6AS7 OTL headphone amplifier

[merlin el mago]

Anyway thank you to remember this other way.

Felipe

 

[kodabmx]

You're welcome, Felipe.

 

[merlin el mago]

It seems some people don't like the battery in series with the grid, but nobody tell me the reason to avoid.

 

[hpeter]

I see. It was drawn with one so I figured I'd show an alternative. I haven't seen what you describe about the RC || battery. Maybe someone else knows?

makes no sense to put anything in paralel, battery is already low z device.

 

[kodabmx]

That's what I thought. The only reason not to like a battery in series is the shelf life of the battery. However, I've pulled a D battery out of a VTVM and after 50 years it was still 1.52V. Eveready for the win, right?

 

[indaco]

If you have a mosquito zapper you can try with the two Ni-Cd 1.2 V batteries inside

 

[kodabmx]

Ni-Cd won't work well on the grid, they go dead in like 30 days, but using it for cathode bias will work. It will charge while the amp is on.

 

[indaco]

Yes I was thinking as cathode bias. I'm planning to try it in the future me too.

 

[merlin el mago]

I want to use as preamplifier, how to calculate R6 value?

 

[indaco]

What's the purpose for paralleled capacitor to R2? It seems to me a little value for C1 anyway

 

[kodabmx]

R6 serves no purpose as it's in parallel with R36, which is 100k. That's fine, and with the 1uF cap makes a -3db point of 1.59Hz. Using this as a preamp is overkill though, unless you're driving a hundred feet of interconnect (if you are, make the 1uF cap larger). It will work fine, but there are much more efficient ways of doing this...

 

[merlin el mago]

Can be 0.1 to 1uF.

 

[audiowize]

Can be 0.1 to 1uF.

Not as a preamp. I wouldn't go any lower than 3uF.

 

[kodabmx]

If you factor for a 1k load (old JLH design) then you need a 100uF cap for a -3db of 1.59Hz. My preamp is 50k (2 100k pots in parallel) so 4uF gives 0.7Hz.

 

[merlin el mago]

As I understood R36 is the load so not a resistor. 100K is the input impedance of my power amps & 300 ohms is the impedance of my headphones.

 

[audiowize]

If you factor for a 1k load (old JLH design) then you need a 100uF cap for a -3db of 1.59Hz. My preamp is 50k (2 100k pots in parallel) so 4uF gives 0.7Hz.

And when you plug in your powered subwoofer with its 10K input impedance...

 

[merlin el mago]

Not as a preamp. I wouldn't go any lower than 3uF.

For interstage or for output cap?

R6 serves no purpose as it's in parallel with R36, which is 100k. That's fine, and with the 1uF cap makes a -3db point of 1.59Hz. Using this as a preamp is overkill though, unless you're driving a hundred feet of interconnect (if you are, make the 1uF cap larger). It will work fine, but there are much more efficient ways of doing this...

R6 serves to discharge C1?

Exactly I use 0.47uF dor interstage capacitor.

 

[jazbo8]

@merlin el mago - please stop repeating the same question!

 

[merlin el mago]

OK

 

[kodabmx]

And when you plug in your powered subwoofer with its 10K input impedance...

It's input cap will be in series with the output cap.