Heath(kit) SP2 low volume - impedance, etc ...? (wordy)

Posted by ToddM (A) on June 3, 2014 at 12:37:57

I'm resuscitating an SP2 (will possibly modify to 2-A status once I get it stable), and while it can sound decent, I'm a bit puzzled about the low volume I'm getting with several amps, including a contemporary Heath 121 as well as a gainclone and Parks Audio get*SET*go. I did a FULL recap, using higher votage ratings and +50% to + 100% capacitance in the PS, a bit higher voltage and close to schematic ratings in the circuit. I've only changed a couple of resistors that were out of spec, the rest seem to be pretty close (albeit measured in-circuit for the most part). I've cleaned the controls with air and a few drops of Caig, and I have new (EF86) and NOS (12AX7, 12AU7) tubes that all test well in there now.

So, what do you think I can check to get more volume with less dial turning? I don't want to start ripping it apart wholesale ... the Hum controls on the outputs, maybe? - they look clean, but can they possibly go bad? I have to crank the front panel dual controls to past 11 to start getting loud, does that sound right? The channels track very closely, so the control isn't high on my list of suspects. Also, the Loudness and Volume controls are much more closely-related than I've ever seen in a preamp, but even with that, it needs to go much further on the dial than I'd expect (notably with the 121, problematic with the gainclone). Was hoping to use it in an all-Heath system, maybe I just need to use it with my HK 770, which is *super* sensitive ...? Never having heard one, I'm not sure that it should (or shouldn't) be necessary to crank it to get a decent volume level. Otherwise, it sounds fine (maybe a bit bass-y, but that could be the Loudness control interaction) ...

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Topic - Heath(kit) SP2 low volume - impedance, etc ...? (wordy) - ToddM 12:37:57 06/03/14 (1)

I had the exact same problem - realistico 15:58:48 06/03/14 (0)

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