Bipolar output stage prefers capacitive or inductive load?

Paul W · 3rd October 2006, 12:02 AM

I'm in the early stages of building a new speaker and can choose a crossover network topology that leans toward a capacitive load...a network presenting a more inductive load is also possible. Which is better for amp performance? A few words of "why" would be appreciated (I'm not a SS amp guy).
Thanks,
Paul

Leolabs · 3rd October 2006, 02:42 AM

It prefer resistive loads.

anatech · 3rd October 2006, 03:18 AM

Hi Paul,
The less reactance, the better for any amplifier. This is especially true of tube amplifiers. The solid state kind are usually less affected by phase angle, but odd things can happen.

Capacitive loads are about the worst for a solid state amp. You effectively reduce the high frequency feedback voltage when things get out of whack. Not good for stability sometimes. Inductive loads won't hurt stability, but the excess dissipation in the output stage is not welcome.

-Chris

darkfenriz · 3rd October 2006, 10:39 AM

Go inductive.

Paul W · 3rd October 2006, 11:39 PM

Thanks guys. I was looking for the lesser of the two evils...slightly inductive it shall be!

parsecaudio · 3rd October 2006, 11:51 PM

Hi Paul W.
When an amp drive a reactive load some precaution can be made.
With capacitive load you should check the stability of the amp.Connect an audio generator and a scope and check the overshoot and ringing on the signal.If instability is produced you should change(or add) a Zobel network.

When a large inductive load is driven you must to protect the output transistors with two diode connected from the negative supply and speaker output and from speaker output and positive supply.

Obviously the betterfor all the amp(tube or solid state) is resistive load.You can also compensate with a RC network the inductive loads

The suggestions of Anatech and Darkfenriz are also excellent.
Cheers
Vittorio

anatech · 4th October 2006, 12:04 AM

Hi Vittorio,
Paul is designing a speaker. We have to worry about what it does.

Paul W,
Slightly inductive is excellent. It should be an easy load for most amps then with minimal phase shifts. Good choice!

-Chris

parsecaudio · 4th October 2006, 12:19 AM

Hi Chris
my worry is that Paul not plans a crossover that cause problems on its amplifier(or worse than it breaks off) .

Slightly inductive is a good choice.A RC network in order to compensate this little inductive load is also possible.
Cheers
Vittorio

anatech · 4th October 2006, 12:30 AM

Hi Vittorio,
Well, let's see what he does. That is always a concern.

I had a guy blow up an Adcom GFA-555II twice. He made his own sub crossover. I asked him to bring it in after hearing the crossover was really hot. The first element was a 220 uF bipolar cap across the input.

-Chris

parsecaudio · 4th October 2006, 12:37 AM

Quote:

The first element was a 220 uF bipolar cap across the input.

UUOOOPSSS!!!!

3rd October 2006, 12:02 AM	#1
Paul W diyAudio Member Join Date: Oct 2003 Location: North Georgia	Bipolar output stage prefers capacitive or inductive load? I'm in the early stages of building a new speaker and can choose a crossover network topology that leans toward a capacitive load...a network presenting a more inductive load is also possible. Which is better for amp performance? A few words of "why" would be appreciated (I'm not a SS amp guy). Thanks, Paul

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3rd October 2006, 02:42 AM	#2
Leolabs diyAudio Member Join Date: Dec 2004 Location: Bukit Mertajam	It prefer resistive loads.

3rd October 2006, 03:18 AM	#3
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi Paul, The less reactance, the better for any amplifier. This is especially true of tube amplifiers. The solid state kind are usually less affected by phase angle, but odd things can happen. Capacitive loads are about the worst for a solid state amp. You effectively reduce the high frequency feedback voltage when things get out of whack. Not good for stability sometimes. Inductive loads won't hurt stability, but the excess dissipation in the output stage is not welcome. -Chris

3rd October 2006, 10:39 AM	#4
darkfenriz diyAudio Member Join Date: Jun 2004 Location: Warsaw	Go inductive.

3rd October 2006, 11:39 PM	#5
Paul W diyAudio Member Join Date: Oct 2003 Location: North Georgia	Thanks guys. I was looking for the lesser of the two evils...slightly inductive it shall be!

3rd October 2006, 11:51 PM	#6
parsecaudio diyAudio Member Join Date: Apr 2004 Location: ventimiglia	Hi Paul W. When an amp drive a reactive load some precaution can be made. With capacitive load you should check the stability of the amp.Connect an audio generator and a scope and check the overshoot and ringing on the signal.If instability is produced you should change(or add) a Zobel network. When a large inductive load is driven you must to protect the output transistors with two diode connected from the negative supply and speaker output and from speaker output and positive supply. Obviously the betterfor all the amp(tube or solid state) is resistive load.You can also compensate with a RC network the inductive loads The suggestions of Anatech and Darkfenriz are also excellent. Cheers Vittorio

4th October 2006, 12:04 AM	#7
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi Vittorio, Paul is designing a speaker. We have to worry about what it does. Paul W, Slightly inductive is excellent. It should be an easy load for most amps then with minimal phase shifts. Good choice! -Chris

4th October 2006, 12:19 AM	#8
parsecaudio diyAudio Member Join Date: Apr 2004 Location: ventimiglia	Hi Chris my worry is that Paul not plans a crossover that cause problems on its amplifier(or worse than it breaks off) . Slightly inductive is a good choice.A RC network in order to compensate this little inductive load is also possible. Cheers Vittorio

4th October 2006, 12:30 AM	#9
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi Vittorio, Well, let's see what he does. That is always a concern. I had a guy blow up an Adcom GFA-555II twice. He made his own sub crossover. I asked him to bring it in after hearing the crossover was really hot. The first element was a 220 uF bipolar cap across the input. -Chris

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