Ok, sorry it has been too long since I have read the first post.
Can you comment specifically on the bass response (round, tight, ...) for your 2 amps with pi-mos devices.
Thanks
Front end supply
Since the PS voltage for the output stage can be different from the front end, it could probably help to get more power to have 7-10v more for the front end. Maybe even a regulated supply for the front end ... But I have experienced - without knowing why - that even simple bypass caps on the supply were only making things worse (oscillation) for this type of amp. So, can you comment on the optimized power supply scheme.
Thanks
Since the PS voltage for the output stage can be different from the front end, it could probably help to get more power to have 7-10v more for the front end. Maybe even a regulated supply for the front end ... But I have experienced - without knowing why - that even simple bypass caps on the supply were only making things worse (oscillation) for this type of amp. So, can you comment on the optimized power supply scheme.
Thanks
Upping just the front stage PS voltage won't give you more power because Laterals are not very efficient output devices. At higher power working regime (say, output current = 5A) we will be loosing 5V at high Rds (about 1 Ohm for Laterals).
As for bypassing, if the circuit is sensitive I usually make it stable using small C + small R all parrallel to big C type of arrangement.
As for bypassing, if the circuit is sensitive I usually make it stable using small C + small R all parrallel to big C type of arrangement.
Front stage PS voltage increase should not have impact on output stage dissipation. 5A for one lateral means 10A for a pair! For a +/-25Vdc supply that is a low load impedance... These Larelas have been used in pairs for more than 100W/8 ohms power amps. I was considering increasing the front stage supply to compensate for the VAS and VGSoff voltage losses.
Thanks for the tip. Do you install this snubber close to the Power caps or on the amp pcb?
Thanks
I did it
Hi juma,
I have finished an implementation of the "F5-Buzquito" and I am quite please with the sound so far. It is definitely an improvement over my F5. I would describe the sound in the same way you did.
I have also used the Toshiba pair K2013/J313 for the VAS. As outputs I have used dual pairs of Laterals K176/J56 (TO-3) that I had for years in stock. However I used different resistors values because of the parts I had. For jfet I have used about 60% of max IDss and for VAS about 60ma to have Lateral mosfet bias of about 1.1A.
I intend to also try to add a crossover displacer to see what it does for the sound...
Thanks again juma for sharing this design with us.
Fab
Hi juma,
I have finished an implementation of the "F5-Buzquito" and I am quite please with the sound so far. It is definitely an improvement over my F5. I would describe the sound in the same way you did.
I have also used the Toshiba pair K2013/J313 for the VAS. As outputs I have used dual pairs of Laterals K176/J56 (TO-3) that I had for years in stock. However I used different resistors values because of the parts I had. For jfet I have used about 60% of max IDss and for VAS about 60ma to have Lateral mosfet bias of about 1.1A.
I intend to also try to add a crossover displacer to see what it does for the sound...
Thanks again juma for sharing this design with us.
Fab
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Hi Zen Mod
CCS. This is the circuit I was planning to use (right part of circuit for xover displacer):
http://www.diyaudio.com/forums/solid-state/129384-mix-gb-f5-amps-idea-2.html#post1615179
Is there any gain to use a Lateral mosfet (K216) as M7 for it or a simple BJT would provide the same result?
Thanks
Fab
R25 value
I don't know how to design solid state circuits so if I am way off, please go easy on me. I can follow directions pretty well and have scratch built many tube amps and pre-amps.
I have built this amp using all the parts in the original schematic (attached) with the exception of the output MOSFETS I used a quad set of 2SK134/2SJ49 as comes in the Hafler DH200. I am using a +19-0--19 volt DC rail supply.
I can't get any current on the 2SK2013/2SJ313 and 2SK134/2SJ49. It occurred to me that R25 would not let much current flow and that seems to be my problem. I adjust R5 & R6 and the offset and the current through the outputs is the same. If I try to balance it out I get 0 bias with 0 offset.
I tried 4k7 in place of the 10k with no different result.
Sure hope you can help me out.
Hi Gabor,
The trick is to adjust it nicely. R5 and R6 set the current through k2013/j313 drivers (try different values, about 100mA worked for me) and voltage drop across R9 and R10 sets the current through output laterals. R25 loads the Q3 and Q4, you might want to lower it somewhat (I liked 4k7 in the end). R23 and R24 degenerate voltage gain MOSFETs and if you change their value, you'll have to readjust R5 and R6.
As you see, this is not an industrial type of amp (build-it-by-manual approach is no good here) and you'll have to find the balance of values that suits your sound preferences.
Just take it easy, don't rush it (don't burn anything) take time to listen, and you'll be fine...
I don't know how to design solid state circuits so if I am way off, please go easy on me. I can follow directions pretty well and have scratch built many tube amps and pre-amps.
I have built this amp using all the parts in the original schematic (attached) with the exception of the output MOSFETS I used a quad set of 2SK134/2SJ49 as comes in the Hafler DH200. I am using a +19-0--19 volt DC rail supply.
I can't get any current on the 2SK2013/2SJ313 and 2SK134/2SJ49. It occurred to me that R25 would not let much current flow and that seems to be my problem. I adjust R5 & R6 and the offset and the current through the outputs is the same. If I try to balance it out I get 0 bias with 0 offset.
I tried 4k7 in place of the 10k with no different result.
Sure hope you can help me out.
Attachments
They are TO3 package, but I looked up the data sheets and am pretty sure I hooked them up correctly. Every where I have looked these devises are referred to as lateral MOSFETs.
Juice
I measure 31.6 mV at the top of R1 and R2, that is about 3 mA.
Is that enough juice?
I measure 31.6 mV at the top of R1 and R2, that is about 3 mA.
Is that enough juice?
Rush, your output MOSFETs are fine (they are Hitachi Laterals too).
If you have 3mA flowing through input JFETs (I suppose they are labeled k170/j74 GR), you'll have to set R5 and R6 to about 700-800R to get some current flowing through Q3/Q4. If you still don't get any current through Q3/Q4 it means that you miswired something.
Current flowing through Q3/Q4 creates the voltage drop on R9/R10 which opens the gates of output MOSFETs and current starts flowing through them too.
R25 has nothing to do with it - it's just a load for Q3/Q4 VAS stage.
If you have 3mA flowing through input JFETs (I suppose they are labeled k170/j74 GR), you'll have to set R5 and R6 to about 700-800R to get some current flowing through Q3/Q4. If you still don't get any current through Q3/Q4 it means that you miswired something.
Current flowing through Q3/Q4 creates the voltage drop on R9/R10 which opens the gates of output MOSFETs and current starts flowing through them too.
R25 has nothing to do with it - it's just a load for Q3/Q4 VAS stage.
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