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Dillen

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Viewing 20 posts - 141 through 160 (of 726 total)
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  • in reply to: Beomaster 1900 ( it just stays in standby mode) #55930
    Dillen
    Moderator

    I use a “glass-hair”/fiber brush.
    But if there is oxidation, you can clearly see it as black flakes.

    Martin

    in reply to: Old timers Beovox 3800.Mid range drivers. #55760
    Dillen
    Moderator

    Welcome back, Peter!

    Martin

    in reply to: Beomaster 900 newbie aux input buzzing question #55724
    Dillen
    Moderator

    Difficult to say what could be the reason, but if you start working or diagnosing keep in mind that Beomaster 900 has positive ground.

    Martin

    in reply to: Beomaster 1900 humming/hiss #55615
    Dillen
    Moderator

    Typical sign of aging capacitors. Grab a service kit and replace the lot.

    Martin

    in reply to: Beomaster 1900 – Volume control issue #55419
    Dillen
    Moderator

    Does your volume control have one or two ICs?

    Martin

    in reply to: Welcome #55314
    Dillen
    Moderator

    Thanks Mark.

    Martin

    in reply to: Welcome #54937
    Dillen
    Moderator

    What happened to my (long) reply to this thread from apprx. four days ago?

    Beomaster 6500 & 7000 improvement of pre-amp circuit

    Martin

    Dillen
    Moderator

    The insulation capacitors are there for a reason.
    I would NEVER remove them.
    Actually, they are signs of a very high quality circuit design.

    So what are they, and why are they here?
    They are small ceramic capacitors placed in strategic places through the signal path, from the signal path to ground.
    They are called insulation caps because they insulate the individual signal path stages HF-wise.
    They are here because you cannot put a load on f.e. a power supply, without seeing some kind of reaction on its power output, and
    because most OpAmps have a very high slew-rate.

    If an OpAmp switches fast from off to on (or vice versa), the current it “accellerates” will have to come from somewhere.
    In other words, a sudden spike commanded on an OpAmp output will see a corresponding (reverse) spike on its power supply rail(s).
    This supply will often be supplying other circuits in the signalpath as well, and these circuits will also see the spike in their supply causing them to instantly produce a spike on their output.
    Actually, the OpAmp itself will almost always also cause a spike, as will most semiconductors (and some capacitors).

    The spike on the power supply rail will of course also affect the very OpAmp that caused it (with a brief delay), and
    the (very!) brief power surge will cause a new spike on its output.
    The result is a very high frequency “ringing” (fading burst of spikes) until the new current flow situation has settled (throughout
    the signal path!).

    As the spike reaches stages with higher and higher amplification and higher currents involved, the corresonding
    spikes on the power supply rails will be larger – again feeding back to the earlier stages.
    If the power supplies are not suitably decoupled, due to f.e. tired/sluggish filter capacitors, this could in severe cases end in
    self-oscillation and a burned amplifier.

    Small caps (100nF or so) are often placed directly on OpAmps (and other circuits handling audio signals) power supply pins.
    This helps quite a bit when viewed from the power supply side.
    But any spike already produced will go on to the next stage, be that tonecontrol, volume or amplification.
    If nothing is done, the spike will continue to the next stage and cause the next OpAmp to (attempt) to
    reproduce this “signal” which, in case of an amplification stage, would only make matters worse.
    The spike will grow through the amplifier, and the more it grows the heavier spikes form on the power supply rail and the
    more ringing will be introduced to the signal.

    This signal could eventually end at the tweeter (as speakers crossovers usually don’t cut off HF), and it can contain quite an amount of energy.
    A Zobel-network on the amplifier output would take some of it, but even this small circuit could be put to hard work.
    Bad power supply filtering caps (the small 10uF) in f.e. Beomaster 5500 can cause ringing throughout the preamp and output stages,
    and the small Zobel network resistor can actually burn from the resulting HF energy contained in the signal.
    The output stage will also run warm.

    Putting an insulation cap (a few pF) on the signal path to ground will drastically improve matters as it will be seen as a
    dead short for the very high frequency contained in the bursts.
    A capacitance this small will have no influence on anything within the audible frequency range.
    Quite opposite in fact, as it will remove spikes and bursts that are not part of the original signal.

    In some cases, – typically early in the signal path, the OpAmps (or whatever circuit handles the signal) power are fed through
    a low-pass filter, often seen as something like 47-100 Ohms in series with the power supply/ies and 100uF to ground.
    This is done for all stages individually, of course, – or it would be pointless.
    The JAMO Promix 200 which is at first glance simple but, by far, one of the best sounding discoteque mixers, uses this in dozens of places.
    Beogram CD5500/6500/7000 does too in the analogue stages.

    I strongly recommend leaving insulation caps well alone.
    It is very high quality circuit design.

    Martin

    in reply to: Beogram 4002 Restoration #53996
    Dillen
    Moderator

    Very nice indeed.
    For shipping considerations, it would also be good to know where you ship from.

    Martin

    in reply to: Beovox 3702 Crossover Capacitor Values #54291
    Dillen
    Moderator

    Depends on the type of Beovox 3702.
    Kits are readily available:
    https://www.beoparts-shop.com/?s=3702&post_type=product

    Martin

    in reply to: Beocenter 8000 tape deck clicking issue #54267
    Dillen
    Moderator

    It’s a known problem with this drive type.
    Glue in a small piece of carton or plastic card (apprx 0,5 mm thickness) here:

    Beocord tikker edited

    You can give the exposed motor bearing a tiny drop of sinter oil.
    The belt for the motor must NOT be tight!

    Martin

    in reply to: Beocord 5500 sticking drawer #54264
    Dillen
    Moderator

    It’s not uncommon to see the Beocords rubber feet missing as they harden with age.
    The outer parts break off, while the inner parts fall inwards where they will often
    get stuck between the Beocords bottom plate and the drawer, causing a braking effect.
    Look in from the front with a torch light.

    Martin

    in reply to: Connecting beocord 9000 to Beomaster 8000 #54215
    Dillen
    Moderator

    Difficult to diagnose from a distance, but I have seen aftermarket cables with
    wrong pin configurations.

    Martin

    in reply to: Connecting beocord 9000 to Beomaster 8000 #54213
    Dillen
    Moderator

    Check continuity in the cables.

    Martin

    Dillen
    Moderator

    Which cartridge are you using?
    And what is the tracking force set to?

    Martin

    in reply to: Tips for adjusting BG4000 platter height #54091
    Dillen
    Moderator

    Solenoid leads touching the platter underside?

    Martin

    in reply to: BeoGram 5005 tonearm too low #53972
    Dillen
    Moderator

    It’s cast metal.
    It can come out if you heat it carefully, not melting the plastic, only softening the glue.

    Martin

    in reply to: Trimpots Beomaster 1200 #54024
    Dillen
    Moderator

    Not sure what you mean?
    VTVM usually refers to a Vacuum Tube Volt Meter (F.e. Bang & Olufsen RV9/RV11 etc.,
    but today most digital meters have a suitable high impedance so will work fine for most readings of this type.

    Martin

    in reply to: Trimpots Beomaster 1200 #54022
    Dillen
    Moderator

    Dont’ use readouts of old and bad components for reference!

    Set the new trimmer in its center position, fit it and refer to the servicemanual for
    the corresponding measuring points and correct settings.

    Martin

    in reply to: Beocenter 3500 issue #53687
    Dillen
    Moderator

    Did you try what I suggested?

    Martin

Viewing 20 posts - 141 through 160 (of 726 total)