You're right also about the fact that hearing another person's setup may be what tells you to change, but still then I have so many "parts" I wouldn't know what to upgrade first haha..
As you say, at the end of the day it sounds quite good to me, and also quite good to many people that I have them listen to it. Maybe just getting a homogeneous set of speakers may sound clearer and constant.
As you say, at the end of the day it sounds quite good to me, and also quite good to many people that I have them listen to it. Maybe just getting a homogeneous set of speakers may sound clearer and constant.
If the amp has only two big 4700 µF caps (voltage rating?), then it can't be AC coupled (and neither is the STA-800). It probably just doesn't have any protection relays, which weren't standard fare at the time. It may have output fuses, in which case the fuseholders should be inspected and cleaned if needed.
The suspect electrolytics aren't so much the big ones. Of course these may be dead (and grey ones typically are standard '70s fare of unremarkable quality), but then the amp would probably emit audible hum. No, those that are most likely to be dried out are small ones, like coupling caps or ones in the feedback. Ideally you'd make a list of all of them, detailing capacitance, rated voltage and polar/nonpolar (in case you come across any NP ones). The ones most suspect would be found near the power amplifier's input stage though.
I'd suggest grabbing a schematic for the STA-800 receiver and comparing the semiconductors in the power amp section to what you find in the SA-800. Maybe they are related at least. If you can't make heads or tails of the internals, provide some photos (not from Mr. Blurrycam).
The suspect electrolytics aren't so much the big ones. Of course these may be dead (and grey ones typically are standard '70s fare of unremarkable quality), but then the amp would probably emit audible hum. No, those that are most likely to be dried out are small ones, like coupling caps or ones in the feedback. Ideally you'd make a list of all of them, detailing capacitance, rated voltage and polar/nonpolar (in case you come across any NP ones). The ones most suspect would be found near the power amplifier's input stage though.
I'd suggest grabbing a schematic for the STA-800 receiver and comparing the semiconductors in the power amp section to what you find in the SA-800. Maybe they are related at least. If you can't make heads or tails of the internals, provide some photos (not from Mr. Blurrycam).
Kind of a forum nooby when it comes to adding photos, other than using the 'LINK' how can I post pictures from my drive?
And luckily Mr.blurrycam isn't a friend of mine so no worries for that 🙂
And luckily Mr.blurrycam isn't a friend of mine so no worries for that 🙂
Attach your pics. See manage attachments after going advanced or post reply.
DiyAudio store them for Members to see long after your computer has been replaced.
DiyAudio store them for Members to see long after your computer has been replaced.
This amp could have a number of issues. From marginal caps (likely, and usually accompanied by excessive hum and noise) to substandard circuit layouts and topologies. It's hard to tell without measurements and a session with the scope.
If the caps have enough capacity to control ripple and thus suppress noise, they may not have the capacity to provide reserves for loud passages and this will cause gross distortion. It's somewhat unlikely for a cap to lose enough capacity to affect dynamics without losing so much capacity that it also becomes ineffective at ripple control. When they're bad they're usually *really* bad.
From the pic it looks like one of their lower end units. Perhaps it's a gutless wonder and doesn't have enough power supply to keep up with the output stage. (if its really light, that's your clue...light and powerful amps didn't exist when your SA800 was made)
Speaking of low end, it could have a quasi-complementary output stage. This is where the outputs are all NPN instead of NPN/PNP pairs. This was done in the 60s and early 70s because PNP power transistors were expensive and unreliable but by the late 70s it was almost unheard of except on low end units. Quasi complementary output stages have distortion that is often an order of magnitude higher than a fully complementary stage of the same build quality. (0.5 vs 0.05% is typical!)
If you have STK hybrid modules ending with roman numeral II, they are quasi-complementary inside. Drop in upgrades to full complementary are possible with some STK families. For example, if you have an STK4042-II with 0.4%THD, replacing this with an STK4042-V gets you 0.08%THD and going to the somewhat rarer XI variant brings that down to a vanishingly low 0.008%.
Also, the transistor bias could be off causing crossover distortion, which is audible in tiny amounts (as low as 0.3% according to Douglass Self). You need a service manual or an oscilloscope and a tone gen to set this. If you get it wrong, you could destroy the output transistors. Don't attempt it without a scope or the service manual.
Some good equipment under the Realistic badge was produced but sadly, there was more bad equipment than good. The old Pioneer made receivers from the 70s and the Foster made stuff in the late 80s was very good. I have an STA2700 which is Foster made and it's great. The thing has nice tuner, cool fluorescent bargraph meters and a fully complementary output stage and it can often be found for under $100.
If the caps have enough capacity to control ripple and thus suppress noise, they may not have the capacity to provide reserves for loud passages and this will cause gross distortion. It's somewhat unlikely for a cap to lose enough capacity to affect dynamics without losing so much capacity that it also becomes ineffective at ripple control. When they're bad they're usually *really* bad.
From the pic it looks like one of their lower end units. Perhaps it's a gutless wonder and doesn't have enough power supply to keep up with the output stage. (if its really light, that's your clue...light and powerful amps didn't exist when your SA800 was made)
Speaking of low end, it could have a quasi-complementary output stage. This is where the outputs are all NPN instead of NPN/PNP pairs. This was done in the 60s and early 70s because PNP power transistors were expensive and unreliable but by the late 70s it was almost unheard of except on low end units. Quasi complementary output stages have distortion that is often an order of magnitude higher than a fully complementary stage of the same build quality. (0.5 vs 0.05% is typical!)
If you have STK hybrid modules ending with roman numeral II, they are quasi-complementary inside. Drop in upgrades to full complementary are possible with some STK families. For example, if you have an STK4042-II with 0.4%THD, replacing this with an STK4042-V gets you 0.08%THD and going to the somewhat rarer XI variant brings that down to a vanishingly low 0.008%.
Also, the transistor bias could be off causing crossover distortion, which is audible in tiny amounts (as low as 0.3% according to Douglass Self). You need a service manual or an oscilloscope and a tone gen to set this. If you get it wrong, you could destroy the output transistors. Don't attempt it without a scope or the service manual.
Some good equipment under the Realistic badge was produced but sadly, there was more bad equipment than good. The old Pioneer made receivers from the 70s and the Foster made stuff in the late 80s was very good. I have an STA2700 which is Foster made and it's great. The thing has nice tuner, cool fluorescent bargraph meters and a fully complementary output stage and it can often be found for under $100.
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