Author Topic: QRV-08 hum  (Read 27000 times)

0 Members and 1 Guest are viewing this topic.

Offline CapRock

  • Member
  • **
  • Posts: 38
  • Karma: +0/-0
  • Custom title, please change to something cool.
Re: QRV-08 hum
« Reply #60 on: April 21, 2011, 11:28:13 PM »
So I wired it up today and tested it and it works.  there is no buzz/hum until the last 2 steps of my attenuator and it is almost not audible, so it is very low.  LED's are still dark though.  I tried to adjust the bias trimpots and they have no effect on the voltage across R1/E1.  E1 was reading .006VDC and R1 was reading .022VDC.  The sound is good and it stays tight and clean even when very loud.  I have to leave the jumpers on though because when I remove them the sound was crackling and distorting.  Any Idea why the trimpots wont work?  Also, as I said before I am not very familiar with oscilloscope's, so what is it exactly that you would like me to measure and how do I measure it?  I'm  sure my friend that owns the scope will be able to help me though this, thanks.

Offline peranders

  • Administrator
  • Reached Nirvana
  • *****
  • Posts: 1230
  • Karma: +6/-0
  • Gender: Male
  • Forum owner
    • Sjöström Audio
Re: QRV-08 hum
« Reply #61 on: April 25, 2011, 07:53:29 PM »
The reason why the LED's not are on is that the input voltage is too low, assuming that the regulators are correct.
/Per-Anders Sjöström, owner of this forum

Homepage with my DIY hifi stuff

Offline CapRock

  • Member
  • **
  • Posts: 38
  • Karma: +0/-0
  • Custom title, please change to something cool.
Re: QRV-08 hum
« Reply #62 on: April 27, 2011, 07:46:56 PM »
since my voltage is not high enough do you think I am still not hearing the full potential of the amp?  If it is worth it I will continue to search for the problem.

Offline peranders

  • Administrator
  • Reached Nirvana
  • *****
  • Posts: 1230
  • Karma: +6/-0
  • Gender: Male
  • Forum owner
    • Sjöström Audio
Re: QRV-08 hum
« Reply #63 on: April 27, 2011, 08:23:05 PM »
The amp will most likely work properly but the power supply rejection isn't so high so clean supply is essential but as you have noticed a small of hum will slip through. It would be interesting to see how your raw voltage look like. Depending how it look you can disable the LM317/337 preregulators. By this you will "earn" 2-3 volts but it could be tricky if you don't have the right tools.
/Per-Anders Sjöström, owner of this forum

Homepage with my DIY hifi stuff