hi guys, most of us in australia know what an sc480 amp module is so i guess this is directed at you. I'm getting +22v DC offset on the speaker outputs and the negative rail isnt discharging at all when power is switched off, does anyone have any ideas as to the cause of this problem?
Ok, got it working. was a faulty transistor on the negative feedback, replaced and fixed. 🙂
thanks sss
thanks sss
Congrates! we hv heard a lot about SC480. How about giving schematics of the circuit? We will be happy to study it.
MP
MP
I'm not sure, but I suspect that the schematic for the SC480 amplifier as published by Silicon Chip is protected by a current copyright. That being the case, you should not post it here.
Commentable Thoughts
Thats True They have copyrights and u shouldnot post it here.
Regards
Ampman
AudioFreak said:
Thats True They have copyrights and u shouldnot post it here.
Regards
Ampman
AudioFreak said:
thats true, and is the reason why i did not post a schematic. however there are amps that are... extremely close in design, that are F.T.P
Want to know about the performance. Has anybody tried to increase the output power by changing output devices?
Performance
Output Power 50 watts into 8ohms 70 watts into 4ohms
Music Power 77 watts into 8ohms ;105 watts into 4ohms
Frequency response -1dB at 14Hz and 70kHz (at 1W- see Fig.1)
Input sensitivity 0.875V for 50ohms into 8ohms
Harmonic distortion <.05% from 20Hz to 20kHz; typically <.003%
Signal-to-Noise Ratio -114dB unweighted (22Hz to 22kHz); -119dB A-weighted, both with respect to 50W into 8ohms
Damping factor >140dB at 100Hz & 1kHz, with respect to 8ohms and without PTC thermistor
Protection fuses plus "Polyswitch" PTC thermistor
Stability unconditional
Output Power 50 watts into 8ohms 70 watts into 4ohms
Music Power 77 watts into 8ohms ;105 watts into 4ohms
Frequency response -1dB at 14Hz and 70kHz (at 1W- see Fig.1)
Input sensitivity 0.875V for 50ohms into 8ohms
Harmonic distortion <.05% from 20Hz to 20kHz; typically <.003%
Signal-to-Noise Ratio -114dB unweighted (22Hz to 22kHz); -119dB A-weighted, both with respect to 50W into 8ohms
Damping factor >140dB at 100Hz & 1kHz, with respect to 8ohms and without PTC thermistor
Protection fuses plus "Polyswitch" PTC thermistor
Stability unconditional
Sc480
Recently I built the SC480 just for sake of it, I have too many
amplifiers to be concerned with another one.
Well, to make the story short, the SC480 amazed me so much
with its tonal qualities that I keep it now in a high degree of
preference that I never thought it would be possible.
I've read so many derrogatory comments about this amplifier
that I thought I would say something about it.
It is not an amplifier that pretends to be the top of Ab class
(as I often read about others, very pretencious), but is very
reliable, first of all, easy to construct and to me is very HiFi.
Bass punchy, distinctive sound stage, mid range and treble
very transparent and doesn't give me any amount of objectionable heath that I have to use a fan, actually it runs
very, very cool.
Being very happy with it I only can say this was a definitive
surprise to me.
I don't use any PTC (what an horrible thing at the output!),
I don't use 3055/2955, I use MJL15024/15025 and this pair
makes a lot of diference, I had MJL15003/15004 until I
changed them and that made a LOT of difference in the overall
quality.
The supply is very standard, two 10,000 uf and putting out
+- 40 volts, 40 mA bias current.
An excelent amplifier, to summarize.....
Recently I built the SC480 just for sake of it, I have too many
amplifiers to be concerned with another one.
Well, to make the story short, the SC480 amazed me so much
with its tonal qualities that I keep it now in a high degree of
preference that I never thought it would be possible.
I've read so many derrogatory comments about this amplifier
that I thought I would say something about it.
It is not an amplifier that pretends to be the top of Ab class
(as I often read about others, very pretencious), but is very
reliable, first of all, easy to construct and to me is very HiFi.
Bass punchy, distinctive sound stage, mid range and treble
very transparent and doesn't give me any amount of objectionable heath that I have to use a fan, actually it runs
very, very cool.
Being very happy with it I only can say this was a definitive
surprise to me.
I don't use any PTC (what an horrible thing at the output!),
I don't use 3055/2955, I use MJL15024/15025 and this pair
makes a lot of diference, I had MJL15003/15004 until I
changed them and that made a LOT of difference in the overall
quality.
The supply is very standard, two 10,000 uf and putting out
+- 40 volts, 40 mA bias current.
An excelent amplifier, to summarize.....
hi jmateus,
You raised a good point in your post, a few relative minor changes can make a difference. My SC480 amp has the standard amp modules with the PTC and 3055/2955 output devices. So any comments I make are based on the stock standard kit. I gather you made your own PCBs which may make a difference. The original PCBs are too big in my opinion to fit into a case nicely.
My PSUs are a dual mono with 2 x MUR860 bridges per channel and 2 x 4,700uF caps. So this may be better or worse than the standard one.
The performance of mine is good, much better than I anticipated from the standard kit, but it not a the top of my list of amps. I must try your mods, any recommendations on replacement TO3 devices.
BTW: I built mine for the same reason, just the sake of it.
You raised a good point in your post, a few relative minor changes can make a difference. My SC480 amp has the standard amp modules with the PTC and 3055/2955 output devices. So any comments I make are based on the stock standard kit. I gather you made your own PCBs which may make a difference. The original PCBs are too big in my opinion to fit into a case nicely.
My PSUs are a dual mono with 2 x MUR860 bridges per channel and 2 x 4,700uF caps. So this may be better or worse than the standard one.
The performance of mine is good, much better than I anticipated from the standard kit, but it not a the top of my list of amps. I must try your mods, any recommendations on replacement TO3 devices.
BTW: I built mine for the same reason, just the sake of it.
Sc480
Yes, I made my own boards to be acommodated a little better
in a case relatively small.
But my big mod, the one that gave me a lot of difference in the
amplifier sonics was the replacement of the output transistors,
being the higher speed devices from On Semi MJ15024 and 25.
What a difference, the amplifier that was put aside for a while
became one of my favourites now and it works really well with
three diferent speakers. It´s a pleasure to listen to it now.
Another recommendation I have is to use silver mica caps, on
the base collector of Q3 10 pf, and also the 68 pf base collector of Q5. It really makes a difference. The input cap, well, I never
use electrolytics at the input, even non polarized, I prefer the
polypropylene ones or even polyester.
If you could make your power supply a little heftier the better,
10,000UF or higher represents a big factor on reproduction
of bass frequencies and power available.
That´s about it, a mediocre amplifier can be transformed in
a decent performer if you can consider these modifications.
Yes, I made my own boards to be acommodated a little better
in a case relatively small.
But my big mod, the one that gave me a lot of difference in the
amplifier sonics was the replacement of the output transistors,
being the higher speed devices from On Semi MJ15024 and 25.
What a difference, the amplifier that was put aside for a while
became one of my favourites now and it works really well with
three diferent speakers. It´s a pleasure to listen to it now.
Another recommendation I have is to use silver mica caps, on
the base collector of Q3 10 pf, and also the 68 pf base collector of Q5. It really makes a difference. The input cap, well, I never
use electrolytics at the input, even non polarized, I prefer the
polypropylene ones or even polyester.
If you could make your power supply a little heftier the better,
10,000UF or higher represents a big factor on reproduction
of bass frequencies and power available.
That´s about it, a mediocre amplifier can be transformed in
a decent performer if you can consider these modifications.
Mr. Mateus, i was not so lucky, or so competent as you are.
I had not good experience with this amplifier...second time constructed my dear friend....and result not enougth to me.
See you all guys what i have done, trying to make it sounding good to my ears.
Well boys, this one was enormous frustration to me.
I tried all the resources i have to make it sound good
I could not, it is sounding only reasonable, the brigths are poor,
a little mufled, and i am using fast transistors, able to many
Megahertz to reach the 3db roll of.
I tried to change input capacitor, i use many values and many
material, from old Poliester, to Ceramic and passed througth oil
capacitors...very old Cherry capacitors.
The Miller cap was changed, from 8 to 220 pf...the best value was 22pF
I used Silver Mica capacitors to feedback and Miller functions.
The output coil was changed many times...tried 1.5uH, tried 3,2uH, tried 4.6uH
and tried the standard schematic value.....also the parallel resistor was changed;
starting from 22 ohms and descending till reach 2,2 ohms...also test removing this
Coil as Mr. Graham use to advise us....no way....bass is loosen...imprecise, alike one
Enormous drum with the leather loosen...not well stretched.....
Yes guys, i tried to change input current, also i change transistors, matched 5 percent...
tried BC557, BC556, tried 2SA1015A, also tried BC640...tried magnificent BF421L and
2N5401 also.
The followed transistors i keep them as schematic, drivers i tried BD139/140, tried TIP41/42,
of course tried the ones in the schematic too.... 340 and 350, but they are almost identical to
BD139 when working....better only in specs....the best result in driver position, was AKSA drivers.
To Output, i tried the MJE3055 and MJE2955..... and decided by Sanken hi frequency units, hi
power monsters, 2SA2922 and its complementary (the correct one..sure!).
Off set was low... under 30 milivolts...voltage i used stabilized electronic supply, tried one non
stabilized also, and voltage was tried between 37 and 45 volts.....better result with 43 Volts plus
and minus.
I made changes in bias current..... big and small biased it was..... VBE, despite normal was increased
in the small transistors....result no good also....tried to reduce bias to output...to 550 milivolts....no result,
tried 575, 600 and 612 milivolts....better result with 612..... did not increase because of temperature.
It works not too hot...and do not produce the power this supply can produce.... Output Sanken has 120 of gain,
The drivers only 90.... was tried changes in emitter resistor, the driver one...made it floating....no good result,...put
them direct to output line...nothing different!.... tried other values to bias capacitor and drivers emitters capacitors.
Well, the amplifier is stable, but stable producing some sound nothing special...very standard, i can say that it is
very poor sound, despite a respectable good friend told me the amplifier sounded wonderfull, i have deep suspections
that his speaker made the miracle....i also tried 4 speaker brands....and always poor sound.
I was not lucky with it.... i am giving up of this circuit....for you guys, better luck!
regards,
Carlos
I had not good experience with this amplifier...second time constructed my dear friend....and result not enougth to me.
See you all guys what i have done, trying to make it sounding good to my ears.
Well boys, this one was enormous frustration to me.
I tried all the resources i have to make it sound good
I could not, it is sounding only reasonable, the brigths are poor,
a little mufled, and i am using fast transistors, able to many
Megahertz to reach the 3db roll of.
I tried to change input capacitor, i use many values and many
material, from old Poliester, to Ceramic and passed througth oil
capacitors...very old Cherry capacitors.
The Miller cap was changed, from 8 to 220 pf...the best value was 22pF
I used Silver Mica capacitors to feedback and Miller functions.
The output coil was changed many times...tried 1.5uH, tried 3,2uH, tried 4.6uH
and tried the standard schematic value.....also the parallel resistor was changed;
starting from 22 ohms and descending till reach 2,2 ohms...also test removing this
Coil as Mr. Graham use to advise us....no way....bass is loosen...imprecise, alike one
Enormous drum with the leather loosen...not well stretched.....
Yes guys, i tried to change input current, also i change transistors, matched 5 percent...
tried BC557, BC556, tried 2SA1015A, also tried BC640...tried magnificent BF421L and
2N5401 also.
The followed transistors i keep them as schematic, drivers i tried BD139/140, tried TIP41/42,
of course tried the ones in the schematic too.... 340 and 350, but they are almost identical to
BD139 when working....better only in specs....the best result in driver position, was AKSA drivers.
To Output, i tried the MJE3055 and MJE2955..... and decided by Sanken hi frequency units, hi
power monsters, 2SA2922 and its complementary (the correct one..sure!).
Off set was low... under 30 milivolts...voltage i used stabilized electronic supply, tried one non
stabilized also, and voltage was tried between 37 and 45 volts.....better result with 43 Volts plus
and minus.
I made changes in bias current..... big and small biased it was..... VBE, despite normal was increased
in the small transistors....result no good also....tried to reduce bias to output...to 550 milivolts....no result,
tried 575, 600 and 612 milivolts....better result with 612..... did not increase because of temperature.
It works not too hot...and do not produce the power this supply can produce.... Output Sanken has 120 of gain,
The drivers only 90.... was tried changes in emitter resistor, the driver one...made it floating....no good result,...put
them direct to output line...nothing different!.... tried other values to bias capacitor and drivers emitters capacitors.
Well, the amplifier is stable, but stable producing some sound nothing special...very standard, i can say that it is
very poor sound, despite a respectable good friend told me the amplifier sounded wonderfull, i have deep suspections
that his speaker made the miracle....i also tried 4 speaker brands....and always poor sound.
I was not lucky with it.... i am giving up of this circuit....for you guys, better luck!
regards,
Carlos
Attachments
I am terrible sorry Mr. Mateus, yes, i heard a good sound from your 480
But i could not make it good here in my home, using the speakers i have here.
I made audio recording, hi-quality reflections there...hehe...i have not the correct chamber to put speaker and microfone.... some Isobaric....do not remember the name.... a closed chamber with absorbing material and made with non vibrating heavy gauge steel...lucked by rubber alike a submarine....perfect separation from environment noises.
regards,
Carlos
But i could not make it good here in my home, using the speakers i have here.
I made audio recording, hi-quality reflections there...hehe...i have not the correct chamber to put speaker and microfone.... some Isobaric....do not remember the name.... a closed chamber with absorbing material and made with non vibrating heavy gauge steel...lucked by rubber alike a submarine....perfect separation from environment noises.
regards,
Carlos
Attachments
I made a series filter to speaker, air core, and sounded much better
And transference of bass was better (it likes enormous inductances...crazy that!).... and i also switch mid range off. use special tweeter and sounded a little better.
This amplifier needs some special speaker...you can see it is different because of enormous value to output coil.
Also work interesting when reaching 80 watts RMS in power peaks
regards,
Carlos
And transference of bass was better (it likes enormous inductances...crazy that!).... and i also switch mid range off. use special tweeter and sounded a little better.
This amplifier needs some special speaker...you can see it is different because of enormous value to output coil.
Also work interesting when reaching 80 watts RMS in power peaks
regards,
Carlos
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