FET Audio | Hi-End Audio & Electronics DIY Electronics & Repair

April 1, 2011

FDA-1 PCM1794A DAC for Sale / PCM1794

Filed under: DAC — Spencer @ 12:10 am

Last Update: April 1st, 2011

Change U11 from TA7805 to L4941BV for a more dynamics and details sound.  TA7805 remains a good mellow sound signature.  The kit will only provide TA7805 as standard.

Update: Oct 14th, 2010

There is some minor update on FFT measurement in Rev 4 manual.

FDA-1 PCM1794A DAC Manual Rev 4.1

FDA-1 PCM1794A DAC Manual Rev.5 (Updated Aug 23, 2011)

FDA-1 PCM1794A DAC Manual_r6 (Update on 12th Dec, 2011)

FFT measurement and power supply connection diagrams are added in this Rev 4 Manual.

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These kits are designed to replace the obsolete PCM63 balance DAC kit (aka D1V3 and D1V33).

Please click on the link below to download complete manual for Product Specifications, Circuit Description, Circuit Diagrams, Assembly Instructions, PCB Layout, Interface Specifications, Bill of Materials and FFT measurements: PCM1794A DAC Manual Rev3

Price information refer to Store page: http://www.fetaudio.com/store

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A. Introduction:

  • These DACs are designed for the serious audiophile. They utilize the best DAC chip -PCM1794A that is capable of producing a super dynamic range of 127dB in stereo mode and 132dB in mono mode!
  • The I/V and analogy sections are custom designed and use 100% discrete components.  The I/V converter is a “Current Steering” topology and the analogy section is a pure ‘Class A’ non negative feedback driver and output buffer stages. With this combination, the sound will be musical, dynamic, accurate and real.
  • In Single End version, the DAC uses one circuit board with one PCM1794A DAC chip working in Stereo Mode. In Full Balance version, the DAC uses two circuit boards (one Master and the second Slave) and two PCM1794A DAC chips, each configured in mono mode (namely Mono L and Mono R) to deliver super dynamic range of 132dB.
  • Users can start with Single End version to see if the performance is up to the expectation of Hi-Fidelity. To protect your investment, a very clear and simple upgrade path is built into the design. Users of the Single End version can easily upgrade to the True Full Balance version anytime by adding a second slave DAC board! The sonic improvement of the Full Balance version brings new meaning to the word ‘High-Fidelity’!
  • These ‘serious audiophile’ DACs are peppered with high quality audiophile grade components that are selected because of their complementary sonic signatures after many exhaustive hours of listening tests.  Audio transistors, Paper-In-Oil capacitors, Silmic II capacitors and Dale resistors are widely used in the DACs.
  • However, the most important feature is that these DACs sounds musical, dynamic, open and warm with an unparalleled resolving power. These are truly remarkable DACs capable of holding themselves against any branded DAC costing many times more!

B. Specifications:

  1. DAC chip: Texas Instruments PCM1794A 24bit/192k best in class DAC
  2. Digital Receiver: Crystal CS8416 24bit/192k digital receiver
  3. I/V and Analogy Filter: Discrete transistor I/V (current steering) operating in pure Class A mode with NO global feedback for the best sonic performance
  4. Digital Input: SPDIF, AES, Toslink and I2S Bus (RCA, XLR female, Optical and 8×2-pin header)
  5.  Bit/Sampling Frequency: Up to 24bit/192k
  6. Analogy Output: Stereo Channels (Single End) @ 1.5Vrms (expandable to Full Balance output by using two boards @ 3Vrms)
  7.  Output Impedance: 150 ohm Single End mode; 300 ohm Full Balance mode
  8. Auto muting for noiseless operation when no audio/digital signal is detected or when a digital error occurs (e.g. AC-3 signal) or when powering up or down
  9. Power supply: AC 17~18V x 2, 0.5A and AC 8~9V x 1, 0.5A; total consumption 7W/board
  10. Display LEDs: PLL Lock, 48k, 96k and Mute (for CS8416 input only)
  11. Distortion: Typically at or less than 0.02% 1kHz at FS, 20kBW Single Ended @ 1.5Vrms.  At full bandwidth typically no more than 0.04%.
  12. Board: 6 x 8 inches double sided 1.6mm gold plated FR4; 6 x M3 supporting holes; max height part 35mm.

C. A lot of Audio grade components are included in the kit:

1.      Elna silmic II capacitors in all analogy power supply

2.      Russian PIO K40Y-9 for Low Pass Filter in IV section

3.      Sanyo OS-Con capacitors in digital supply

4.      Panasonic film capacitors for supply bypass

5.      Vishay Dale resistors in all signal path

6.      Low ESR filter capacitors by NCC or Panasonic

7.      High speed rectifiers BYV27 series

Refer to Bill of Materials for component provided in the kit.

D. Pictures:

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February 20, 2011

FDA-1 PCM1794A DAC Upgrade!

Filed under: DAC — Spencer @ 10:11 am

This is a simple upgrade:

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Change U11 7805 regulator to ST L4941BV.  The different is the sonic of the sound – more dynamic and clean.

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LM7805 is a more mellow sound with less clarity but it is still very good.

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Enjoy!

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January 4, 2011

Subminiature Tubes (6111, 6021) on 9-Pin socket (6DJ8, ECC88, 6922 etc)

Filed under: Tube — Spencer @ 9:14 pm

Since I have solder the subminiture tube on the SE mu-stage preamp, it do not allow easy swapping of tubes and thus lack lots of fun.  Thus I have found some 9-pin extention sockets and find a way to put a submini tube onto it.   I solder the leads of submini tube onto a pin head with 1mm diameter size.  The pin head can be inserted into the 9-pin socket.  Thus now I can swap tubes easily again!

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In picture, the tube is 6021 to replace the 6DJ8 tube on my SE mu-stage preamp.  I put the two triodes in parallel and thus there will be only 5 connections from submini tube onto socket.

 

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December 31, 2010

Hybrid Balance Mu-Stage preamp with subminiature tube

Filed under: Tube — Spencer @ 11:08 pm

This is a new made preamp – Hybrid Balance Mu-Stage.  Dual triode medium gain subminiature tube like 6N16B-V, 6N18B-V, 6N28B-V, 6111, & 6021 etc… can be used.  The choice of submini tube is due to its low noise and good microphonic effect. 

Features: 

  1. Hybrid (Mosfet + Tube) mu-stage design with full balance at input and output
  2. Supply voltages: +128V, +59V, -69V and two 6.3V DC – all regulated supply
  3. Tube biased at about 1.5mA at about 60V plate voltage
  4. Mosfet IRF710 as Source Follower biased at about 7.5mA
  5. Gain about mu of the tube, about 20 to 40 times
  6. Non feedback design and thus tube may need to match for gain.
  7. Tube can be replacable using IC sockets, the submini tube is first soldered on 8-pins leads and then inserted into IC socket.

FFT measurment:

FFT Balance Mu Preamp

Update new photo on Jan 3rd, 2011 …..

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December 23, 2010

FDA-1 PCM1794A DAC with Headphone Buffer (K170/J74 x 6 pairs)

Filed under: DAC — Spencer @ 12:00 am

The is a V1 FDA-1 PCM1794A DAC board.  I have implemented a headphone buffer on to it and the result is super!  Details is on the photos.

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Features of the buffer:

  1. K170/J74 x 6 pairs is used for each channel.  Idss of matched pairs is at about 6.5mA.
  2. DC supply at +/-20V DC and thus ok to drive high impedance headphones.
  3. Bias of each channel is about 40mA after warm up.
  4. Gain of buffer is x1.  The loudness is high enough for most headphones.
  5. A 100k(A) volume is used for gain reduction at the buffer input.
  6. Only SE DAC is used but the sound is transparent and full of details.

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