Hello.....
Just wondering, what actual component in a preamp can cause loud crackling feedback on speakers?
It's not the power amp at fault as it's been tested with another preamp and all is fine...
Just wondering, what actual component in a preamp can cause loud crackling feedback on speakers?
It's not the power amp at fault as it's been tested with another preamp and all is fine...
I tried that, but the speakers are fine working with the other preamp, so I used a 2nd pair of speakers to double make sure, and the same thing, speakers are fine, no crackling using another preamp, and, I did test the speakers by doing what you said, it made no difference, my guess is, maybe a cap has gone bad, like, the KEF subwoofers, crackle loud and buzz when a certain cap goes bad, I'm hoping it's the same theory...
Yeap, I tested the mains supply to see what type of voltages were coming in and that is all ok, I also tested the mains transformer inside the preamp, all again again. I know I'll have to end up removing caps but it is a pain in the butt!!! can't test them in circuit...
Failing transistors can be a cause of noises/crackles too. Have you looked for more obvious things like dry joints ? If its a cap then I would be looking at small ceramic or tantalum types first.
Hi Mooly, I haven't removed the main circuit board yet, been to busy, but will get on it today. The Preamp is around 14 years old almost, but, very good components were used as it was around 2k when it was new... I'll check caps and transistors today, what main points would I check caps? On output stages? Funny thing is, there is NO!!! crackling when I use the digital optical input, it only crackles when I'm using the phono stage inputs.
The company that make it was Ditton, a English company, but they went broke if I remember, sold stock and the name to some company in China... So it's non existent to find a service manual or even the owners manual online...
It sounds a bit different to the type of preamp I was imagining tbh.
As its much more modern then prime suspects could be SMD (surface mount) caps that have leaked. You need to have a good visual look at it all first. If its just the phono stage crackling (so line level OK ?) then it should be an easy fix to identify the phono section and repair/replace components as required.
As its much more modern then prime suspects could be SMD (surface mount) caps that have leaked. You need to have a good visual look at it all first. If its just the phono stage crackling (so line level OK ?) then it should be an easy fix to identify the phono section and repair/replace components as required.
If you need a hand let me know. I'm fairly good at debugging. My phono stage had a problem where the left channel only worked when you had a DMM on to measure the supply voltage! If you can take a picture to post that would be helpful.
Can I just double check. Is it both channels or just one?
Can I just double check. Is it both channels or just one?
Hi bill, it's both channels, and actually, I only tried the digital out once, when no sound as I heard the speaker hum, so I presumed it was working, I double checked but nothing is coming out of it while music is playing, music (in optical input) it does play music in all the phono stages even while it is crackling loud...
I'll take a few pics of it and underneath the main power supply board...
I'll take a few pics of it and underneath the main power supply board...
You'll need to scope it, there's no other way to know where it's exactly coming from, anything else is just guessing.
By the thread title the classic culprit is frayed tinsel wires in the speaker, with sparking wire ends brushing each other.
So much so that in the dark you can see the tiny blue sparks, go figure 😱 .
But if speaker works well with other amps or even other inputs, it's in the preamp/input connectors/pickup cable/pickup itself.
Probably some type of corrosion creating a poor contact.
But only scoping will pinpoint it.
By the thread title the classic culprit is frayed tinsel wires in the speaker, with sparking wire ends brushing each other.
So much so that in the dark you can see the tiny blue sparks, go figure 😱 .
But if speaker works well with other amps or even other inputs, it's in the preamp/input connectors/pickup cable/pickup itself.
Probably some type of corrosion creating a poor contact.
But only scoping will pinpoint it.
The burn doesn't necessarily indicate a problem but it is a sign of things running hot and hot parts can fail.
I would suggest you carefully measure the voltage output of those regulators (on the heatsinks) and see if the voltages you get seem reasonable. You need to be careful measuring and one slip with the meter leads could be disastrous. So be careful.
Although we don't know what the voltages are we can still check if there is output and whether it is reasonable. See what the devices are, for example 7812 or LM317 etc etc and determine what the expected voltage for each would be. There doesn't look enough extra parts for the regulators to be discrete.
I would suggest you carefully measure the voltage output of those regulators (on the heatsinks) and see if the voltages you get seem reasonable. You need to be careful measuring and one slip with the meter leads could be disastrous. So be careful.
Although we don't know what the voltages are we can still check if there is output and whether it is reasonable. See what the devices are, for example 7812 or LM317 etc etc and determine what the expected voltage for each would be. There doesn't look enough extra parts for the regulators to be discrete.
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