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Pioneer Spec-2 Rebuild

Looking great EW!! :thmbsp:

I also see a lot of lifted traces on these old PCBs. I just run a wire to replace the trace. Easiest way to fix it.

Interesting that the SPEC-2 and SX-1250 use 2SB600/2SD555 outputs. These are also used by the Technics SA-1000, 6 per channel for the rated 330 wpc. I am guessing the SPEC-2 also uses 6, hence the exceedingly high power output at the onset of clipping. Certainly a conservatively rated unit.

The SPEC-4 being a later design has slightly better specs and not at all shabby, compared to the SPEC-2 methinks...
 
Hey EW, I'm assuming you re-apply thermal paste/grease to all the transistors before you reattach them to the heat-sinks, can you recommend any brand or paramters you look for when you're buying the paste? or is it general not that important as long as you apply any paste?
 
That's cool oldtubes, I find that the better quality receivers used them. Nice devices, very reliable. They run extremely cool on the SA-1000 without the need of a fan. I've cranked her to insane levels with hardly a sweat!!!
 
EchoWars said:
cascoded input differential
Click to expand...
I have no idea what this means but I think I suffer with it as well!

:lmao: :lmao: :lmao:


Glenn:
I have what is probably a dumb question but one that keeps coming to mind when I read about some of the restorations you do. Keep in mind I don't know anything about the repair of the equipment.

I assume that, when they were new, all Spec 2's connected to the same equipment would produce the same sound. I wonder what part of the Spec 2 produces that sound and does a restoration change the sound that is produced? Or has the sound deteriorated and the restoration is bringing the back to what it was when was new?

Hope this makes sense. Your write ups like this are terrific. Very much appreciate the opportunity to look over your shoulder.


Terry
 
Good question.

I think a properly designed piece should certainly have a sound of its own, but that sound should be due to the design and layout of the piece, and not due to the individual parts. If swapping one or a dozen pieces, it should still retain its character.

I never really got to hear many of these pieces back in the day, and even if I did I doubt that it would matter 25+ years later. All I can do at this point is to get it running with the best parts I can find and ensure that I haven't introduced some sort of instability to the equasion. If the end result measures good, is stable, and sounds good, then I hope I've done my job as best I can. Whether I've changed the sound from that of the original, I dunno. If so, I hope it is for the better.

That's about the best answer I can give...but I'll reiterate a point...a properly designed piece should have you listening to the overall design and not the individual components, so unless you've gone totally nuts with modifications it ought to retain its basic character.
 
EchoWars said:
Good question.

I think a properly designed piece should certainly have a sound of its own, but that sound should be due to the design and layout of the piece, and not due to the individual parts. If swapping one or a dozen pieces, it should still retain its character.

I never really got to hear many of these pieces back in the day, and even if I did I doubt that it would matter 25+ years later. All I can do at this point is to get it running with the best parts I can find and ensure that I haven't introduced some sort of instability to the equasion. If the end result measures good, is stable, and sounds good, then I hope I've done my job as best I can. Whether I've changed the sound from that of the original, I dunno. If so, I hope it is for the better.

That's about the best answer I can give...but I'll reiterate a point...a properly designed piece should have you listening to the overall design and not the individual components, so unless you've gone totally nuts with modifications it ought to retain its basic character.
Click to expand...


Being non-technical, not a whole lot of argument with that- other than to say that any given piece should have you listening to the music above all.
 
Thanks for the info Glenn!! I always like to read your tech threads, espescially when they are based around a Spec-2!! I'm glad Retro got you going on his Spec's, you'll learn a lot, just in time to get mine!! Keep up the good work! And once again.... Thank you for sharin'.

Ron
 
EchoWars said:
......ensure that I haven't introduced some sort of instability to the equasion. If the end result measures good, is stable, and sounds good...........
Click to expand...

I was wondering what do you do if it goes unstable with modern high-speed parts in place? Alter the feedback? Sounds like tricky work nonetheless, best left to wizards like yourself! Impressive work - thanks for sharing it with us.

One other thing - why not replace all the resistors? Or are there just too many of them.
 
There are so many different values of resistors that even if I decided to do it, I'd have to order a ton of them that I don't have...and I've already got a pretty thorough stock. Plus I don't think there'd by much to gain.

As far as stability, most of these amps already have a dominant pole designed in, so you can put in the fastest transistor you can find and the amp won't be any faster unless you alter that. Still, anything is possible and you have to check. One method might be to put a small cap across the feedback resistor (5 - 10pf).
 
For a variety of technical reasons...one of which is the method that Pioneer uses to mute the sound on startup, the servo is a no-go. Instead, I built a little circuit board to allow adjustment of the offset. Not as cool as a servo, but it gets the job done.
 
That's pretty neat EW, better than factory!

I wonder why Pioneer didn't provide pots for adjusting DC offset. Perhaps the design was not as sensitive to DC offset as others? mmm

Given the cost (nearly a grand in 1970s dollars) this wasn't cheap. So cost was not a reason for excluding these adjustments.

It does have a unique (for Pioneer) impedance selector switch in the back...
 
Great thread, thanks for answering my Q, EW, I forgot I asked it :)
I have also been wondering about how components affect sound of a component as TWantiques asked as well. I thought that you would give the components a bit more merit, but I guess overall or as a whole the sound is determined 90% by design.
 
It's Baaaaaack!!!!

Got the SPEC 2 back on Saturday and I am here to tell you, it SMOKES ALL my expectations!

EW, you da man!

Not mentioning any names, but one fella who got a good listen to it, is talking about selling his Sansui G-22000 and going seperates all the way. Anchoring his new system would be........, if you guessed a Pioneer SPEC 2, you'd be right.

That Amp just kicks a$$$$$$.......


Retro
 
Good to hear you got yours back and it's working great. Sweeeet!!

I'm thinking about getting one. No preamp though. I would drive it off the SX-1980.
 
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