Tick, tick tick…sound

Hi:


My Krell FPB-400cx amplifier developed a strange problem, please help me diagnose it.


One day, between the songs, I felt there was metronome like tick, tick tick… sound coming off the loudspeakers. The interval of ticks was twice per second from right channel and once per second from left channel and it was of very low volume. I started disconnecting the equipment and ended with amplifier plugged to wall and loudspeakers plugged to amplifier and nothing else. The continuous tick, tick tick… sound was still there. I shutdown the amplifier, unplugged it from wall and after two days of rest when connected just the loudspeakers to amplifier, the tick, tick tick… sound was still there.


I sent the amplifier to Krell and after through checkup and extensive testing they have failed to reproduced the problem and emailed me that the unit is performing up to factory standards.


I am confused and uncertain as shipping costs a lot and I don’t want the strange problem back.

Can anybody help me in this regard?
 
Yeah, I've seen that very problem with a self-designed solid state amp. A quiet "tick, tick, tick". I traced it to an RF oscillation, as the amp was making like a QRP rig, putting out a 3.54MHz sine wave. It was about 1.0Vp-p, not much, and not enough to fry the finals. However, that ticking sound was definitely a side effect.

Fixed that RF oscillation by readjusting the Cdom, and it went away.
 
Maybe you have an appliance in your house that is putting out interference, either conducted or radiated.

Hi:

I already did that before sending the amplifier for repair and I am sure that something within the amplifier was wrong.
Here is what I think. Krell took some time to put my amplifier on test bench. I think perhaps things have reset within amplifier or it has some oscillation that starts due to continuous use of amplifying music, heat…etc.
I am looking at more technical inputs so I can ask them to take another look at this or that before they send it back. Any more help..?
 
Hi:


My Krell FPB-400cx amplifier developed a strange problem, please help me diagnose it.


One day, between the songs, I felt there was metronome like tick, tick tick… sound coming off the loudspeakers.Can anybody help me in this regard?

I always put a low value capacitor across the input to my amps to filter out RF.

It really depends on where the HF is coming from. It could be too much gain in the amp. I have found that filtering the VAS is vital for a stable amp. I usually use a 220pf in the VAS.
 

Ian Finch

Member
Paid Member
2010-04-11 4:22 am
Coffs Harbour, NSW
No comments on how there could be different but apparently related frequency pulses in either channel? I would think that says the source of the pulses is different or just interacts differently with either channel and therefore it's likely generated internally.

There has to be a microprocessor and associated monitoring circuits inside that monster which would be the first suspects I'd consider looking at for erratic behaviour, using a 'scope to analyse the waveforms. If you can hear a sound, you can see and characterise it too, given suitable instruments.