Hi there - I have been building a simple LM3875 based kit using an old EI transformer. The transformer has varios output points including three I am using for 24-0-24 output. When I wired it up to the rectifier board I got a decent 33.7 v output and everything seemed perfect.
However, I've added the two channels to the mix and soldered on the input sockets and now when I plug it in and switch on the transformer makes a ticking noise.
Can anyone tell me what this is? Is this the "hum" lots of other people have mentioned? Why didn't the transformer make this noise before?
Thanks for any tips.
However, I've added the two channels to the mix and soldered on the input sockets and now when I plug it in and switch on the transformer makes a ticking noise.
Can anyone tell me what this is? Is this the "hum" lots of other people have mentioned? Why didn't the transformer make this noise before?
Thanks for any tips.
lndm said:
Each "tick" is detectable and it's approx 120 bpm...
Moving the various bits and pieces around doesn't affect the sound.
Hmmm, odd. Could it be the xfmr rapidly heating and expanding?
Whether so or not, it may be best to sweep your circuit with your dmm. A long shot, sweep the circuit with a cro?
Whether so or not, it may be best to sweep your circuit with your dmm. A long shot, sweep the circuit with a cro?
I had a transformer make the same noises. It was melting (too much current draw). Is it getting hot to the touch?
Eeerrk!BrianDonegan said:
Not that I've noticed (I did try to see, but didn't want to leave it plugged in too long - no detectable heat for the 10 seconds or so I leave it on for).
As I said, it didn't make this sound before I wired up the actually amplifiers and the inputs. Is it worth me doing some tests with the ol multimeter?
Sorry - I'm fairly new - what sort of thing should I be checking? (and what do you mean by cro?).lndm said:
Thanks for helping me out.
Um. I mean an Oscilloscope (cathode ray oscilloscope). I figured you would first check that the circuit is performing as expected with your dmm. The oscilloscope could help track down an oscillation which may cause a large current draw. These can be hard to detect in other ways.
I'm guessing that the transformer is saturating during the short current pulses to charge the caps. It's possible that your amp is oscillating and drawing a lot of current even without an input signal and the transformer is just not up to the task. How big is it?
Garnett said:
The first time I read this as 120 bps (i.e. 120Hz.) I wondered how you could discerned 120 ticks per second... But, you really said something like 2 ticks per second. So can I change my guess? 😉
Ok, I don't have a real good guess. Might be picking up something external like a cell phone....
if u r using those 25A or 35A rectifier in a square can, that could be the problem. There seems to be alot of faulty ones everywhere in the market. I had them too...I remember the transformer giving out a buzz...think it was saturating!
Hi guys. Thanks for the replies. The rectifier board is one that came with the kit, and I'd be surprised if the fault lay there, simply because when I wired it to the transformer, everything worked fine and it gave exactly the output I expected.
The problem only began when I introduced the amp PCBs.
I am sure the problem is not external interference, since the ticking does not seem to fluate regardless of the position of any of the bits and pieces.
The problem must lie either in the amp PCBs or the input sockets I have connected. I think your suggestion about oscillation could well be right (or does the slower rate of "ticks" mean otherwise?).
Unfortunately I don't know how to check. My multimeter doesn't have an oscilloscope. Anyone got any ideas?
The problem only began when I introduced the amp PCBs.
I am sure the problem is not external interference, since the ticking does not seem to fluate regardless of the position of any of the bits and pieces.
The problem must lie either in the amp PCBs or the input sockets I have connected. I think your suggestion about oscillation could well be right (or does the slower rate of "ticks" mean otherwise?).
Unfortunately I don't know how to check. My multimeter doesn't have an oscilloscope. Anyone got any ideas?
My guess is that your amp is 'motorboating' - i.e. oscillating at a low frequency. What are the power / signal / output arrangements like? Are you sure that the PSU capacitors are correctly connected? Have you put an expendable speaker on the outputs, to see what's coming out (don't use a good driver at this stage though)?
Thanks dnsey and others.
I will try to check everything this weekend and report back when, doubtlessly, the results mean nothing to me 🙁
Dnsey, I'm pretty sure the capacitors are correctly connected. Wouldn't I have found out quite quickly when connecting the rectifier board to the transformer? The fact that the DC output voltages are as expected made me think this problem shouldn't be anywhere but on the amp boards or in the wiring between them, the PSU and the input and output sockets.
Am I missing something?
I will try to check everything this weekend and report back when, doubtlessly, the results mean nothing to me 🙁
Dnsey, I'm pretty sure the capacitors are correctly connected. Wouldn't I have found out quite quickly when connecting the rectifier board to the transformer? The fact that the DC output voltages are as expected made me think this problem shouldn't be anywhere but on the amp boards or in the wiring between them, the PSU and the input and output sockets.
Am I missing something?
I was just asking to make sure really. If one of the caps was disconnected or faulty, it might well give rise to motorboating, but might make little difference to the measured PSU output. Reversed electrolytics usually make themselves known quite clearly, but I've known them to continue functioning to some extent, but with reduced effect.
Have you tried smallish caps across the supply rails close to the amp chips to aid stability?
With your meter you should be able to check the input current by using the AC amperes setting on the meter and connecting across the fuse terminals with removal of fuse of course.
If the current is reasonable it may be loose core piece responding to the short peaks of current charge to the caps as was stated earlier.
You could also momnitor the DC current by putting meter in DC amperes mode and connectingon to the caps. this could be done on both legs to see if reasonable.
If there is no signal to amps there should be very little current draw in both cases (AC and DC).
If the current is reasonable it may be loose core piece responding to the short peaks of current charge to the caps as was stated earlier.
You could also momnitor the DC current by putting meter in DC amperes mode and connectingon to the caps. this could be done on both legs to see if reasonable.
If there is no signal to amps there should be very little current draw in both cases (AC and DC).
also you could short inputs on amp to make sure there is no signal, hence should not be using much current.
And when you are done checking current, don't forget to switch your probes back to the Voltage holes before checking voltages, and they act as a short in Current testing mode, and things get smokey. Not that I've ever done that... 😉
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