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The 6N13S "Artosalo" OTL headphone amplifier
The 6N13S "Artosalo" OTL headphone amplifier
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Old 14th April 2018, 05:02 PM   #1
indaco is offline indaco
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Default The 6N13S "Artosalo" OTL headphone amplifier

Dear diyaudio friends,

I would like to post this headphone amplifier project made possible also thanks to the contribution of Artosalo, so with your consent I called the 6N13S "Artosalo" OTL. As mentioned in other previous posts and how most of the OTL is specific for high impedance headphones, let's say from 150 ohms up.

The circuit is similar to that of an already known OTL based on 6SN7 and 6080, except that lower distortion is reached by distortion cancealing principle. Also it's present a resistive voltage divider between the two tubes so that the ouput tube can be properly biased.

An important thing to mention is that the B+ voltage has to be well filtered, and I have seen it's more liable to noise than filament PSU.

As for this job, I used AC filament supply for the 6N13S tube and SMPS supply for ECC82. A transistorized B+ regulated supply running for both. Another thing, the B+ PSU produces much heat to lower the voltage to the right value (if a trasformer with higher secondary VAC is used, like I did), so the transistor must be protected with a proper heat-sink.
This one should also be placed in the right geometry, if the case is wooden made (I placed the heat-sink downwards, facing the floor).
Attached Images
File Type: jpg Amp. Initial.jpg (70.6 KB, 645 views)
File Type: jpg Amp. final.jpg (68.0 KB, 633 views)
File Type: jpg 20180414_172452.jpg (237.4 KB, 627 views)
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Old 14th April 2018, 07:41 PM   #2
pcan is offline pcan  Italy
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The 6N13S "Artosalo" OTL headphone amplifier
Some components values are different between the two schematics. What are the final values ​​you have chosen?
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Old 14th April 2018, 10:36 PM   #3
indaco is offline indaco
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The second schematic is that I used for the amplifier, a little bit more gain and about the same output distortion of the first one
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Old 15th April 2018, 06:35 AM   #4
gideon1990 is offline gideon1990  Netherlands
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You forgot to show us the guts
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Old 15th April 2018, 09:52 AM   #5
indaco is offline indaco
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Of course, two pics were in a previous post (but around at the beginning of the work). For completeness I put both before and after
Attached Images
File Type: jpg 20180326_202914.jpg (769.5 KB, 503 views)
File Type: jpg 20180326_202947.jpg (915.0 KB, 453 views)
File Type: jpg 20180415_112949.jpg (386.3 KB, 175 views)
File Type: jpg 20180415_113028.jpg (743.6 KB, 184 views)
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Old 15th April 2018, 03:17 PM   #6
indaco is offline indaco
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This is the schematic for the filament supply regulation. I noticed that this transistor (BU508AF) works well and offer no noise at the output. R1 and R in the circuit must be chosen on the base of the input voltage and the desired voltage for B+. There is also a current limiter and the needing of the bleeder resistor.
Attached Images
File Type: jpg BU508 PSU.jpg (43.4 KB, 227 views)
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Old 15th April 2018, 05:02 PM   #7
gideon1990 is offline gideon1990  Netherlands
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That transformer is really good looking as well
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Old 15th April 2018, 07:01 PM   #8
merlin el mago is offline merlin el mago
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Quote:
Originally Posted by indaco View Post
This is the schematic for the filament supply regulation. I noticed that this transistor (BU508AF) works well and offer no noise at the output. R1 and R in the circuit must be chosen on the base of the input voltage and the desired voltage for B+. There is also a current limiter and the needing of the bleeder resistor.
Isn't for filament supply I guess is for B+, right?

I have the same design with 7N7 driver also make it thanks to artosalo.
Attached Images
File Type: gif 6SL7_6SN7_artosalo 12dB 2Vrms THD 0.12%.gif (103.9 KB, 218 views)

Last edited by merlin el mago; 15th April 2018 at 07:03 PM.
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Old 15th April 2018, 07:23 PM   #9
indaco is offline indaco
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Yes, it's right for B+
It should work for both circuits (they are very similar indeed).
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Old 16th April 2018, 08:43 AM   #10
merlin el mago is offline merlin el mago
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What's your Vin and what's the total current of your load (mine 140mA)?

Last edited by merlin el mago; 16th April 2018 at 08:45 AM.
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