Mike,
one another thing. For this low power application the MJE drivers looks overkill to me. This transistors are great, but under 100mA the B of them falls. So I would try to use BD139/140 as driver. You can reduce the driver's bias to 8-10mA. They are faster than MJEs (50MHz), and has flat B from 2mA up...
sajti
one another thing. For this low power application the MJE drivers looks overkill to me. This transistors are great, but under 100mA the B of them falls. So I would try to use BD139/140 as driver. You can reduce the driver's bias to 8-10mA. They are faster than MJEs (50MHz), and has flat B from 2mA up...
sajti
Hi sajti !
Yes, you are right, the mje15030 is a bit overdimensioned...
What do you think about mje243/253 as drivers ? (Have some left)
Is it correct that the bd139/140 have ft=150mhz ?
But i planned to increase vsupply to +/-36v, in this case the bd139
would reach the limit. (but also cascode and predriver)
Mike
Yes, you are right, the mje15030 is a bit overdimensioned...
What do you think about mje243/253 as drivers ? (Have some left)
Is it correct that the bd139/140 have ft=150mhz ?
But i planned to increase vsupply to +/-36v, in this case the bd139
would reach the limit. (but also cascode and predriver)
Mike
MikeB said:
I never used MJE243/253. When I checked the datasheet, I found big difference between the B characteristic of the npn, and pnp. The BD139/140 has Ft=50MHz, very linear B from 1mA up to 150mA. I used one amplifier made in Hungary which had +/-37V psu, and used BD139/140 as driver (output was 2 pairs of BD249C/250C). This amplifiers are very reliable lot of them still works, and they are 25 years old....
For VAS I recommend to use BC639/640, which use same chip as BD1396140, but in TO-92 package. I used some of them in my amplifier...
sajti
To sajti : If you use moderm output device with high beta, are 340 / 350 useable. 30 W / 0.5 A is enough and as you certainly know, price is very good. I was using this transistors in amp, where they drive four parallel connected BD 911 / 912. This amp had more than 120 W / 4 Ohm and more than 300 units still work with 100 % reliability.
mikeb! about offset output voltage problem ,I think that you like to use so small resistor in input stage example 1K .Offset voltage is decrease by feedback but the amount of feedback is so small so offset voltage is big
mikeb! the current through each diff transistor is 1mA .Have you tried biasing it with 2mA .Slone biased it with 2.5mA .Perhaps the sound of will be more powerful
mikeb! the current through each diff transistor is 1mA .Have you tried biasing it with 2mA .Slone biased it with 2.5mA .Perhaps the sound of will be more powerful
Hi thanh !
Yes, more feedback decreases DC-offset, but the amount of feedback
possible is limited by the fact that olbw needs to be "flat" for low tim.
As i use tripledarlingtonout the sound is already very powerful.
But the mainpoint is, matching devices is not only for low dc-offset,
it is mandatory for low distortions. So, if i have dc-offset, i know matching
is far from perfect. With "simple" matching i get dc-offset easily below
20mv, but lower is difficult due to thermal variations.
And, input-dc-offset can only be eliminated by matching devices, if
you have inputoffset, higher gain can even increase dc-offset !
Mike
Yes, more feedback decreases DC-offset, but the amount of feedback
possible is limited by the fact that olbw needs to be "flat" for low tim.
As i use tripledarlingtonout the sound is already very powerful.
But the mainpoint is, matching devices is not only for low dc-offset,
it is mandatory for low distortions. So, if i have dc-offset, i know matching
is far from perfect. With "simple" matching i get dc-offset easily below
20mv, but lower is difficult due to thermal variations.
And, input-dc-offset can only be eliminated by matching devices, if
you have inputoffset, higher gain can even increase dc-offset !
Mike
thanh said:
Below 1mv ? Even commercial amps are above 1mv...
I'm satisfied with < 50mv. Then adding a dc-cap to the feedback
would give ~1mv
The "powerful sound" also makes strong deep sound, but the whole
sound get's more "intense", giving the feeling that the plays effortless.
Also you can hear the amp saying "gimme more !"
With "soft sound" i mean that the sound is not bright/harsh. I hate
"smooth sound", i want clear trebles. If i want smooth sound i can
still drop bandwidth below 16khz.
A good example are hihats and triangles, with "smooth sound" they
get lifeless, with bright/harsh sound they get annoying/distorted.
With good amp you can hear these absoulutely detailed, making
fun to hear them.
Mike
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