157.128.218.206
In Reply to: RE: My MG-20 manual lists the midrange-ribbon crossover as 3 KHz. posted by hemholtz on October 22, 2009 at 17:37:57
The first IIIas had a 3-ohm ribbon. IIIas having ribbon serial nos. after SN 63744 have different ribbons ... Magnepan changed it to a 2ohm-resistance (presumably by widening it?) and so they introduced a 1-ohm resistor in series with the ribbon, to bring the total back to the 3-ohm value assumed by the IIIa crossover component values. (This is not the ribbon-attenuation resistor.)
My own IIIas have a 2-ohm ribbon (and the 1-ohm resistor) ... likewise the T-IVa ribbons you sent me are 2-ohms (but without the resistor).
Can you tell me how wide your 3.5 ribbons are? For instance, my 2-ohm IIIa ribbons are about 1/4" wide (as are your T-IVa ribbons) ... in contrast to the 3-ohm ribbon of the 3.6, which is only about 1/8" wide.
And when you measured the ribbon resistance, did the value of 3-ohms which your meter showed exclude the intrinsic resistance of the meter leads (which you can get by simply shorting the connectors)? Or was it the total of the ribbon resistance plus the meter leads?
Regards,
Andy
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