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Help! - Bizzare issue with K&H 0300 and Crane Song Avocet

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Help! - Bizzare issue with K&H 0300 and Crane Song Avocet

Postby themarqueeyears » Sat Oct 31, 2020 11:44 pm

My left K&H 0300 connected to my Crane Song Avocet makes a loud clicking noise and sometimes a big kinda electronic woosh sound!

I've tested all the outputs with my right 0300 and it's definitely not an issue with the Avocet as the right 0300 is perfect.

The left (seemingly faulty) 0300 works perfectly being switched by my Mackie Big Knob.

But if I connect it to any of the three Avocet speakers outs (left or right) then there's a loud click or occasionally woosh when muting or changing speakers outputs.

I've double checked and the issue isn't the Avocet.

What could if failed in my left 0300 that would cause it to not work correctly with a relay switched monitoring controller like the Avocet but work perfectly with a manually switched controller like the Mackie Big Knob?

I've tried de racking the Avocet, different mains leads, different line leads - nothing improves the situation. (I'm certain the Avocet is functioning perfectly -as it works perfectly with all my other monitors including my right 0300!)

It has me absolutely baffled.

Any theories?
Anybody .... help!!

Thanks
tmy
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Re: Help! - Bizzare issue with K&H 0300 and Crane Song Avocet

Postby Hugh Robjohns » Sun Nov 01, 2020 12:05 am

When I hear weird clicks the first thing I check is the balanced signal cables, and particularly the continuity of the screen. I'd also check the grounding of the speaker via the mains cable and wall socket.

But if after checking all that the concern is towards a faulty speaker, my first guess would be a failed input blocking capacitor on the O300 or maybe an RFI filter problem. It's possible that its reacting to changing DC conditions on the Avocet output.
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Re: Help! - Bizzare issue with K&H 0300 and Crane Song Avocet

Postby themarqueeyears » Sun Nov 01, 2020 12:39 am

Hugh Robjohns wrote:When I hear weird clicks the first thing I check is the balanced signal cables, and particularly the continuity of the screen. I'd also check the grounding of the speaker via the mains cable and wall socket.

But if after checking all that the concern is towards a faulty speaker, my first guess would be a failed input blocking capacitor on the O300 or maybe an RFI filter problem. It's possible that its reacting to changing DC conditions on the Avocet output.

Hi Hugh,

Thanks for your reply, I was hoping you might see the question and bring your expertise to offer some ideas.

I've tried de racking the Avocet and plugging in only the left 0300 into one output of the Avocet and nothing else plugged into the Avocet and switched mains cables and line cables and tested the line cables with a cable tester.

The issue is definitely the speaker, I had wondered if there was some DC issue with the Avocet switching as opposed to the Mackie Big Knob (with which the left 0300 works perfectly)

Your reply makes me feel you're probably right here - with the greater question being will Sennhiser be able to fix a now discontinued monitor?

Perhaps a qualified tech can do it?
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Re: Help! - Bizzare issue with K&H 0300 and Crane Song Avocet

Postby Hugh Robjohns » Sun Nov 01, 2020 9:55 am

I'd certainly contact Sennheiser as a first step... but a skilled tech should be able to track the problem down and sort it.
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Re: Help! - Bizzare issue with K&H 0300 and Crane Song Avocet

Postby themarqueeyears » Wed Nov 04, 2020 2:00 pm

Hugh Robjohns wrote:I'd certainly contact Sennheiser as a first step... but a skilled tech should be able to track the problem down and sort it.

Hi Hugh,

I contacted Sennheiser, unfortunately they don't do SMC repair on the main board inside the 0300 and as an entire new amp board costs £1000 plus fitting they suggested going for a new pair of 0310A's which unfortunately I can't afford at the moment.

So I had a good friend (who's a very experienced tech) have a look and there's a SMC resistor burnt out on the 0300 amp board at the XLR input acting as a link to ground.

He tested the Avocet outputs and confirmed as you mentioned a tiny DC off set when muting or switching speakers (I presume this is normal and the Avocet isn't broken!!)

He agreed this failed resistor means without any DC block it could be causing the click, he also inserted an isolating transformer in line between the Avocet and 0300 XLR input and the click was virtually silent - so everything point towards your diagnosis.

The only odd thing Sennheiser said was, if the back is taken off the 0300 the whole speaker needs re-calibrating. I can imagine this is true if a speaker cone is replaced or an amp module but just opening the back up - mmmh. I didn't here any phisssh sound like it was sealed and under pressure.

Well hopefully after it's had this tiny grounding resistor replaced the clicking issue will be gone and the speaker isn't suddenly un-calibrated :shocked:

Thanks for your input.
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Re: Help! - Bizzare issue with K&H 0300 and Crane Song Avocet

Postby Hugh Robjohns » Wed Nov 04, 2020 3:40 pm

Sounds like you've found a great tech there, and I'm glad he was able to track down the problem. I'm a little disturbed at the idea of a grounding resistor being 'burned out' though as I'm struggling to imagine what would have caused that...

I wouldn't worry too much about the re-calibration thing. As you say, repairs to the amps or replacement speakers would require recalibration, but not a repaired input grounding resistor.
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Re: Help! - Bizzare issue with K&H 0300 and Crane Song Avocet

Postby themarqueeyears » Wed Nov 04, 2020 4:29 pm

Hugh Robjohns wrote:Sounds like you've found a great tech there, and I'm glad he was able to track down the problem. I'm a little disturbed at the idea of a grounding resistor being 'burned out' though as I'm struggling to imagine what would have caused that...

I wouldn't worry too much about the re-calibration thing. As you say, repairs to the amps or replacement speakers would require recalibration, but not a repaired input grounding resistor.

Yes, my tech friend echoed that thought too, he was also concerned about what might have caused the grounding resistor to fail, especially as my 0300's have essentially never been moved in the 12 years I've had them and always been plugged into my Avocet.

I'm pleased to hear you think I'll OK on the calibration issue - that's good to hear.

Thanks again for your help and thoughts - it's much appreciated.
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Re: Help! - Bizzare issue with K&H 0300 and Crane Song Avocet

Postby Hugh Robjohns » Wed Nov 04, 2020 5:31 pm

I imagine the most likely causes are either unwanted sustained DC from connected source equipment, or instantaneous high voltage surges in the ground such as during a nearby lightening strike.

Most equipment includes DC-blocking capacitors on outputs, but the golden eared prefer to omit them as they introduce unwanted phase shifts and (potentially) distortion... although I can't say it's ever bothered me! I believe the Avocet is DC-coupled...

Connecting the speakers via isolating transformers will obviously protect the speaker inputs from any stray DC... but if there is any DC on the source output that could act to saturate/magnetise the transformer, and the transformer itself could, if low quality, introduce its own phase shifts, distortion, and frequency response anomalies....

There's no free lunch whichever way you turn!
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Re: Help! - Bizzare issue with K&H 0300 and Crane Song Avocet

Postby James Perrett » Wed Nov 04, 2020 5:36 pm

It might be worth checking the output of the Avocet with an oscilloscope - just in case it is sending out spurious high frequency signals. It may also be worth finding out the reason for the DC offset on the output which is producing the clicks.
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Re: Help! - Bizzare issue with K&H 0300 and Crane Song Avocet

Postby themarqueeyears » Fri Nov 06, 2020 3:51 pm

James Perrett wrote:It might be worth checking the output of the Avocet with an oscilloscope - just in case it is sending out spurious high frequency signals. It may also be worth finding out the reason for the DC offset on the output which is producing the clicks.

My tech friend, did put an oscilloscope on the Avocet outputs (all three analog outs that feed my different speakers) and all three outputs had the exact same tiny mili-volt DC output on switching or muting - this drops to zero once the switching has taken place, so there's something about the design of the Avocet that creates a very tiny DC voltage when muting or changing speaker outputs - I'm not convinced there's something wrong with the Avocet as my tech pal said the DC was so tiny he couldn't imagine it would damage a DC blocking resistor or capacitor.

My other speakers and in fact other 0300 are working perfectly with the Avocet, though I have lost a bit of confidence in my unit in case it's very occasionally is outputting something nasty of that channel - unlikely, but of course possible - such is the nature of unknown failures.

I have another friend who uses 0300's and his left 0300 has developed a different fault and lost 6dB of gain - our 0300's are getting pretty old (14 years) which may be the issue?

I'm getting mine repaired over the weekend - so hopefully I'll be ok for a while at least.
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Re: Help! - Bizzare issue with K&H 0300 and Crane Song Avocet

Postby themarqueeyears » Fri Nov 06, 2020 3:55 pm

Hugh Robjohns wrote:I imagine the most likely causes are either unwanted sustained DC from connected source equipment, or instantaneous high voltage surges in the ground such as during a nearby lightening strike.

Most equipment includes DC-blocking capacitors on outputs, but the golden eared prefer to omit them as they introduce unwanted phase shifts and (potentially) distortion... although I can't say it's ever bothered me! I believe the Avocet is DC-coupled...

Connecting the speakers via isolating transformers will obviously protect the speaker inputs from any stray DC... but if there is any DC on the source output that could act to saturate/magnetise the transformer, and the transformer itself could, if low quality, introduce its own phase shifts, distortion, and frequency response anomalies....

There's no free lunch whichever way you turn!

Interesting points, I'm very vigilant about unplugging the mains during lightening storms, so I'm hopeful that wasn't the cause.

Are you saying it is normal for the Avocet to output a tiny amount of DC on muting/switching - I think that's what you meant about being DC coupled?
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Re: Help! - Bizzare issue with K&H 0300 and Crane Song Avocet

Postby Hugh Robjohns » Fri Nov 06, 2020 4:29 pm

themarqueeyears wrote:My tech friend, did put an oscilloscope on the Avocet outputs (all three analog outs that feed my different speakers) and all three outputs had the exact same tiny mili-volt DC output on switching or muting - this drops to zero once the switching has taken place, so there's something about the design of the Avocet that creates a very tiny DC voltage when muting or changing speaker outputs - I'm not convinced there's something wrong with the Avocet as my tech pal said the DC was so tiny he couldn't imagine it would damage a DC blocking resistor or capacitor.

Your tech friend is correct. That effect sounds like coupling capacitors discharging, and wouldn't normally be anything to worry about.

I have another friend who uses 0300's and his left 0300 has developed a different fault and lost 6dB of gain

That's most likely a fault where one side of the balanced signal is missing. The most likely cause is a cable fault, but it could be a faulty output driver in the source, or a connection fault inside the speaker (dry joint on the XLR connector, perhaps). That one should be very easy to track down.
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Re: Help! - Bizzare issue with K&H 0300 and Crane Song Avocet

Postby Hugh Robjohns » Fri Nov 06, 2020 4:33 pm

themarqueeyears wrote:Are you saying it is normal for the Avocet to output a tiny amount of DC on muting/switching - I think that's what you meant about being DC coupled?

I haven't seen the schematics for the Avocet, so I don't know the detail of the circuitry. I had it in the back of my mind that it has DC-coupled outputs (meaning no DC-blocking capacitors), but I could easily be making that up in my anticipated senile dementia... ;)

Your tech's description of small DC pulses on switching suggests signal capacitors charging and discharging... but that would be perfectly normal.

Fractions of a millivolt -- or even whole millivolts -- on the output of the Avocet aren't going to fry a tie-down resistor. It took something far more significant to do that!
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Re: Help! - Bizzare issue with K&H 0300 and Crane Song Avocet

Postby themarqueeyears » Fri Nov 06, 2020 8:22 pm

Hugh Robjohns wrote:
themarqueeyears wrote:Are you saying it is normal for the Avocet to output a tiny amount of DC on muting/switching - I think that's what you meant about being DC coupled?

I haven't seen the schematics for the Avocet, so I don't know the detail of the circuitry. I had it in the back of my mind that it has DC-coupled outputs (meaning no DC-blocking capacitors), but I could easily be making that up in my anticipated senile dementia... ;)

Your tech's description of small DC pulses on switching suggests signal capacitors charging and discharging... but that would be perfectly normal.

Fractions of a millivolt -- or even whole millivolts -- on the output of the Avocet aren't going to fry a tie-down resistor. It took something far more significant to do that!

I'm now wondering what happened, I have properly filtered and protected mains and a bespoke star earthed distribution board, I also unplug the mains in a storm, though it's possible there was a storm in the middle of the night I didn't hear! - which is why I now unplug the system from the mains at the end of each day.

Thanks for your thoughts on the 6dB drop in level on my friends 0300, I've passed this information on so he can check over his cables etc.
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Re: Help! - Bizzare issue with K&H 0300 and Crane Song Avocet

Postby themarqueeyears » Mon Nov 09, 2020 1:39 pm

Not good news.

We replaced the failed 0 ohm resistor but unfortunately (as suspected as possible) on switching on the 0300 is blew it's slo blow mains fuse - thus rather dramatically revealing the issue that must of caused the resistor to burn out originally.

There's clearly something going on with my left 0300 that's not good.

Unfortunately (probably for commercial reasons) Sennheiser are not prepared to part with schematic for the circuit and don't offer component level repairs, only complete board replacements at £1000 plus fitting and recalibration another £200-£300!

Therefore my tech has said without the schematic he's not prepared to take it any further which is fair enough - there's so many potential places that could be causing the issue it could take an unrealistic number of man hours to sort out.

I'm going to be philosophical, I've had 12 years service from my 0300's (not great - but not too shabby either) I'll sell my right 0300 and left as driver spares, as there are no more drivers left for repairs so there's bound to be some value left in them.

I've decided my next monitors will be from ATC, I need a company with a better support reputation and track record, I have friends with ATC monitors 25 years old that have been serviced by ATC and brought back to studio service, which sounds a bit more like my Yorkshireman approach of fixing stuff rather than throwing it away!
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