Audio Research D-70 shut-down *thump* with Quatro's

[Ross B.]

My ARC D-70 MkII causes a low-frequency *thump* when it shuts off. I have been told this is normal for this amplifier, and is not harmful. However, I am concerned because the Quatro amplifiers boost the gain of the low frequency, in compensation for the high-pass input filter. Because this thump is coming from the power amp, not the preamp, it's not being filtered, and therefore is being *amplified* by the Quatro's! I measured 9V/21 DBu peak at the output taps.

I'm investigating possible solutions, including a mod published by ARC. I wanted to know if others have experience with this pairing, as I know ARC + Vandersteen is a popular combination. I know Richard is very concerned about excessive low-frequency signals being sent to the woofer section...

[GdnrBob]

Wouldn't the internal crossover reduce the amps output to what the Quatro requires to produce the proper level of sound?

If so, then it shouldn't be as high as you measured at the output taps.

 

But, as I am a humble gardener, I might have it wrong.

B

[Richard Vandersteen]

This "thump" is not a problem.  9V is not that big compared to the low bass on some recordings.  You should still investigate the ARC mod as it may improve other aspects of the sound.  RV

 

 

[Ross B.]

6 hours ago, Richard Vandersteen said:

This "thump" is not a problem.  9V is not that big compared to the low bass on some recordings.  You should still investigate the ARC mod as it may improve other aspects of the sound.  RV

 

 

Thanks Richard, that puts my mind at ease.

The mod just shorts the output to ground on power-off, so the stray voltage doesn’t go to the speakers. I’m waiting on a response. Even if they don’t have the original parts, it’s just some wire and a couple relays, I can source that.