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Very Simple 3BJT Headphone Amplifier
Very Simple 3BJT Headphone Amplifier
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Old 3rd October 2019, 06:25 PM   #41
syrbinche is offline syrbinche  Germany
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Great circuit! I have just tested it and it's really good! Very very loud, so i have to lower that otherwise gonna burn my headphones



I took 10ohm resistor in the R4 position and have like 90mA thru 2xBD139



I have +/-24V power in my setup and i wonder if this could be modified for 48V?

Does it make sense to do that?
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Old 3rd October 2019, 07:25 PM   #42
Osvaldo de Banfield is offline Osvaldo de Banfield  Argentina
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What warranty that both hemicycles receive equal amplifying factor (or gain)? The input transistor has a gain of about 10 (1200Ω collector/120Ω emitter). The upper final transistor is a follower, so gain ≈1. The lower final transistor ???
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Old 3rd October 2019, 07:47 PM   #43
Mark Johnson is online now Mark Johnson  United States
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Very Simple 3BJT Headphone Amplifier
Sounds like a question that motivated hobbyists might attack very quickly using circuit simulation software.
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Old 3rd October 2019, 08:07 PM   #44
Osvaldo de Banfield is offline Osvaldo de Banfield  Argentina
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Yeah, but over any simulation, is good to know what one is doing, because if not, you can't understand what the simulation is saying to you.

This is like an example, a professor told us in the university. Suppose you have a tester (VOM) that is malfuctioning. Suppose also that with this VOM you read 50V, for example, in the 220V power line. Do you touch the wires under those conditions?
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Old 3rd October 2019, 08:36 PM   #45
Mark Johnson is online now Mark Johnson  United States
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Very Simple 3BJT Headphone Amplifier
Fantastic! Good luck and best wishes.
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Old 12th November 2019, 03:40 PM   #46
gasboss775 is offline gasboss775  United Kingdom
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In LT spice I tried replacing the 1K2 resistor with a current source using a jfet and resistor. The THD was reduced to around 0.09% ( mostly 2nd order )

image.png
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Old 21st November 2019, 05:36 PM   #47
gasboss775 is offline gasboss775  United Kingdom
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I have built the original circuit using both TIP41 and 2SC3852A transistors and would say it definitely sounds better with the TIP41s.
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Old 21st November 2019, 10:53 PM   #48
avtech23 is online now avtech23  Australia
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Very Simple 3BJT Headphone Amplifier
Have you tried it with the jfet current source to compare with the original design?
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Old 22nd November 2019, 06:52 PM   #49
gasboss775 is offline gasboss775  United Kingdom
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Quote:
Originally Posted by avtech23 View Post
Have you tried it with the jfet current source to compare with the original design?
Yes, but not thoroughly tested. First impression was there was greater clarity at the high end.
The open loop gain was much higher as expected.

Note these comments pertain to using TIP41s as the output transistors, with the 2sc3852a's it sounded bad! Very muddy and distorted.

I used a J112 and a 180 ohm as the current source the current was around 10.5mA. I will probably try again with other jfets.
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Old 23rd November 2019, 09:44 PM   #50
Mark Tillotson is offline Mark Tillotson
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Quote:
Originally Posted by Osvaldo de Banfield View Post
What warranty that both hemicycles receive equal amplifying factor (or gain)? The input transistor has a gain of about 10 (1200Ω collector/120Ω emitter). The upper final transistor is a follower, so gain ≈1. The lower final transistor ???
The 2SC3852 is extremely high current gain (guaranteed > 500), so there's a lot of feedback available. The circuit is dominated by feedback, and that transistor enables it to perform very well. The gain is stabilized by the feedback (masking imperfections of the output stage).

Give it a more linear output stage it will perform even better I suspect. The lower transistor is the obvious low-hanging fruit.
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