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distorted sound quality BM 2000

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Donald Brownlie
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Donald Brownlie posted on Sun, Mar 8 2020 12:34 PM

HI THERE, Very new member of the Beoworld forum and need to pick the collective brains of all you fine Lads and Lassies. Afriend of mine has just purchased a beautiful beomaster 2000 amp which sounded oh so sweet when purchased from a Radio Enthusiast privately. it has however developed a distortion in the left AUDIO Channel. I have done all the swapping of speakers etc and fault is in the unit. Investigation notes that THE SOUND THROUGH THE HEADPHONE SOCKET IS PERFECT ON BOTH CHANNELS. though in older amps, the headphone socketis wired early in the amlifier stage, the 2000 seems to have it wired post output, therefore presumably heavily "potted down". Any one had this fault or any pointers to cause.

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ProGram
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Hi there,

the headset socket has built-in switches for the 1 pair of speakers. I would suggest those for the fault.

Chris

 

Donald Brownlie
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Thanks for the idea ProGram. have switched speakers across the 1 AND 2 speakers connecyions to no avail. whether they are attached via speakers 1 or speakers 2, the distortion is on whichever speaker is designated LEFT OUTPUT. ERGO, If I swap the wires the right speaker will distort with left channel feed. As I said, headphone output is perfect on both channels. I feel it is a left channel feed fault on the output but circuit diagram seems vague on the notation of the components of the stage.

Dillen
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Dillen replied on Tue, Mar 10 2020 11:34 AM

Which version of Beomaster 2000 do you have?
Photo or 4-digit type number.

Martin

Donald Brownlie
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The Beomaster is 2000/Type 2912 model, Martin, and I feel that this will be a well known, if not a stock, fault to the more well-versed Techs on the forum, the likes of yourself. Donald

Dillen
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Dillen replied on Tue, Mar 10 2020 4:18 PM

Well, it certainly isn't one of the most fault-prone models. They are generally fairly good.
Normally I would check the power supply to the amplifier for ripple, but since the distortion is only in one channel, I would suspect
the output stage hybrid chip in this case.
The headphones are paralleled with the speakers (through a resistor if I remember correctly). That the distortion seems to be
only from the speakers and not in the headphones could point to a load-problem in the hybrid chip.

Don't buy from China. It will almost certainly be fake or something counterfeit.

Martin 

Donald Brownlie
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Ok Martin, sounds like a plan to me. yes, the headphone routing is through a 220 resistor. would it in itself be enough to dampen any distortion if it is on a directly parallel circuit to the speaker? just a thought.  Donald

Dillen
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Dillen replied on Thu, Mar 12 2020 5:56 AM

It all depends on where the problem is. The load of the headphones is very far from that of a speaker.
Since only one channel is affected, we can rule out power supply problems.
Since headphones have no distortion, we can rule out problems upstream of the amplifier,
and since the distortion is in both outputs 1 and 2, we can also rule out the speaker sockets and the Speakers 2 switch as the cause.
All left now is the speaker contact inside the headphones socket (that mutes Speakers 1 when a plug is inserted) and the amplifier chip.
Check for cracked solder joints around the amplifier chip, - or replace it.

Martin  

Donald Brownlie
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Hi FOLKS, Sorry for the delay infinalising the thread. due to unforeseen postal issues between DEUTSCHE POST and the UK, ithas takenover three weeks to obtain the STK 463. Happily it did solve the problem and the 2000 is playing sweet as a bird. Thanks especially to Martin for your help and guidance. DONALD

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