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Old 8th December 2012, 01:00 PM   #1
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Default The Morgan Jones mini tube headphone Amplifier

I want to build The Optimized Morgan Jones Amplifier but I have question about output cap beacuse I want to use film instead lytic: the schematic uses 470uF 350V, really is necessary so big or I can use a small film cap like 27uf or 10uF or less?

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Old 8th December 2012, 02:25 PM   #2
jam is offline jam  United States
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Too small a capacitor and you will have bass rolloff. Figure input impedance of headphones and calculate the rolloff with selected capacitor.

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Old 8th December 2012, 02:30 PM   #3
jam is offline jam  United States
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First-order continuous-time implementation


Figure 1: A passive, analog, first-order high-pass filter, realized by an RC circuit
The simple first-order electronic high-pass filter shown in Figure 1 is implemented by placing an input voltage across the series combination of a capacitor and a resistor and using the voltage across the resistor as an output. The product of the resistance and capacitance (R×C) is the time constant (τ); it is inversely proportional to the cutoff frequency fc, that is,


where fc is in hertz, τ is in seconds, R is in ohms, and C is in farads.
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Old 8th December 2012, 02:31 PM   #4
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I calculate 265uF for a load of 300 ohms (HD600), do you know if I can substitute the cathode resistor/capacitor with a 1.9-2.0-2.1V 20mA LED?

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Old 8th December 2012, 03:18 PM   #5
Stixx is offline Stixx  Germany
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Here you go...

But when you want my opinion you'd better spend the money on output transformers than trying to pass the audio signal through humongous film capacitors.
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Old 8th December 2012, 03:23 PM   #6
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I once built a version of this amplifier - using a triode-connected EF86 on the front end, but with the same 6922 back-end - I did use electrolytics on the output, bypassed with Dayton polypropolenes. Really, it sounded quite good and certainly changed my mind about the "sound of electrolytics". If I remember correctly, I just used some Panasonics from Digikey.
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Old 8th December 2012, 03:27 PM   #7
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Thanks Stixx, I'm currently using the Valve Wizard mu-follower, I'm satisfied but I received advice that my Senhs HD600 plays better with an output impedance of 120 ohms, the mu-follower I'm using have an output impedance of 257 ohms so to big also I know HD600 have an output impedance of 300 ohms so the question is: wich value of SE output line transformer have I to install?, mu-follower schematic:

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Old 8th December 2012, 03:31 PM   #8
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Quote:
Originally Posted by kstagger View Post
I once built a version of this amplifier - using a triode-connected EF86 on the front end, but with the same 6922 back-end - I did use electrolytics on the output, bypassed with Dayton polypropolenes. Really, it sounded quite good and certainly changed my mind about the "sound of electrolytics". If I remember correctly, I just used some Panasonics from Digikey.
I eard people used EF86 for MM phono preamp with great success.
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Old 8th December 2012, 03:40 PM   #9
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A weakness of that MJ circuit is that it uses electrolytics to set the LF rolloffs. This is the most likely scenario to make electrolytic distortion a problem. Add an input coupling cap to set the LF rolloff, then ensure that the electrolytics are big enough to have very little signal voltage across them.
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Old 8th December 2012, 03:43 PM   #10
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Before the pot? Wich value?
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