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  1. #1
    Junior Member
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    SB3 volume output lower on left than right channel - please help

    Have an SB3 that is unfortunately out of warranty. The volume output is different (lower on left than the right channel) both through the rca outputs and also the headphone socket on the SB3.
    Have tried updating the firmware and returning the unit to factory settings but neither helped.
    I suspect a hardware problem but have not been able to find any reference to similar issues on the forum with the SB3.
    Anyone have an idea where the problem might lie? Might it be a simple job to trace to the faulty circuit part and component that is causing this?
    Last edited by Tagore; 2009-11-29 at 05:31.

  2. #2
    Senior Member gizek's Avatar
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    Did you perform any tweaks on SB ? There is no balance control on SB, isn't there ? What happens when you go with volume all the way up or almost down - any changes in balance.

  3. #3
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    I haven't done any tweaks and the L&R channel output imbalance remains the same whatever the volume output level.
    For those that know the SB3, is there a particular part of the circuit / component that is likely responsible for the output difference?
    Would send for servicing here but understand that where I live, Singapore, Logitech don't support SB3 servicing.

  4. #4
    Senior Member gizek's Avatar
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    Is left, lower output channel in any way distorted ?

  5. #5
    Senior Member Phil Leigh's Avatar
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    If there is a hardware problem it is likely to be in the handful of components that comprise the final analogue stage right next to the analogue output sockets.
    You want to see the signal path BEFORE it gets onto a CD/vinyl...it ain't what you'd call minimal...
    Touch(wired/W7)+Teddy Pardo PSU - Audiolense 3.3/2.0+INGUZ DRC - MF M1 DAC - Linn 5103 - full Aktiv 5.1 system (6x LK140's, ESPEK/TRIKAN/KATAN/SEIZMIK 10.5), Pekin Tuner, Townsend Supertweeters,VdH Toslink,Kimber 8TC Speaker & Chord Signature Plus Interconnect cables
    Stax4070+SRM7/II phones
    Kitchen Boom, Outdoors: SB Radio, Harmony One remote for everything.

  6. #6
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    thanks for the responses. if I get bold enough might open it up or let an electrician friend of mine take a look at it.
    the left channel out put is not at all distorted just a lower in volume than the right. I would use balance but my pre-amp doesn't have it and the software plugin that I found for the SB3 to alter volume balance between left and right loads but doesn't have any effect.
    Shame they don't service it here and also that the SB3 is now hard to buy new as well. not keen on the duet really. oh well, will try and find one in the UK rather than here in Singapore.

  7. #7
    Founder, Slim Devices seanadams's Avatar
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    The fact that it occurs on both the RCA and headphone outputs really narrows down the problem because it rules out a dozen components in the RCA drivers.

    I haven't seen this problem before, but I would say it is most likely the PCM1748 DAC or the 10uF cap connected to pin 7 of that chip.

    Those are readily available parts but the DAC is not easy to replace.

    Here's a partial SB2 schematic that I posted years ago. SB3 is the same but the component numbering is different, and there is no alternate footprint for the AKM part.

    http://web.archive.org/web/200606160...ms.com/dac.pdf
    Last edited by seanadams; 2009-12-17 at 08:34.

  8. #8
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    Appreciate the link and suggestions. Have replaced ICs and capacitors in other equipment before so am confident of doing the repairs. Any pointers for how to confirm if either of these are indeed the faulty components?

  9. #9
    Founder, Slim Devices seanadams's Avatar
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    Quote Originally Posted by Tagore View Post
    Appreciate the link and suggestions. Have replaced ICs and capacitors in other equipment before so am confident of doing the repairs. Any pointers for how to confirm if either of these are indeed the faulty components?
    Play a sine wave test tone and measure RMS volts to ground, before and after the caps. If the left is different from the right before the caps, then it's the DAC, if it's different after the caps then its the caps. I might be oversimplifying, but that's where I would start.

  10. #10
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    Thanks for the information here, Sean.

    This has given me the required knowledge to fix my SB3 which was showing a 20dB loss on the left channel. The fault did, indeed, turn out to be the decoupling cap between dac and op amp.

    As a quick fix, I removed the decoupling cap, eliminating the op amp from the circuit, and took the dac output directly to the second decoupling cap, immediately prior to the lp filter at the output sockets.

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