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Buffalo III: high pitched 'squeak' from one channel
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Joined: 1/27/2008(UTC)
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Location: Edinburgh
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I have just received and put together a Buffalo III and Legato - the kits are really well organised and it was very straightforward.
Everything works and I can play music, but there is a low-level high-pitched tone on the right hand channel. It's independent of the volume, and of whether there's a lock/digital input connected. It's drowned out by music but audible during silences. It's only audible on the SE output, not on the balanced output.
On an oscilloscope it looks like a saw-tooth, about 100mv p-p on the DAC output pins I would guess around 7.5kHz. It's there whether or not the DAC is connected to the Legato. I think it might be an oscillation in the AVCC module - touching the top right hand resistor on the AVCC makes it go away, and it comes back slowly (about 3s). Moving the AVCC causes slight shifts in frequency. Current draw for the DAC is about 390ma, VD is 5.25v. The AVCC output (when not connected to the DAC) is 3.49v.
Can you suggest what I might try to make it go away permanently?
Thanks,
Matt
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Rank: Administration
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Hmm this is a new one. I would try shifting over the AVCC module so that one side of the DAC is not powered and the other is powered with the "good" side. Just to double check. I would also test the AVCC module on its own. Simply feed it 5V and look at the outputs. It does sound like you have an AVCC module that has gone bad for one reason or another. It wouldn't hurt to look over the solder joints on the AVCC module. Edited by user Sunday, September 18, 2011 1:02:45 PM(UTC)
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Rank: Member
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Joined: 1/27/2008(UTC)
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Location: Edinburgh
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Thanks for the suggestion. The squeak disappears when the left-hand side of the regulator powers the right-hand side of the DAC.
I did do a quick check of the solder on the module, but I'll reflow the joints to see if that solves it. Could it be a problem with QP4 do you think?
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Rank: Administration
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Joined: 10/24/2006(UTC)
Posts: 3,979
Location: Nashville, TN
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Yes my top three suspects would be R6, QP4, or the opamp. This is the first i have ever heard of this happening, so it hard to give concrete guidance. :)
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Rank: Member
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Joined: 1/27/2008(UTC)
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I've checked the solder joints and it's not made any difference. Would it be possible to return it for an exchange?
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Rank: Member
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Joined: 1/27/2008(UTC)
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Or should I try replacing the opamp and transistors, in which case could you tell me what transistors they are?
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Rank: Administration
Groups: Administration, Customer
Joined: 10/24/2006(UTC)
Posts: 3,979
Location: Nashville, TN
Thanks: 25 times
Was thanked: 89 time(s) in 83 post(s)
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It wouldn't hurt to try to replace both transistors on the right side. But it could be a damaged opamp. They don't take well to over voltage. The transistors are BC860. Edited by user Monday, September 19, 2011 12:35:44 PM(UTC)
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Buffalo III: high pitched 'squeak' from one channel
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