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    Building, troubleshooting and testing of these amplifiers should only be
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Headphone amp OTL

I need to know the output impedance of attached schematic? also I need to know if I have to change some resistors & caps values to use 6SN7 in place of 12SX7?

TIA
Felipe
 

Attachments

  • head_amp_schem 6SN7 + EL34 OTL.jpg
    head_amp_schem 6SN7 + EL34 OTL.jpg
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Koonw

Member
2013-04-09 9:37 pm
Please see attached. You should increase the value of output capacitor if you use low impedance hp.
 

Attachments

  • el34 hp output impedance.png
    el34 hp output impedance.png
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  • el34 hp output impedance -2.png
    el34 hp output impedance -2.png
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  • el34 hp FFT-1.png
    el34 hp FFT-1.png
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Koonw

Member
2013-04-09 9:37 pm
Thank you, do you now anyway to improve the amp?

Well the noise level is very low so that is very quiet as claimed. EL34 can output 120V at 1.5% THD if bias @ half HT (+125V), then if only 1 to 10V is required to drive the hp. that is still very good bias point. Second, gain of 6SN7 stage can be reduced and also bias EL34 @ about 1/2 HT, so what gain do you want so I can try to come up one meet your need.
 
Hi

A suggestion : to use the double triode 6SN7 in SRPP mode rather than to put 2 triodes in parallel.

This tube is perfect for that as its µ is constant when Ip > 5 mA. It will give very low harmonic distorsion.

Polarization points should be revisited but maybe Koonw can give a try with Spice.

B+ for SRPP can be reduced introducing a RC network in the B+ line.

Jacques
 

Koonw

Member
2013-04-09 9:37 pm
Here is SRPP sim you requested, please have a look. Unable to get srpp stage distortion lower than 0.1%, and noise floor looks like higher.


Edit: Sorry noise level is no difference based on 20k load
 

Attachments

  • el34 hp srpp-1.png
    el34 hp srpp-1.png
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