I’ve had this Pioneer SX-780 sitting on my lab floor for about 6 years now and I said that now is the time. It had a failed Darlington power pack when I got it, the STK-0050. The single good pack I donated to a friend to get his 780 going. That pack is still going strong 5 years later.
I’ve seen two options, this Pyramid Audio package, very simple circuit that uses these four pin Darlington outputs, STD03P and STD03N.
The other option is a much bigger circuit, designed by someone that hangs out here and audiokarma I believe, it uses standard off the shelf BJTs.
I don’t have schematics for them, but from what I understand both are fairly well known so I’m hoping people have formed opinions on them.
For the first option, those Darlington devices are no longer available, but I was smart enough to buy a couple dozen of each back when Digikey had them. I have this single Pyramid board in the pic and was planning on etching some of my own to make more. So I have everything needed to go that route.
Same with the second option. A few years back I had about 100 of those green boards made up. I have plenty of the TO220s and TO3P devices as well as everything else. So I wouldn’t need to buy anything for either option, just etch a board for the first option.
Would going from the original Darlington pack to a board that uses Darlingtons be the way to go? I know the second option is probably more widely used. Not sure which offers better performance, but wanted to get opinions of the two hopefully. I’m working on the receiver now, the outputs will be taken care of last.
Thank you,
Dan
I’ve seen two options, this Pyramid Audio package, very simple circuit that uses these four pin Darlington outputs, STD03P and STD03N.
The other option is a much bigger circuit, designed by someone that hangs out here and audiokarma I believe, it uses standard off the shelf BJTs.
I don’t have schematics for them, but from what I understand both are fairly well known so I’m hoping people have formed opinions on them.
For the first option, those Darlington devices are no longer available, but I was smart enough to buy a couple dozen of each back when Digikey had them. I have this single Pyramid board in the pic and was planning on etching some of my own to make more. So I have everything needed to go that route.
Same with the second option. A few years back I had about 100 of those green boards made up. I have plenty of the TO220s and TO3P devices as well as everything else. So I wouldn’t need to buy anything for either option, just etch a board for the first option.
Would going from the original Darlington pack to a board that uses Darlingtons be the way to go? I know the second option is probably more widely used. Not sure which offers better performance, but wanted to get opinions of the two hopefully. I’m working on the receiver now, the outputs will be taken care of last.
Thank you,
Dan
Hi Dan,
Myself (RCS16) and at the request of a fellow AK member, we designed the discrete module now ~10 years ago, It's very popular, more expensive than the Pyramid however but its more rubust, probably better for multiple speakers or low Z. You can use 200W Onsemi or 150W Onsemi or Toshiba devices. I offer kits with both types. I doubt that you would hear any difference.
On AK I provided the pcb fab data for free, that I assume is what you used. the HS is something that you need to reproduce. I sell these kits on ebay btw.
I did not use Sanken devices for the reason that I suspected at that time, those devices would be EOL before the Onsemi or Toshiba devices would be EOL. It turns out my suspicions where correct. 🙂
Rick
Myself (RCS16) and at the request of a fellow AK member, we designed the discrete module now ~10 years ago, It's very popular, more expensive than the Pyramid however but its more rubust, probably better for multiple speakers or low Z. You can use 200W Onsemi or 150W Onsemi or Toshiba devices. I offer kits with both types. I doubt that you would hear any difference.
On AK I provided the pcb fab data for free, that I assume is what you used. the HS is something that you need to reproduce. I sell these kits on ebay btw.
I did not use Sanken devices for the reason that I suspected at that time, those devices would be EOL before the Onsemi or Toshiba devices would be EOL. It turns out my suspicions where correct. 🙂
Good Luck
Rick
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That is pretty cool upgrade that you can use standard 220 devices and power resistors for discrete Darlington.
Second option seems best choice.
Second option seems best choice.
Agreed. Great to see those options available to keep those old beauties alive.
Another option is to remotely wire a ready amp module, use the PCB to run wires to the new module.
Use the existing holes in the PCB for the various points needed by the module, which you can mount in a convenient location in the chassis, paying attention to ventilation.
Class AB and Class D modules / populated PCBs should be available for the existing rail voltages.
The STK audio amp modules were mostly stereo output stages with a common supply, so it should not be very difficult to do.
Use the existing holes in the PCB for the various points needed by the module, which you can mount in a convenient location in the chassis, paying attention to ventilation.
Class AB and Class D modules / populated PCBs should be available for the existing rail voltages.
The STK audio amp modules were mostly stereo output stages with a common supply, so it should not be very difficult to do.
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Ohhhhh, okay you’re RCS16. Yes, we had a long conversation via PM over at audiokarma right before my daughters were born, back in March of ‘21. Yeah, I’ve had these boards for awhile. You helped with answering some questions on them and it’s definitely the way I went. You told me that you were selling kits and I had no intention of doing the same and stealing your sales, but I did go a bit overboard with having the boards made. Seemed so much cheaper to have them made in bulk.
Right after posting this thread I thought to myself that I had no idea what the future of this receiver would be, but if I’m 3-4 years down the road if its in someone else’s hands and it fails, I would want to at least have available parts.
Nearly done with the second board. I went with the NJW1302/3281, but for the 150w devices I’m guessing you mean NJW0302/0281? I’m curious as to what other outputs would work? Would the NJW21193/21194 work in a pinch? I know they’re a bit slower for outputs, but would that be noticeable. Just asking because I have dozens and dozens of them. Luckily the 1302/3281 and 0302/0281 are still available, but really curious as to what all will work well in here. Out of curiosity, with the 2A diodes you used being EOL, and me not having any, is the MUR220 a good option here? Only 2A diode I have, otherwise I could step up to a 3A with a slower recovery time, like a 1N5404 or UF5404.
That would have definitely been another option. If these two kits weren’t available and I didn’t already have the necessary parts for them I would have gone this route.
I did some work several years back for an amplifier manufacturer (I won’t say who) and did some amplifier repair for them. There came a point where they either refused to pay me or couldn’t pay me, don’t know which. So I ended up with a bunch of parts in exchange for pay, and a small portion of those parts was roughly 200 of these ST TDA7294 chips. I have these single channel boards for them.
They run at a +/-40v supply max, so with the SX-780 having 40v rails I’d probably want to drop thr voltage to maybe 35v. I read you don’t want to run these at they’re max voltage, but maybe that’s just for the TDA7293. From what I’ve read they seem to be a pretty decent chip and having so many of them I’d like to put them into use. I have a couple small receivers that have bad output devices (like STK-0100) I may try them in. I’d like to find a ready made board that will support two of the TDA7294 in parallel for each channel. I see that running them in parallel makes life easier on them, especially on lower loads. Ultimately for the SX-780 this fully discrete option outlined above is the way to go. Need to find a use for all of these chips though lol.
Dan
TDA7293 and 94 are the only power integrated circuits that I have loved in my life, if it turns out that yours are authentic, congratulations.
Oh, well that is good to hear. I really had no idea as to their viewed quality in the community. I have to imagine that they are authentic as they were purchased by a pretty large and well known amplifier company. I’m sure that nearly everyone here has heard of them. I guess it’s possible though, I’m 99% certain they are though. The other thing that I got an absolute crap load of are these N channel mosfets. Again, no idea if they’re seen as decent devices or what to do with them. Play maybe???
Well everyone, thank you for the comments. Got both boards installed and monitored the bias on this side
And then DC offset on this side
Let it run for a bit and it seems very stable. Measured output into 8 ohms
Looks like I’m getting a clean 55w minimum both channels driven before clipping on the waveform.
I did do a bit of a restoration on the whole unit. All electrolytics, many of the transistors, cleaned all of the controls, polished the relay contacts. The original 8000 uF filters were measuring around 3800 uF on my Peak ESR70, so not too healthy.
Off to clean all of the knobs, faceplate and replace lamps. Thank you again!
Dan
Got the lamps switched over, tried both LED wedge lamps and incandescent, I went with the incandescent. Here is the inside after the work.
And the face after getting the front and knobs all cleaned up.
Sadly the plastic faux walnut vinyl isn’t in nearly as good shape with bubbling and such. I have a bunch of walnut veneer in the shop, I’m considering that. Not sure, the veneer is a bit thicker than the thin plastic sheet. With the silver front and warm white lighting it might look really nice wrapped in a birdseye or figured maple. Hmmmm.
Anyways, looking sharp. This thing has been sitting on my shop floor, completely dismantled with a bare heatsink, knobs all in a sandwich baggie, and blown fuses for 6 years, longer probably. I bet it started to think it was never going to be able to play a single sweet note of music again, destined to the electronic recycling or torn to shreds as a parts unit.
Thanks to you folks in the community she sings again and I can tell she is loving every minute of it. Can’t compare to the original STK packages, but boy, does this thing have authority! Sounds incredible. I have it wired to my modified Athena bookshelf speakers (altered crossovers and driver swap) and I’m liking what I’m hearing.
Dan
And the face after getting the front and knobs all cleaned up.
Sadly the plastic faux walnut vinyl isn’t in nearly as good shape with bubbling and such. I have a bunch of walnut veneer in the shop, I’m considering that. Not sure, the veneer is a bit thicker than the thin plastic sheet. With the silver front and warm white lighting it might look really nice wrapped in a birdseye or figured maple. Hmmmm.
Anyways, looking sharp. This thing has been sitting on my shop floor, completely dismantled with a bare heatsink, knobs all in a sandwich baggie, and blown fuses for 6 years, longer probably. I bet it started to think it was never going to be able to play a single sweet note of music again, destined to the electronic recycling or torn to shreds as a parts unit.
Thanks to you folks in the community she sings again and I can tell she is loving every minute of it. Can’t compare to the original STK packages, but boy, does this thing have authority! Sounds incredible. I have it wired to my modified Athena bookshelf speakers (altered crossovers and driver swap) and I’m liking what I’m hearing.
Dan
Something sitting around for 6 years,
Then finally getting finished makes for even a better story.
Probably really woke up after all that work.
SOA likely better than original.
Incandescent lamps look great
Overall panel design deserves nice soft glow.
Very nice
Then finally getting finished makes for even a better story.
Probably really woke up after all that work.
SOA likely better than original.
Incandescent lamps look great
Overall panel design deserves nice soft glow.
Very nice
You can look for the 'alpha-cellulose' paper that has the printed patterns for Formica sheets, that might work as a repair to vinyl, it is only slightly thicker than news papers, or about the same as 'burl' sheets used in furniture making.
Formica is this paper with a mostly Bakelite backing.
Or simply use fade proof ink on adhesive sheet to make a cover, print your own pattern.
Formica is this paper with a mostly Bakelite backing.
Or simply use fade proof ink on adhesive sheet to make a cover, print your own pattern.
Thank you very much. I have several pieces that have been sitting for a long time and it really does feel good getting this one done. Maybe I’ll put it in my daughters’ room. I really like the incandescents, they ended up being a touch softer and the light is better diffused/spread out, less hot spots.
Dan
Good morning. Could you sell me two complete kits to build the new stk0050? I need it, I have to bring my Pioneer back to life. Thank you
See post #2 for availability.
Would the NJW21193/21194 work in a pinch?
Possibly but I have never tried them to be certain
Would the NJW21193/21194 work in a pinch?
Possibly but I have never tried them to be certain
Not sure if you did it or not, but a trick that I picked up from someone online is to use aluminum foil on top of the bulbs to get more light downwards (as the bulbs are pointing up) and to spread out better helps keeping heat out of the top of the case too (probably not helping to the vinyl situation), it worked well in my SX 680
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@saabracer23 - do you still have this pyramid-audio.com board? Any chance you could PM a couple of photos of it? I have 7 of each of the STD03N/STD03P and think I've found a use for them . . .
Rich