HQ Power VPA21000U1 low freq. oscillation? - diyAudio
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Old 19th February 2015, 04:14 PM   #1
djduck is offline djduck  Estonia
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Join Date: Dec 2012
Location: Tartu vald, Estonia
Default HQ Power VPA21000U1 low freq. oscillation?

I noticed that when playing certain songs from Spotify, there are some fairly large low frequency oscillations going on when the bass drops. And it's not all songs, only some. For an example, Delta 9's Speaker Worship shows some ~10Hz oscillations that I'm pretty sure are not supposed to be there.
My question is, whether this would be an amplifier issue or a Spotify issue or what?
The amp itself is very nice, tho. Very good quality not only for something made by HQ Power, but in general. For an amp rated at 100WPC/4Ohm and 70WPC/8Ohm, it certainly has a large heatsink, plus two Sunon fans. All caps except two big PSU caps are Nichicon or Panasonic, and there are even four ELNA audio grade lytics. All metal-film resistors, thick PCBs, large toroid, etc... Just all very nicely made. And it's easily one of the best sounding pro amps I've ever owned.
Maybe I could start by changing the input caps? There are 100uF Nichicons on the inputs, which would, with the 20K input impedance, make a low-pass filter of about 0.8Hz and 0.08Hz at -3db. If I, however, swap these for 4.7uF PETP caps, they would make a low pass filter of 16.93Hz and 1.69Hz at -3db, which would be a much more reasonable low filter, plus they're better quality caps.
I'd like to hear
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Old 20th February 2015, 01:09 AM   #2
MAAC0 is offline MAAC0  Portugal
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Join Date: May 2010
Spotify and streaming service tracks suffer from the digital audio watermarking issue...perhaps you are hearing just that.
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