What would be the correct output cap for this OTL Headphone Amp?

pingfloid · 08:17 AM

This amp sounds great, and it can perfectly drive the Sennheiser HD-650 headphones. But the bass is rolled off, probably because of the low value (40 uF) of the output cap. What could be a reasonable value? 220 uF? I will have to replace it with an electrolytic cap, because there is no space for an oil cap.

The values in red is what I have measured

Another issue is that it gets extremely hot. I guess that it is the cathode resistor (1k/25W). Next week I will borrow a thermal camera and I will have a hot look at it.

flatheadmurre · 1st December 2011, 08:26 AM

Try to add anotherone in paralell and check if performance is getting better.

There´s some reasonably priced speaker crossover PP caps around.

briansune · 1st December 2011, 10:14 AM

Beautiful wires making Really Good!!

pingfloid · 1st December 2011, 11:41 AM

A closer view:

briansune · 1st December 2011, 12:25 PM

But to remind 90degree is not a good idea in wires and signal wire @@

radiostar · 1st December 2011, 01:56 PM

WOW, nice, but as briansune says 90 not recomended!

kevinkr · 1st December 2011, 04:18 PM

Quote:

Originally Posted by radiostar

WOW, nice, but as briansune says 90 not recomended!

Not an issue at audio frequencies. Nice layout, and very well executed. (Relatively speaking)

ruffrecords · 1st December 2011, 10:12 PM

250uF will give you 3dB down with 32 ohm headphones. If you want 1dB down at 20Hz then you will have to double that.

Cheers

Ian

pingfloid · 1st December 2011, 10:13 PM

This 90 deg issue, could i be the reason why I am listening to a local FM radio when I use this amplifier on my house (not in my office), even with the volume pot turned down?

pingfloid · 1st December 2011, 10:15 PM

Quote:

Originally Posted by ruffrecords

250uF will give you 3dB down with 32 ohm headphones. If you want 1dB down at 20Hz then you will have to double that.

Cheers

Ian

Hi Ian. Thank you for the information.

I am using 300 Ohm headphones (Sennheiser HD-650).

Is there some formula for caltulating the otuput cap? I would like to learn the maths

1st December 2011, 08:15 AM	#1
pingfloid diyAudio Member Join Date: Jan 2004 Location: Bangkok	What would be the correct output cap for this OTL Headphone Amp? This amp sounds great, and it can perfectly drive the Sennheiser HD-650 headphones. But the bass is rolled off, probably because of the low value (40 uF) of the output cap. What could be a reasonable value? 220 uF? I will have to replace it with an electrolytic cap, because there is no space for an oil cap. The values in red is what I have measured Another issue is that it gets extremely hot. I guess that it is the cathode resistor (1k/25W). Next week I will borrow a thermal camera and I will have a hot look at it. Last edited by pingfloid; 1st December 2011 at 08:17 AM.

1st December 2011, 01:56 PM	#6
radiostar diyAudio Member Join Date: Apr 2009	WOW, nice, but as briansune says 90 not recomended! __________________ tubes.rs facebook.com/tubes.rs

1st December 2011, 10:12 PM	#8
ruffrecords diyAudio Member Join Date: Jun 2007 Location: Holt, Norfolk	250uF will give you 3dB down with 32 ohm headphones. If you want 1dB down at 20Hz then you will have to double that. Cheers Ian __________________ Ian

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1st December 2011, 08:26 AM	#2
flatheadmurre diyAudio Member Join Date: Mar 2011 Location: Jarna	Try to add anotherone in paralell and check if performance is getting better. There´s some reasonably priced speaker crossover PP caps around.

1st December 2011, 10:14 AM	#3
briansune diyAudio Member Join Date: Sep 2011	Beautiful wires making Really Good!!

1st December 2011, 11:41 AM	#4
pingfloid diyAudio Member Join Date: Jan 2004 Location: Bangkok	A closer view:

1st December 2011, 12:25 PM	#5
briansune diyAudio Member Join Date: Sep 2011	But to remind 90degree is not a good idea in wires and signal wire @@

1st December 2011, 10:13 PM	#9
pingfloid diyAudio Member Join Date: Jan 2004 Location: Bangkok	This 90 deg issue, could i be the reason why I am listening to a local FM radio when I use this amplifier on my house (not in my office), even with the volume pot turned down?

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