John Curl's Blowtorch preamplifier part II - Page 2151 - diyAudio
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Old 19th March 2012, 04:00 AM   #21501
bcarso is offline bcarso  United States
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Quote:
Originally Posted by 1audio View Post
Actually the 100 Ohm source impedance is enshrined in that place where all useless and progress defying standards are: the EU IEC standards. There are also maximum output standards and sensitivity standards and everything needed to make a bureaucrats heart glow.
What would we do without them? Aside from perishing from the earth of course
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Old 19th March 2012, 04:11 AM   #21502
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Quote:
Originally Posted by 1audio View Post
Actually the 100 Ohm source impedance is enshrined in that place where all useless and progress defying standards are: the EU IEC standards. There are also maximum output standards and sensitivity standards and everything needed to make a bureaucrats heart glow.
Meanwhile, such headphones are not considered as high end. However, kilovolt going by wires to human heads to drive electrostatics sounds quite different than 100 Ohm standard resistors...
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Old 19th March 2012, 05:08 AM   #21503
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Hi,

Quote:
Originally Posted by steveh49 View Post
That's about 1 ma (order of magnitude) base current in the output transistor. Is that enough to turn off one of the opamps transistors reliably?
Most Op-Amp's do not have much more quiescent current in the output stage. I probably would look for even lower Beta Transistors (Video ones), but these seem to rare now. What I used to use in the 80's was Mini TO-3 case (forgot what they call them now) video one, beta around 30...

If you must have more current you can always add a resistor across the transistor BE connection. This depends on the Op-Amp you use.

I have not found the need to add these resistors back when I used this circuit to drive line output transformers and headphone outputs in mixing desks using these freaky east-german open collector output "Audio" Op-Amp's. There I used (obviously) a PNP Transistor and "ring of 2 CCS" (317's not around)... So shutting down halve the Output was no issue.

As said, the same trick works for NE5534, where Pin 5 is open collector output.

Ciao T
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Old 19th March 2012, 05:34 AM   #21504
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Well, that's all there is, Folks! You are on your own. (with the HP amp)
Personally my HP amp is direct coupled tube drive into Stax Electrostatics. Beats an IC anytime!
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Old 19th March 2012, 08:32 AM   #21505
Bonsai is offline Bonsai  Taiwan
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I loaned the work Stax amp (also the tube version) and matching headphones for about a year in Japan. They are wonderful, especially the midrange and top end. Someone clearly took a lot of time to get that set-up to sound good.
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Old 19th March 2012, 09:16 AM   #21506
PMA is offline PMA  Europe
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This was one of my headphone amps, produced in small series. With opamps, buffering is unavoidable.
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Old 19th March 2012, 09:22 AM   #21507
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This is another one, a 2 box design prototype. Discrete sounds better.
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Old 19th March 2012, 10:39 AM   #21508
zinsula is offline zinsula  Switzerland
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If these integrated amps which have been brought up are able to dissipate the extra power, you can force the output stage into class A (for a given headphone impedance) by resistor or ccs to one rail.
Quick'n dirty solution to avoid the "starved output stage" problem.
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Old 19th March 2012, 12:53 PM   #21509
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JC,

Is the plan a stand-alone product or integrated into something else ?


.
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Old 19th March 2012, 02:37 PM   #21510
Bonsai is offline Bonsai  Taiwan
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Quote:
Originally Posted by PMA View Post
This is another one, a 2 box design prototype. Discrete sounds better.
What did you do differently on he discrete design?
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