The likelihood of fake sanken parts steered me away from that one, have this one running at 82v.
1PC NJW0281/NJW0302 450W+450W HIFI Stereo Amplifier Board Assembled AMP Board | eBay
Is going to be used in a semi PA application, has very low bias but surprisingly sounds good considering.
1PC NJW0281/NJW0302 450W+450W HIFI Stereo Amplifier Board Assembled AMP Board | eBay
Is going to be used in a semi PA application, has very low bias but surprisingly sounds good considering.
Cost of the parts is lower, less likely to have been counterfeited in my experience.
Has 2mv of offset on one channel, 4 on the other, so some care went into matching those parts anyways. Nothing fishy about the part markings, soldering is nice, no flux residue, has a zobel network.
The board in question by the op may be fine also, who knows?
Certainly not me or you...
Oh, and I have received legitimate mt200 sanken parts from eBay before, so I know that they don't all come from the same fake source.
I'd say there is definitely risk involved, that it will arrive in one piece for starters!
Has 2mv of offset on one channel, 4 on the other, so some care went into matching those parts anyways. Nothing fishy about the part markings, soldering is nice, no flux residue, has a zobel network.
The board in question by the op may be fine also, who knows?
Certainly not me or you...
Oh, and I have received legitimate mt200 sanken parts from eBay before, so I know that they don't all come from the same fake source.
I'd say there is definitely risk involved, that it will arrive in one piece for starters!
Thanks for sharing your feedback on this:
4 pairs of 150w devices and 84v rails.... reminds me of the venerable Adcom GFA-555ii. on a 675-700 va trafo (30kuf per channel) , I have measured 8 ohm clipping at about 290watts. With a 1.2kva trafo and 44kuF per channel, for the same voltage, I got about 380 watts into 8 ohms. I forget the 4 ohm rating... with 1000va and 30kuF, about 350watts into 8 ohms...
Both the 2sd424 used in the GFA 555 and the njw0381 in this kit have a 100ms SOA of 0.4A at +/-90v rails, but the njw has a much better gain spec. At 10v & 5A, the 2sd424 was about 45, while the njw is over 120! At peak currents... this kit might just have lower distortion in the driver/predriver stages...
As expected, they said their supplier did not have schematics or wiring instructions... too bad I had already pulled the gun on ordering them...
Did you notice that the blurb further down says the power transistors are pulled from older boards ! They are not NEW!
What do they mean by comparable to LM3886 amp ? Is the LM3886 their standard for good sound ?
I have the L12 boards. Used it only for a short while as I was moving home. Sounds quite nice but I thought that the HF was a bit polite. I could be wrong as it was all done in a hurry. I remembered about it after reading about it here. Unfortunately I may not be able to check it again right now as I'm going out of town for a week. I have the LM3875 amps also. But the L12 is better I think. Let me see if I can check the L12 again before I leave.
What do they mean by comparable to LM3886 amp ? Is the LM3886 their standard for good sound ?
I have the L12 boards. Used it only for a short while as I was moving home. Sounds quite nice but I thought that the HF was a bit polite. I could be wrong as it was all done in a hurry. I remembered about it after reading about it here. Unfortunately I may not be able to check it again right now as I'm going out of town for a week. I have the LM3875 amps also. But the L12 is better I think. Let me see if I can check the L12 again before I leave.
As expected, they said their supplier did not have schematics or wiring instructions... too bad I had already pulled the gun on ordering them...
This was exactly the answer I got.
My answer is even simple - I do not order what can be scrap with fake parts.
Simple that!
Use the LM3886 as comparative reference is also a poor choice.
I can make my own projects, but the Brazilian costs is very high and the final amplifier will be quite expensive.
I saw in the forum schematics from L7 amplifier. It uses technics used by other person here in the forum. So it is not an original idea. This amplifier aceptes some improvements to give bether performance - it can be my choice.
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The 3281 one is definitely a bit subdued, has nearly no bias, runs cold. The transformer is 800va, and the ac line here is 120v, going through an 8 amp circuit breaker. I figure it may produce 350w. I put some industrial polypropylene input caps, and some small polystyrene decoupling on it, to try and wake it up a bit. If it lives long enough, it will reside in a relatives party house after installing a protection board.
It doesn't sound bad through my magnepans, plenty of bass, with a modern dac as a source, just doesn't compare to my big fet amp is all.
The first board, with the mt200 parts, may be a clone of a McClaren amp perhaps, although they ran at lower voltages though.
It doesn't sound bad through my magnepans, plenty of bass, with a modern dac as a source, just doesn't compare to my big fet amp is all.
The first board, with the mt200 parts, may be a clone of a McClaren amp perhaps, although they ran at lower voltages though.
Here is the one I am using, not a high fidelity unit, more of a PA amp really.
1PC NJW0281/NJW0302 450W+450W HIFI Stereo Amplifier Board Assembled AMP Board
1PC NJW0281/NJW0302 450W+450W HIFI Stereo Amplifier Board Assembled AMP Board
The width of th heat sink is 62mm, I used a couple pieces of metal that I had laying around, am going to add a pair of 1.625 X 1.75 X 10 heat sinks using fasteners, and heat sink paste. The heat sinks will be off set so that the fins will leaf together in the center under the board, a fan at one end will do the rest.
It hasn't even warmed up to room temp so far with just the plates, 4 ohm load.
Maybe it will get warm at 450watts...
It hasn't even warmed up to room temp so far with just the plates, 4 ohm load.
Maybe it will get warm at 450watts...
I think your plan should work, the bass is actually pretty good, am using 10uf input capacitors so that helps with that also.
Also put some small Wima fkp2 off the inputs, replacing the ceramic parts that came on it.
While there may be a place to successfully add some additional local decoupling, the locations near the 4 transistors didn't work for me. So now, same value film caps will do, and I'm letting it be for now.
I agree that cold transistors never sound very good.
Also put some small Wima fkp2 off the inputs, replacing the ceramic parts that came on it.
While there may be a place to successfully add some additional local decoupling, the locations near the 4 transistors didn't work for me. So now, same value film caps will do, and I'm letting it be for now.
I agree that cold transistors never sound very good.
I use F-3dB ~ 2Hz for the passive single pole input filter.
This requires an RC time constant of ~80ms
You can get that 80ms from 10uF into 8k2, or from 1uF into 82k, or any of many other combinations.
That 2Hz was arrived at by being one octave below what I could hear as slight changes in the relative frequency balance between low bass and the upper range.
It may be that I could have got away with using F-3dB = 4Hz.
But there is lots of opinion that going to one decade beyond the wanted pass band removes any level effects and removes most of the phase effects. So I stuck with using and recommending one decade beyond the wanted pass band, i.e. 2Hz to 200kHz for the passive filters to the input to a wideband Power Amplifier
This requires an RC time constant of ~80ms
You can get that 80ms from 10uF into 8k2, or from 1uF into 82k, or any of many other combinations.
That 2Hz was arrived at by being one octave below what I could hear as slight changes in the relative frequency balance between low bass and the upper range.
It may be that I could have got away with using F-3dB = 4Hz.
But there is lots of opinion that going to one decade beyond the wanted pass band removes any level effects and removes most of the phase effects. So I stuck with using and recommending one decade beyond the wanted pass band, i.e. 2Hz to 200kHz for the passive filters to the input to a wideband Power Amplifier
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