Buzzing Transformer in Amp

HaMMuS

HaMMuS

HaMMuS

Associate
Joined
11 Jul 2003
Posts
386
Location
Newcastle Upon Tyne, UK
Hi all,

I have a set of Videologic Digitheatre DTS speakers, which have the amp integrated into the sub. Recently a transformer in the sub has started to make quite a loud buzzing noise which is starting to get distracting.
My question is: would it be possible to replace the offending hardware?

There seem to be two transformers in the sub, a larger one and a smaller one, I think its the larger one that's making the noise, but i may just replace both if possible. How do i go about finding a model number or something to I.D them? I'm pretty experienced with soldering so that aspect shouldn't be a problem.

Many Thanks

Mikey
 
You can get toroid transformers which tend to cause less hum, but you need to get the correct voltage and VA rating. A good one can be up to £50. I have no clue how much you payed for your Videologic Digitheatre DTS speakers. If they were £300 then it's worth repairing them, is they were £30 it's probably not.... ;)

EDIT: Do you have a multimeter?
 
they were around £200-£300 i cant remember exactly, either way i would like to repair them. I have a multimeter what do you need me to test?
 
Sound like they are a half decent setup, I'd probably repair them if I were you. Just remember you'll be close to mains voltages so be very careful.

Basically you need to find the output voltage of each transformer on the secondary windings. Do you have any pics of the wires that go from the transformers to the PCB's and I should be able to tell you what wires to measure.

Each transformer should have at least 3 wires going from the transformer to the PCB's.

Also, if you could also get pics of any large capacitors that are are on the PCB's, as these are used for smoothing and can also cause humming if they are old or leaking...

Finally, does the buzzing sound like 50Hz?
 
buzzing sounds like its at 50hz, just played a 50hz sine signal and they were the same pitch, will try n get pics asap
 
 
Right, if the sound is 50Hz then there's definately a problem with the PSU part of the circuit.
HaMMuS said:
Both transformers: Caps Closeup: http://img249.imageshack.us/img249/696/dsc00723sk2.jpg
Something could be up with the cap on the left in the final pic?

Let me know if you need more detailed pics of anything
Click to expand...
The caps should not be swollen at all, the tops should be flat. Also, that brown gunk on the top of the left looks like electrolyte (the stuff that's in the caps), so I would say you've got at least 1 leaky cap.

In old PA and hifi amps the caps are the first thing to go, they go bad with age basically. The branded ones tend to last a little better but they still go. I haven't heard of C.Y.E. so I would change the caps first.

If this doesn't fix it then you can replace the transformers, but I think you would have to try and source the same ones with the same fittings which won't be easy... You could use other transformers but you'd have to improvise when you mount them as you have limited space...

I can see that it says 5200uF 35v on the largest caps, so when ordering replacements, make sure they match or exceed these numbers. If you order 6000uF 50V it will work fine, but you also need to make sure the replacement caps will fit in the PCB...

I can't see what it says on the smaller caps, but the same thing applies, if it says 3300uF 25V then when getting replacements try and match these values.

If you want to know the theory behind linear PSU's, just google "full wave bridge recifier".
 
You must log in or register to reply here.
Back
Top Bottom