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Digital to analog converter
Jundac Five
Last revision on July 2011

Jundac Five PCB
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  1. Non oversampling DAC
  2. 16 bit DAC resolution (TDA1545A)
  3. Open loop I/V converter
  4. Semi parallel regulator
  5. Low filtered output
  6. Optional external clock for very low jitter
  7. Constant 75 ohm load for digital section (PCB + loaded lines)
  8. Low noise regulators (6x)
  9. Bipolar low noise solid states (BC550C/560C)
  10. One digital input
  11. High toroidal power transformer
  12. Two power transformer
  13. Small capacitors power supply (300µF)
About design
    The Jundac Five is a 16bit non-oversampling digital to analog converter. It integrates one S/PDIF or AES/EBU input, an optional input clock and stereo fixed analog output.

The DAC chip is Philips TDA1545A; it can operate from 32kHz to 192kHz sampling frequency. The I/V stage uses discrete, solid state technology, in an open loop (feedback-free) configuration. A comfortable environment coupled to a particular way to drive IREF pin allows reaching an incredible quality audio level.

A non oversampling DAC don't use any digital filter. Data coming from CD are directly converted to analog; there is no coloratura introduced by digital filtering, noise shaping or dithering. Before output, the signal is smoothed by a sweet first order low pass filter. To reach best listening quality, it can be coupled to an synchronous or asynchronous low jitter clock.

Power supplies in a DAC are critical to the overall design. The Jundac Five uses six very low noise separate regulators. These power supplies use polypropylene capacitors and two separated power transformers.
To achieve the full music sonic attributes, we recommend using 200VA to 300VA power transformer for analog section. This transformer powers the DAC stage and the analog section (I/V converter and low pass filtering).

When designing high quality device, each stage is important:
  • digital (with or without digital filter),
  • DAC chip,
  • i/v stage,
  • low pass filtering,
  • regulators,
  • power supply (transformers),
  • passive components and wiring,
  • grounding and link to earth,
  • drawing PCB,
  • chassis and mechanical vibrations.
You must care about each detail, everything is important. Digital filter is important in global quality, but each stage is as important.

Relative audio quality level
audio quality level

To obtain best sounding, ensure to power on 48 hours before listening.

Technical documentation
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Technical description
Jundac Five
    The Jundac Five use Cirrus CS8416, 32K to 192KHz DIR (digital interface receiver) chip. The CS8416 provides digital de-emphasis needed for reading some CD recorded with pre-emphasis. The input can be RCA, BNC or XLR with 75 or 110 Ohm. Jundac Five auto switches to external clock when signal is detected.

Before DAC, digital data are re-clocked to avoid digital delay and reduce jitter and noise. The DAC chips TDA1545A from Philips allows 16bit resolution. PCB is 75 ohm compliant, all lines are loaded with 75 ohm terminal resistors.

Jundac Five
    The data stream feed a Philips TDA1545A 16 bit DAC chip followed by feedback free I/V stage with very sweet low pass filter. The low pass filter is first order filter cutting at 70KHz using polypropylene film and foil capacitor. The BC550C/560C were chosen for their high quality sounding, each transistor are matched.

The Jundac Five uses very low noise regulators:
  • LT1763 for the digital section,
  • LT3080 for analog and DAC stage.
The analog section use three very low noise regulator LT3080 form Linear Technology in a semi-parallel configuration.
Semi-parallel regulator
In a semi-parallel regulator, i3 is adjusted to never become negative. Thus, the analog stage is never directly powered by the regulator, this improve transient response. The LT3080 ensure line regulation.

Pictures of analog signal:

Jundac Five, low filtered output signal
Low filtered output signal
Jundac Five, detail
Jundac Five, Dirac impulse response
Dirac impulse response

IREF current

The IREF pin is the secret of the TDA1545A
    I never find that datasheet for TDA1545A is very clear. There are a lot of interrogations about the interesting IREF pin. In our prototype we test various configurations, starting with the standard one recommended by Philips.

After some measurement, it appears that some information is omitted like the full scale current output is proportional to VDD. The most important find is that sound quality depends of IREF pin driving method.

Jundac Five, VREF driving IREF for TDA1545A
Diagram of VERF
The incredible audio quality level reach by this kit is due to original way to manage reference current pin. This way is different from Philips recommendations. We develop a reference tension in discrete technology dedicated to this chip. The TDA1545A reaches unknown dimensions with very large and strong bass, good definition and fine treble. It changes from all other realizations. Low noise transistors and high quality capacitors (no electrolytic capacitors) are used to drive this crucial pin.

Jundac Five, VREF stage
VREF stage
Jundac Five, IREF filtering
Detail of 10µF 100V stacked capacitor
for IREF filtering
Jundac Five, output signal cliping
Cliping when VREF exceed max capabilities

Power supplies
Power supplies in a DAC are critical to the overall design. The Jundac Five uses six very low noise regulators: three for the analog section and three for digital section. These power supplies use polypropylene capacitors and two separate power transformers. For electrolytic capacitors, Elna Silmic II for analog, and Nichicon LF for digital, are used. Ultra fast recovery surface mount rectifier diodes are used in analog and digital stages.
Detail of load resistors on TDA1545
Detail of 75 ohm load resistors
on TDA1545
Nichicon LF
Nichicon LF for digital ps
Wima polypropylene film capacitor
Wima polypropylene film cap

Power supply in Jundac Five
Diagram of power supply
There is three LT1763 for digital section in a cascaded configuration (+8V, +5V, +3.3V) and three LT3080 for analog section in a cascaded configuration (+27V, +22V, +5.6V).

We took particular attention in decoupling. Digital data, and particularly the clock signal, carry digital information with high (X MHz) and low frequency (20Hz to 20kHz) noise modulation. This modulation has direct impact on audio rendering. It is important to provide wide band decoupling. Jundac Five uses high frequency capacitors mixed with high quality MKP capacitors. It results in a very natural and analog sound without metallic aspect.

Detail of decoupling
Detail of decoupling
Detail of decoupling
Detail of decoupling
Detail of decoupling
Detail of decoupling

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