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Pioneer A-80 Integrated

chicks

chicks

Lunatic Member
Picked up this A-80 @ the GW a couple of days ago. I like the nice clean look of its face. Internally, it's a rat's nest, however. Build quality definitely not the same as the '70's Pioneer gear. I think this one was built from '82-'84 or so. Has a similar look to my Rat Shack STA-2270 receiver. I like the built-in MC transformer, and switchable MC impedance matching (will need to get a MC cart one of these days). 150Wpc, very low distortion, "Dynamic Power Non Switching", whatever that means. Two power supply voltages, one for normal listening, a higher one for the peaks.

Seems to be a very rare bird in the US, not much info out there. This one has multiple input voltages, probably the US Military version. It was set at 110V when I got it, possibly causing some stress on the internals.

Protect relay wasn't clicking, and the power light is burned out (why did they use incandescent bulbs for the power/protect lights, and LED's everywhere else? :screwy: ) Troubleshooting revealed that R42 & R43, a pair of 10 ohm 1/4W dropping resistors on the driver boards, were wide open. No sign of heat distress on either one, they simply failed - probably poorly made.

Replaced both (a major job, as the driver boards are vertically mounted and a PITA to access and remove), powered up, and heard the protect relay click! :banana: Offset measured ~3mv on each side, good to go.

Well, almost - left channel now works fine, right is still dead. More troubleshooting to come...

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I have the A-70, the little brother to your amp. Mine is supposed to be something like 100wpc(IIRC). Yours must be approaching monsterhood for power. I'd like to hear your impressions when you get it running.
 
chicks said:
powered up, and heard the protect relay click! :banana: Offset measured ~3mv on each side, good to go.

Well, almost - left channel now works fine, right is still dead. More troubleshooting to come...
Click to expand...

If the voltages on both channels check ok then it might just
be a case where you're loosing the signal because of a dirty
switch or control.
 
I found one of those in a dumpster a couple of months ago. It had some loose solder joints but after it got warm it worked fine and sounded very good. Then one day I was impatient and didn't want to wait for it warm up and began fiddling with the internals and I herd a little pop and that was the end. I do plan to get it fixed because i really liked the sound and power.
 
The marketing blurb talks about the "Non-switching Design" without really explaining what it means...

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Specs:

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glen65 said:
it might just be a case where you're loosing the signal because of a dirty switch or control.
Click to expand...

What he said. My A-90 had a frustratingly difficult to clean problem with the big rectangular push buttons. On the plus side the guy I bought it from thought it was broken so I got it very cheap. My initial attempt at troubleshooting was to work the all the switches, when I started getting crackly audio I figured I knew what to clean.
 
Yep, the internals are different but I bet those pesky switches are the same. Mine is still a pain in the shorts to test and service since the linestage and tone control boards are vertical behind the faceplate.

I still don't understand the "Dynamic Power Non Switching" circuitry. I understand what it does just not how it does it. My bulbs were burned out for the power indicator as well so I rigged up two LEDs for the green and red indicators. I didn't like the way it looked with the power switch in green and all the other LEDs in red so I switched them. Now power on is red and the 3 second pre-relay click is green.
 
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non-switching NSA explained

I have an A-80, it needed a volume control - which I now have and just (haha, cobbler's kids....) need to put it in...

The non switching part of it is like the sx-3800,3900, d5000,d7000 and such.

Think of it in terms of idle current.

Half of a push pull circuit is idle at any time. But you STILL want idle current to flow on that half.

On a regular amp it DOESN'T!!!

The signal driving the other side interferes and turns OFF the idle current, "switching" off the transistor. It takes time to "wake up", during which there is distortion.

Non-switching in the amp chops off the interfering part of the signal, so idle current always flows in the idle side, keeping that half perpetually "awake"

That cuts even more distortion out of the amplified signal.

Dynamic power, however has to do with where the heat is dissipated - the output transistors at a high frequency or the "dynamic power" transistors at a lower frequency...

the "lower voltage" (at a slightly lower current, thus reducing the dissipation a bit) is achieved using series pass transistors, and where does the "extra voltage" go? up in heat...

(post not done until this is gone, more to come)
 
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In short (to put it crudely) they're attempting to take advantage
of the benefits of a class A design within a class AB amp.
 
The non-switching part seemed reasonable to me. The dynamic power circuit doesn't appear to add anything to the music listening experience but it does add complexity to the circuit. The only marketing angle I could think of was lower power consumption (higher efficiency) in non-peak or idle conditions. Is this what you'd call a class G or H amp.
 
I have an A-80 fully restored by a local pioneer dealer who likes to work on vintage items. Had the same thing with the left channel. They replaced the transistors and RES, cleaned it up and it has rolled ever since. The parts were only $17.00. I hooked it up with a C-21 preamp and boy the sound is crystal clear. I have another one I am working on.

You will enjoy the amp. I really cannot turn it up much. It is driving a pair of HPM 100s (200w version) and a pair of CS-99a. Most impressive is the sound quality from the apple TV that I run through it.
 
Scuzzer said:
The non-switching part seemed reasonable to me. The dynamic power circuit doesn't appear to add anything to the music listening experience but it does add complexity to the circuit.
Click to expand...

The idea is to increase the amplifiers headroom.

The only marketing angle I could think of was lower power consumption (higher efficiency) in non-peak or idle conditions. Is this what you'd call a class G or H amp
Click to expand...
Yes, Class G and H essentially accomplish the same thing. That
is to increase rail voltage with increased signal levels. The two just
do it in a different fashioned. The class G works by "stepping"
between multiple fixed voltages as the signal changes. An example
of class G would be the Proton "Dynamic Power on Demand"
setup that was used in the D1200 amp that came out in the
mid to late 80s, NAD used it too. The Class H does it by continuously
varying the voltage and keeping it just above signal levels.
An example of this would be Carver amps.
 
Scuzzer said:
My bulbs were burned out for the power indicator as well so I rigged up two LEDs for the green and red indicators. I didn't like the way it looked with the power switch in green and all the other LEDs in red so I switched them. Now power on is red and the 3 second pre-relay click is green.
Click to expand...

I was planning on replacing them with LEDs. What value series resistor did you use? How did you mount them? Hot glue? Maybe I'll go with Yellow for the protection color... :scratch2:
 
fine amp! mine has leds on pc board on the right side of it. have you noticed the (missing ?) bolts on the power transformer? very nice amp the phono section is just awesome
 
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