Bipolar output stage prefers capacitive or inductive load? - Page 2

forr · 4th October 2006, 12:06 AM

A capacitive load adds a phase lag to the feedback voltage.
According to D. Self, lowering the impedance of a speaker using some RC or RLC networks to make it resistive is not a good idea : the amplifier will have to deliver more current which means more distorsion. A good amplifer does not suffer from instability with usual loads.

parsecaudio · 4th October 2006, 12:24 AM

Hi forr
this is not always true.
For different reasons some amplifiers with a large amount of NFB or some tube amp do not like reactive loads.
When compare the distortion on a tube amp that drive a inductive load with the same load compensated with a RC network we can see that the distortion decrease.Test this in order to believe....If we speak about sound we can discuss to the infinite

Cheers
Vittorio

Paul W · 4th October 2006, 10:31 PM

No concern about destroying amps. Even the capacitive version isn't as reactive as many ESLs...and it is the more reactive of the two.

Given other constraints, the XO will be as resistive as practical. The inductive/capacitive question is just an opportunity for me to select the best overall compatibility between speaker and amp.
Paul

d3imlay · 7th October 2006, 10:28 AM

Is there a model I could use as a worst case scenario for capacitive testing and another one for inductive testing? I think a 220mfd cap across the output may be a bit much for capacitive.

anatech · 7th October 2006, 02:44 PM

Hi d3imlay,
220uF is not a reasonable load for any amplifier.

A 45 ° phase angle on your load would be a stressful test for an amp. Resistive loads are the most common, I've heard of people adding 0.22 uF across and 8 ohm dummy load as well.

Really, you just have to check your designs into a standard load and provide safety margins. The 0.22 uF cap is more for testing stability.

-Chris

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4th October 2006, 12:06 AM	#11
forr diyAudio Member Join Date: Dec 2004 Location: Next door	A capacitive load adds a phase lag to the feedback voltage. According to D. Self, lowering the impedance of a speaker using some RC or RLC networks to make it resistive is not a good idea : the amplifier will have to deliver more current which means more distorsion. A good amplifer does not suffer from instability with usual loads.

4th October 2006, 12:24 AM	#12
parsecaudio diyAudio Member Join Date: Apr 2004 Location: ventimiglia	Hi forr this is not always true. For different reasons some amplifiers with a large amount of NFB or some tube amp do not like reactive loads. When compare the distortion on a tube amp that drive a inductive load with the same load compensated with a RC network we can see that the distortion decrease.Test this in order to believe....If we speak about sound we can discuss to the infinite Cheers Vittorio

4th October 2006, 10:31 PM	#13
Paul W diyAudio Member Join Date: Oct 2003 Location: North Georgia	No concern about destroying amps. Even the capacitive version isn't as reactive as many ESLs...and it is the more reactive of the two. Given other constraints, the XO will be as resistive as practical. The inductive/capacitive question is just an opportunity for me to select the best overall compatibility between speaker and amp. Paul

7th October 2006, 10:28 AM	#14
d3imlay diyAudio Member Join Date: Sep 2004 Location: Ohio	Is there a model I could use as a worst case scenario for capacitive testing and another one for inductive testing? I think a 220mfd cap across the output may be a bit much for capacitive.

7th October 2006, 02:44 PM	#15
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi d3imlay, 220uF is not a reasonable load for any amplifier. A 45 ° phase angle on your load would be a stressful test for an amp. Resistive loads are the most common, I've heard of people adding 0.22 uF across and 8 ohm dummy load as well. Really, you just have to check your designs into a standard load and provide safety margins. The 0.22 uF cap is more for testing stability. -Chris

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