Genelec 1031A built 1996, low noise on right speaker

[el-folie]

Hi, I have these speakers since 1998, I´m second owner bought from a studio. The speakers never had a single problem since a few days ago when suddenly the right speaker developed a perceivable noise on the bass chassis, treble chassis is clean with the usual hiss. One can hear it with an ear close to the bass chassis and sometimes it gets louder so that one can hear it sitting like 1m away at listening position. As a general hint, these Genelecs are the completely discrete ones, large main board and several cards soldered onto it.

So far I did the following:
- resoldered/reflowed all Molex pins, PA driver board pins, big transistor/resistor pins
- exchanged the 22uf/100v electrolytics from bass and treble boards
- reconnected every possible connection a few times
- as described in the service manual proper calibrating of offset and bias.

Result:
The noise stays. Also, on the right speaker the faint 50Hz hum is a bit louder than on the left speaker. Funny thing: the noise even stays when muting the bass driver. But I guess that doesn´t mean much as the mute is in front of the PA driver board and the main bass amplifier.

Questions:
Can anyone confirm the low noise (slightly softly modulating/crackling) is normal for Genelec after 25 years in use? Or is it even so that after that much running time that noise would be normal to develop for any power amplifier due to aging components? If so, which components usually make for such a modulating kind of low noise? Like "chiauuuuuuchchchrrrrrrshhhhhhhhshhhhhjjjewwwwww" plus 50 Hz ontop of course. The noise sounds like crushing paper with a low pass filter on it and at still a low volume, not loud... The usual suspects would be all electrolytics of course, but they all measure ok, nothing leaking. Also all transistors measure out ok, no shorts. So, the tantals?

Would be grateful for any input from Genelec owners and amplifier repair men. Apart from the low noise the pair still plays absolutely fine.

 

[mrclunk]

Have you check the bias hasn’t drifted out of spec?
There’s a service manual on here somewhere.
I had a dead tant (c7?) in one of mine, it was buried in a very hot area of the power amp.

 

[el-folie]

Hi, thanks, yes offset/bias calibrated to spec as per service manual. Also checked c7 tantal, no short, measuring fine. (I read about c7 before so checked all that I could before posting here).

 

[fazer]

Does it make noise when the inputs Are unplugged? Have you shorted the input jacks to see if it still is noisy? I had problems with noise on my pair of 1031’s. It was due to a nosy muting transistor. Pretty easy to replace by cutting the transistor from top of PCB and solder to the legs of the removed transistor.

 

[el-folie]

Thanks, yes, noise stays witch input unplugged, also when muted by the DIP switch on the back of the pcb.

Edit: Oh, I see, you probably just meant that it´s easier to just cut the transistor legs and solder a new one to them, right? I´m generally ok with dis- and reassembling equipment, doesn´t bother me...

 

[el-folie]

Does it make noise when the inputs Are unplugged? Have you shorted the input jacks to see if it still is noisy? I had problems with noise on my pair of 1031’s. It was due to a nosy muting transistor. Pretty easy to replace by cutting the transistor from top of PCB and solder to the legs of the removed transistor.

And yes, noise stays with input pin 2 or 3 shorted to GND.

 

[el-folie]

I went through the schematics again. If I have it correctly, the mute circuit is connected to the EQ board, so that by shorting the input signal after the EQ board at the input of the PA driver board it should take the mute circuit and its components out of the equation. That way I could find out if the fault is before or after PA driver board and bass main amplifier circuit.

So, can I safely just ground pin 1/2 at the PA driver board witout destroying something? I mean there are even jumpers for those pins on the cards, amybe exactly for this purpose?

 

[fazer]

You would ground pin 2 and 3 together on the input xlr jack. This shorts the balance input. You do not connect it to pin 1. It’s common mode input. Balanced. Usually when you simple unplug the input from the speakers it should be quite. Just thinking the noise could be coming from your monitor out cable feeding the input.

You can have problems also with the speakers being plugged into one ac outlet and your Monitor controller and daw plugged into another outlet creating ground loops. I have a furman outlet power conditioner with my monitor controller, powered speakers, daw and interface all plugged in at one point.

The mute transistor created noise in one of my 1031’s one time and was replaced and the speakers worked correctly for me. This might be ok in yours.

You have already checked the ribbon cable which is one of the main problems that creates noise when the cinch plug on the main board becomes fatigued.
I like to check this with the speaker on and the back amp plate swung open. I then will play with the ribbon cable to get it into a contact where the balanced input is connecting and the buzz will go away and the audio feed will start to play correctly. It’s a little tricky

You may have something else going on that requires a bench tech to Diagnose. Power supply filter caps which have to much ripple comes to mind. You need a scope an look at the waveform amplitude/voltage and confirm it’s in spec.

 

[el-folie]

You would ground pin 2 and 3 together on the input xlr jack. This shorts the balance input. You do not connect it to pin 1. It’s common mode input. Balanced. Usually when you simple unplug the input from the speakers it should be quite. Just thinking the noise could be coming from your monitor out cable feeding the input.

You can have problems also with the speakers being plugged into one ac outlet and your Monitor controller and daw plugged into another outlet creating ground loops. I have a furman outlet power conditioner with my monitor controller, powered speakers, daw and interface all plugged in at one point.

The mute transistor created noise in one of my 1031’s one time and was replaced and the speakers worked correctly for me. This might be ok in yours.

You have already checked the ribbon cable which is one of the main problems that creates noise when the cinch plug on the main board becomes fatigued.
I like to check this with the speaker on and the back amp plate swung open. I then will play with the ribbon cable to get it into a contact where the balanced input is connecting and the buzz will go away and the audio feed will start to play correctly. It’s a little tricky

You may have something else going on that requires a bench tech to Diagnose. Power supply filter caps which have to much ripple comes to mind. You need a scope an look at the waveform amplitude/voltage and confirm it’s in spec.

Thanks for the thorough reply!

I also tried shorting pins two/three, it didn´t cure the noise. Though still, shorting the input signal at the PA driver card will be a good test to know if the cause is before or after that point. If before it could be the muting transistor, if after could be anything after 25 years of use.

I do have a scope to look for the noise - I just thouhgt to ask here first if someone had a similar problem before. I also still think the noise could be due to aging electrolytics throwing the regulators/offset/biasing off in a fluctuating way.

Anyhow, thanks for the input, if I find the cause I´ll post it here...

 

[Whoops]

Questions:
Can anyone confirm the low noise (slightly softly modulating/crackling) is normal for Genelec after 25 years in use?

No, it's not normal. I have my Genelecs 1031for the same amount of time and they are quiet.

What you should do after 25 years is to change all the Electrolytic capacitors and Tantalum capacitors.
Lytics are problematic in this speakes and the tamtaluns will fail short. Just replace all of them

Or is it even so that after that much running time that noise would be normal to develop for any power amplifier due to aging components?

No, not normal

If so, which components usually make for such a modulating kind of low noise? Like "chiauuuuuuchchchrrrrrrshhhhhhhhshhhhhjjjewwwwww" plus 50 Hz ontop of course. The noise sounds like crushing paper with a low pass filter on it and at still a low volume, not loud...

Record the noise and show us, if we have a listen it will be easier to understand what type of noise it is.

The usual suspects would be all electrolytics of course, but they all measure ok, nothing leaking. Also all transistors measure out ok, no shorts. So, the tantals?

Doesn't matter replace all Lytics and Tantalums, it's cheap, easy and better safe than sorry. 25 years it's a long time for Electrolytic capacitors

 

[el-folie]

No, it's not normal. I have my Genelecs 1031for the same amount of time and they are quiet.

What you should do after 25 years is to change all the Electrolytic capacitors and Tantalum capacitors.
Lytics are problematic in this speakes and the tamtaluns will fail short. Just replace all of them



No, not normal



Record the noise and show us, if we have a listen it will be easier to understand what type of noise it is.



Doesn't matter replace all Lytics and Tantalums, it's cheap, easy and better safe than sorry. 25 years it's a long time for Electrolytic capacitors

Thanks a lot! Will renew all caps anyway in the end. I justthought the noise was common and wanted to search for its origin. Anyway - will do a recording of the noise, it´s still quite low in volume though. I´ll record L and R speakers for comparison...

 

[el-folie]

No, it's not normal. I have my Genelecs 1031for the same amount of time and they are quiet.

What you should do after 25 years is to change all the Electrolytic capacitors and Tantalum capacitors.
Lytics are problematic in this speakes and the tamtaluns will fail short. Just replace all of them



No, not normal



Record the noise and show us, if we have a listen it will be easier to understand what type of noise it is.



Doesn't matter replace all Lytics and Tantalums, it's cheap, easy and better safe than sorry. 25 years it's a long time for Electrolytic capacitors

Here are two recordings. Both hand-held with a TLM103, so any low rumble is my hand muscles moving and ambience noise in the house. The crunchy noise from the right bass cone can become double in volume sometimes after being powered on for some hours, this was just a short test right after switching on. So, does this noise sound familiar? Maybe really just dying main filter caps, the big 10000µF ones?

 

[SIXTYNINER]

Here are two recordings. Both hand-held with a TLM103, so any low rumble is my hand muscles moving and ambience noise in the house. The crunchy noise from the right bass cone can become double in volume sometimes after being powered on for some hours, this was just a short test right after switching on. So, does this noise sound familiar? Maybe really just dying main filter caps, the big 10000µF ones?

Hello el-folie
interested about the 2 attached files
that unfortunately give me error
when click on for open/download them
any chance for a working link ?
cheers