The Story So Far...
Been awhile, as I had a few setbacks and needed a fresh start with these guys. Here's where we left it...
3 pre's total. My own plus a couple that "came down from the mountain, where
HE (hint, rhymes with "Lee") said...
'taketh these two, and maketh one to blow Kev's mind and ears off'". So, first strategy is to make my own the guinea pig, then we'll take some lessons learned and get Kev's done in due time.
With my own, I've pretty much eliminated the freaky intermittent but unobtanium relay issue. How? Well, remember I'm mostly a digital kind of guy with just about everything local, streaming, or a download away (and I deal with FLAC when and where I can). I have a decent enough turntable with a good nuff cartridge for me, and been known to spin an LP or two, plus a nicely cal'd Nak BX300 for a traveling tape or two.
I also have an EQ with two tape loops, which is a great match for the 3000's once you pull the "processor" jumpers off the back and insert it there.
So.. all the above said.. I really just need two inputs - Phono 1 (MM, I won't be purchasing a MC cart anytime soon), and (hmm.. choices.. ) Aux for the input from the DAC. That takes the relay count on the 3000's all the way down to THREE. Less relays, less chance of a problem. The rest are hardwired now after careful planning and a schematic I could read (thanks Rick at StereoManuals!). I kept the output relay, just because.. I dunno why, but anyway.. That's the first thing we have going.. (Kev, the relays I saved from mine plus what Lee sent should be enough to make sure ALL of yours work properly.. so I'll not do the "relay cheat" mod to the one I end up fixing as yours)
But THEN.. I decided.. hey.. I see a couple of IC's here that are 14 pin quad opamps, one being the main output buffer amp and the other being the tone control (I sometimes will use that). I had these super duper OPA 4134's I had made up and figured heck.. let's try them..
Put them in and fired it up, tone control "defeat" ON. Hmm.. seems noisier than with the old 741 style amps, WTF? Ok.. well the buffer amp choice doesn't seem too good. Now let's see about those tone controls..
click.. KERPOW!!! CV D9's, if you feed them the right (well, really.. WRONG) signal, can really do a good job of sounding like a gun, complete with brain hemorrhage.. WTF?? Blew a fuse in the WOPL'd 400 too! Ok.. now I really think that OPA 4134's just are not going to work here, at least in THIS case!!
And then there was the fiasco above with the wrong application type of deoxit, taking apart switches, and the like.. Ok.. the RIGHT deoxit's on order and should be around next week. I still have another set.. we be ok ..
Now, BACK to the opamps. Joe and I had a few emails back and forth about what the problem could be and what to do about it. Joe pointed out that the ratings are "Maximum allowed" and I should listen to them, being as how the OPA's are 18 volt max.. BUT the 3000 is supplying +/- 20 volts! Ok.. upon reflection that wasn't a smart idea trying to go a couple of volts over. What can we do?? Well, we looked at the two regulators (78mg and 79mg mfg part numbers) and the associated circuit. Learned from Joe how it all works, and more importantly.. how to RECALC for a lower bipolar voltage output!
So.. we're going to take the 20's down to +/- 17 or 16 volts (haven't decided yet... but I have resistors coming for both scenarios). That will bring the +/- VCC's (supply voltages) down to reasonable levels for most of the uber fidelity opamps out there.
End result - Mouser order has been placed. Resistors to re-engineer the 20 volts down a bit, and while at it a combination of Nichicon Muse and FG electrolytic caps to perform a good full recap all around. Should be here next week, and then we'll see..
The other thing I am mulling over ARE those dang unobtanium relays... The positive 20 will be coming down a few volts, but it still should be enough to pull the relay contacts. But, just like the opamps, now it's got me thinking.. hmm.. maybe that also opens up the chance of finding a good current replacement relay - again, now that the coil voltage will be less.
Joe I remember back in the days of Aviation Electronics having these relays that came in a TO-5 style metal can package, with leads long enough that if you preform it correctly should fit the footprints. Ring any bells (and maybe part numbers)??
