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Valve PP amps more tolerant of under 8ohm speakers?

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SiDog

(A)

I am building an 8ohm output 15W PP valve amp, and am gathering from the posts here it is more important to have a fully stable 8ohm speaker load with SE and OTL valve amps - are PP valve amps slightly more tolerant of a less stable load?
I have speakers pretty close to 7ohms with a zobel network on the bass driver.
Cheers.

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Re: Valve PP amps more tolerant of under 8ohm speakers? - zarniwoop 13:58:29 09/02/03 (0)
Another thing to consider is the reactive component of a speaker. It would be nice if speakers were just resistive loads, but they almost always are not even close. PP amps can work into reactive loads much more linearly than SE.
If you look at some speaker impedance vs frequency and phase angle plots you can see that many modern speakers are not that "SE friendly" from this perspective.
I am using speakers that dip to ~4 ohms on a PP triode amp, but I connect them to the 4ohm tap. This works quite well. I would even recommend trying speakers that remain closer to nominal 8ohms on the other taps for evaluation purposes if you have other taps available.
have fun
Re: Valve PP amps more tolerant of under 8ohm speakers? - pp man 23:47:10 09/01/03 (0)
Hi.
I regularly use speakers with dips to 4 ohms on an 8 ohm tap with no problems. It does depend on the design of the amp to some extent, but I can see no problems with 7 ohms.
Chris Jennings
Re: Valve PP amps more tolerant of under 8ohm speakers? - Tiny Daddy 19:32:58 09/01/03 (1)
A lot of PP amps use feedback and it could be that feedback amps are more tolerant.
- The real source impedance is relevant (not the nominal one) - mb-de 05:21:38 09/02/03 (0)
  Hi there,
  the issue is:
  What is the real source impedance of the amplifier.
  OTL and some SE do have a source impedance of several ohms.
  Good PPs with some overal NFB usually have a source impedance smaller
  than one ohm.
  The source impedance and the speaker impedance form a voltage divider
  - if the speaker has a widely varying impedance over frequency, the
  combination of amplifier and speaker will produce linear distortion -
  some frequencies will be more attenuated than others.
  The lower the source impedance of the amplifier, the less pronounced
  will these frequency response variations be -
  The rest is left for you to figure out.
  Regards,
  ---mb---
  ======

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