Cubie - small F5 variant with GR grade JFETs and LatFETs

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T

toxic ingestion

Member
Joined 2012
juma said:
.... but the gate resistor do just that - they are part of the low pass filter which they build with the parasitic capacitance of the FET.
So LP filter is there anyway - it's just the choice will you increase its C or R component.
The only place where you can "improve stability directly" is in the semiconductor development process - people who work there are supposed to do their best to decrease parasitic reactive properties of the parts we use - all the rest is about filters...
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Thank you juma. As someone who knows little (me), information like this turns on the light and causes many things to suddenly make sense. I had never looked at the gate or base resistor as working with the capacitance in the semiconductor to stablize an amplifier by creating a filter. I knew they could stabalize, but did not recognize the mechanism. And your earlier point that increasing the gate resistors on the input to the JFETs could prevent the need for a Miller compensation cap later was helpful, as well. I recall NP previously writing that increasing the input resistor also made the amplifier sound more tube-like.
 
D

drazen

Member
Joined 2009
Juma Hi, thanks for your reply,

Yes, my intention is to use a MOSFET cap multiplier from "Sipi amp 2sk2013/2sj313", which I have tried and I have 16 Vdc. That's enough power for my 95 dB speakers.
After the holiday starts working on the amplifier, and of course I'll report the results here.

I follow those who know, my respect for your work.
 
juma

juma

Member
Joined 2005
Ok, then it's settled - you'll just have to adjust the resistors in JFETs' drain circuits. Of course, since the JFETs' Id will be higher, the gain of the input stage will be lower and so will be the feedback. That will change the sound a bit, to a more mellow nuance, but (if you don't have GR grade JFETs) that can be changed by using the BJTs at the input (similar to this - post #217). F5 topology can be modified in numerous ways, whole lotta experimenting going on... :)
 
juma

juma

Member
Joined 2005
e_fortier said:
I always knew you were a smart man :p
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Not really, somewhat experienced maybe... :D
All those "wars of strong beliefs" are somehow funny (pro & contra tubes, BJTs, JFETs, transformers, capacitors, expensive cables, etc...) in the light of human capacity to deploy so much passion over insignificant stuff. I suppose that's the proof of love - there's no passion without it, but too much passion usually goes down the wrong pipe... :)
 
e_fortier

e_fortier

Member
Joined 2001
juma said:
Not really, somewhat experienced maybe... :D
All those "wars of strong beliefs" are somehow funny (pro & contra tubes, BJTs, JFETs, transformers, capacitors, expensive cables, etc...) in the light of human capacity to deploy so much passion over insignificant stuff. I suppose that's the proof of love - there's no passion without it, but too much passion usually goes down the wrong pipe... :)
Click to expand...

Agree 100%;)
 
D

drazen

Member
Joined 2009
Hi Eric,

I have not started working on the amplifier, holiday and wedding of my daughter spent almost all their free time.
But of course I'll make the amplifier. I have LatMos 2SK135 / J50 and other parts, except 2SK170GR (I have a BL), so I do not know whether to do with BJT input stage.

BR
 
juma

juma

Member
Joined 2005
Finally, the Cubie and the friends settled down and they are playing the music again. :)
Searching for an apartment in Berlin was a tough experience, but it's over, life and music can go on... Oh wait, it's still 6-8 weeks till you get a broadband connection - until then, this 32 kbit/s link will serve you fine... :rolleyes:
 

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flg

flg

Member
Joined 2005
Oh Juma :confused: I had a girl friend back when I was younger ('85) who just had to be a Berliner. She finally found an apartment by chasing down residences from the Obituaries in the paper. I spent several 4-5 week vacations there. I guess to me that would be Manhattan or San Francisco, but, around Christmas the sun barely is up at 9:00A and it's dark by 4:00P!!! I totally enjoyed my time with her there. I lived in Arizona USA then. Very South, nice temps... Thanks for bringing that up
 
J

jameshillj

Member
Joined 2005
Suggest you move that cabinet between the speakers so you have a bare wall and add a simple Schroeder diffuser (QRD) there instead - despite the unequal speaker wire lengths that some people say is deleterious, the benefits are quite clear - amp(s) on a low bass on the floor between is okay if the system will tolerate a longer IC without requiring a balanced line.
 
Rembulan

Rembulan

Member
Joined 2006
juma said:
Yes, it smells like an extortion...
The options are: chasing Toshiba GR leftovers on the net or using a BJTs input solution like you got in your new amp (which sounds very nice to me and the others who tried it - the main difference being the presence of the input and feedback cap which is nothing - there are people there who even put disastrous things like transformers in the signal path) :D
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I am sorry if I jump for something not too important.
Whats wrong with transformer ? mind to share.
 
Rembulan

Rembulan

Member
Joined 2006
juma said:
Yes, it smells like an extortion...
The options are: chasing Toshiba GR leftovers on the net or using a BJTs input solution like you got in your new amp (which sounds very nice to me and the others who tried it - the main difference being the presence of the input and feedback cap which is nothing - there are people there who even put disastrous things like transformers in the signal path) :D
Click to expand...

I am sorry if I jump for something not too important.
Whats wrong with transformer ? mind to share.
 
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