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Pioneer Spec-2 Rebuild

dewam said:
Retro or Echo:
I have followed this thread from the start thinking it may be of use to me at some time. Some time is now. Did you find that the rebuild of the Spec-2's changed much due to the condition of the units? Especially the difference between the 2 good units. I see you have been shipping in the original box, is that working out or are you using extra packaging? If either of you wish to discuss the costs involved, please PM me. Thanks Den
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Den,
My suggestion would be to PM EchoWars directly on this.

As far as the rebuild improvements go, Glenn (EchoWars) is using better parts than Pioneer used originally, which automatically improves things. As far as the SPEC 1 rebuilds go, I know Glenn used Blackgate caps for replacements there.
As far as easily noticeable sound improvements go, music seperation and clarity are at the top of the list after the rebuild. If you walked into a room blindfolded, and listened to one my rebuilt SPEC 1/SPEC 2 systems hooked up to some not-so-forgiving speakers like Infinity RS-4.5's, Ohm Walsh 4's, Thiel CS3.6's, Vandersteen 2C's (I've had this combo actually set up on all these speakers and more), etc., you'd think you were listening to a much more expensive system than you are.
I will have an EchoWars rebuilt SPEC 1/SPEC 2 combo hooked up to my Thiel CS3.6's at the AK Fest this year in Detroit, if you can, you should make your way there for a listen. You won't be disappointed.



Retro
 
OH GREAT!!!!!!!!!!

Now after everyone on ebay reads this thread the price of specs 2's will be up to $1500.00 for the clapped out junkers. good job guys.

what a great thread. how about some pics of the rebuilt unit.

I sold my sx-1980 and replaced it with a spec1, spec2, tx-9500II system and it just plain kicks but. what a great hobby
 
DS1784 said:
I sold my sx-1980 and replaced it with a spec1, spec2, tx-9500II system and it just plain kicks but. what a great hobby
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And I suppose you had a few $$$ left over too! Remember, once you go seperates, you never go back! :D

We had pictures all the way through the process of the first SPEC 2 rebuild and when the AK server crashed the last time, all pictures were lost... :sigh:

Glenn (EchoWars) is in the process of rebuilding my third SPEC 2 right now, I'll bet if we ask real nice, he might take some pictures of the rebuild. :yes:

Pretty please Glenn.... :D




Retro
 
Yous guys leave EW alone so he can get my 700C done. LOL Just joking.:music:
I wouldn't mind to see pics of the inards of a Spec2 myself.
 
Retro, re second spec 2, sounds like the rail voltage switch for 4 ohm operation is not dropping both rails, dc is the result and the amp stays in protection.
 
The switch only controls the relay that switches in the proper secondary for 4 or 8 ohm operation (as well as switching to alternative resistors on the driver board for a different current limiting curve via yet another damn relay)...it isn't possible that one rail can use the 8 ohm winding, and the other the 4 ohm winding. But...the switch does commonly get dirty and prevent the relays from engaging, resulting in the amp remaining in protection.
 
Yep, fun and games with relays switching different curves for the VI limiting etc. Another example of a 70's amp not capable of driving real world impedances. The output stage is boderline at best, letalone into 4 ohms, they had to drop the supply or the whole thing would have exploded. Awesome design....relays in the primaries, relays in the VI loop, relays everywhere. Lovely big amp to look at, great for the collection, but that's all.
 
restorer-john said:
Yep, fun and games with relays switching different curves for the VI limiting etc. Another example of a 70's amp not capable of driving real world impedances. The output stage is boderline at best, letalone into 4 ohms, they had to drop the supply or the whole thing would have exploded. Awesome design....relays in the primaries, relays in the VI loop, relays everywhere. Lovely big amp to look at, great for the collection, but that's all.
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Just curious John, do you own a SPEC 2?



Retro
 
Hi Retro,
When it comes to power amps, I have too many. The spec 1 pre and spec 2 amp I sold last year- the spec 1 apparently going to pioneer's display in their head office here in Aus. I compared it to the following power amps: Denon POA1500II, Denon POA2800, Sony TAN77, Hitachi HMA8300, Kenwood L07m's Yamaha M80,MX600,MX630 all of which I still own. All in real time AB'd on my technics comparator. The pioneer was not the worst by any means- that mantle went to the Hitachi. It was however the amp that was worth the most, impressed me the least and had a design that was seriously flawed to my way of thinking. I therefore decided to sell the preamp which after getting over $800 for, thought I might as well sell the amp too. I did, but subsequently picked up a RT909, TX9500II, SA9800, CTF900 and perhaps with hindsight I should have kept it for a better collection. I get seller's remorse everytime I sell old gear, and I'd love to keep it all, but some 70's gear was designed purely for numbers- in the case of the spec2 it was watts, not performance. The spec 4 and the SA9800 use two transformers, two cap banks whereas the spec 2 just uses a big tx and 4 (2 parallel) caps. Wind up the secondary voltage, put an evil VI limiter on it and what do you have? An amp that dishes out >300watts at 8 but less than 250 watts at 4 ohms. That is not a good design in my book. Most of my speakers are 4ohms and the big amps that can deliver current sound way better- even my integrated HK PM660 almost doubles down to 2 ohms. The transformer wasn't good enough, the caps not big enough and the output stage nowhere near good enough- but oh, was it nice to look at- YES. Anyway, it gave me the money to buy better hifi, the latest Pioneer A91D integrated is better again. Less 8 ohms power but a way better sound. Anyway hope I didn't upset spec lovers, I am a hifi lover, restorer and tech not only obsessed with the look, but the substance and the all important :thmbsp: :thmbsp: design.
 
I've measured output on the Spec 2 running a 4 ohm load at 425W. If you could not get more than 250W out of one, I'd suggest that the current limiting was mis-adjusted (hell, you can set the current limit anywhere from too-conservative to non-existent).

I've rebuilt about a dozen Spec 2's in the last two years, and yeah, there are things about the Spec 2 design that I don't like (the stupidly complex protection scheme, the inability to adjust offset, and some other minor things), but power output and overall sound quality are not among them.

I would not pretend that the Spec 2 is the end-all/be-all of amplifiers. But if you are into 70's vintage silver amps and need lots of power (or just want lots of power), you could spend a lot more and do a lot worse. If I were collecting Pioneer gear, they'd unabashedly be my main amps...no excuses necessary.
 
Not upset at all restorer-john, just digging the juicy tid-bit's on the SPEC gear. They will deliver all the power and sound I need for years to come !!! :yes:
 
EchoWars said:
I've measured output on the Spec 2 running a 4 ohm load at 425W. If you could not get more than 250W out of one, I'd suggest that the current limiting was mis-adjusted (hell, you can set the current limit anywhere from too-conservative to non-existent).

I've rebuilt about a dozen Spec 2's in the last two years, and yeah, there are things about the Spec 2 design that I don't like (the stupidly complex protection scheme, the inability to adjust offset, and some other minor things), but power output and overall sound quality are not among them.

I would not pretend that the Spec 2 is the end-all/be-all of amplifiers. But if you are into 70's vintage silver amps and need lots of power (or just want lots of power), you could spend a lot more and do a lot worse. If I were collecting Pioneer gear, they'd unabashedly be my main amps...no excuses necessary.
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Took you long enough! :D

As far as powering 4 ohm speakers.........LOL!!!

That's just about all I have! How about AR-9's, Thiel CS3.6's, Ohm Walsh 4's, ADS L1290's, Allison One's, etc., etc., etc.

We were just down to Army's place last weekend listening to his twin SPEC 2 powered Infinity RS-4.5's and they didn't even break out in a sweat.....

And guess what, I too am a hifi lover and not only obsessed with the look, but the substance and the all important design.

Sorry John, I think you made a HUGE mistake selling off your SPEC 1/SPEC 2 combo. :yes:




Retro
 
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Trying to give me post post sellers remorse..it's working. :yes: I can always look at the nudies of my sold Spec1 on axel's site- the shots are from my Spec1. :thmbsp: I especially loved the alps volume pot. Ok, back to the spec 2. It limits in 8 ohm switch position with a 4 ohm load at around 225 watts. Read the service manual regarding limiter settings and adjustment section 6.2. My spec 2, correctly adjusted, hit around 250 watts at 4 ohms before visible waveform limiting. 425 watts continuous BCD is complete dreaming. It'd be way outside the SOAR for the 3x150watt 15A transistors per rail. One channel, peak for a few seconds with the limiter bypassed maybe, but not correctly adjusted as per the original design.
 
It limits in 8 ohm switch position with a 4 ohm load at around 225 watts. Read the service manual regarding limiter settings and adjustment section 6.2.
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I've performed this adjustment many times and have no need to review it.

Don't confuse a static 4 ohm load (with the rear voltage switch in the wrong position) for real-world performance. You are assuming that you have a nominal 8 ohm load with an impedence 'hole' of 4 ohms or less at someplace in the frequency band that will tax the amplifier with some music material. Too many assumptions.

With the rear switch in the 4 ohm position and the current limit properly adjusted, I can push a little over 58VRMS into a 4 ohm load. The current limit does NOT come into play...the signal clips, it is voltage limited, not current limited.
 
EW, 58volts RMS at 4ohms is 841watts- more than double the 8 ohm power by a long margin- not possible on the lower rail. You are mistaken, 58 volts on the cro is 41volts RMS and corresponds to approx 420watts, apparently what you said you had measured??
 
I just glanced at my cheat-chart for power output which was written for 8 and 4 ohm and followed the wrong column to the voltage, so you are correct...I mis-spoke (or mis-typed, or mis-read...whatever). Actual voltage measured was a tad over 41V...I stand corrected.

Still, my point is that power into 4 ohms is voltage limited...the current limiter does not come into play.
 
Great thread EW! I've gone through it, and I have some questions:
Long story short, the last guy to fix it replaced one of the STV-4H thermal diodes with an STV-3H diode. There's where my missing diode drop went. Hard to see WTF, since they look identical, and they aren't marked in a fashion that tells you what they are.
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I had to replace a STV-4H in one of two Kenwood L-05M mono amps. Total unobtainium. And none my hulks had one. But I found an STV-3H in a quaint sort of antique parts shop — NOS. He had ONE! Phew! He also had the specs on hand for both the '4' and the '3'. The form was a bit different, but the spec parameters were so close to being identical that I saw no problem — especially considering the alternative.

Back at the tatami ranch and working without a net (ie a manual): I had recapped the amp already. I installed the varistor, dialled in the DC offset, then powered up on a light bulb tester. Then I put both amps on the pre-amp and some test speakers. Everything was sounding GREAT, and I could not find any discernible difference between the left and right. And since then on the main speakers, both channels have remained sounding very fine indeed. QUESTION: have I hamstrung the amp in some way that I am not detecting? Can you explain why our results are so different?

NEXT: do you do a resistance reading for each R when you rebuild, or do you read voltages down the line — or both?

Is there any point in checking every transistor on the board for comparative readings in the instrument’s 'diode mode'?

AND: Should we replace the mica insulators on the output trannies? Recently I just cleaned them up and reused them because I found that the ones I hand on hand were the wrong size (smaller).

ALSO: In a Pioneer SA-8500 (Jpn model 8900) I found a 2SC1626 with no thermal grease. The 2SA816 on the same board (switch control) had grease. Is this weird?

I'm using the only grease I can get locally in a computer building supply shop. It's from Sunhayato (Tokyo I think) — a silicon grease rated for 200 Centigrade. Sound OK? — LORNE
 
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