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Output cap for OTL headphone amp
Output cap for OTL headphone amp
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Old 27th October 2019, 02:19 PM   #1
edwtsui is offline edwtsui  Hong Kong
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Default Output cap for OTL headphone amp

Hi,

I am going to build the Morgan Jones headphone amp. My challenge is that it requires a 470uF cap for output. The cap is so large such that a film cap is not possible and electrolytic is the only choice. Could anyone suggest a good electrolytic for me?


https://www.pearl-hifi.com/06_Lit_Ar...timization.pdf
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Old 27th October 2019, 02:48 PM   #2
nautibuoy is offline nautibuoy  United Kingdom
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I've used Elna Silmic RFS and Nichicon FG 'Fine Gold' electrolytics to good effect as output caps;

Elna Silmic RFS Electrolytics | Hifi Collective

Nichicon FG Type | Hifi Collective

I'm currently working on a HPA project and have a pair of the Nichicons installed for the output caps for 32ohm headphones, however, most of my headphone listening is with 600ohm BeyerDynamic DT880 heaphones and that impedance brings film output caps into range (I'm using 56uF film caps)

Of course these are just my own views on the suitability of those caps and YMMV.
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Old 27th October 2019, 03:14 PM   #3
sevenup2278 is offline sevenup2278  Netherlands
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Quote:
Originally Posted by nautibuoy View Post
I've used Elna Silmic RFS and Nichicon FG 'Fine Gold' electrolytics to good effect as output caps;

Elna Silmic RFS Electrolytics | Hifi Collective

Nichicon FG Type | Hifi Collective

I'm currently working on a HPA project and have a pair of the Nichicons installed for the output caps for 32ohm headphones, however, most of my headphone listening is with 600ohm BeyerDynamic DT880 heaphones and that impedance brings film output caps into range (I'm using 56uF film caps)

Of course these are just my own views on the suitability of those caps and YMMV.
Those won't work for the Morgan Jones amp as it runs at 220V DC.
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Old 27th October 2019, 03:29 PM   #4
nautibuoy is offline nautibuoy  United Kingdom
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Quote:
Originally Posted by sevenup2278 View Post
Those won't work for the Morgan Jones amp as it runs at 220V DC.
Fair enough - I didn't look up the HPA design so wasn't aware of the 220V.
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Old 27th October 2019, 03:31 PM   #5
edwtsui is offline edwtsui  Hong Kong
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Quote:
Originally Posted by sevenup2278 View Post
Those won't work for the Morgan Jones amp as it runs at 220V DC.
I can try to lower the DC offset to around 85VDC, question is is it safe to use 100VDC Nichicon or Elna electrolytic?
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Old 27th October 2019, 03:53 PM   #6
Stixx is offline Stixx  Germany
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Quote:
is it safe to use 100VDC Nichicon or Elna electrolytic
Why should you? There are plenty of suitable caps with higher voltage rating, such as these https://www.digikey.com/product-deta...X30-ND/3565526

Which is what I used when I built the MJ 14 years ago, //ed with some nice film caps.
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Old 27th October 2019, 04:10 PM   #7
edwtsui is offline edwtsui  Hong Kong
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Quote:
Originally Posted by Stixx View Post
Why should you? There are plenty of suitable caps with higher voltage rating, such as these 400MXC220MEFCSN30X30 Rubycon | Capacitors | DigiKey

Which is what I used when I built the MJ 14 years ago, //ed with some nice film caps.
It is because those audio grade electrolytic caps are limited to 100VDC, that's why I am thinking to lower the DC offset on the output. Is the Rubycon good for audio?
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Old 27th October 2019, 04:58 PM   #8
rayma is offline rayma  United States
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Please don't use an output capacitor rated at less than the power supply voltage, very bad practice.
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Old 27th October 2019, 05:17 PM   #9
Frank Berry is offline Frank Berry  United States
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Whatever you use, make sure that you add a resistor (10k, perhaps) across the output to prevent blowing out your headphones if you plug them in after powering up the amplifier.
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Old 27th October 2019, 05:18 PM   #10
Stixx is offline Stixx  Germany
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Rubycon caps could be considered audio grade... it is highly subjective. What makes an electrolytic cap 'audio'? It is still a electrolytic cap,
and I'd rather use one with the appropriate voltage rating (with a safe margin) than to alter the B+ of the amplifier (btw. this is not DC offset!!
100V of DC offset will absolutely positively destroy any headphone) which will likely have an effect on the sound of the MJ.
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