|
Home | Forums | Rules | Articles | diyAudio Store | Blogs | Gallery | Wiki | Register | Donations | FAQ | Calendar | Mark Forums Read |
Solid State Talk all about solid state amplification. |
|
Please consider donating to help us continue to serve you.
Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving |
![]() |
|
Thread Tools |
![]() |
#501 |
diyAudio Member
Join Date: May 2005
Location: Denmark
|
I totally agree on this....
This way we can also remove the input capacitor...with the risk to introduce DC offset if the source is poor... This is also the version i currently have running in my simulator...(sims really good...2.harmonc at -110 dB..and higher order barely existing |
![]() |
![]() |
#502 |
diyAudio Member
Join Date: Dec 2005
Location: the north
|
MiiB
Nice. You have our circuit in mind. It is good to have you. I have learnt a few things from you. Hope to see someone bias 2SK170 from negative supply rail. In the meanwhile a diagram for mikelm. It was long ago I posted it for swordfishy But it is so nice. Isn't it ...............??? mosfet VAS is back
__________________
lineup |
![]() |
![]() |
#503 | |
diyAudio Member
Join Date: Oct 2001
Location: Denmark
|
Quote:
with resistive load you will have unity gain. but with a capacitive load it will start working as the gain fall below unity. try 470pf - 2.2nf. It works well. Last edited by sonnya; 29th May 2011 at 08:42 PM. Reason: added text |
|
![]() |
![]() |
#504 |
diyAudio Member
Join Date: May 2005
Location: Denmark
|
This is what I'am currently thinking....Higher power version Hawksford cascode..and two sets laterals..LED biased current sources...Simple circuit... hopefully some builders...
![]() Distortion is so low it's hardly worth mentioning at -115 dB 2. order...at+/-25 V..output-swing.. |
![]() |
![]() |
#505 |
diyAudio Member
|
|
![]() |
![]() |
#506 |
diyAudio Member
Join Date: Dec 2005
Location: the north
|
I see. Good.
I will wait. No hurry.
__________________
lineup |
![]() |
![]() |
#507 | |
diyAudio Member
Join Date: Jun 2004
Location: NZ
|
Wise words clearly based on a lot of experience.
![]() Quote:
|
|
![]() |
![]() |
#508 |
diyAudio Member
|
mmmm - interesting reading this again in light of swordfishy's latest version because that does have very low distortion indeed, so I expect the sound will be more neutral than warm . . . but the larger VAS mosfet does roll off OLG more than anything I've tested in spice to date - so perhaps it has the best of both approaches.
I never expected to see a feedback amp with a Push Pull o/p that can operate with normal loads without any compensation - truly a step forward. p.s. does anyone know where I can buy 2sk170's or Lsk170's in europe ? the ones I have will probably only arrive in about six weeks - can't wait that long Last edited by mikelm; 29th May 2011 at 10:43 PM. |
![]() |
![]() |
#509 |
diyAudio Member
Join Date: May 2005
Location: Denmark
|
Mike....
the BF862 part in my circuit might be even better....it's easy to get...and has less noise and twice the gain... |
![]() |
![]() |
#510 |
diyAudio Member
Join Date: Sep 2001
Location: Melbourne, Australia
|
Wow, this has moved along......
Brief comment on the fb resistor: it does not destabilise anything at all. By using the series fb resistor to set up the DC operating conditions of the amp we actually simplify the circuit. In practice, it will have an almost constant DC current through it, fixed by R4, the source/gate resistor of the VAS. Idss for the 2SK1780 is listed as ranging from 2.6ma to 20mA, in three distinct ranges. I'm hoping that SWF is using the BL series, the middle range, 8-12mA. 2/3 of the Idss is correct, but as pointed out the fact the gate bias is positive indicates either the stage current is too high or the grade of the jfet is inappropriate. This is a low transconductance device with very low noise, around 22mS. That means Id increases by 2.2mA for each 100mV of gate potential increase. (22mA for each volt). A BF862 will therefore generate another 6dB of loop gain, and compensation might need revisiting. An increase of VAS degeneration could do this, of course. I don't actually recommend a cap across the fb resistor to stabilise things. I prefer a combination of miller cap on the VAS, and phase lead from VAS drain to fb node. In my experience it's more predictable, more stable. It does work, but to me it's less elegant. Mike, interesting that the mosfet VAS actually rolls off at HF!! This can only be the capacitance at the gate pulling back slew rate, but it's not what SWF found at the outset. This certainly explains why lag compensation is not required even though we have about 75dB of loop gain. SWF, the rating of the S170 is 400mW. For reliability I gun for no more than one third of this, 135mW, so you are on the limit, particularly as your climate is subtropical. OTOH, you should try for 2/3 of Idss for best results. Fortunately, you only have low voltage across the device. Cheers, Hugh Last edited by AKSA; 30th May 2011 at 12:30 AM. |
![]() |
![]() |
Thread Tools | |
|
|
![]() |
||||
Thread | Thread Starter | Forum | Replies | Last Post |
10 Watt Single End, JFET input - Lateral N-MOSFET output | lineup | Solid State | 86 | 4th April 2015 04:54 PM |
Lateral MOSFET, How do I calculate power output | synonymous | Solid State | 4 | 18th December 2007 07:54 AM |
Calculating VAS current for mosfet output | bogdan_borko | Solid State | 21 | 11th April 2006 04:57 AM |
New To Site? | Need Help? |