With the resurgence of good Hi-Fi, where more and more people buy good headphones and listen to a lot of music thanks to streaming, it’s sad to see the things the mastering engineers (and in the end the artist) do to music. The recordings are getting worse. Even old records that get the “Remastered” or “Expanded” treatment doesn’t sound as good as the original. Why?
A friend of mine bought a new amplifier, but he wasn’t pleased with the sound. So he called me and asked if I could recommend a good old amplifier that could drive smaller speakers because he likes the aesthetic of older things. And the venerable NAD 3020B was the first one that came to mind. When I was young, this was the first affordable amplifier that sounded good.
It’s not a powerhouse by any means, putting out (a very conservative estimate) 2 x 20 watts. But the phono stage accepts both MM and MC pickups which is excellent, and the sound quality is exceptional. So he scoured the used market and finally found a NAD 3020B. Unfortunately, when he got it home, there was a loud hum from the output. So I told him to send it to me so I could fix it.
After fixing my Pro-Ject Speedbox II SE I thought I check how it worked and if I could improve it. I’m in the process of comparing my bench version against the Speedbox, and my model is winning big time! I’ll get back when I have a nice unit up and running…
A lot has happened since I wrote this…
Since I wrote this blog post, a lot has happened when it comes to audio on the Raspberry Pi. There are now cheap I2C audio DAC HATs that connects directly to the GPIO pins of the Raspberry Pi, and thus eliminates the need to go trough USB. This lowers the jitter that USB introduces and there are several cards to choose from.
I’ve tried two different cards, the HifiBerry DAC+ that uses the Texas Instruments PCM5122 DAC (PDF) and handles music all the way up to 24-bit 192kHz. I also tried the ESS Sabre based DAC DACBerry3+ from eBay. My personal favourite is the HifiBerry. To me it sounds better, but there are some quirks when it comes to set it up. You need to set the volume with alsamixer to 96% output otherwise you get distortion. There’s none of that problem with the DACBerry3+ because it doesn’t have software controllable volume settings.
The Raspberry Pi is a really small computer with an ARM 700Mhz processor in it. It has dual USB ports, Ethernet, HDMI and analog video out and sound. But the sound output is terrible. The audio is PWM driven to about 11-bits per sample, witch makes it practically useless as an audio playback unit. And all my plans for projects with the Rasp involves audio.
This is the filter changes I did to the Gigaworks DAC to remove the second opamp and to straighten out the filter section of the DAC.
You can see the original values and the values that I changed to in parenthesis. Just tap the signal from the lifted resistors (and maybe add output caps of 4.7uF) The before/after RMAA tests of the modifications can be found here.