Amp In A Box FETs Matching

[POTL]

Tell me about the fets matching
On what parameter to look, what data should be?
How can I select transistors for the mu-amp cascade?

I'm interested in switching from 9 to 18 volts
On my layout, the transistors work either 9 or 18 volts
Put those that were.

As an example, let's take a Marvel Drive schematic

[POTL]

Hey
I know that you are here.

[jubal81]

This is just a preamp design with J201 in place of tubes. Biasing with the drain resistor is a crap shoot, but you can make any J201 work - just don't trust any FETs from Tayda.

Just multiply the supply voltage by .6 and adjust the trim pots to get that voltage on the drains.

[KarenColumbo]

Extremely good read about matching: http://viva-analog.com/characterizing-and-matching-2n5457-jfet-transistors/
More "esoteric", but fascinating nonetheless: http://viva-analog.com/easy-jfet-curvature-extraction-method-120426/

[Plexi]

This is just a preamp design with J201 in place of tubes. Biasing with the drain resistor is a crap shoot, but you can make any J201 work - just don't trust any FETs from Tayda.

Just multiply the supply voltage by .6 and adjust the trim pots to get that voltage on the drains.

+1
Just use trimpots...is the same that match before place w/fixed resistor.
Good advise about multiply by .6
I always trim to 4.5/5v.

[POTL]

Did not quite understand what it means
Good advise about multiply by .6

[Plexi]

Overal voltage needed at drain...multiplying by 0,6.

Example: you feed the circuit with 9v.
9 x 0.6 = 5.6v (from 4.5v to 5.6v will be fine)

[POTL]

cool
And transistors on this value should be very close?
For example 4.8 and 5.0)
Or any values ​​in this range will do?

[Plexi]

That will be determined by each Jfet's inconsistencies.
Sometimes, the Rd (resistor to Drain) is setted by design: in this case, any value to bring you that % of in Voltage.
Then, you need to set the Rs (source), and get the exactly point where it can amplify, without distort (in bad way), or just cut (no sound).
That's why is recomended place trimpots there.

Setting Jfets is something a bit difficult to understand if you like to get the 100% of each fet using math's and all the theory, but simple if you use your ear and experience to simplify some "costumes" about: when you know wich Res values are commonly used on each kind of Jfet, or copy that stages from another designs

[POTL]

That will be determined by each Jfet's inconsistencies.
Sometimes, the Rd (resistor to Drain) is setted by design: in this case, any value to bring you that % of in Voltage.
Then, you need to set the Rs (source), and get the exactly point where it can amplify, without distort (in bad way), or just cut (no sound).
That's why is recomended place trimpots there.

Setting Jfets is something a bit difficult to understand if you like to get the 100% of each fet using math's and all the theory, but simple if you use your ear and experience to simplify some "costumes" about: when you know wich Res values are commonly used on each kind of Jfet, or copy that stages from another designs

Adjusting the bias of transistors is not a problem for me.
I have already collected many schemes and even started to develop my own.
My method is as follows
1) I configure each transistor by ear
2) I set the potentiometer gain below half
3) I decrease the volume on the guitar, until the sound becomes almost pure
4) I turn the trimot up to that point until the sound is good.
5) I check the sustain, whether the notes are dying out correctly (avoid strange sounds like Fuzz Face with bias pot)
It's all.
The pedal for 4-6 transistors is tuned for 1-2 minutes, works perfectly in all combinations of pedal and guitar adjustments

[GGBB]

How can I select transistors for the mu-amp cascade?

The FETs in a mu-amp don't need to match: http://www.geofex.com/article_folders/foolwfets/foolwfets.htm.

[POTL]

How can I select transistors for the mu-amp cascade?

The FETs in a mu-amp don't need to match: http://www.geofex.com/article_folders/foolwfets/foolwfets.htm.

2 any FETs in mu amp will work without problems in a range of 9-18 volts?
I always built layouts in 9 volts, I tried 18 - I liked the sound (I struggle with noise) it is interesting to make the switching of 9-18 volts