The Apogee MiniDAC is a pro-audio two channel digital analog converter. It received very good reviews when it was first introduced. The price dropped after a few years, making it good value for money. I managed to get hold of one and of the firewire interface board a little later. The firewire board is a BridgeCo design, running an ARM processor. The firewire interface deploys a smart architecture where multiple firewire units can be used together with one unit delivering the master clock to all other units. Due to the firewire architecture the computer's driver can also be the master. The Apogee driver on OSX by default uses the DAC's internal clock as external clock input. In this setup the computer audio driver is slaved to the DAC.
The MiniDAC has a balanced output running at pro-audio level of +24 dbU. I wanted to find out if it would bring more to use this balanced signal, or to ungracefully 'unbalance' it by using the hot signal and ground the return (this is what a XLR to RCA adapter does). Visio 2013 professional activation key. Looking at the print layout and number of op-amps used, I concluded that the MiniDAC already actively unbalanced the output of the AD1955 DAC chip, then does some switching (jumpers) and audio level adjustments (the blue trim-pots), and then (re)creates a balanced audio signal (the op-amps in the middle, left of the trim-pots) and driving the XLR outputs (on the far left). After all, you cannot adjust the audio level of a real balanced stereo signal with two trim-pots…
This would imply that a XLR to RCA adapter would not impact audio quality. The XLR output level can be reduced to consumer audio levels using the internal trim-pots. I suggest using Neutrik XLR to RCA adapters; the cheap ones I first tried, well . are cheap.
The supplied power supply of the MiniDAC is a simple switched type. Internally the Apogee 'processes' the voltage from the power supply and converts it to the different voltages internally needed. This DC-DC conversion uses a high frequency switcher and small transformers. So in principle it does not matter what type of external power supply is used since the internal DC-DC conversion completely isolates the external power supply from the internal electronics. However many people replace the external PS and mention noticeable improvements.
Apogee's Mini-DAC, a professional quality, 24 bit, 192kHz digital-to-analog (D/A) converter, is the ultimate portable and compact solution for studio playback, reference monitoring, and FireWire connectivity to your digital audio workstation (DAW), computer, and premium home audio systems. Mini DAC, mini-me, mini-mp The PSU specs and barrel connector dimensions are as follows: Output: 12 volts DC 1-2 A (1000-2000 mA), center pin of barrel is positive (+). Apogee Products Defining the Art of Digital Audio Since 1985 For over three decades, Apogee products and technologies have set the standard for audio recording. Countless GRAMMY® and OSCAR® winning performances by the world's most successful artists have been captured with Apogee gear. From personal recording interfaces for iPhone and iPad to multi-channel Mac based. Apogee Products Defining the Art of Digital Audio Since 1985 For over three decades, Apogee products and technologies have set the standard for audio recording. Countless GRAMMY® and OSCAR® winning performances by the world's most successful artists have been captured with Apogee gear. From personal recording interfaces for iPhone and iPad to multi-channel Mac based.
I think that they are right, but not because the voltage 'quality' has improved. I think they are right because any switched mode PS produces a certain amount of HF radiation and often has considerable leakage from primary to secondary. The wires connecting the PS to the MiniDAC act as an antenna, making things worse. You can test this yourself: measure the voltage between the MiniDAC's enclosure and ground with a digital voltmeter. Then replace the power supply with a linear transformer based one and measure again.
Switched mode PS's aren't bad or evil; take a look inside one of the best audio streamers, the Linn Klimax (15000 Euro price range) and you will not see conventional 50Hz based mains transformers:
It all boils down to proper engineering: it's easier to engineer a good linear (transformer based) power supply than a good switched mode power supply. And it's very easy to engineer a bad switched mode PS…
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The Apogee MiniDAC is a wonderful converter. But how does it work? Well, first of all, you can't download the schematics from the net. So how it exactly works I don't know. But looking at the components inside reveals at least some info.
Therefor my guess is as follows:
1. Two times CS8416 input digital receiver/PLL chip. Looking at the number of inputs and print layout, I guess the two units are needed because of the number of inputs to be switched.
2. Wavefront AL1402, that's an ADAT receiver chip which decodes the 8 channel (optical) ADAT stream into 4 stereo pairs.
Apogee Mini Dac Firewire Connector
3. Xilink Spartan XC2S50 FPGA chip. 1728 logic cells, 32k RAM. Used for the interpolation and digital filter I guess. And also part of the dual clock concept.
4. Crystal running at 24,576 MHz. Must be a VCXO, since most dual clock/PLL implementations use a VCXO. This means first clock is generated by the CS8416's PLL. This one suppresses high frequency jitter (lets say >10kHz). Second clock/PLL is build using the FPGA and VCXO. This has a narrow lock range, typically +/- 150 ppm, but good low frequency jitter suppression.
Apogee Mini Me
5. Analog Devices AD1955 DAC chip. That's a stereo DAC with current outputs and on chip analog volume control. Memorex expressit label design studio free download windows 10. I don't think the volume control is used but I'm not sure.
6. Multiple types of Op-Amps, including OP275 (dual op-amp from Analog Devices) and OPA134UA (single op-amp from Texas Instruments).
So no Asynchronous Sample Rate Converter (ASRC) chips?
Apogee Mini Dac Firewire Connector
4. Crystal running at 24,576 MHz. Must be a VCXO, since most dual clock/PLL implementations use a VCXO. This means first clock is generated by the CS8416's PLL. This one suppresses high frequency jitter (lets say >10kHz). Second clock/PLL is build using the FPGA and VCXO. This has a narrow lock range, typically +/- 150 ppm, but good low frequency jitter suppression.
Apogee Mini Me
5. Analog Devices AD1955 DAC chip. That's a stereo DAC with current outputs and on chip analog volume control. Memorex expressit label design studio free download windows 10. I don't think the volume control is used but I'm not sure.
6. Multiple types of Op-Amps, including OP275 (dual op-amp from Analog Devices) and OPA134UA (single op-amp from Texas Instruments).
So no Asynchronous Sample Rate Converter (ASRC) chips?
Apogee Mini Dac Firewire Connector
Well not on the MiniDAC itself but on the USB and Firewire board. More precisely, the AD1896 is used on the USB board and the SRC4190 on the Firewire board. These ASRC's are required since in the USB and Firewire interfaces, the input channel (i.e. towards the computer) carries the active SPDIF/AES source. So for example the Firewire interface is set to 96kHz sample rate and the SPDIF input is selected and plays on 44.1 kHz. Then the Firewire input on the computer carries the digital stream coming from the 44.1kHz SPDIF source, but now sample rate converted by the ASRC to 96kHz. This enables recording of SPDIF/AES streams and is intended to be used with Analog to Digital converters without computer interface such as the Apogee MiniME.
Talking about the Firewire interface, it's a BridgeCo design using their DM1100E chip. They have a nice paper on it called System design for audio record and playback with a computer using FireWire. It's sort of an alternative to TC Electronic's DICE chip, which is used in the famous Weiss converters. An interesting paper by TC Electronic on JetPLL and the DICE chip is called Clean Clocks, Once and for All?Both designs are based around an ARM processor. Note that the BridgeCo design didn't survive and the DICE won … however ARM rules them all …
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