FirstWatt J2

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#1,521
With the scarcity of the crucial parts in this amp, I'm confident that Papa is sleeping well.

Regarding enclosures, you can't stop the counterfeiters. But they will be stuffing them with opamp stuff and class D.

That being said, back to the altered J2 circuit.
 
#1,522
gary s said:
Look on ebay for the Semisouth device, heaps listed out of China - absolutely not one would be the real thing. Fakes and counterfeits every where!!!

Buyer beware.
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I bought some from aliexpress. The vendor was a nice guy who didn't know what they were and he gave me a refund. the only time I bought semis from a non reputable vendor. I have heard that the Chinese govt is clamping down on counterfeiting, which is good news for everyone.
 
#1,526
Where's the button to delete the fake news and conspiracy theories?

Give me detail and insights on the J2, please. I think it's great how Nelson laid out some bread crumbs and there's been an incredibly creative effort over the space of 10 years to work up some hardware to emulate the Master. That's what's got my focus.

Enjoy.
 
#1,529
Soundhappy said:
It's allowed to organise pcb Group Buys for amps build who are consciously made for an illegal counterfeit copy
of original First Watt enclosures ?
A new trend on the forum ? 🙁 With the Moderators blessing ?
Click to expand...

Counterfeit is when you build something to be indistinguishable from the original, and try to sell it as a real one.

If you build something in your basement for your personal enjoyment, even if you push as far as building it in a case that look like the original, i don’t see counterfeit, i see DIY
 
#1,532
Itsmee said:
How well matched do the CCS FETs need to be if not using 2SK3497?
Click to expand...

I'll take a stab at this. The feedback loop for the auto-bias is measuring the combined current from the CCS and output device. So at first blush it should auto-correct for any mismatch.

However, the distortion profile is at least partly influenced by the ratio of current being sourced from the CCS and output device, so large auto-corrections would change that. I therefore think you want to match them, although critical matching is probably not required.

That's my guess, anyway. 😉

Cheers,
Jeff.
 
#1,533
There are some rules here on DIYAUDIO and some mods to have an eye on it. There is Nelson Pass, who is probably the owner of the design. I consider these mods and Nelson the right people to pop in and/or take action against anything that is not within the rules and Nelson's business interest.
So why should we start judging other fellow's behaviour?
I really can't understand what the base therfore could be.

So let us come back to the topic.
 
#1,539
EUVL said:
> So a 2mA and a 6mA will act the same as two 4mA?

Yes.

But the one I posted, I use a fixed drain resistor and adjustable current source with an extra source resistor trimmer.
Guess why ?


Patrick
Click to expand...

Still struggling with this.

On the first reading I missed the part about the "fixed drain resistor". That's the resistor in the positive leg of the LTP, right?

The voltage gain of a common source amplifier is proportional to Rd / Rs. Rs, because it's a CCS, is nearly infinite, right? So a small change to Rs should make no change in the gain.

But if Rs is really nearly infinite then a small change to Rd won't make any difference either.

So is this where we need to abandon "nearly infinite" and find out what the impedance of the CCS actually is, or do I have the wrong end of the stick?

Cheers,
Jeff.
 
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