help on headphone amplifier

[theChris]

ok, i'm looking into makeing a tube-based amplifer for some sony mdr-v6 headphones. these are not the mdr-v600 headphones that many people don't like, but rather, the mdr-v6 which is supposedly the same as the new 7506 headphones.

in anycase, the headphones are listed as over 100dB @ 1mW and should thus be pretty efficient. they are also listed as 64ohm, and have a common signal group at the headphones. they are reported as being easy to drive and efficient.

ok, so i was thinking of making a tube amp for them, mainly just for fun. I was looking for a target of 50-100mW @ 64ohm, and stereo. this means i'd need signifigant biasing current for the output device right? approximately 40mA?

i was looking into maybe using a pair of 6v6gt pentodes for the output stages, 1 per channel. i was also looking into adding a voltage gain stage using a half of a 6sn7 per channel. i was planning on using 200V for my plate voltage for both the 6sn7 and the 6v6. i'm not entirely sure if i want a voltage gain stage or not.

then comes in the transformer. i was wondering what i should do for this section. i was looking into either a 125-0-125, 100mA, but that means i would have to choose between 100mA and ~200V or do 200mA and ~100V. or are these transformers rated in AC volts. the site with the transformer seems to indicate a DC value in typical useage.

here are my questions:
1.) 6sn7gt and 6v6gt -- good choices or not for this low power app.
2.) where can i find a cheaper transformer? i can't seem to find aything under $60 for the 400Vct+ @ 100mA nor anything under $30 for 200Vct @ 100mA

[woody]

If you look on http://headwise.com/ you can find several good
headphone amps, you might look at the Morgan Jones clone of the EarMax amp. In paticular the power supply can be done realy
cheap.


Woody

[Richard C]

That'll be www.headwize.com

[theChris]

hmm, i have seen the headwise site.

not sure were to get a 20V - 200V step up transformer...

in anycase i kinda wated to try 6v6 and 6sn7 for a kinda themed amp. sony v6 headphones, 6v6 output devices. well, you see what i mean...

is it possible to use the 6v6 below 250V? possibly at 100V?

[Brit01]

I've been trying to calculate how he came to 172V at the voltage divider with 27K resistor on the optimized Morgan Jones Headphone amp.

pic attached.

Please can someone show the calculations?


I understand how he calculated 218 Volts from 220 on the second leg but how did he come to 172V on the first part?

Vout = (R2/R4+R2) * Vin
27000/27120 * 220

Many thanks

[Gordy]

Originally posted by theChris

in anycase, the headphones are listed as over 100dB @ 1mW and should thus be pretty efficient. they are also listed as 64ohm, and have a common signal group at the headphones. they are reported as being easy to drive and efficient.

ok, so i was thinking of making a tube amp for them, mainly just for fun. I was looking for a target of 50-100mW @ 64ohm, and stereo. this means i'd need signifigant biasing current for the output device right? approximately 40mA?

The mdr-v6 is rated at 106 dB for 1 mW. Therefore 2 mW gets you 109 dB, 4 mW gets you 112 dB, and 8 mW gets you 115 dB. That is subjectively *very loud*. So if you allow, say, four times that for some headroom then you should have plenty. In other words; 32 mW will be plenty for this application.

Now, what is the best way to provide 32 mW into 64 Ohms? My choice would be by transformer, but from the opening post I guess that you don’t want that. So you might just be left with the White Cathode Follower…

[Stixx]

I've been trying to calculate how he came to 172V at the voltage divider with 27K resistor on the optimized Morgan Jones Headphone amp.

Brit, where do you see 172V?
The schematic shows 108V, and that's what it was in my built (roughly). After I converted my MJ to LED bias in the first stage (thread here on diyaudio) voltage at this point was rougly 140V which dropped back into place after I changed the 27K to 33K.

calculations (very quick): 27K at 4mA drops 108V. 220 - 108= 112. Of course slight variations apply.

[Brit01]

Thks Stixx.

Yes you're right. It was late at night. I read the article again on the way to work the next day and it made sense.

I have some 6N6P's I'd like to use. I love the sound of these in my Aikido and have various spare I want to try in this headphone design.

[Stixx]

Brit,
Are you using the 6N6p's in the first or second stage in your Aikido?
I built one using 6CG7 and 6H30 with a regulated supply (courtesy of Salas)...
Mind disclosing your cathode resistor values for the 6N6P?

The Morgan Jones headamp should be easily adapted to run 6N6P in the cathode follower...
though my Aikido sounds much better than my MJ did

[Brit01]

Hi Stixx,

I'm using 5687 in the first stage and 6N6P in the second. I did have 6N1P's in the second but I needed less gain and actually preferred the 6N6P's. It sounds superb, and I'm running this into an old carver SS power amp with Klipsch speakers.

I'll look up the Cathode resistor values when I get back home. I think they were in the region of about 300 ohms but I'll have to verify that.

I did the wiring for the MJ last night and just realised I had the pins in reverse

I am wiring on a breadboard. Luckily I'm using small cable connectors to wire the components so I can interchange values easily without soldering anything.


Maybe I'll try the Aikido headphone configuration also.
The MJ project is my first point to point wiring job.
The Aikido was built using his circuit board.