CF after gain stage

Brit01 · 23rd December 2009, 10:54 AM

Just breadboarded a SV83 CCS on a simple common cathode gain stage.

After testing it successfully as a linestage, I decided to hook up a pair of headphones through 220uF output caps. Sounded reasonable.

Now what I've seen in the majority of headphone amps are CF's following the gain stage.

Is this necessary? What advantages/benefits does it give to the circuit?

SY · 23rd December 2009, 11:00 AM

Lower output impedance and lower distortion.

Brit01 · 23rd December 2009, 11:24 AM

Great that's what I was thinking but just wasn't 100% sure.

Is reduction in distortion a significant amount or just minimal?

SY · 23rd December 2009, 11:42 AM

That depends on your voltage amplifier tube and the impedance of the headphones. If the headphones' impedance is greater than about 10x the effective plate resistance of the voltage amplifier, the distortion reduction will not be large. But for lower impedances, it can be very significant- the 'phone's impedance will definitely change the slope of the effective load line.

23rd December 2009, 10:54 AM	#1
Brit01 diyAudio Member Join Date: Jul 2008	CF after gain stage Just breadboarded a SV83 CCS on a simple common cathode gain stage. After testing it successfully as a linestage, I decided to hook up a pair of headphones through 220uF output caps. Sounded reasonable. Now what I've seen in the majority of headphone amps are CF's following the gain stage. Is this necessary? What advantages/benefits does it give to the circuit?

23rd December 2009, 11:00 AM	#2
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	Lower output impedance and lower distortion. __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

23rd December 2009, 11:42 AM	#4
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	That depends on your voltage amplifier tube and the impedance of the headphones. If the headphones' impedance is greater than about 10x the effective plate resistance of the voltage amplifier, the distortion reduction will not be large. But for lower impedances, it can be very significant- the 'phone's impedance will definitely change the slope of the effective load line. __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

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23rd December 2009, 11:24 AM	#3
Brit01 diyAudio Member Join Date: Jul 2008	Great that's what I was thinking but just wasn't 100% sure. Is reduction in distortion a significant amount or just minimal?

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