A different (?) line level circuit

Mosquito · 02:12 PM

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

godfrey · 4th December 2010, 03:13 PM

Quote:

Originally Posted by Mosquito

... can someone point out if there is some mistake in the original drawing or in my translation to LTSpice?

Dunno. Can you show us what it looks like in LTSpice?

Quote:

Originally Posted by Mosquito

It seems to me that the freq response is somewhat restricted, and not 5 to 600Khz as claimed...

What do you get?

Mosquito · 03:52 PM

Your desire is an order

Mooly · 4th December 2010, 03:54 PM

I don't use Lt spice but a couple of quick thoughts.

At the top end R6 looks a problem, try 2k2

At the bottom end increase C6 to 220uf

Mooly · 4th December 2010, 03:57 PM

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.

Mosquito · 4th December 2010, 03:58 PM

Thanks Mooly, I'll try these mods/fixes
cheers
J

godfrey · 4th December 2010, 04:12 PM

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.

godfrey · 4th December 2010, 04:24 PM

As long as Mooly's changing everything anyway...
I'll agree with increasing C6, and vote for increasing C1 as well.

Mosquito · 4th December 2010, 04:57 PM

Thanks godfrey, you're right I missed to attach the picture by first, and then correct..

Ok can you suggest suitable signal mosfet from those in the default LTSpice library? (I've changed some componens figures in order to have the voltage figures pointed out in the original drawing, not any other reason than that)
Thanks again
J

godfrey · 4th December 2010, 05:13 PM

Quote:

Originally Posted by Mosquito

Ok can you suggest suitable signal mosfet from those in the default LTSpice library?

Nope, I'm pretty clueless regarding both LTSpice and mosfets. It looks like you can get the Spice model for BS170 from Fairchild over here though.

4th December 2010, 03:54 PM	#4
Mooly diyAudio Member Join Date: Sep 2007	I don't use Lt spice but a couple of quick thoughts. At the top end R6 looks a problem, try 2k2 At the bottom end increase C6 to 220uf __________________ ------------------------------------------------------- *A simulation free zone.* *Design it, build it, test it.*

4th December 2010, 03:57 PM	#5
Mooly diyAudio Member Join Date: Sep 2007	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. __________________ ------------------------------------------------------- *A simulation free zone.* *Design it, build it, test it.*

4th December 2010, 03:58 PM	#6
Mosquito diyAudio Member Join Date: Sep 2009 Location: Santa Fe, Argentina	Thanks Mooly, I'll try these mods/fixes cheers J __________________ I know how to walk over grapes

4th December 2010, 04:57 PM	#9
Mosquito diyAudio Member Join Date: Sep 2009 Location: Santa Fe, Argentina	Thanks godfrey, you're right I missed to attach the picture by first, and then correct.. Ok can you suggest suitable signal mosfet from those in the default LTSpice library? (I've changed some componens figures in order to have the voltage figures pointed out in the original drawing, not any other reason than that) Thanks again J __________________ I know how to walk over grapes

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4th December 2010, 04:12 PM	#7
godfrey diyAudio Member Join Date: Nov 2009 Location: Cape Town	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.

4th December 2010, 04:24 PM	#8
godfrey diyAudio Member Join Date: Nov 2009 Location: Cape Town	As long as Mooly's changing everything anyway... I'll agree with increasing C6, and vote for increasing C1 as well.

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