Dear to All,
I'm a newbie in amplifier tweaks 🙂
I have a Harman Kardon HK 990, which I would like to improve.
I red it has some MJL3281A and MJL1302A power transistors.
Can they be replaced by newer models like MJL4281A (NPN) and MJL4302A (PNP) without replacing alf of the comonents on the board ?
Will this upgrades make the amplifier sounding much better?
Maybe some of you know this amp and have some advise.
The bias have been setted to 38mV as specified on the manual.
Thanks a lot for helping 🙂
Manu
I'm a newbie in amplifier tweaks 🙂
I have a Harman Kardon HK 990, which I would like to improve.
I red it has some MJL3281A and MJL1302A power transistors.
Can they be replaced by newer models like MJL4281A (NPN) and MJL4302A (PNP) without replacing alf of the comonents on the board ?
Will this upgrades make the amplifier sounding much better?
Maybe some of you know this amp and have some advise.
The bias have been setted to 38mV as specified on the manual.
Thanks a lot for helping 🙂
Manu
thank you for your answer.
I red many posts where people were very pleased with the sound the power transistors upgrade provided, that's why I was interested.
I red many posts where people were very pleased with the sound the power transistors upgrade provided, that's why I was interested.
People usually hear what they want to hear when it comes to upgrades to amplifiers. The main concern normally with the output stage is whether it can produce the power needed to drive your speakers reliably. It's normally "if it aint broke don't fix it" section of an amplifier. If the amp isn't sounding as good as it used to, sometimes electrolytic capacitors may be failing. If the amp never did sound great to begin with and you want to try to improve it, you are usually better off just getting a better amp, otherwise you need to re-engineer the amplifier which isn't a simple or inexpensive task. Building one of the many DIY amplifier designs available here will be easier and likely will sound better in the end.
OK. So no upgrades regarding bad quality capacitors, poor quality wires from transistors to speakers out or so would improve the sound quality of my hk990???
What a shame. So I don't understand how people tweaking their amps by replacing the power transistors find a much deeper, wider, detailed sound. Placebo. Effect?
Do the power transistor downgrade with the time and working hours or they stay at their top performances till the end
What a shame. So I don't understand how people tweaking their amps by replacing the power transistors find a much deeper, wider, detailed sound. Placebo. Effect?
Do the power transistor downgrade with the time and working hours or they stay at their top performances till the end
would you define what you mean by "improve"?
If you have an hk990 that meets/exceeds manufacturer specs, you will need decent test gear to confirm improvement.
If you want to change how it "sounds", well, that's a different kettle of fish.
Again, what sonic changes are you looking to make?
For example, if you know what you're doing, you can easily cause change by varying the output stage bias or changing the frequency compensation. Those may be easier than:
0. establishing a baseline of the product's current performance
1. acquiring sufficiently matched output devices that are ...
2. confirmed NOT to be fakes
3. removing the old devices and installing the new devices (including care with the thermal management system)
4. testing for performance "improvements" relative to your baseline
mlloyd1
If you have an hk990 that meets/exceeds manufacturer specs, you will need decent test gear to confirm improvement.
If you want to change how it "sounds", well, that's a different kettle of fish.
Again, what sonic changes are you looking to make?
For example, if you know what you're doing, you can easily cause change by varying the output stage bias or changing the frequency compensation. Those may be easier than:
0. establishing a baseline of the product's current performance
1. acquiring sufficiently matched output devices that are ...
2. confirmed NOT to be fakes
3. removing the old devices and installing the new devices (including care with the thermal management system)
4. testing for performance "improvements" relative to your baseline
mlloyd1
In addition to finding genuine output devices, you need to find enough to allow for matching. The HK990 uses a pair of ThermalTrak output devices that will need to match the rest of the devices somewhat closely for best current sharing. Normally the easiest way to accomplish this is to buy a set of devices from the same build batch. This isn't possible when the devices aren't identical. This is a bigger problem as the desired devices are obsolete.
Thanks a lot for Your replies.
It's a bit more difficult than what i thought...
Has the Amplifier has some years (8) I was just thinking in replacing some caps, and the power transistors by new ones, and, probably better with the new technologie...
It's a bit more difficult than what i thought...
Has the Amplifier has some years (8) I was just thinking in replacing some caps, and the power transistors by new ones, and, probably better with the new technologie...
What just happened here?? If a DIY forum isn't about ******* your self up, to a point where you need serious mental- and co-geek help - then what is it for then?
Sweet jezuz, take the freak' thing apart, and let us know how you are doing. I had a 990 in the door today, and it's way hotter in the left channel, but it sounds AWSOME!
Sweet jezuz, take the freak' thing apart, and let us know how you are doing. I had a 990 in the door today, and it's way hotter in the left channel, but it sounds AWSOME!
I agree,
But i'm not good and equipped enough to make my own measurements.
Regarding the temperature you have to set the current on each board... i did it on mine, quite easy. you will find the information in the manual of the HK990.
Mine sounds good too, but felt a bit of bass when the volume is low on my spakers.that's why i was thinking in replacing the big caps by new/bigger ones to try to improve the current, and maybe other parts... if you have some advise.I saw an american company wheach is "improving" the power and sounds, but they just do it for the 110volts hk990 version, so useless for me for my 220v one.
Regards
Emmanuel
But i'm not good and equipped enough to make my own measurements.
Regarding the temperature you have to set the current on each board... i did it on mine, quite easy. you will find the information in the manual of the HK990.
Mine sounds good too, but felt a bit of bass when the volume is low on my spakers.that's why i was thinking in replacing the big caps by new/bigger ones to try to improve the current, and maybe other parts... if you have some advise.I saw an american company wheach is "improving" the power and sounds, but they just do it for the 110volts hk990 version, so useless for me for my 220v one.
Regards
Emmanuel
The most usefull mod is new and bigger caps at the power supply. These caps are components that age.
New, bigger and of better quality is a worthwhile change at PSU caps.
Electrolytic caps at signals do not age.
Electrolytic caps at rails aging... might be....but way less than the caps at PSU next to the rectifiers. The aging here comes from hight ripple current in those, and it goes worse at power up.
IMO a total recap is a waste of money and is à good way to just damage the PCB.
New, bigger and of better quality is a worthwhile change at PSU caps.
Electrolytic caps at signals do not age.
Electrolytic caps at rails aging... might be....but way less than the caps at PSU next to the rectifiers. The aging here comes from hight ripple current in those, and it goes worse at power up.
IMO a total recap is a waste of money and is à good way to just damage the PCB.
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