Mystery MOSFET mono amplifiers with 2SK135 and 2SJ50 - a little help? - Page 2 - diyAudio
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Old 28th April 2012, 09:15 AM   #11
Join Date: Jan 2005
It'd work but i think it would be better to run both off the same transformer winding, or have two totally separate windings isolated from each other.

Last edited by Tekko; 28th April 2012 at 09:32 AM.
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Old 28th April 2012, 09:58 AM   #12
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Default Maplin 150W MOS-FET Amplifier Module

This was a good example of the use of the Hitachi MOS-FETs that gave good and reliable results at low cost.

During 2005 I was actually in negotiations with Maplin to produce a commercial version of this same circuit.

Dollar for Dollar it is PRETTY GOOD.
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Last edited by KatieandDad; 28th April 2012 at 10:01 AM.
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Old 28th April 2012, 11:14 AM   #13
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I can't tell if those are similar in design to mine. I'll try to draw up that schematic later.

I've now connected the transformer as per Tekko's advice. Just using one and the same rail for both amps.

Listening now, it sounds considerably better than with the wal wart (not surprisingly), and I can now play quite loud - no clipping. There is quite a bit of 50Hz hum however, but that is probably caused by my sloppy temporary wiring (speaker wires and power wires are crossed). They're hanging loose right now. Will have to find some wood planks to bolt them to, or something.

They appear to sound rather nice, but it is hard to really say, due to the hum, and because I'm only using my rather poor test speakers (nice drivers but poor cabinet). Don't dare to plug in my primary speakers, yet.

This is fun!

EDIT: Could the lower voltage cause hum? There was none with 12V, but there is with 30. It's probably supposed to run at 45-50V.

EDIT2: I tried playing without a pre-amp and just adjusting the volume with the computer. Worked well, sounded better. But more hum! Then when I unplugged the power cord, there was an increasingly loud sizzle sound, kind of when you pour water into a hot frying pan. Freaky! That did not happen when I used the pre-amp, then it would just turn off with a smooth popping sound.

Last edited by Coconuts 500; 28th April 2012 at 11:28 AM.
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Old 28th April 2012, 11:25 AM   #14
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Lower voltage shouldn't cause hum on its own unless you have crap caps. It will however distort badly as it will clip early.

Clipping is bad for speakers so get PSU right before you try good speakers.
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Old 28th April 2012, 11:44 AM   #15
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From what i can tell, those modules have two 1000F 100V capacitors in series across Vcc and GND, these add up to a total of 500F, nowhere near enuf filtering.
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Old 28th April 2012, 11:51 AM   #16
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That's true actually. I didn't think of that. Remembered them as 2200 for some reason, and assumed they were in parallel. 500 - that's ridiculous. What were they thinking?

Puzzling. These are rated at 100V each - why would they be in series?

EDIT: Upon closer inspection, they aren't exactly in series. There's a big resistor (10K, 2 or 3 W), and an LED in between them.

Last edited by Coconuts 500; 28th April 2012 at 11:57 AM.
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Old 28th April 2012, 01:05 PM   #17
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They're in parallel.
Easy to see, because traces of both sides are visible : + traces of both lytics are connected in parallel by the fuse holder leads.

I've seen these modules before, even recognise the ECN-CPA4 print, few decades ago, for the likes of me can't recall the rest of the story (the moment to jump off a bridge is due).
It doesn't count how one deals with winning, but how to handle a loss ( DjT)
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