Headphone amp OTL

[merlin el mago]

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

 

[lisoformio]

EL34 in the output stage for headphone drive?
Where did you find that schematic?

 

[Koonw]

Please see attached. You should increase the value of output capacitor if you use low impedance hp.

 

[merlin el mago]

EL34 in the output stage for headphone drive?
Where did you find that schematic?

A High Performance, Vacuum Tube Headphone Amplifier

 

[merlin el mago]

Please see attached. You should increase the value of output capacitor if you use low impedance hp.

I use HD600 = 300 ohms

 

[Koonw]

I use HD600 = 300 ohms

Good, only 0.5db drop @20hz with 47u output cap.

 

[merlin el mago]

Good, only 0.5db drop @20hz with 47u output cap.

Thank you, do you now anyway to improve the amp?

 

[Koonw]

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.

 

[merlin el mago]

About the power I guess I don't need a lot for Sennheiser HD 600.

 

[Koonw]

About the power I guess I don't need a lot for Sennheiser HD 600.

How about these changes?

THD 0.05% @1Vp out 300 ohms hp
Max gain ~3
Output impedance ~70 Ohms

 

[merlin el mago]

Sounds good

 

[Hyperman75]

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

 

[merlin el mago]

Thanks Jacques.

 

[Koonw]

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

 

[Hyperman75]

Well done, Koonw !

0.1% is very low and excellent in my point of view.

In sims, noise floor depends on the sim parameters.

Real noise floor will be higher, no matter the stage, because of the real PSU.

So I think it is a good circuit Merlin el mago can try. Not too much components to change.

Jacques

 

[hpeter]

i have nice experience with screen driven 6l6

 

[merlin el mago]

How about these changes?

THD 0.05% @1Vp out 300 ohms hp
Max gain ~3
Output impedance ~70 Ohms

I guess you don't have calculated the xfeed loss?

 

[Koonw]

I guess you don't have calculated the xfeed loss?

Please see attached.

 

[merlin el mago]

I use the attached xfeed

 

[merlin el mago]

Thanks for your help Koonw!