SPEC-2 Refurb Help Please

[Surgeon]

Miklemke,

I'm glad it was an easy fix...

I've been listening to mine for a week or two since going through them and have been fighting with myself to pull them back out of the rack to replace their Q1/2SA798 transistors to lower the DC offset voltage... Guess I'll tackle that job this week sometime...


Glenn,

If you're still following this thread I have a question about adjusting the current limiter...

If I adjust the current-limiter to kick-in @ 30V(28V) into a 4-ohm load as the manual says, my basic math implies a 225(200)-watt limit -- not 250! What am I misunderstanding?

(And I'll pm you later this week about the extra 2SA798's I now have.)

 

[laatsch55]

But the speaker setting is on 8 ohms, i believe thats the biggie here. The 4,8 ohms speaker switch actually switches the speaker relay, IIRC. Adjusting the current limiter as such does not bring it in at 400 watts into an 8 ohm load, as i've had my model k's running that continuous at times.
Having said that, I've had some Cerwin-Vega DS-9's running at 4 ohms at over 300 watts also.


There has been some debate as to why Pioneer didn't show a 4 ohm rating, some seem to think the Spec 2 isn't capable of 250watts at 4ohms. Retro would disagree as would I, after I ran the DS-9's with the Spec2, I hooked a Phase Linear 700 to them and didn't notice that much more than the Spec 2 did.
After looking at the schematic, the 4,8 ohm switch I can't say for certain influences the meters, although it does go to the collector of the 2sd313 on the meter amp board.
After a day thinking about this I believe Pioneer uses the 4ohm load on the 8 ohm setting to trigger the current limiters without having to produce a potentially damaging event. If you think about it, the current limiters are employed due to a low load, speaker terminal shorting , or an output gone bad, bad times to be adjusting the limiters. .
The 4, 8 ohm switch (after researching the service manual again) is for changing the current limiting value at a 4 ohm load.

 

[Surgeon]

But the speaker setting is on 8 ohms, i believe thats the biggie here.

I guess you're right Lee... Maybe when I get them back on the bench to replace Q1 I'll do a power test of sorts...

On a separate subject -- do you know anyone around here that's an expert on the CT-F1000 cassette deck? Reason I ask is I bought a belt/pully kit; installed it; and now my ff/rew works perfect -- but the initial "rew" when a tape is inserted isn't working. (It's supposed to take any slack out of a tape when it's 1st inserted.) The insert solenoid is "clicking" correctly, but just isn't doing it's job, and I can't find a close-up of how it's linkage to the ff/rew levers works...

 

[EchoWars]

Miklemke,

I'm glad it was an easy fix...

I've been listening to mine for a week or two since going through them and have been fighting with myself to pull them back out of the rack to replace their Q1/2SA798 transistors to lower the DC offset voltage... Guess I'll tackle that job this week sometime...


Glenn,

If you're still following this thread I have a question about adjusting the current limiter...

If I adjust the current-limiter to kick-in @ 30V(28V) into a 4-ohm load as the manual says, my basic math implies a 225(200)-watt limit -- not 250! What am I misunderstanding?

(And I'll pm you later this week about the extra 2SA798's I now have.)

If you connect 4 ohm speakers to the unit with the switch set to 8 ohms, yes, you'll effectively limit the output to about 200W before the current limit jumps in. But hopefully you're not doing that.

But the speaker setting is on 8 ohms, i believe thats the biggie here. The 4,8 ohms speaker switch actually switches the speaker relay, IIRC.

Nope. Flipping the impedance switch from 8 ohms to 4 ohms does two things: First, it swaps in a different set of transformer secondaries (with a relay that looks a lot like a speaker relay). Second, it swaps in a different set of current limiting resistors via the right-hand reed relay on each driver board.

Adjusting the current limiter as such does not bring it in at 400 watts into an 8 ohm load, as i've had my model k's running that continuous at times.

I don't know what that means, but the meter is calibrated at 8 ohms, so wattage gets doubled from that if you're running 4 ohm speakers.

Having said that, I've had some Cerwin-Vega DS-9's running at 4 ohms at over 300 watts also.


There has been some debate as to why Pioneer didn't show a 4 ohm rating, some seem to think the Spec 2 isn't capable of 250watts at 4ohms. Retro would disagree as would I, after I ran the DS-9's with the Spec2, I hooked a Phase Linear 700 to them and didn't notice that much more than the Spec 2 did.
After looking at the schematic, the 4,8 ohm switch I can't say for certain influences the meters, although it does go to the collector of the 2sd313 on the meter amp board.

This transistor is simply a regulator to supply the voltage needed to activate the relays.

After a day thinking about this I believe Pioneer uses the 4ohm load on the 8 ohm setting to trigger the current limiters without having to produce a potentially damaging event. If you think about it, the current limiters are employed due to a low load, speaker terminal shorting , or an output gone bad, bad times to be adjusting the limiters. .
The 4, 8 ohm switch (after researching the service manual again) is for changing the current limiting value at a 4 ohm load.

Bravo. We set the current limit with a 4 ohm load and the switch at 8 ohms to prevent damage to the amp. :yes:

I've rebuilt probably 30+ Spec 2's. Typical testing for full power at clipping is about 340W @ 8 ohms, and about 420W @ 4 ohms. My only real criticism of the Spec 2 is insufficient heatsink capacity. If you expect to push it hard into low impedances on a regular and extended (>30 min at a time) basis, some active cooling solution is a good idea.

 

[laatsch55]

Surgeon, Pustelniakar is the Pioneer tape master. Check the DIY, and Tape forum, undoubtly he's covered that subject and it may even be in a "sticky".