scone said:
Oh sorry, I meant to ask how big of a trafo did you use for the opa627/buf634 preamp. I should have specified...I'm hoping to get by with a 2 x 15V 80VA trafo, do you think that will be sufficient?
That's gonna work excellent. I use a 2 x 18V 50VA trafo. Quiscent current of the circuit is only 55ma if I remember correctly.
NI OPA549:
R1,R3 = 1k
R2,R4 = 10k
R5 = 2R7 1W
R6 = 0R10 3W (Wirewound, 5 x 20mm, matched with DMM)
C1,C2 = 100uF (5mm grid, 10mm diameter)
C3,C4,C5 = 100nF (5mm grid, 6 x 7,5mm)
I use the snubberized CarlosFM PSU.
The gain of the OPA549 is set to 11, but the voltage divider in front formed by R1 - R2 sets the total voltage gain to 10.
You need a preamp or a buffer with gain (I use Vg=3) in front of this amp.
R1,R3 = 1k
R2,R4 = 10k
R5 = 2R7 1W
R6 = 0R10 3W (Wirewound, 5 x 20mm, matched with DMM)
C1,C2 = 100uF (5mm grid, 10mm diameter)
C3,C4,C5 = 100nF (5mm grid, 6 x 7,5mm)
I use the snubberized CarlosFM PSU.
The gain of the OPA549 is set to 11, but the voltage divider in front formed by R1 - R2 sets the total voltage gain to 10.
You need a preamp or a buffer with gain (I use Vg=3) in front of this amp.
Inverting OPA549:
R3 = 10k
R4 = 100k
Pot = 100k trimmer (to null out DC offset)
R5 = 2R7 1W
R6 = 0R10 3W (Wirewound, 5 x 20mm, matched with DMM)
C1,C2 = 100uF (5mm grid, 10mm diameter)
C3,C4,C5 = 100nF (5mm grid, 6 x 7,5mm)
The gain of this amp is also 10. I have not yet buildt it, but it should work ok. The both amps have an input impedance of 10k.
You need a preamp or a buffer with gain here also.
It would be interesting to test the Bridge-Parallell topology with these amps (with closely matched ouput resistors of course).
R3 = 10k
R4 = 100k
Pot = 100k trimmer (to null out DC offset)
R5 = 2R7 1W
R6 = 0R10 3W (Wirewound, 5 x 20mm, matched with DMM)
C1,C2 = 100uF (5mm grid, 10mm diameter)
C3,C4,C5 = 100nF (5mm grid, 6 x 7,5mm)
The gain of this amp is also 10. I have not yet buildt it, but it should work ok. The both amps have an input impedance of 10k.
You need a preamp or a buffer with gain here also.
It would be interesting to test the Bridge-Parallell topology with these amps (with closely matched ouput resistors of course).
Alcaid said:
Like these here at only 1.20$ each.
http://www.futurlec.com/Potentiometers/CERM100K.shtml
Thanks a lot for all the information, Alcaid. I just made a couple small perfboards with the NI OPA549. They sounds great I just popped thim in instead of the 3875's I had. This amp is also using the CarlosFM snubberized psu. Have a look at the small board.
The resistors are mounted underneath. There is a slight hum, so I will make a couple more and see if the grounding can be perfected a bit The bridge-parallel thing, sounds exciting.
Steen.
I just popped thim in instead of the 3875's I had. This amp is also using the CarlosFM snubberized psu. Have a look at the small board.The resistors are mounted underneath. There is a slight hum, so I will make a couple more and see if the grounding can be perfected a bit
The bridge-parallel thing, sounds exciting.Steen.
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