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Group Buy for the Through Hole Folded Cascode CEN IV boards

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#103
We have a source for 3€ each. Guess you will not pay that.
So we are searching for workarounds, as posted earlier.
But this needs to be proven before communicating.
So time and patience required.
No need for everyone to be shouting out for those.

Bill of material for your own reference and not to be published.
Please respect that.


Patrick
 
#105
So here is an update on the (non-) availability of the cascode devices :

The NMOS and PMOS cascode devices specified in the BoM have long delivery time at Mouser and DK.
There are very few TO92 MOSFETs available on the market which are still active (not obsolete).
To get round this we have simulated the circuit with a pair of JFETs.
Distortion is ~1.5dB higher, which is of course no issue in reality.
They are available in large quantities at Mouser (>>10,000).
The resistor values in the gate-biasing potential divider WILL have to be changed.

Fran will order some, measure them, before testing them in circuit.
This will of course take some time.
Once this is done, you will receive information from Fram with respect to the necessary changes.

These JFETs have unfortunately large variations between devices, which may mean low matching yield.
They are quite low cost, on the other hand (< 40 cents in quantities of 100+).
I therefore suggest that you get organised for group buy & matching.
(e.g. one person in Europe, one on the American continent.)
Not only would you save costs, but your yield would improve significantly when matched from a pool of 100+.

We shall of course provide information on matching circuit as well as how to calculate resistor values.


Patrick
 
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#107
I was asked about the required matching setup.

You cannot test with one of these transistor testers.
They don't give us the information we need.

You need to measure the Vgs of the JFET under ~5mA bias.
You will need +/-9V supply (or 2x 9V batteries), digital multimeter, and a current regulating diode (E562 from Mouser).
The attached schematics is adapted from Erno Borbely's JFET New Frontier Part 1.

JFET Measurement.png


This is shown for N-JFETs.
You need to reverse polarity for P-JFET, without saying.


Patrick
 
#110
One of you has found a enay dealer in the USA who has both MOSFETs in quantities.
Price are very reasonable, 99.9% positive.

So we need someone from the GB subscribers in the US to purchase.
Preferrably also do the matching.

Or the Europeans buy for themselves as a Group.


Patrick
 
#115
I have managed to source 35 of the N channel and maybe a similar qty of the P. From reputable sources that I have used before.
If all tests out OK I can offer them here to builders in the UK/ Europe
I need to read up on testing them .
I see that CPC have pushed the delivery date back another week.

Link to the US seller?....
Edit think I've found it
 
#117
As a GB2 participant, I would like to help, but have no BOM to give me an idea of what to search for except for TO-92's.

I purchased a solderless breadboard today, and will try to build up a transistor matching unit based on the above. May take awhile though. Like the idea of the Jfet if MFet not available.

To buy a few of the E562 diode's, I will have to see if I need some other components in order to make shipping worthwhile. Such is DIY🙂
 
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