phillips ah578 power amp

[tmomirov]

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

[JKent]

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!

Kent

[tmomirov]

Kent , Yes i spoke with Mr. Rapp and also seen the info you list but neither of it says it will take a 4 ohm load , But you will be given it a 4ohm load runing 2 pair of 8ohm speakers dont you think ? Thank you for your time Greg

[JKent]

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.

Kent

Kent

[tmomirov]

Thank you Kent for the advice i'll keep it on the shelf as decoration piece till more information can be aquired