6080 6sn7 OTL headphone amp

the thermionic watercooler

6080 6sn7 OTL headphone amp

Postby coop402 » Thu Feb 06, 2020 5:00 pm

I built a headphone amp based on this circuit.
It sounds great with Senn 650's.

I used a 6sn7 octal instead of a 12au7, in hopes that it would work. I made sure that I had enough 6.3 amperage.

My b+ voltages are the same as the schematic. I am not a tube math guy. I just like to build.

Can any of you tell me how to optimize my B+ for that 6sn7 tube? I think the goal is to hit the sweet spot,
just not versed in that.

Image
coop402
 
Posts: 145
Joined: Wed Nov 04, 2009 7:43 am

Re: 6080 6sn7 OTL headphone amp

Postby Thermion » Sat Feb 15, 2020 7:08 am

Coop42,

I ran some Tube CAD simulations on your circuit for both 12AU7 and 6SN7. I ran the simulations with a cap bypassed cathode resistor in place of the LED, but that should work out OK for this purpose. The circuit parameters are pretty good for either a 12AU7 or 6SN7. If it sounds great right now I wouldn't make any changes.

I'm not sure what you meant by optimizing the B+. Usually you would optimize the plate and cathode resistors to set your operating point for a given B+. I certainly wouldn't go lower than 170 volts B+, but if you have the capacity to go higher you might want to alter the plate resistor value.

One thing to note, in order to get the 1.5 volt bias that you get with the LED I had 4 ma of current running through the tube in my simulations. This gives a voltage drop of 88.4 volts across the plate resistor instead of the 80 volts indicated by your schematic. Do you have actual voltage measurements of the B+ and other voltages? Minor variations are nothing to worry too much about. So again, if the amp sound good I would leave it alone and enjoy the music.

Jonathan
Thermion
 
Posts: 177
Joined: Mon Jul 07, 2003 6:04 pm
Location: Fisher, IL

Re: 6080 6sn7 OTL headphone amp

Postby coop402 » Sat Feb 15, 2020 8:52 am

Thanks Thermiom,

I am going to check the numbers today.
Does Tube Cad have a way that you could share those simulations with me? I know it is incredibly useful as a tool,
but it would do me a great service to see how you created the simulation.

Turns out, I found out this is close to a Bottlehead Crack (I was told, if not the same thing). Looks like they bias a lot of their amps with that specific led.
I guess Dark Voice makes a chinese version with a 6sn7.

Either way to you point, it sounds great. I found the power supply schematic, super simple uf4007 rectifier, caps and resistors, no chokes.
I am pretty freaked out by how fast the music detail and transitions are. Maybe directly couple helps this. I just used a 150v Antek torodial transformer.
This is a super simple project to build, plus it sounds way above it price point.

Something interesting on the bottlehead site is that they sell a constant current (cascode, I guess) upgrade. That looks pretty cool.
coop402
 
Posts: 145
Joined: Wed Nov 04, 2009 7:43 am

Re: 6080 6sn7 OTL headphone amp

Postby Thermion » Mon Feb 17, 2020 7:21 am

I can either print out the Tube CAD simulations or save as pdf, so that will be easy to share.

Shannon gave me a bunch of red LEDs a while back to experiment with, but I never got around to it. Looks like maybe they could be fun to play around with. Morgan Jones has quite a bit of information on the HLMP6000 LED in his book. In the book he indicates a formula for calculating the current through a HLMP6000 to generate a given voltage drop. According to the equation 1.6 volts would require 4.66 ma. I know you are not a tube math guy but I bring this up for a good reason. There are some problems with the voltage numbers on your schematic. An 80 volt drop across the 22.1k plate resistor implies an operating current of 3.6 ma which is too low for the HLMP6000.

Would it be possible to get measurements of the B+, voltage across the plate resistor, and the voltage across the LED? Then I can run some simulations that are targeting actual operating conditions.

JT
Thermion
 
Posts: 177
Joined: Mon Jul 07, 2003 6:04 pm
Location: Fisher, IL


Return to diy hifi

Who is online

Users browsing this forum: No registered users and 20 guests