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Old 30th October 2008, 12:04 PM   #11
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Thank you lineup.

What substitute should I use for 2SC1740/2SA933 ?

I have for the moment the MJE340/MJE350.
50V/0.15A vs 300V/0.5A.

Should I use this 2 transistors with a higher supply voltage ?
Also I would like a higher bias, if possible.
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Old 30th October 2008, 01:17 PM   #12
lineup is offline lineup  Sweden
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how much bias is the output?

Voltage across R360/value of R360, 68 Ohm = Current
Volt/68ohm=current in resistor
you should not need more than 2-5 mA Class A for best result
(to drive any power amp input)

the 4 input transistors works at ~0.3 mA per each
thi is a good value and should NOT be raised to more than ~0.5 mA
(the current in each is like 50 % of current in 22k resistor=
Volt/22k= current in resistor

Replacements:
2SC1740S:
BC550C, 2SC2240 ... TO-92 low noise, high gain NPN

2SA933S:
BC560C, 2SA970 ... TO-92 low noise, high gain PNP
--------------------

I would not go more than 0.5 mA for each input transistor
Example: use 15k (instead of 22k)
15Volt/15k = 1 mA
1 mA/2 = 0.5mA for each T

I would not use more than 5 mA for output stage transistors
0.340 Volt across 68 Ohm resistors
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Old 30th October 2008, 08:41 PM   #13
lineup is offline lineup  Sweden
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Predator864

These are the values I would used.
With R2, R14 at 2k2, the output stage will idle at 3.8 mA Class A.
This would be well enough for 99% of everything one Line preamp will need to do.

The gain is bit below x4.
-3 dB bandwidth, with my capacitors: 4 - 800.000 Hz
Distortion 1Vrms/10kohm output: < -100 dB for all harmonics.
(-100 dB = 0.001 %)

Not bad for 6 standard BC550C/560C TO92 transistors!
Enjoy
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