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Old 3rd December 2016, 08:09 AM   #1
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Join Date: Jun 2010
Default Need suggestions for CCS and parallel feed OT implementation

I'm building a 6SN7/6AS7 headphone amp similar to the attachment. I want to add Cascode Constant Current Source to plates. How do I do it? Are there any schematics or PCBs I can use for this? I can buy Speedball kit for Bottlehead Crack but I want a cheaper substitute since I'm on a budget.

Question 2, this is probably a stupid question but is it possible to use parallel feed OT to output stage?(like Espressivo amp).
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Old 3rd December 2016, 03:41 PM   #2
bigwill is offline bigwill  United Kingdom
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Re: CCS, you could avoid some added complexity by bootstrapping the anode of the first ecc88 via the low impedance drive from the cathode of the 6AS7. All that is needed is an extra capacitor and resistor. The distortion may be a minuscule bit higher than a true CCS but probably not enough to care about. 90% of the performance from 20% of the parts is often a good compromise, especially as there is a lot less potential for failure.
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Old 3rd December 2016, 09:12 PM   #3
PRR is offline PRR  United States
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You want frills or you want "better"?

Looks to me like that huge 6SA7 is running 75V 25mA or less than 2W of its 14W rating. The 25mA may be OK in hi-Z phones but disappointing in 32 Ohm phones: 10mW output at high THD.

That is IF the 6SN7 is biased to swing the big triode ALL the way. I suspect it can't do that.

250V-400V of B+ would justify the bottles you got.
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Old 4th December 2016, 07:23 PM   #4
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I want to add 10M45S or something similar to plates. And may be even line level output transformers to 6AS7 but I don't know how to.

I'm not rigid about the schematic I posted. I'm open to any headphone amp design as long as the amp is...

(1) Parafeed
(2) Some form of CCS on Plates
(3) Reasonably low cost
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