A different (?) line level circuit

Hi everyone!
I was trying this circuit from G.Velez (Gabevee) just to see the behaviour on LTSpice. I'm a newbie on electronics as well as in the use of Spice, so, independently if you like this circuit or not, can someone point out if there is some mistake in the original drawing or in my translation to LTSpice?
"Solid State Tube" Preamplifier
It seems to me that the freq response is somewhat restricted, and not 5 to 600Khz as claimed...
Thanks in advance
J
 

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Mooly

Administrator
Paid Member
2007-09-15 8:14 am
In fact increase all the caps C3 C4 and C7 as well by a factor of ten. Also what load is on the end of C4 ?

As I say I don't use LT but whats the output impedance of the generator... if that's high that will add to HF roll off.
 
The main problem is probably that you're using power mosfets instead of small-signal mosfets.

I see you changed a few other component values as well, but that shouldn't make much difference except for R13, which he says should not be changed, but you've changed from 330R to 2.2K. There's a capacitor missing too. That shouldn't affect high frequency response but might be important for something else?

btw I've no idea how I missed the schematic in your first post. I could swear it wasn't there when I first looked. :confused:
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
That looks better. Remember at LF it's only the size of the various caps that are the limiting factor.

At hf the device properties do play a big role. Charging and discharging stray capacitance is the limiting factor. R6 is a real practical problem in that it sets limits on the negative output excursion i.e. if you load the output more (reduce R5) then the output will clip on the negative half cycle at higher outputs.

Experimenting with a simple current sink rather than a resistor might be interesting. Also try testing with squarewaves ;)
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
It varies so always best to play safe and assume (as you have with R5) that it could be as low as 10k... a passive volume pot could be that for instance. Or it could be as high as 100k to 1meg.

In practice of course you won't be swinging the output between the rails but it's still good practice to have a good margin.