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phillips ah578 power amp

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Hi everyone , i recently purchased a phillips ah578 power amp its a massive amp i'm looking to power my acoustic research tsw910 speakers and the only information i see on that amp (far few between) is that its only a 8 ohm amp , and my speaker are 4ohm . With that being said the amp has a-b-a+b switching now running 2pair of 8ohm speakers now wouldnt that equate to a 4 ohm load but there is no information on the amp that its capable of handling a 4 ohm load .So in closing it would be greatly appreciated if anyone can give me some insight about this amp . Thank you Greg


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Hi Greg

First problem: You won't find much searching for Phillips with 2 Ls. Search "Philips AH578" and you'll find some things.

Cool looking amp. You can find the service manual here: http://www.mfbfreaks...578/22ah578.pdf or here: http://www.hifiengin...ps/ah-578.shtml

But why not ask the designer? Earl Rapp said he designed the AH578 when he was an EE at Philips. You can email him: earlrapp@comcast.net

Here are the specs:

  • Continuous power: 210 watts per channel
  • Power band: 20 to 20,000Hz
  • Total harmonic distortion: 0.08%
  • Load: 8 ohms
  • Frequency response: 10 to 30,000Hz
  • Channel separation: 60dB
  • Damping factor: 90
  • Signal to noise ratio: 100dB
  • Input sensitivity: 1V
  • Rated impedance: 50K ohms
  • Subsonic filter: 12dB octave
  • Inputs: 2
  • Speaker terminals: 2 sets
  • Dimensions: 200 x 457 x 381mm
  • Weight: 28.6kg

Good luck!


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OK. Well, one would think the designer could answer your question. Anyway.... short answer: NO

Here is an explanation from our own johnieo: "The lower impedance (4 Ohm) speaker would draw too much current from the amp and overload its output transistors. An amp intended to drive 8 Ohm speakers can only produce half the current needed to drive a 4-Ohm speakers, so if one connected a 4-Ohm load to it, it would fry the output transistors. . . . An amp rated for 4 Ohms CAN drive 4, 6, and 8 Ohm speakers, but not other way around."

There have been discussions elsewhere here about amps suitable for driving 4 ohm speakers. Most recently Tom Tyson wrote about bargain-priced Crown amps. Too bad--the Philips sure looks nice. Good luck.



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