CFP output amplifier - Is it worth the hassle?

ash_dac · 8th October 2006, 04:20 PM

Hi,

Is a CFP output stage based amplifier worth pursuing ?

The design in Walt's book is an op amp (NE540) and CFP output stage credited to Signetics Corp'. The design has 0.02uf capacitance across the vbe multiplier, 500uf across the bias diodes, 0.01uf across the local feedback resistors, and 10pf across the feedback resistor !

The output stage has a gain of 4 !

My first try in LT Spice lead to oscillating output and I have had a look on the forum and it seems CFP output stages are a real pain to stablise. I can't even get the design stable in LT SPice!

djk · 9th October 2006, 12:13 AM

Is it worth it?

A good question.

About 10 years ago I did a commercial design that was to replace a gainclone type design based on a NS chip. The prototype worked perfectly as designed, no changes needed. It sounded better and cost about the same. Maybe I got lucky.

I needed rail-to-rail operation from low voltages and an IC front end, otherwise I may not have used the CFP topology. I ran a voltage gain of 3 in the output stage. It helped to make the IC in the front end slower than the output stage. I used a 5532 to drive MPSA06/56 drivers and 3055/2955 outputs.

8th October 2006, 04:20 PM	#1
ash_dac diyAudio Member Join Date: Jan 2005 Location: UK	CFP output amplifier - Is it worth the hassle? Hi, Is a CFP output stage based amplifier worth pursuing ? The design in Walt's book is an op amp (NE540) and CFP output stage credited to Signetics Corp'. The design has 0.02uf capacitance across the vbe multiplier, 500uf across the bias diodes, 0.01uf across the local feedback resistors, and 10pf across the feedback resistor ! The output stage has a gain of 4 ! My first try in LT Spice lead to oscillating output and I have had a look on the forum and it seems CFP output stages are a real pain to stablise. I can't even get the design stable in LT SPice!

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9th October 2006, 12:13 AM	#2
djk diyAudio Member Join Date: Feb 2001 Location: USA	Is it worth it? A good question. About 10 years ago I did a commercial design that was to replace a gainclone type design based on a NS chip. The prototype worked perfectly as designed, no changes needed. It sounded better and cost about the same. Maybe I got lucky. I needed rail-to-rail operation from low voltages and an IC front end, otherwise I may not have used the CFP topology. I ran a voltage gain of 3 in the output stage. It helped to make the IC in the front end slower than the output stage. I used a 5532 to drive MPSA06/56 drivers and 3055/2955 outputs.

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