DAC in the Box

arduino based linestage using 12B4 tubes

DAC in the Box

Postby jwhitmor » Thu Mar 19, 2015 12:20 pm

I was not sure there would be room to put a USB DAC inside the Budgie Tube preamplifier case, but it fits nicely near the bottom. The USB port provides 5Vdc power, and the DAC's built in charge pump allows a full +/- 1 Volt RMS swing without requiring a bipolar supply. Supports up to 24/96 sampling, with distortion < 0.005%.
I had it wired directly to the pre-amp input 2 terminal block, but I decided I wanted direct access to the DAC output for experiments, so I installed the back panel RCA jacks. Most of the time the DAC output is cabled right back to a pre-amp input with a set of short interconnect cables.
(I tried to make the label match the Park's Audio panel font) =:o
Attachments
DAC_back.JPG
Back view
DAC_back.JPG (279.55 KiB) Viewed 1825 times
DAC_front.JPG
Inside view
DAC_front.JPG (335.06 KiB) Viewed 1825 times
If it is not making X-rays, your B+ is too low.
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Re: DAC in the Box

Postby Shannon Parks » Thu Mar 19, 2015 2:39 pm

Squeezed in perfectly, Jim! One of my original ideas was to have Bluetooth module support with the Budgie Preamp, and it would get regulated 5V from U2. I even had a 2P Euro connector there, but ditched it after the first few prototypes. I think I was worried what folks might use it to charge their phones or something similar. (???)

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Re: DAC in the Box - Part 2

Postby jwhitmor » Mon Mar 23, 2015 6:14 pm

On March 14th (a.k.a. Pi Day, 3.14) an online seller offered "Raspberry Pi" (model B) single board computers for $25. I purchased one, and plugged in a SD memory card loaded with "Volumio" ' (ver. 1.5 Pi). Volumio, is an open source audiophile application that you can download from: https://volumio.org/get-started/. It offers "Bit Perfect" playback of digital audio files, controlled from a browser based GUI, accessable from any PC on your home network. Volumio will run on several different SBC's and low powered devices. The Raspberry Pi is the least expensive. Mine is running on a 5 volt 1.0 amp power adapter that had a former life as a cell phone charger. You also need a DAC that will connect to both your Raspberry Pi, and your pre-amplifier. I took the easy way out, with a DAC that connects with a USB cable (input) and has line level, RCA jacks for output. See the photos above. The amazing thing is... The software is very user friendly. I have had plenty of long nights trying to decipher and debug some open-source software programs running on a Linux distro. Volumio, just started up and worked. No manual needed, the GUI is not complicated. So far, I would say it really is "Bit Perfect". Much more so than the program I was using with Windows 7. At only 5 watts, I don't even need an on-off switch for the Raspberry Pi. That is good, because the boot up time for the SBC / Volumio software, is maybe 3-4 minutes.
New discovery: The Volumio GUI works on every version of the (free) Firefox browser that I own. The laptop running the up-to-the-minute version of the operating system / browser you have to buy does not display it correctly for some reason.
If it is not making X-rays, your B+ is too low.
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Re: DAC in the Box - Part 3

Postby jwhitmor » Mon May 25, 2015 11:11 pm

My USB connected DAC sounds good, but there is some low level noise from the Raspbery Pi USB port. Using an ultra low noise 5 volt power supply for the DAC did not reduce the noise significantly.
Next I switched to a DAC connected to the Raspberry Pi using the i2s interface, once again powered by a very low noise power supply. The i2s interface is very quiet, and the DAC sounds even better.
If it is not making X-rays, your B+ is too low.
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