Hi everyone, just yesterday I received an Eidetic GB 1b amplifier in generally very good condition, if a little dusty internally. I cleaned it out a bit, checked the output fuses and cleaned the terminals and fired it up with a DMM on each speaker terminal to check for DC. Both outputs showed 500mV initially, after 20 minutes warm up the RC dropped down to 60mV (still way too high for my liking) but the LC stayed at the 400mV mark.
Since there were no buzzes or hums, I tentatively connected it to my extremely sensitive Sansui SP300 speakers, now 52 years old and still wonderful, a high pitched pop at switch on (usually a muted slight thump with the DIGI 125) and all was well for 30-40 mins or so, then a sparkly crackling began in the LC and I disconnected immediately with no issues.
Ok, so I have a little information gleaned from this site and little else, is there a proper circuit diagram available anywhere here? Maybe there is a leaky cap or two on the main boards, but I am not familiar with Mosfet circuitry and all the caps will be 30+ years old now. The amp is #327. The main filter caps are all in unmarked silver cans, so I have no idea of the capacity yet.
The other thing is, since it comes with no user manual as such, I have no idea how to change the rear 4-8 ohm/1-2 ohm plug on the back ... yes I know it pulls out, but there is an inner lug on the plug that only allows for one way of orientation. Does the plug need to be removed for 1-2 ohm use? I have no idea.
Any further information would be very valuable to me, as this one will be a work in progress. As it is, it comes nowhere near the standard of my tuned up DIGI 125 and I'm keen to have it in tip top shape.
I'm considering replacing the 10uF 35V input caps with some Nichicon Muse BP versions that I've just received from Digikey.
*** I also would like to know about the second version which uses the OPA627 input op-amps, are they just a drop in replacement for the LM357s, or are there a couple of other items that need adjusting to make those OPA627s work correctly? I have no idea yet which trim pot may be used for DC adjustment or bias.
Any help here would be much appreciated! Is Greg Ball still around on this site?
Since there were no buzzes or hums, I tentatively connected it to my extremely sensitive Sansui SP300 speakers, now 52 years old and still wonderful, a high pitched pop at switch on (usually a muted slight thump with the DIGI 125) and all was well for 30-40 mins or so, then a sparkly crackling began in the LC and I disconnected immediately with no issues.
Ok, so I have a little information gleaned from this site and little else, is there a proper circuit diagram available anywhere here? Maybe there is a leaky cap or two on the main boards, but I am not familiar with Mosfet circuitry and all the caps will be 30+ years old now. The amp is #327. The main filter caps are all in unmarked silver cans, so I have no idea of the capacity yet.
The other thing is, since it comes with no user manual as such, I have no idea how to change the rear 4-8 ohm/1-2 ohm plug on the back ... yes I know it pulls out, but there is an inner lug on the plug that only allows for one way of orientation. Does the plug need to be removed for 1-2 ohm use? I have no idea.
Any further information would be very valuable to me, as this one will be a work in progress. As it is, it comes nowhere near the standard of my tuned up DIGI 125 and I'm keen to have it in tip top shape.
I'm considering replacing the 10uF 35V input caps with some Nichicon Muse BP versions that I've just received from Digikey.
*** I also would like to know about the second version which uses the OPA627 input op-amps, are they just a drop in replacement for the LM357s, or are there a couple of other items that need adjusting to make those OPA627s work correctly? I have no idea yet which trim pot may be used for DC adjustment or bias.
Any help here would be much appreciated! Is Greg Ball still around on this site?
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