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Rodgers S-100C amp distortion problem

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  • Rodgers S-100C amp distortion problem

    I have 3 of these S-100C amps. 2 have been working fine in their original condition for almost 2 years since i started using them daily. The other one lost power, a while ago.

    Last night the amp that amplifies my choir & great has permanently failed resulting in awfully distorted sound when pressing the keys on the console. I have messed around with the culprit amp quite a bit attempting to resolve the distortion by turning the amp dials and trying to polish the 5 connector pins to see if the distortion was caused by corrosion.

    Its certainly the amp causing the distortion, and not from the console, as i made sure by switching the amps for a test.

    After reading up on some previous S-100C amp problem threads, im finding that many members to point to capacitor Q5 as a frequently failing part.
    attached in the S-100C amp schematic

    I am considering removing the Q5 and possibly Q4 caps from my power dead S-100C amp and replacing them on the newly culprit S-100C amp

    Is it possible that distortion could be caused by a bad capacitor? or more likely a different problem would allow for distortion?

    thanks all
    Attached Files

  • #2
    Q5 is actually a PNP transistor, the 'bottom half' of the pre-driver stage for the output transistors. The original part for the S-100C and earlier versions does appear to be prone to failure based on my own experience and that of others I know that own these amps. Rodgers seems to have fixed the issue with the S-101 and later versions that use the same basic design with a few revised components.

    I'd be wary of swapping in Q5 from the dead amp since you don't know the exact cause of the failure.

    According to the Rodgers transistor substitution list, a suitable generic replacement would be the NTE 129, available from a number of sources.

    --- Tom
    Rodgers 660 with additional analog rack sets (practice), 36D/C in digital conversion, Yamaha CVP-107


    • #3
      On the board are two larger resistors, one is a power resistor and the other is something like 2 Watts. Check that they are not loose and that the solder joints are good. I once got four S100's, none of which worked, and all were fixed by re-soldering those resistors. I think the heat may cause them to loosen over time.

      What "amp dials" were you turning? You didn't mess with the Bias Adjust, did you?