• These commercial threads are for private transactions. diyAudio.com provides these forums for the convenience of our members, but makes no warranty nor assumes any responsibility. We do not vet any members, use of this facility is at your own risk. Customers can post any issues in those threads as long as it is done in a civil manner. All diyAudio rules about conduct apply and will be enforced.

GB "long and skinny" FirstWatt J2 clone PCBs

Jump to Latest
#244
Hello
please add me to the buy. i would like 1 set
thanks

North America & RoW
------------
Malvin 1 set
kevinheem 1 set
Soundslave 1 set
mattattnet 2 sets
Myint67 1set
twitchie 1 set
flamethrower1 1 set
necplusultra 1 set
WBS ???
Scott Stansbury - 1 set
nashbap 1set
mlwebb 1 set
Gnub 2 sets
Feds27 1 set (see page 21)
bologna1 1 set
leejh 1 set
AMB4 1 set
thompsontechs 2 sets



EU
------------
pfisla 2 sets
gig 1 set
Dr.Strangelove3 1 set
malisz ???
dieter12 2 sets
pistollero - 2 set
Spades 1 set
Rodeodave 1 set
MEPER 2 sets
iBuell 1 set


Unknown
------------
RustySanwa 2 sets
 
#252
hifibluedevil said:
FYI, in my real J2 amp Papa used all bl grade jfets 2 each K170 and 2 each J174s per rail, and no dual 2jl109s. I have no way of measuring them though.
Click to expand...

Just to be sure I understand that would be two J170's for the CCS(Q3 and Q4 in Jeff's schematic) and two J74's instead of the four J109's in the LTP(Q1A,Q1B,Q2A,Q2B)?

Am I correct in my understanding that the two sides of an LTP should match closely, so the Idss of Q1 should be equal to Q2? Also, if the CCS is producing the chosen 8.5ma(as per Jeff's analysis) do we need Q1 and Q2 to be greater than or equal to 8.5ma?

Thanks.
nash
 
#253
Hi Nash,

The SJ109s are a pair of SJ74s in a single plastic package. So you can use 2 SJ109s per channel (as the early factory J2s did), or 4 SJ74s (as hifibluedevil's factory J2 does).

You don't actually have to have the LTP doubled-up. You could use a single SJ109 per channel, or 2 SJ74s. But then it's not really a J2 -- or at least it's farther from the factory spec.

The two legs of the LTP should match. So in my schematic you'd match Q1A and Q1B, and then separately match Q2A and Q2B. It's not terribly important to match within a leg (ie: Q1A and Q2A).

The sum total of the LTP transistors should be well over 8.5mA. However, if you're using the factory spec of 4 BL-grade JFETS (whether 2 SJ109s or 4 SJ74s), then you're guaranteed to be have at least 24mA.

Cheers,
Jeff.
 
#256
JeffYoung said:
Hi Nash,

The SJ109s are a pair of SJ74s in a single plastic package. So you can use 2 SJ109s per channel (as the early factory J2s did), or 4 SJ74s (as hifibluedevil's factory J2 does).

You don't actually have to have the LTP doubled-up. You could use a single SJ109 per channel, or 2 SJ74s. But then it's not really a J2 -- or at least it's farther from the factory spec.

The two legs of the LTP should match. So in my schematic you'd match Q1A and Q1B, and then separately match Q2A and Q2B. It's not terribly important to match within a leg (ie: Q1A and Q2A).

The sum total of the LTP transistors should be well over 8.5mA. However, if you're using the factory spec of 4 BL-grade JFETS (whether 2 SJ109s or 4 SJ74s), then you're guaranteed to be have at least 24mA.

Cheers,
Jeff.
Click to expand...


Thanks Jeff for the detailed response on how you matched each leg of the LTP.


Regarding the ccs what does the factory J2 use?

The schematic shows R11 as 100k. I think your simulation used 110k or 120k for the 8.5ma result. Any change suggested?


nash
 
#257
Nelson told me factory J2s had CCS currents from 8mA to 12mA. (Or at least that's what I understood -- I hope I'm not misquoting.)

The simulations changed R11 just to be able to compare the results at the same gain (similar to volume matching when ABX testing). For a single instance the exact value isn't critical; I used 100K.

Cheers,
Jeff.
 
You must log in or register to reply here.
Top Bottom