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The 6N13S "Artosalo" OTL headphone amplifier
The 6N13S "Artosalo" OTL headphone amplifier
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Old 16th April 2018, 06:10 PM   #11
indaco is offline indaco
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For the power tube is 40mA each section, 2 mA x 2 for the ECC82 so rounded up about 100 mA. Mine has V(in) 370 V and V(out) 255V...with the current draw by the tubes settles to 160V.

For these values I used R1=60k and R2=150k
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Old 19th April 2018, 03:56 PM   #12
artosalo is offline artosalo  Finland
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Here is another 6N13S headphone amplifier idea (=simulation so far) for low impedance headphones (32 ohms), now with White cathode follower.
Gain is 7.5 dB, Pout vs. THD at the schematic.

Click the image to open in full size.

Last edited by artosalo; 19th April 2018 at 04:00 PM.
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Old 19th April 2018, 04:04 PM   #13
merlin el mago is offline merlin el mago
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Interesting but a don't have low impedance headphones.
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Old 19th April 2018, 04:07 PM   #14
alexkhar is offline alexkhar  Russian Federation
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The 6N13S "Artosalo" OTL headphone amplifier
If I have headphone with 80Ohm impedance what I have to do?
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Old 19th April 2018, 04:13 PM   #15
artosalo is offline artosalo  Finland
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With 80 ohms and higher impedance headphones the linearity increases.
So no problem.

As an example, with 300 ohms phones and 20 mW, THD is some 0.02 %.
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Old 19th April 2018, 06:32 PM   #16
indaco is offline indaco
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Hi Arto,
your ideas are always interesting...as mentioned in my newer post, now I'm looking for project to realize for a friend of mine, having a Final sonorous headphones (16 ohms). It's a pity that your project is for heaphones over 32 ohms, it's anyway worty to take in consideration...
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Old 19th April 2018, 06:40 PM   #17
indaco is offline indaco
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I have another remark to make. I've heard that the use of NFB is not much suitable for classical music listening, rather for rock or similar music it's OK. Of course to lower in some way the output impedance it's necessary....could be, like in your project, a "degrade" of the tubey sound?
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Old 19th April 2018, 07:05 PM   #18
artosalo is offline artosalo  Finland
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This works fine with 16 ohms too. At 16 mW, THD = 0.23%

Quote:
I've heard that the use of NFB is not much suitable for classical music listening, rather for rock or similar music it's OK.
Typical example of the many opinions you can find.
It is hardly based on any research.

Last edited by artosalo; 19th April 2018 at 07:07 PM.
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Old 19th April 2018, 07:41 PM   #19
pcan is offline pcan  Italy
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The 6N13S "Artosalo" OTL headphone amplifier
Nice design! It seems that C1 will charge trough the headphone driver (R4), have you checked already in simulation the transient current trough R4 at turn on? 560uF is the most common value for this capacitor on other designs of this type, but I also have a full box of Nichicon 200V 1700uF, and I will rather use the bigger value, if they will fit the purpose without damaging the headphone. I would put something in parallel to the headphone to protect it from C1 failure/short, or if the headphone is connected to a already turned on amplifier. Is a zener diode a good choice?
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Old 19th April 2018, 08:11 PM   #20
artosalo is offline artosalo  Finland
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As I said in the beginning, this is now an design idea and a simulation, not a completely ready circuit diagram.
I agree, there should be something to protect the headphones ( and ears) in case of C1 failure.

Concerning the value of C1, 2200 uF is a total overkill.
220 uF gives proper low frequency response even with 16 ohms headphones.
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