ECdesigns PowerDAC-BX User manual
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Introduction
The PowerDAC-BX is a discrete multi-bit DA converter without -any- amplifiers or buffer
circuits in the signal path. PowerDAC-BX has fixed output.!
Balanced linear power-supply and resistor attenuator are used to generate the output signal.!
The PowerDAC-BX is intended for driving amplifiers and headphones.!
Highlights
•Custom DAPI receiver offers high source immunity!
•Toslink input!
•Connect to (pre)amplifiers using RCA!
•Connect to headphones using 3.5mm HP cable and attenuator!
•Firmware upgradable!
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Block diagram
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Batteries are used in the examples above to simplify the theory of operation, in reality these are linear
power supplies as shown in block diagram above. Each set of switches (top, bottom) represents a
separate divider. We have: two batteries, an RCA output (VU meter), two equal resistors R, and two
electronic switches. Batteries are a short circuit for AC signals (audio signals). The resistor sets attenuate
the battery voltage in order to generate an analogue output signal.
A/D) Upper switches on maximum plus, lower switches on maximum minus, currents cancel, zero output
voltage.
B/E) Only upper or lower switches on maximum, currents partially cancel, attenuated output voltage.
C/F) All switches on maximum and same polarity, all currents add, maximum output voltage.
In all 3 cases we have four resistors with value R in parallel and batteries are short circuit for AC. So
output impedance in all examples remains constant 0.25R regardless of switch position.
By changing the electronic switch settings we can have no voltage, half positive, full positive, half negative
and full negative output voltage.
In the practical converter we also have two converters for generating the output signal (matrix system).
This ensures that only the lowest bits have to change state around the zero crossing as each converter
starts at minimum or maximum and progresses up or down in small steps, not in the middle like with most
multi-bit DACs.
The lower bits are switched with R4R, the upper bits of each converter are split up in sub bits (fractal
system). This helps to further lower output impedance to 50 Ohms with given switch limitations, increase
accuracy and minimise glitches.
The end result is an accurate and clean multi-bit power DA converter with low enough output impedance
to directly drive the outputs. This way all lossy analogue circuits and related unavoidable degrading,
typically required for conventional DACs can be avoided.
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PowerDAC-BX
PAGE 1
DAC type
4 x 20 bit Fractal-7 matrix, discrete, switch & resistor-based multi-bit power converters
Digital input
1 x Toslink 16/24 bit: 44.1 kHz / 48 kHz / 88.2 kHz / 96 kHz / 176.4 kHz / 192 kHz
Power Supply
Internal fixed linear power supply
Standard 230V (option: 115V)
Power Consumption
Approx. 2 Watts
Output impedance
50 Ohms
Output voltage
1.77 V rms
Output
2 x RCA output, headphones can be connected through RCA to jack converter cable
RCA35 and a suitable attenuator
LED indicator
Dim = power on, bright = locked
PowerDAC-BX and
headphones
The PowerDAC-BX makes it possible to directly drive many headphones (32 Ohm and up)
without any analogue amplifier or buffer in the signal path. In other words the headphones
are directly driven by a balanced power supply, a number of digital on / offswitches and a
resistor array. This eliminates all distortion and degrading that is typically introduced by
conventional headphone amplifiers. With this distortion and degrading completely
removed it is obvious that we end up with a much cleaner signal that lets one listen much
deeper into the recording and offers a more realistic representation of the recorded music.$
A suitable passive volume control should be used to set desired output volume to
headphones or directly to an amplifier.
Bandwidth
Theoretically 100 MHz (based on switching speed)
Distortion
< 0.001% (0dB)
Technical specifications
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PowerDAC-BX
PAGE 2
POWER
Output Voltage
shifts
attenuation
in dB
Volume
Fixed output
-
Output
1.77 V ms
0dB
Technical specifications
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PowerDAC-BX
PAGE 3
DAPI firmware
update!
The DAPI firmware can be updated using the USB socket and jumper setting
positions for firmware update.
Dimensions
Width: 23cm, Height: 5cm, depth: 23cm
Weight
1.5 kg
Technical specifications
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Jumper settings
Disconnect the mains power cable from the PowerDAC-BX !
In order to access the jumpers, remove the PowerDAC-BX TOP cover by removing 6 x 2mm hex bolts.!
Carefully remove or place jumpers using tweezers.!
When replacing the top cover, make sure side, rear and front panels lock into the top cover slots correctly before
tightening the 6 hex bolts.!
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Firmware update
To update the PowerDAC-BX firmware you need to download the STM32CubeProgrammer.!
You need to ACCEPT Licence Agreement (click button) and on the next screen you need to fill-in your E-mail
address to be able to download STM Cube programmer (you need to use confirm via email sent to you before
you can download the STM Cube-programmer).!
The email sent to you contains the Download now button to start the download.!
Goto link below to download the STM Cube programmer (Win/Lin/Mac):!
https://www.st.com/en/development-tools/stm32cubeprog.html#get-software!
Download and install STM32CubeProgrammer!
Disconnect the mains power cable from the PowerDAC-BX !
Use tweezers to set jumpers to PROGRAM configuration (see Jumper settings on previous page).!
Download and unzip latest pdrs-firmware.zip!
Now connect a USB cable from the PowerDAC-BX to your computer and start the STM32CubeProgrammer.!
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Screenshots here from
STM32CubeProgrammer
On the right hand side of the screen you should see:!
Port: USB1, if not then try the refresh button on the right
side of the Port dropdown button.!
If not working check jumper settings and USB cable
connection.!
Now press the Connect button.!
Then use the Open file button to load the firmware file.!
Click the Download button to load firmware file in the
PowerDAC-BX.!
After message: File download complete!
Press the OK button on message window.!
Finally click on the Disconnect button to finish session.!
You can then close the STM32CubeProgrammer.!
Remove the USB cable between PowerDAC-BX and PC.!
Set jumpers to the normal positions.!
After power-up PowerDAC-BX the new firmware is used.
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