My DIY amp restore

[MrBoat]

and general checkup. Started with an old Pioneer SA-8500 following basic voltage checks (per service manual, which is quite complete, in spite of a few minor errors) and visual inspection. Found some leaky caps so decided just to replace them all. There was audible distortion/clipping at about half range on the volume and it just got worse from there. I remember how this, and others like it used to sound, and this was not it. Also, some of the voltage readings were erratic or unstable. What could it hurt? These units from the mid 70's are very smartly laid out and every section is removable and nearly the entire harness is wrap connection. I remember wrapping connections in electronics school for testing and I thought it was a more serviceable, albeit reliable connection.

Here we are with two boards (EQ and amp control circuits) still not reinstalled, since I had just gotten finished the switch circuit and power amp sections. I took my time and double/triple checked my work, and also tinned all of the leads on the replacement parts. I did also replace the two, large 15000uf 50v capacitors. I was pleased to find that the Kemet replacements were the exact diameter and just a little shorter than the originals. I had to make adapters since the replacements only have two pins, instead of dual pairs like the originals.

The power light had also been out forever so I replaced that with a much better LED. The mechanical power up relay itself looks new, physically, and still functions as it should. Also noted was a lack of magic smoke escaping. Big relief there, and again when setting the junction point, and idle voltages.

And finally, the real test with @William Lemmerhirt old JBL S38 speakers. This combination is a winner. Even without subs, these speakers pack a punch.

I had been sure I was satisfied with these old systems before, yet modern audiophilia was telling me I was mistaken, while now blaming source, room and modern speakers being too revealing for crappy recordings as an excuse, really. At some point, I wanted to come back to my stomping grounds and just thumb a nose at what passes for audiophilia these days. This reincarnation was the right thing to do, and the 'before/after' difference was actually quite remarkable.

According to Ohms Law, this unit, while rated at 60wpc, is putting out just north of 66wpc. I like that the err is on the north side of the line, while many affordable products tend to barely make their stated values.

Next on the block? Pioneer SX-780. It works but has been on my closet shelf for over 25 years. It also does not sound as it should. I have purchased a pair of pcb's that replaces the Darlington IC power packs.

 

[KEW]

Nice to see some of the vintage stuff being reconditioned into service!

My theory is that the large companies (such as Pioneer) had not yet established detailed reliability data for components/circuits, so they erred on the side of "over-building" these units. At the same time, I believe more modern manufacturing techniques have improved such things as when/if a capacitor will leak, so it seems like a win-win to me!

 

[MrBoat]

Nice to see some of the vintage stuff being reconditioned into service!

My theory is that the large companies (such as Pioneer) had not yet established detailed reliability data for components/circuits, so they erred on the side of "over-building" these units. At the same time, I believe more modern manufacturing techniques have improved such things as when/if a capacitor will leak, so it seems like a win-win to me!

Still completely functional 40 years on is a testament to the overbuild approach. Holds true with just about any appliance. My hopes of the more modern replacement parts being somewhat superior as an upgrade of sorts in itself. It's amazing though, how just this little redo managed to stabilize all of the otherwise erratic measurements prior to the work.

Bass and treble seemed to be the most affected both before and after. Before as a symptom, and after as a pleasant correction and to that end, the effect of the adjustment controls. I was having to move the bass and treble controls a lot before hearing an audible difference and it really didn't improve the sound, but rather just changed it a bit. Now they function as an EQ of this era should.

From what I have gathered of Japanese technologies, from electronics, to food, to woodworking, or anything they put their hands on, really, is that they don't like getting caught being underperforming. They tend to exhibit some pretty lofty benchmarks in any engineering that they do.

 

[Out-Of-Phase]

Very nice classic electronics. I can just visualize that receiver all lit up at night in a dark room. Beautiful.

Hang on to those.

 

[KEW]

Still completely functional 40 years on is a testament to the overbuild approach. Holds true with just about any appliance. My hopes of the more modern replacement parts being somewhat superior as an upgrade of sorts in itself. It's amazing though, how just this little redo managed to stabilize all of the otherwise erratic measurements prior to the work.

Bass and treble seemed to be the most affected both before and after. Before as a symptom, and after as a pleasant correction and to that end, the effect of the adjustment controls. I was having to move the bass and treble controls a lot before hearing an audible difference and it really didn't improve the sound, but rather just changed it a bit. Now they function as an EQ of this era should.

From what I have gathered of Japanese technologies, from electronics, to food, to woodworking, or anything they put their hands on, really, is that they don't like getting caught being underperforming. They tend to exhibit some pretty lofty benchmarks in any engineering that they do.

It is strange, but the Japanese do not seem to be especially creative/innovative. However, let them see a new idea and they will put it into production with amazing attention to detail and clean our clock on the manufacturing/quality side!
Once when I was teaching Manufacturing Engineering Technology, I had Robert Moog (of Moog synthesizer fame) come give a speech for our student Society of Manufacturing Engineers group.
He had found investors in what was clearly a winning technology and solicited MIT graduates to help with the mechanicals. They did all of their calculations and ended up with 20 screws to assure a sound body when the top and bottom clam shelled together. Not much later Casio (and others) came along with a refined design where you aligned the top and bottom shell and a sharp rap of the palm of your hand and they were snapped together in less than a second! Moog was a high quality product, but they lost a lot of market share real quick to products that offered 80% of the performance at 40% of the cost! The screw system would probably be better for the long haul, but the snap-fit was fine for at least 5 open-close cycles and how often are you going to open it up?
Similar thing with RAAL tweeters - my understanding is it was David Fabricant of Ascend that asked RAAL if they could make a tweeter which sacrificed the ability to disassemble and replace the ribbon - that is what allowed him to offer a speakers with the RAAL tweeter around the $1500/pr price range, and, later Dennis with the BMR speakers, Philharmonitors and mini-phils!
I guess I drifted off of the original topic which was the Japanese ability to take an idea and execute it with amazing efficiency and quality (which their quality approach came for William Demming - a brilliant U.S. quality guru who could not stir up interest among US manufacturers in his approach to quality control for "zero defects")!
I guess my tangent is that many times, companies with great ideas plan to produce the best product they can, but don't later consider investigating marginal sacrifices for significant cost reduction to allow their products to get the full market penetration it could! TheJapanese (and now China et al) are good at this!

 

[MrBoat]

It is strange, but the Japanese do not seem to be especially creative/innovative. However, let them see a new idea and they will put it into production with amazing attention to detail and clean our clock on the manufacturing/quality side!
Once when I was teaching Manufacturing Engineering Technology, I had Robert Moog (of Moog synthesizer fame) come give a speech for our student Society of Manufacturing Engineers group.
He had found investors in what was clearly a winning technology and solicited MIT graduates to help with the mechanicals. They did all of their calculations and ended up with 20 screws to assure a sound body when the top and bottom clam shelled together. Not much later Casio (and others) came along with a refined design where you aligned the top and bottom shell and a sharp rap of the palm of your hand and they were snapped together in less than a second! Moog was a high quality product, but they lost a lot of market share real quick to products that offered 80% of the performance at 40% of the cost! The screw system would probably be better for the long haul, but the snap-fit was fine for at least 5 open-close cycles and how often are you going to open it up?
Similar thing with RAAL tweeters - my understanding is it was David Fabricant of Ascend that asked RAAL if they could make a tweeter which sacrificed the ability to disassemble and replace the ribbon - that is what allowed him to offer a speakers with the RAAL tweeter around the $1500/pr price range, and, later Dennis with the BMR speakers, Philharmonitors and mini-phils!
I guess I drifted off of the original topic which was the Japanese ability to take an idea and execute it with amazing efficiency and quality (which their quality approach came for William Demming - a brilliant U.S. quality guru who could not stir up interest among US manufacturers in his approach to quality control for "zero defects")!
I guess my tangent is that many times, companies with great ideas plan to produce the best product they can, but don't later consider investigating marginal sacrifices for significant cost reduction to allow their products to get the full market penetration it could! TheJapanese (and now China et al) are good at this!

More than anything, I guess, is to look inside something like this and see a design that is completely serviceable. Everything made after say, 1985, looked, and often was/is disposable. I had not considered this when I took the project on. It was a pleasant surprise. Another instance being, when I went to put new belts on my first Toyota, and discovered they had tensioning bolts which amounted to pretty much a one hand operation. Whereas American cars, tightening the belt involves a tire iron, brute force and a wrench.

 

[MrBoat]

Very nice classic electronics. I can just visualize that receiver all lit up at night in a dark room. Beautiful.

Hang on to those.

The receiver I have had for about 30 years. I keep everything forever. It is nice to look at and listen to this stuff again.

 

[William Lemmerhirt]

@MrBoat
That was fun to see my ol’ 38’s I your pics. Just in case you were ever curious, I do miss them. Their performance always surprised me. The horizontal monitor design may be the reason, idk, but I always felt like their imaging was excellent. Guitars always sounded so great on them(and the 312’s). I’m glad to see you enjoy them. Hope things are good.

 

[MrBoat]

@MrBoat
That was fun to see my ol’ 38’s I your pics. Just in case you were ever curious, I do miss them. Their performance always surprised me. The horizontal monitor design may be the reason, idk, but I always felt like their imaging was excellent. Guitars always sounded so great on them(and the 312’s). I’m glad to see you enjoy them. Hope things are good.

Even the impact from tom-toms hits you in the chest with these. As a near field monitor, I can tell you that they are 'killer.'

 

[MrBoat]

My new near field setup. FTW!

Standing between a pair of these with something like Boston's "Smokin?" Highly recommended. This is what I had been missing from modern audio.

 

[William Lemmerhirt]

Even the impact from tom-toms hits you in the chest with these. As a near field monitor, I can tell you that they are 'killer.'

indeed.

My new near field setup. FTW!

Standing between a pair of these with something like Boston's "Smokin?" Highly recommended. This is what I had been missing from modern audio.

Oh yeah!!! I would would guess anything from Boston would sound fantastic on that rig. I can suddenly hear Kansas wayward son maybe?

 

[MrBoat]

indeed.

Oh yeah!!! I would would guess anything from Boston would sound fantastic on that rig. I can suddenly hear Kansas wayward son maybe?

I ended up listening to a lot of rock, including Judas Priest, Steve Vai, and Stevie Ray Vaughn.

A few observations between this and the Denon AVR. Good recordings sound good on both. The vintage amp translates pretty much everything well, whereas, the AVR is more picky. The AVR can contend in bypass mode, but the advantage goes to the vintage amp because the EQ controls are manual and you do get results with it. A big plus when dealing with compressed and non/less compressed recordings on the fly. With the AVR, I have been tempted to manually EQ on the fly too, but it is not convenient or, as instantaneous as just turning knobs. Also, the working so close to the amp and then back out again gives clues as to how/where to adjust the sweet spot. With the constant directivity designs, it's quite large to begin with, so, something as simple as toeing speakers in or out is quite effective.

So far, this is the best that the Tempests (the JBLs too, for that matter) have sounded with classic rock, and without subs. Really a super performing speaker mixed with this vintage amp. At the end of some tunes, I could not help but slam dunk an F-bomb, for being so thoroughly rocked by the performance.

I like the AVR and it's included bass management and it does a lot of things well, but this old amp is just plain fun with music. I have yet to hook up the CD player and turntable up to it yet. This was only tested so far with the echo dot.

 

[slipperybidness]

@MrBoat
I'm not so sure about that retina-searing LED power indicator!

Otherwise, good work!

 

[KEW]

@MrBoat
I'm not so sure about that retina-searing LED power indicator!

Otherwise, good work!

Not sure how easy it is to access, but I have found coating the back/inside side of the plastic that transmits the light through the metal front panel does a good job of backing down the intensity without any indication (from the exterior) that it is a home-cooked solution.

 

[slipperybidness]

Not sure how easy it is to access, but I have found coating the back/inside side of the plastic that transmits the light through the metal front panel does a good job of backing down the intensity without any indication (from the exterior) that it is a home-cooked solution.

I've had reasonable success with black or similar nail polish. Even a small piece of electrical tape can be fine if you are careful with it.

 

[MrBoat]

I've had reasonable success with black or similar nail polish. Even a small piece of electrical tape can be fine if you are careful with it.

The searing bright light is on the inside. It shines through the factory orange lens. It's really like stock. The first pic with the light is without the faceplate on. The camera begs for a flash, but I don't use it. Otherwise, it's enhanced by the camera.