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Old 23rd September 2005, 07:10 AM   #1
Mushal is offline Mushal  South Korea
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Default 300B SE for Electrostatic Headphone

Hi, Guys..

I'm planning to build the transformer coupled 300B amplifier for Stax Electrostatic Headphone. I'm a beginner for the circuit including the transformers. So, I'm not sure that the attatched schematic which I designed will work or not.

The gain and driver stage is not fixed, but, the output stage is almost same as the typical 300B Single Ended Amplifier. The voltage swing about 600Vpp is transferred to the headphone attatched to the secondary windings. I'm planning to use Lundahl 1677 which is designed for the interstage. Turn ratio is 1:2 and Primary DC Current can be up to 80 mA. The Price is not so bad.

Please, comment your opinions..
and, Recommend me the simple and good-sounding gain and driver stage for 300B SE also.

Best Regards
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Old 23rd September 2005, 08:46 AM   #2
Mushal is offline Mushal  South Korea
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Default Concept Schematics

This is concept schematics..
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Old 23rd September 2005, 02:31 PM   #3
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Hello Mushal,

the Lundahl 1677 has a max rating of 410Vpp and 80mA DC so it there might be too small a margin for your needs. Have you looked into the Sowter 8424 from www.sowter.co.uk? I have used it in severaly amps and it is a very good sounding transformer.

I have drawn a circuit based on amps I've built as a recommendation for your headphone amp:

Click the image to open in full size.

This is a very good sounding setup. It uses an EL34 transformer coupled to the 300b as a driver. The input tube is direct coupled to the EL34. There is no capacitor in the signal path! The amp is not designed for maximum output swing but for sweet spot in sound. You probably won't be listening with 600Vpp too long anyway .

You need two power supplies, one for each channel. The 300B should be heated with DC (not shown here). Try it, you might like it!

Of course as you said if you change the OPT you have a normal 300B amp. In this case I can recommend the Sowter SA08.

Best regards
Michael
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Old 23rd September 2005, 02:45 PM   #4
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I think this circuit won't work as is since the grid of the last stage is floating.

Regards

Charles
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Old 23rd September 2005, 03:18 PM   #5
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Default Go push-pull and be happy

Gee, to me, electrostatic headphones seem to almost cry out for direct (or capacitor-coupled) push-pull triodes. That's the way Stax did it. This is one place where a transformer is not needed. An electrostatic element is push-pull to begin with, so why try to force a single-ended solution that needs a 1:1 transformer? Just my opinion...
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Old 23rd September 2005, 03:29 PM   #6
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Quote:
I think this circuit won't work as is since the grid of the last stage is floating
Charles, you are right. I corrected the schematic. Thanks for pointing that out.

Michael
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