Super Hard On versions and noise

[rankot]

Over here in Europe, you can get them here:
https://www.banzaimusic.com/BS170P-ZETEX.html

Or here: http://www.retroamplis.com/BS170P/en even cheaper

[Lars F]

So I just converted to ver2. Can't do A/B for obvious reasons, but it still sounds great. If there is a difference it is small for sure.
There is still a bit of noise and even though it is perfectly acceptable I must admit those low noise Zetex Mosfet's are tempting.

Regards,

Lars

[PRR]

> how to calculate the input impedance of this circuit?

Depends on the gain (due to D-G feedback). Gain depends on resistors and, full-up, MOSFET parameters. Not an easy calc if this is not already clear.

But to simplify: if the gate resistors are 10Meg (a fine value) then the Zin will not drop "too low" for e-guitar. If they are 1Meg, max gain shaves treble.

[intripped]

Thanks PRR for your answer!
I think that treble shaving when gain increases is a desirable effect, I just wanted to predict the amount of this shaving, since it's not always easy to actually hear it.

Also, I would like to better understand why in the box of rock circuit, the boost circuit has got 1M resistors.

[PRR]

> why in the box of rock circuit, the boost circuit has got 1M resistors.

They were on sale?