Tuesday, December 18, 2012

WAC 49 (BHL phono preamp)

This is an original stripboard layout for the BHL phono preamp (if you are building this you should read up on construction details, and the schematic at  http://boozhoundlabs.blogspot.com/p/jfet-phono-preamp-kit.html).  Depending on the power supply used it's very quiet, I'll be trying a battery supply soon, hoping for even less noise and I'm curious how the sound will be affected.  I've never compared to other phono preamps on my current setup, which is an old Technics SL-Q200 turntable into my KRK V6 II monitors, but, frankly the sound quality that's happening is pretty amazing.  I can't describe it in audiophile terms but, I am hearing great transient response, a certain crispness and laid-backness at the same time, and great overall clarity.  I'm actually hearing little things I've never heard before, on albums I've listened to thousands of time, like The Wall.  It's a pretty snappy sound, and full but not overly full sounding.  I am very happy with my build.  I added 470 uF bypass capacitors in parallel to the 50 ohm resistors on Q1 of each side to get a little more gain.  It's loud enough now but I might add the same to Q2 in the future for even more output.

UPDATE:  I was getting an extreme motorboating kind of sound from one of my wall warts.  The other one puts out something like that but at a very low level--enough to be annoying when the record reaches the end.    Finding the right adapter might take some trial and error.  I switched to a bank of 20 AA batteries, which puts out about 32 VDC, and the noise is pretty low...lower, but there was a slight buzz still.  Swapping out the "POS" RCA cable I had between the turntable and the preamp with cables of higher quality got rid of most of the remaining objectionable noise.  A reminder to me that yes, cables still and always do matter.  Now the overall noise level is quite tolerable and pretty low, but, there is a very faint buzz in the right channel only.  The rest of the noise is a tiny hiss across both channels.  The next variable I'd be curious about is a higher quality turntable, regarding noise performance.