bolted to the case but the level of buzz changes when the cables in/out are 'wiggled' so it must be a mechanical problem
The laminations are bolted up tight, it's a shrouded transformer in a Peavey solid state mixer-amp
My guess is that it has had a knock at some point & the laminations are off-centre, unfortunately it's a US build amp!
Ian

 I think you are right about the knock. It should only buzz if the laminations are loose, or if there's a shorted turn that might start upsetting things. This might also unbalance the outputs, putting a lower voltage on one side, thus upsetting the amp balance, hence the buzz. I was once given a Fenton Weill amp that buzzed. After much fiddling about, I eventually discovered that it was just the transformer hadn't been earthed !. Oh well, can't complain, got a free valve amp from this!

Ken