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Thread: Tascam PA-20 mkII

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    Tascam PA-20 mkII

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    Hi,

    Anyone familiar with the PA-20 mkII?

    I have one which has a fault, on the power up the speaker relay does not trip in, I have tested the relay with a battery, and it pulls in no problem.

    Does anyone have a schematic? I can't any schematics online anywhere.

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    TASCAM PA-20MKII TECHNICAL DOCUMENTATION Pdf Download.

    They appear to have one but I am not chancing signing up!

    The speaker relay is subortinate to the actual audio side and so make some voltage tests on power transistors. There should be 25-40 volts +ve on one transistor and exactly the same negative on the other (NB volts could be on emitters or collectors depending on topoplogy) Next check the speaker conns with the relay energised. NO LOAD. Should be very low, 20-40mV max.

    If the above obtains connect a meaty speaker, a 50W+ guitar speaker is ideal BUT with 20 or so Ohms in series. Does it make nice noises fed with a signal? If so you just need to investigate the relay power circuitry. If that proves impossible Velleman Elects do a kit of a relay delay and offset protection circuit.

    However, how old is the amp? If getting on and especially if it is of the "quasi-complimentary" OP stage type the distortion levels will be an order or two worse than a good modern amplifier.

    Dave.

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    Hi Dave

    Thanks for the link, it is a safe sight. I have that file, it's just a two page user guide, (see pdf, no schematic).

    If I trip the relay with a 9v battery I get clean sound out of the speakers.

    Photo attached of internals.

    Michael
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    There's silly!

    I have found a data sheet for the IC and that includes a protection circuit. Not, unfortunately one using a relay.

    What is the amp used for? 25W into 8 Ohms is not a lot these days into modern compact speakers. The distortion figures are also not outstanding.

    If used for non critical purposes, especially into some rough'ass speakers, I would simply bypass the the relay contacts. Those amp ICs were deployed in hundreds of thousands of mid-level "hi fis" over many years. Music centres, "micro amps" and even some huge ghetto blasters (probably in ICE as well? ) I saw a lot of this kit with similar ICs and cannot remember a single one going ape***t and destroying a speakers.

    If REALLY low fi usage, a keys amp say, just put 2,200mfd 63V caps in each speaker leg.

    "Self fullfilling prophecy" really? If the amp is wanted for a high grade system it's the wrong one! If not, mod it to keep the speakers safe.

    Dave.
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