Even if you use the same part number, there is no guarantee the bias is exactly the same between 2 parts.
This is because the forward voltage of the LED varies from part to part.
Also the current trasnfer ratio varies from part to part.
Of course between the same part number, variation is less then between different types.
So you need to compare both Vf and CTR at least from the datasheets.
Patrick
This is because the forward voltage of the LED varies from part to part.
Also the current trasnfer ratio varies from part to part.
Of course between the same part number, variation is less then between different types.
So you need to compare both Vf and CTR at least from the datasheets.
Patrick
Which SemiSouth Parts are used in the J2? I have a stash of SJEP120R100's. However, I think I saw a review that showed different internals.
SemiSouth was used for the primary single ended device, and IR parts for the current source.
Looks like all is working as expected. Had to increase r33 slightly to have zero dc on output. Right now its just quick and dirty put together using variac, but it produces nice sound. Thanks everyone for parts and boards! This is great community.
Btw, i put that junction wire from underneath, the holes were tiny from top.
Btw, i put that junction wire from underneath, the holes were tiny from top.
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With +/_20 VDC power supply both channels are drawing 3A. I believe 1.5A per channel is fine.
One thing i noticed is that IR mosfets are slightly hotter than bottom SemiSouth Sic. So i measured top side of the outputs with infrared. IRs are ~76degC, SemiSouth are ~56degC.
Heatsinks itself are 32degC.
Is this ok?
One thing i noticed is that IR mosfets are slightly hotter than bottom SemiSouth Sic. So i measured top side of the outputs with infrared. IRs are ~76degC, SemiSouth are ~56degC.
Heatsinks itself are 32degC.
Is this ok?
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I think you'll obtain much better results if you re-tap a new set of holes... so that the IR can be properly screwed into the heatsink. I'd also strongly recommend a large washer...
That could be it. I was reusing old heatsink and spacing was different. I will try the big washer.
It may not look best, but it works.
And sounds great.
If it sounds good, it is good.
And sounds great.
If it sounds good, it is good.
Anyone used smps on J2?
I got bunch of computer grade 19VDC supplies, if they do not fight, and make +/-19, it could work.
I got bunch of computer grade 19VDC supplies, if they do not fight, and make +/-19, it could work.
I put two smps together, and even found dedicated filter, just one, but i do not hear any issues. That filter was likely developed by you, Mr. Nelson. Amp is silent and working great. Started working on wooden chassis.
Thanks again all, for boards and outputs.
Thanks again all, for boards and outputs.
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The speakers are a variation on Gary Dahl's Beyond the Ariel design, Troy Crowe is completing them for me. https://josephcrowe.com/
Meanwhile, my J2 amp has not seen voltage since I got it ~ 8 years ago. Would using my Variac to very slowly increase the line voltage be a safe and effective way to protect the electrolytics and prevent their value from changing much?
I've never heard of any modifications to the J2. Mine has worked flawlessly with a number of speaker combinations, often when using it to bi-amp. The one driver that didn't play nice was the Lowther PM6C. Please be sure to keep us posted on how Troy Crowe's speakers work for you. I enjoy the detailed tests he posts on U-tube.
Based on it having been produced for over 10 years, in far greater numbers than any other First Watt amp, I believe the J2 was the most popular ever sold.
I'm not sure a soft start is necessary but I'm sure others will chime in, possibly Nelson himself.
Based on it having been produced for over 10 years, in far greater numbers than any other First Watt amp, I believe the J2 was the most popular ever sold.
I'm not sure a soft start is necessary but I'm sure others will chime in, possibly Nelson himself.