Tube Headphone Amplifier E182CC

Posted on Aug 21, 2012

To design a Tube Headphone Amplifier we need a triode with uncommon characteristics: enough voltage gain, low internal resistance and good anodic current. My first test was done with the E182CC (figure 1), but there is the limitation on the usable impedance of headphones in the range of 300 to 600 ohms for maximum performance. The output impedance of the amplifier is about 35 ohms, and I don't accept any damping factor less than 8. (About damping factor: for some, a damping factor of 4 or less is acceptable, but only because they have not heard a better tube headphone amplifier like this one.) The tubes that could be used are E182CC or 5687, but with the 5687, the gain is less. The E182CC is auto-biased to ground through the attenuator. It needs the 1K input resistor for stability, probably because there is no shield on middle of the tube.

Tube Headphone Amplifier E182CC
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The LL1630 output transformer (also used in my Tube Headphone Amplifier with Digital Input) has a wide frequency response from 10Hz to 40kHz (+/-0.5dB), and a good inductance value to build a perfect headphone amplifier to drive headphones with impedance from 150 to 600 ohms. The LL1630 transformer here is used with parallel connection of the primaries. It must be gapped for a 10mA DC current, so that in parallel connection, it will run fine with the 20mA or less bias current of the output tube. When ordering this component from Lundahl, ask for LL1630/10mA. About the power supply, I suggest this Reference Power Supply (figure 4) that gives the best result, but is not very cheap to implement. The 100 ohm resistors across the filament supply are center grounded for low noise. The rectification comes from a Hybrid Graetz Bridge (from a Fulvio Chiappetta article in the italian magazine "Construire HiFi") made with 1N5408 diodes and a RCA 5R4 rectifier tube. Although it has semiconductors, the sound depends on the rectifier tube, and the switching characterictic is that of the lower speed device - the tube. The hybrid tube bridge has the advantage that it can be driven from a single transformer secondary (the tube rectifier normally needs a dual secondary transformer). The other components are not cheap, and here the highest quality parts must be used to get the maximum result. About passive components types, I don't leave...

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