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Old 9th July 2009, 01:07 PM   #1
Brit01 is offline Brit01  United Kingdom
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Default John Broskie's headphone design using pentodes

Just built a nice headphone amp but last night I saw one of JB's designs with positive and negative rails. Interesting design. How do this work? Is he allowing an output without big caps? It shows to outputs and I'm trying to work out the signal path here.

I'm currently using big electrolytics on the output to drive the headphones. Would be great to have a pure OTL without any caps like this one.

Has anyone built one of these? What do they sound like?
How would you build the power supply for this? Does anyone have schematics?


Or if there is a thread related to this design please advise.

many thanks
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Old 9th July 2009, 05:34 PM   #2
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Yes the bipolar supply allows the elimination of the output cap. It's really just the same as how most SS amps are built. Headphones are high enough impedance to more easily be driven OTL. Did the article say if this was to drive 32 ohm headphones or 600 ohms? Note that if you built it you would have to fiddle with resistors to get DC on the output close to zero. It looks like JB has done this with the 167 and 156 ohm resistors on the rails. That's just for the simulation though, you would have to play with these values or use a high wattage pot. My personal preference is fixed resistors.

The tubes are strapped as triodes, so it is not a pentode amp.

I don't see two outputs. Do you mean the ground connection?
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Old 9th July 2009, 06:02 PM   #3
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I don't care how clever your design is, or how good it sounds, if I am strapping something to my head and it involves voltages above about 24V, there needs to be, at a minimum, a cap between me and it. Maybe there's an exception for well made and reputable electrostatics, but maybe not.
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Old 9th July 2009, 07:05 PM   #4
iko is offline iko  Canada
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Quote:
Originally posted by dsavitsk
I don't care how clever your design is, or how good it sounds, if I am strapping something to my head and it involves voltages above about 24V, there needs to be, at a minimum, a cap between me and it. Maybe there's an exception for well made and reputable electrostatics, but maybe not.
+1

One thing I'd like to add about the Broskie circuits. A lot of people think he's a genius, and he definitely seems to know his stuff. However, as a learning experience I have tried many of his circuits in simulation, and sadly, many of them did not work exactly as shown. They may work in reality, but this is something that you may want to keep in mind. Just to be clear, I'm not talking about the circuits for which he has pcbs/kits for sale, but those in which he explores ideas. The circuit you're considering may be one of them?
Just my 2c.
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Old 10th July 2009, 01:21 AM   #5
rman is offline rman  Canada
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Quote:
I have tried many of his circuits in simulation, and sadly, many of them did not work exactly as shown.
I built this regulator.

http://www.glass-ware.com/tubecircuits/High_Voltage_Regulator.html]Broskie regulator[/URL]

It didn't work... at least I couldn't make it work.

Cheers.
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Old 10th July 2009, 01:23 AM   #6
rman is offline rman  Canada
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Link didn't work.
Here it is again, I hope.broskie regulator
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Old 10th July 2009, 02:01 AM   #7
iko is offline iko  Canada
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Quote:
Originally posted by rman


I built this regulator.

http://www.glass-ware.com/tubecircuits/High_Voltage_Regulator.html]Broskie regulator[/URL]

It didn't work... at least I couldn't make it work.

Cheers.
OT: give this a try if you want something good that works. Plus, salas is around and is very helpful. In spite of its "simplistic" name, it can run circles around some "super" regulators.
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Old 10th July 2009, 02:20 AM   #8
rman is offline rman  Canada
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Thank's

Have looked at this with interest. I might just try it sometime, maybe this winter.

Cheers.
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Old 10th July 2009, 06:26 AM   #9
Stixx is offline Stixx  Germany
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Quote:
OT: give this a try if you want something good that works. Plus, salas is around and is very helpful. In spite of its "simplistic" name, it can run circles around some "super" regulators.
I definitely second that. My HV shunt has 100+ hours on it, works perfectly and sounds better than any psu I had so far... (headphones amps only...;-))
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Old 11th July 2009, 02:29 AM   #10
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Quote:
Originally posted by ikoflexer


One thing I'd like to add about the Broskie circuits. A lot of people think he's a genius, and he definitely seems to know his stuff. However, as a learning experience I have tried many of his circuits in simulation, and sadly, many of them did not work exactly as shown . . . . Just my 2c.
My experience too. I was interested in his Partial Feedback article but sims of it using LTspice didn't work. I came to the conclusion that it was theoretical and he hadn't tried it for himself.
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