[AMRadio] SX-28 Bass boost circuit


Russell Barber rbarber at pacbell.net
Mon May 28 00:50:22 EDT 2007


Dear group,

I am doing a complete down-to-the chassis rebuild of a SX-28.  I started with the power supply and now and am now finishing the  rebuilding the audio amp and phase splitter.  The schematic shows the bass boost circuit CH2 and C43 being shorted by the bass boost switch SW1D when the bass boost is engaged.  When not engaged, the schematic  shows the plate resistor R37 is shorted out.  This looks like a error to me so I built the circuit differently, I wired it so the CH2 and C43 are engaged with the bass boost switch open.  When the bass switch is shorted, it shorts out CH2 and C43. Also the plate resister is always inline.
   The issue I now have is that I only have 2 db of bass at 950 Hz.  The audio chain is flat out to 15 KHZ and has less than 1% distortion at 1 watt across 5K.  All appears to be normal except the rather weak and too high in frequency bass boost.  
   Has anyone seen this issue and could shed some light on what is going on?

Best regards
Russ Barber
N3HPX/6


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