I sure hope Juma has the time to join in and guide us with the required mods so this HA can be turned into a small power amp and/or a pre-amp. My speaker only requires 0.5W into 8 ohm to sing. The speakers are normally connected to a 0.75W Darling tube amp and it's loud enough for evening listening.
p.s. My Juma HA will sing this week-end, about 90% soldering is done.
TIA,
Eric
You could just try it at low volumes. I don't think it's going to hurt the MOSFETs as they can handle multiple amps and the existing 10R degeneration resistors will handle the current limiting for you. This amp can probably easily do 1.5w. Probably want big heatsinks and keep the 68R resistors and set bias high like 500mA.
I am listening to it some more. Even with the incorrect input R5 it sounds fantastic. I might add 1uF 320v film input cap but DC coupled input has some real nice sound.
I am listening to it some more. Even with the incorrect input R5 it sounds fantastic. I might add 1uF 320v film input cap but DC coupled input has some real nice sound.
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bare bones buffer (BBB)... LTS for the interested. R1/R4 emulate the volume pot... people should use their own NE5532 model as a sub ckt..
too late to edit... i might as well add, probably the most flexible and interesting design , thanks Juma!
Nothing to change for preamp duty - maybe just lower bias current. Try 50mA and listen for difference at typical load that preamp drives: 10 - 100k (Zin of the power amp).
Low power amp is also easy: IRF640/9640 (much more powerful but still in TO-220 case, in order to use the same PCB) instead of IRF610/9610, Source resistors 0R47 instead of 10R, feedback resistors 100R (3W) and 20R (0.5W) instead of 1k/220R, bias current 0.5A or more, much bigger heatsinks (there is no active thermal compensation circuit so will have to rely on bigger heatsinks and thermal equilibrium of natural convection). NTCs, F5 style, can be added too.
Active thermal compensation can be ensured by using a CCSs instead of bootstraps for the input pair. Voltage reference for that CCS should be a BJT (connected as diode) in thermal contact with output MOSFETs. That works very good.
Low power amp is also easy: IRF640/9640 (much more powerful but still in TO-220 case, in order to use the same PCB) instead of IRF610/9610, Source resistors 0R47 instead of 10R, feedback resistors 100R (3W) and 20R (0.5W) instead of 1k/220R, bias current 0.5A or more, much bigger heatsinks (there is no active thermal compensation circuit so will have to rely on bigger heatsinks and thermal equilibrium of natural convection). NTCs, F5 style, can be added too.
Active thermal compensation can be ensured by using a CCSs instead of bootstraps for the input pair. Voltage reference for that CCS should be a BJT (connected as diode) in thermal contact with output MOSFETs. That works very good.
Thanks a lot Juma for all your help and Prasi for such a nice and compact layout.
I ordered some PCB and after giving a few away I'll have 4 left so perfect for a pre-amp and then power amp.
Thank you,
Eric
I ordered some PCB and after giving a few away I'll have 4 left so perfect for a pre-amp and then power amp.
Thank you,
Eric
It is done!
will order PCB's for the stereo amp (with vol control+ i/p coupling cap+final values of components) and Nazar LM317/337 PSU (dual rail) tomorrow..
The list as of today is
xrk- 1 set
gannaji- 1 set
saheb- 1 set
kram- 1 set
btesize-1 set
rumina-1 set
nicusim-1 set
My understanding of 1 set is; 1 PCB of amp and 1 pcb of PSU. If you want something other than 1 of each, please let me know.
the size of amp PCB is 50mmx100mm and that of PSU is 50mmx85mm.
Reg
Prasi
edit: both PCB's are double sided with plated holes and vias with green solder mask and while silk. 35umCu.
will order PCB's for the stereo amp (with vol control+ i/p coupling cap+final values of components) and Nazar LM317/337 PSU (dual rail) tomorrow..
The list as of today is
xrk- 1 set
gannaji- 1 set
saheb- 1 set
kram- 1 set
btesize-1 set
rumina-1 set
nicusim-1 set
My understanding of 1 set is; 1 PCB of amp and 1 pcb of PSU. If you want something other than 1 of each, please let me know.
the size of amp PCB is 50mmx100mm and that of PSU is 50mmx85mm.
Reg
Prasi
edit: both PCB's are double sided with plated holes and vias with green solder mask and while silk. 35umCu.
Attachments
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yes, sure..
xrk- 1 set
gannaji- 1 set
saheb- 1 set
kram- 1 set
btesize-1 set
rumina-1 set
nicusim-1 set
potepuh-1 set
reg
Prasi
B1 Buffer works really well. Very clear and dead quiet.
I finally got enough motivation to build a B1. I even made a rig to measure Idss so I could match my 2Sk170's. The circuit is surprisingly simple and an easy build in P2P. It provides a nice FET input stage and buffered output so that a volume pot can be used without changing the impedance to the amp. It actually all fits on a small 4x6cm veroboard. I am not using 10mF caps but 2.2mF are sufficient given that I am feeding it with my highly filtered and regulated 15v from the main rails. This preamp is perfect cool in keeping with the design aesthetics if you want a single ended class A preamp There is no scratching sound from the volume pot now.
I finally got enough motivation to build a B1. I even made a rig to measure Idss so I could match my 2Sk170's. The circuit is surprisingly simple and an easy build in P2P. It provides a nice FET input stage and buffered output so that a volume pot can be used without changing the impedance to the amp. It actually all fits on a small 4x6cm veroboard. I am not using 10mF caps but 2.2mF are sufficient given that I am feeding it with my highly filtered and regulated 15v from the main rails. This preamp is perfect cool in keeping with the design aesthetics if you want a single ended class A preamp There is no scratching sound from the volume pot now.
Attachments
Hi Eric,
your request noted in below list
xrk- 1 set (1 PSU+1 Stereo HA)
gannaji- 1 set (1 PSU+1 Stereo HA)
saheb- 1 set (1 PSU+1 Stereo HA)
kram- 1 set (1 PSU+1 Stereo HA)
btesize-1 set (1 PSU+1 Stereo HA)
rumina-1 set (1 PSU+1 Stereo HA)
nicusim-1 set (1 PSU+1 Stereo HA)
potepuh-1 set (1 PSU+1 Stereo HA)
e_fortier-2 PSU
reg
Prasi
just a suggestion to people interested in pcb's, just quote the latest list and add your 'diyaudio' username and particulars of your requirement. i will note it down...i will contact at a later date with prices and payment formalities in a PM...
Hi Prasi,
Thanks for adding my name for the GB.
I have just calibrated 2 of the board and noticed that when orienting the board the right way, i.e. with the output transistors on the right side, you have to turn P1 and P2 counter clockwise to increase the bias, it's usually more intuitive to turn clockwise to increase bias. Maybe you could rewire P1, P2.
Just my 2 cents.
p.s. Worked right away. Thanks.
BR,
Eric
Thanks for adding my name for the GB.
I have just calibrated 2 of the board and noticed that when orienting the board the right way, i.e. with the output transistors on the right side, you have to turn P1 and P2 counter clockwise to increase the bias, it's usually more intuitive to turn clockwise to increase bias. Maybe you could rewire P1, P2.
Just my 2 cents.
p.s. Worked right away. Thanks.
BR,
Eric