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Old 4th Jan 2003, 5:14 pm   #2
Posts: n/a
Default Re: Improving Bush DAC90A sound quality.

I've restored at least 8 DAC90A sets and found no specific problems with LW sensitivity once the sets are properly aligned - both mixer and IF stages.

Regarding their 'muffled' sound, this can be due to the IF being too 'tight' thus cutting the sidebands and reducing the higher audio frequencies. I doubt the aerial/mixer stages have such hi-Q that they restrict the sidebands, even on LW.

Re-alignment with wobulator if possible will help. (LW/MW signals are 9 kHz appart. Strong daytime sigs should be at least 18 kHz appart so IF bandwidth can be about 10 kHz for reasonable audio quality without too much splash from adjacent channels.)

A number of Bush sets have an IF bypass capacitor from V3 to earth - 0.003 - 0.005 usually. Try reducing this as it is also a treble cut. Reducing the 'tone corrector' across the audio output transformer is also a good idea. But beware when reducing these capacitor values - too great a reduction may lead to various forms of instability.

BTW - less treble is transmitted by broadcsater on LW/MW these days for various good reasons. What was reasonable treble response in the past now makes many sets sound 'woolly', so altering capacitors to improve this is a reasonable practice.