LM4780 Balanced Dual Mono-Block Amps

Bought the dual mono LM4780 kit from Peter Daniels’ @AudioSector.com and received it in the mail the other day. I’m excited, because the National Semiconductors’ LM4780 chip package allows for easy implementation of a bridged/balanced configuration of differential (e.g. balanced XLR/TRS) inputs from professional level sources. Most “pro” grade equipment uses XLR as it allows for longer cable runs and provides a greater degree of noise and signal interference rejection.

On my EMU 0404 USB DAC I’m forced to “balun” from the TRS output into the Denon PMA-850’s RCA line input (note: in this configuration I’m using the EMU 0404 as a pre-amp as well). Sadly the PMA-850 has been blowing fuses and has started to sound muddy and as much as I’d like to pull it apart it’s full of 1970s Japanese solid state circuit technology that I wouldn’t feel comfortable playing with. The LM1875/LM3886 & LM4780 [etc] packages (aka Gainclones or Chip Amps) have a really simple circuit topology and as a result have become really quite popular over the past decade in the DIY audio community.

So I’m excited to finally do some soldering and enclosure design for this kit. Also, I was able to breadboard a slightly better power supply circuit for the EMU 0404 using a LM317 chip; I have a decent 7.5V DC 2A wall wart that I could use to feed the LM317 and then down-regulate to 5V DC 1A for cleaner audio. In my tests, using a bank of D alkaline batteries, there was a definite increase in clarity. My one concern with the EMU 0404 is whether the USB is galvanically/transformer isolated from the line outputs, as I’m sure the USB out of the Mac Mini server is not great for noise. Again, in my limited tests, the external linear regulated LM317 power supply using both USB and Toslink SPDIF inputs improved bass and high-end clarity.

Also, I’ll probably be adding some speaker toe spikes to the old Advent Heritage tower speakers. I found some cheap ones @Parts-Express, $0.48 each. Not bad.

Sam Catch's Gainclone build, Back - on Flickr

“Gainclone build BACK” by Sam_catch, on Flickr (CC License)

lm1875set4 by Nonexistence, on Flickr

“lm1875set4” by Nonexistence, on Flickr