FirstWatt J2

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#1,821
Schematic j2c
 

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#1,823
J2 with mosfets

I'd like to compare my EVUL based J2 with a mosfets based J2. Here's why.

The J2 is a very satisfying amp.
I could get into what I hear, but I'm sure no one cares.
I think that if a mosfet based J2 were available, and comes close to the J2, more people could built it and enjoy it. I thought I might have been too ambitious in wanting to build a J2. I mean, how different could it be from a F3, F5 F4, F7? It's different, and it's fun listening to it

So my question is, can mosfets be dropped in place of the R100 jets without blowing up the output stage?
How much circuit tweaking would be required?

Thanks in advance.
 
#1,826
vdi_nenna said:
I'd like to compare my EVUL based J2 with a mosfets based J2. Here's why.

The J2 is a very satisfying amp.
I could get into what I hear, but I'm sure no one cares.
I think that if a mosfet based J2 were available, and comes close to the J2, more people could built it and enjoy it. I thought I might have been too ambitious in wanting to build a J2. I mean, how different could it be from a F3, F5 F4, F7? It's different, and it's fun listening to it

So my question is, can mosfets be dropped in place of the R100 jets without blowing up the output stage?
How much circuit tweaking would be required?

Thanks in advance.
Click to expand...

Not sure if this helps but as per Nelson himself... See Post 1127 & 1130

FirstWatt J2
 
#1,831
> I think we were hoping for the J2X version.

Spiced that a long time ago.
It only works well if you have very well matched parts to cancel 2nd harmonics.
But the whole point of J2 is about 2nd harmonics, right ?
So why would you want to get rid of that by going balanced ?

And of course it will double your costs for SJEPs.


Cheers,
Patrick

.
 

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#1,835
EUVL said:
vdi_nenna

If you intend to build, you should use the final version in post#89, and not that in post#1 :
UDNeSS, or You don't need Semisouth's

Gerber files in post#90, #91.


Patrick
Click to expand...

Thanks Patrick, I spent a few hours last night reading posts and trying to figure out the latest version.

I found UDNeSSV2a.zip to have a later Last Modified date than UDNeSSV2.zip. Maybe they are completely different boards?

Is it still possible for the original poster/thread starter to edit post number 1?
Would save OP explanations and reader time finding the latest and greatest version of schematic and PCB.

Thanks,

Vince
 
#1,837
doing balanced UDNESS fix Issue with unobtainable part

would you please briefly describe 3rd and 2nd harmonic sound


EUVL said:
> I think we were hoping for the J2X version.

Spiced that a long time ago.
It only works well if you have very well matched parts to cancel 2nd harmonics.
But the whole point of J2 is about 2nd harmonics, right ?
So why would you want to get rid of that by going balanced ?

And of course it will double your costs for SJEPs.


Cheers,
Patrick

.
Click to expand...
 
#1,839
Hello there.

First a huge thanks to Jeff and others who've made this possible. I've just got to know of this project and from what I can tell there are 2 versions (one with the hard to come by Semisouth and the other a variant with probably easier to get parts proposed by EUVL). Apologies if I got this wrong. I posted these questions to the GB on the "Long and Skinny" boards but didn't get a reply. May be this is the right place.

I have a few questions pertaining to the Semisouth version. Just to make sure I've got everything covered and possibly help someone else get started.

- I think these are the steps to follow:

  • See if you can afford 4 Semisouth SJEP120R100 (don't need to be matched)
  • Get 8 matched SJ74BL (or at least 4 matched per channel) and 4 matched (or 2 matched per channel) SK170GR (mostly from seller punkydawgs on Ebay)
  • Get PCBs L & R
  • Get rest of the items from the BOM


- On the PSU front I could locate Jeff's PSU. Is that the right one? Looks like there is also the CRC supply. Pros/Cons?

- Any special specs for an "audio" grade mains toroid transformer?

- If one wanted a soft start (to avoid the loud pop through speaker) is there an add on circuit you recommend?

- Is any kind of speaker protection built-in? If not, any suggested circuit?

- Is any kind of thermal auto-off protection built-in? If not, any auggested circuit?

- I assume this is rated at 25 Watts? What is the maximum power consumption?

- Silly question maybe but would you say the amp is quiet/silent with no input?

- Is there a suggested enclosure? Again importing one will be expensive so if there was (ideally) a CAD drawing I could check with a local company. Would like some suggestions on how to spec the heat sinks on the side?

Thanks again.
 
#1,840
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