DIY Front End 2022

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#901
Mark Johnson said:
Maybe someone might want to create a PCB which allows builders to use Nelson's DIY Front End 2022 circuit, as a front end for the First Watt M2x (?). It would be a daughter card, just like all the other daughter cards which the Store ships in the M2x board set ("Ishikawa" , "Tucson" , "Mountain View" , etc.). Images below.

I doubt that I'll do this myself. Three years ago I laid out and released Gerber CAD files for the "IPS6" daughter card, which is quite similar, and I'm not too interested in a do-over. But there may be someone who wants to hear Nelson Pass's 2022 front end circuit (daughter card) playing through the M2x output stage. They might decide to lay out a board and publish their Gerbers here. That would be fun, that would be fugly.

_
Click to expand...
Preferably using JFE2140 - instead of 2SK170 option
 
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#903
I found it useful when building a JFET testing jig, to make the series gate resistor big; I chose 22K. Why? Because WHEN (not if) you install a device incorrectly, your jig will forward bias a gate-drain or gate-source PN junction diode. WHEN (not if) this happens, you want to limit the forward bias current, or else you'll damage the device. I completely destroyed several JFETs with this exact mistake, until I revised my jig to include a 22K resistor in series with the gate. Now, incorrect installation is nonfatal.
 
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#905
kannan_s said:
Hi
what are the Current Source Transistors in this build ? is it J113 and if so how did you select the correct J113 as I have bought 30 of them and all of them have more than 6mA and most of them above 10mA. Do you have extra PCB's as I want to use JFE2140 as i have those.
thanks
kannan
Click to expand...

For Q3 I used J113, measuring Id, as ZM's lower left diagram using resistance decade box instead of a pot.
Just dial in the value. Handy tool. Eliminates the extra step of removing the pot from the circuit to read the value.

Decade Box.jpg

All my J113 Idss > 15mA. No problem using as CCS.

For Q4 I used some 2N5486 I have that happened to have 9mA Idss, measured as ZM's upper left diagram. (Note in my pic the jumper for R8, or zero ohms). No resistor needed if Idss is the desired ccs current.

A constant current diode is, a JFET binned by Idss with gate and source connect internally and only two pins, (pin-1)anode or drain and (pin-2)cathode or gate and source shorted.

I only ordered enough to build a few boards. I'll share the gerber files if you'd like to have your own boards made.
 
#906
Hi Cinco
please send me the Gerber Files so that I can get it fabricated. For Q3 "A little under 3 ma" was stated. Were you able to get such J113 and where did you purchase J113 ? My stash has minimum of 6mA only and not suitable for Q3 duty
kannan
 
#908
Howdy kannan,

I got mine at Mouser. I bought about qty 50 a couple years ago to experiment with. 6mA would work with a resistor. I think Nelson stated he has 600,000. Much bigger sample size, so better chance to find characteristics for certain applications. Cheaper per unit too!

It'll be tonight before I get home to zip up and PM the files.
 
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#916
Forgot to mention DS voltage around 12V in that case mentioned. So if the FE voltage the junction of Q1-Q2 sources is lower, it would require lower resistance. I am yet to assemble the FE board that I received. Easier to employ CRD with correct value.
 
#919
Hi,

Now that I have ordered my PCBs 😀 let’s move forward.
Could someone recommend a decent stereo volume control for this preamp. Thinking of 20k ohm, log but I guess it could be a linear one with a resistor across. My DAC will be driving the FE 2022 so maybe 10k pot would be ok..

Thanks
Eric
 
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