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Thread: Teac 4010-S preamp issue

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    Teac 4010-S preamp issue

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    My repair of that old beat up Teac 4010-S was pretty successful. It doesn't blow up anymore.


    Transport works great, just need some reel holders and I'm inbusiness. Just got one annoying issue:

    The preamp is EXTREMELY NOISY (as in, hissy). It sounds like there's 24 tracks of blank tape running at 3 3/4 ips in the background, which gets mixed in with the ENTIRE source input signal, reguardless of volume. Can it be saved, or is that just the way those things were built?

    thanks!
    -callie-

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    Has the machine been professionally calibrated in recent history?

    This might explain part of the problem if the bias, level and eq internal setting are amiss.

    Extreme hiss is also a sign of worn out heads and dried out caps.

    Do the heads still have "shape" or are they flattened right down? If the guide posts and lifters are showing flat spots, chances are the heads are worn too.

    Heads are reasonably cheap to replace on a 1/4" machine and re-capping the channel cards is also not a huge expense so, it is restore-able if you have the time and patience to do it.

    Cheers!

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    well....

    The heads have a slight amount of wear, but it's even, and it shouldn't be an issue right off the bat. I haven't played a tape on it yet, since I don't have reel holders yet, but that's coming next. I replaced the belt (since all that was left of it was goo), and the transport seems to work pretty rock solid and smoothly (though I won't know FOR SURE until I get reel holders)

    No, it has not been calibrated, probably since it left the factory. And seeing as how a capacitor blew up on me when I first got it, I wouldn't be surprised if the preamp needed to be recapped as well. Here's what it's doing:

    When I monitor from the headphone jack, and set the monitor to tape, it's fine. noiseless. I'm hoping that it'll play back tapes just fine.

    But, when I switch the monitor to source, there's a constant NOISE (as I described in the post earlier) that does not increase or decrease with any volume knobs -- So reguardless of what the levels are on the preamp, a constant noise resides in the SOURCE circuit.

    So how would I go about fixing this? Who's the best source for capacitors, if I need to re-capp?

    Also, the volume pots are VERY crackly when I adjust them. Is there a way to clean up those?

    Just a side project while I'm here at school. I think I'm the only person with a reel-to-reel in their dorm room.

    -callie-

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    I wonder of the noise you refer to is 60 cycle hum, that is occuring because the filter caps in your power supply are too old and no longer filtering. Look at the terminals of the filter caps with an oscilloscope. If you see anthing other than DC levels there is an issue there.

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    Also, the volume pots are VERY crackly when I adjust them. Is there a way to clean up those?
    I use products from Caig Laboratories for cleaning pots and switches.

    Deox-it and Calilube MCL are miracle workers!

    http://www.caig.com

    Cheers!

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    The noise is NOT 60 Hz hum. It sounds like whitenoise. Very much so.

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    Quote Originally Posted by The Ghost of FM
    I use products from Caig Laboratories for cleaning pots and switches.
    Crackling pots can also mean some DC bias voltage on them.

    I'm not sure of the circuit of this deck, but as its an older one it may well use a single rail with the audio signal lifted with a DC offset voltage. Newer equipment runs on a split rail, so that the AC audio waveform swings around zero volts between (say) +15 and -15 volt rails. On older gear (like my 70's Akai) this waveform swings around, say, 6 or 12 volts on a rail upwards of 20 volts.

    These voltages are blocked from the input and output using caps, and you'd put caps between stages and before and after pots. Seeing you've had other problems with caps, and noise which could relate to caps, its a good place to start. Use a multimeter to check for DC voltage on the pots - if its there, that's you're problem.

    Another possibility with the hiss problems could just be an old input stage. It depends on how bad the hiss is. I have used some very noisy home brew gear from the 70's (i.e. stuff dad built then!) based on circuits that were supposed to be 'low noise' at the time - an example being a balanced mic preamp using two BC109's followed by an LM301. Very nice sound, but noisy as anything.

    If you find voltage, replace the caps (I'm guessing on gear of this vintage it shouldn't be too difficult a job, just make sure you get the values right and have a schematic and parts list nearby - and be prepared to have to realign all of the levels, bias levels etc) and see if this hiss disappears.

    Hope this helps!

    Cya
    Andrew

    EDIT: Just re-read the post detailing the problem with noise. If it doesn't change with volume knobs, the noise doesn't relate to old design in the preamp, so some of the above doesn't apply. Feed a signal in and see how the noise level compares to the signal. If you blow holes in your eardrums you just had the level up too loud, otherwise we go back to caps etc. after those level controls; try changing the blocking caps directly after them first.
    Last edited by arjoll; 03-05-2005 at 01:30. Reason: Re-read the noise problem

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