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Old 2nd October 2006, 11:02 PM   #1
Paul W is offline Paul W  United States
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Default 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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Old 3rd October 2006, 01:42 AM   #2
Leolabs is offline Leolabs  Malaysia
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It prefer resistive loads.
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Old 3rd October 2006, 02:18 AM   #3
anatech is offline anatech  Canada
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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
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Old 3rd October 2006, 09:39 AM   #4
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Go inductive.
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Old 3rd October 2006, 10:39 PM   #5
Paul W is offline Paul W  United States
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Thanks guys. I was looking for the lesser of the two evils...slightly inductive it shall be!
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Old 3rd October 2006, 10:51 PM   #6
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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
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Old 3rd October 2006, 11:04 PM   #7
anatech is offline anatech  Canada
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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
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Old 3rd October 2006, 11:19 PM   #8
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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
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Old 3rd October 2006, 11:30 PM   #9
anatech is offline anatech  Canada
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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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Old 3rd October 2006, 11:37 PM   #10
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Quote:
The first element was a 220 uF bipolar cap across the input.
UUOOOPSSS!!!!
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