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Old 21st November 2011, 07:58 AM   #4001
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Join Date: May 2006
Location: Holland
Hi qusp,

Quote:
John, can buried zeners or other forms of reference be used for lower noise? i guess there is some reason you chose straight zeners though, no feedback perhaps?
The zener noise is filtered by a RC filter (330R / 470uF), then buffered by a Darlington.

I used these circuits based on perceived sound quality. They offer very low noise and fast local current feedback.

Quote:
nice one, ive been using those panasonic pps for a while now too, very nice caps. cool looking module for sure; i pictured you using bulk foil trimmers =)
The trimmers are Bourns cermet multiturns. Their output voltage is also filtered. For the MOSFET current buffer I use 250K trimmer with 1uF SMD film cap and for the DC reference voltage I use 1K trimmer with 470uF Sanyo Oscon capacitor
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Old 21st November 2011, 08:34 AM   #4002
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Hi JOSI1

Quote:
In your designs you are using MELF resistors. Do these resistors have an electrical advantage compared to 0805/1210 or is it just for easier/better mounting and soldering?
They offer a very high level of reliability and are only used in less critical positions.

Plain SMD resistors need to be positioned with the text facing upwards for easy inspection. This takes extra time during manual assembly.
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Old 22nd November 2011, 06:03 AM   #4003
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Hi John, can you explain us a bit about your grounding philosophy?

I see the supply lines being decoupled to gnd just after the regulators. You also mentioned your grounding for the tda (using separate lines running to pin 5). How are you using the top plane?
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Old 23rd November 2011, 09:06 AM   #4004
JOSI1 is offline JOSI1  Germany
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Hi John,

in post #4000 so mention that you are using a separate transformer (2x12V) for the power supply of the SD-Transport (3V3). Do You use the same common mode voltage regulator concept as for the MK8?
Which part of the power supply is already located on the latest SD-Transport module and which part has to be realized externally (transformer, rectifier, smoothing cap, common mode cap multiplier, ???)
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Old 23rd November 2011, 11:30 AM   #4005
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Quote:
Originally Posted by studiostevus View Post
Hi John, can you explain us a bit about your grounding philosophy?

I see the supply lines being decoupled to gnd just after the regulators. You also mentioned your grounding for the tda (using separate lines running to pin 5). How are you using the top plane?
-----


Further to this, I had a closer look at the layout... It seems like:
  • ...+5V (Reclocker) and -15V are decoupled to the same GND line
  • ...-5V supply is decoupled to the GND belonging to the -15V supply?
  • ...all GND lines in the supplies are connected to a common GND plane (top)
  • ...decoupling of the supply lines to the chip is done quite far away from the TDA

:Confused:
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Old 23rd November 2011, 09:39 PM   #4006
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Hi studiostevus,

Quote:
Further to this, I had a closer look at the layout... It seems like:

...+5V (Reclocker) and -15V are decoupled to the same GND line
...-5V supply is decoupled to the GND belonging to the -15V supply?
...all GND lines in the supplies are connected to a common GND plane (top)
...decoupling of the supply lines to the chip is done quite far away from the TDA
All common mode voltage regs on the MK8 are decoupled with 1uF SMD film cap close to the regulator output. There are no electrolytic caps on the regulator outputs.

The references of all 4 common mode voltage regulators are connected to the ground plane that serves as GND reference:

Masterclock, synchronous BCK divider and synchronous WS / DATA reclockers all have local RC filters located very close to these circuits. The resistor for the masterclock RC power supply filter is a low noise Honeycomb Mobius resistor.

The TDA1541A power supply SMD film decoupling caps are soldered directly to the chip pins, underneath the chip as close to the IC housing as possible (attached picture).

So TDA1541A power supply decoupling is actually pretty close to the chip.

The 14 active divider decoupling caps are also soldered directly to the TDA1541A pins. Only 14 pins of the TDA1541A are connected to the MK8 module using a customized IC socket.
Attached Images
File Type: jpg tdadec.jpg (77.5 KB, 1148 views)
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Old 23rd November 2011, 09:54 PM   #4007
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Hi JOSI1

Quote:
in post #4000 so mention that you are using a separate transformer (2x12V) for the power supply of the SD-Transport (3V3). Do You use the same common mode voltage regulator concept as for the MK8?
Yes, the SD-transport runs on a similar common mode power supply consisting of a common mode capacitance multiplier driving a common mode 3.3V filtered buffered zener regulator.

The binary stepped shunt volume control still runs on conventional 3.3V and 5V power supplies that will also be replaced with common mode power supplies.

There will be 3 small toroidal transformers in total. One 2 x 12V transformer is used for isolated +5V and -5V supply for the DAC chip. One 2 x 18V transformer is used for isolated -15V supply for the DAC chip and isolated +5V supply for masterclock and connected circuits. The third 2 x 12V transformer is used for isolated 3.3V supply for the SD-transport.

Quote:
Which part of the power supply is already located on the latest SD-Transport module and which part has to be realized externally (transformer, rectifier, smoothing cap, common mode cap multiplier, ???)
The SD-transport MK2 module will need a small add-on module that contains a 3.3V common mode voltage regulator. I am currently using an air wired setup for testing.

Transformers, rectifiers and common mode capacitance multipliers will all be located on the power supply module. These are the parts that need to be added externally.
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Old 24th November 2011, 08:15 AM   #4008
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MK8 concept schematics.

I attached TDA1541A-MK8 concept schematics.

On the top there are 4 common mode voltage regulators for +5V, -5V, -15V, and +5V. They consist of cascaded filtered buffered zener diode regulators.

This works as follows, T1 and D5 form a 10V - 1.2V = 8.8V pre regulator. This pre regulator is placed in the ground reference line. T5 and D1 form a 6.2V - 1.2V = 5V post regulator that is referenced to the 8.8V GND reference provided by the pre regulator. R7 and C23 filter the zener diode noise.

The 5V post regulator is placed after the 8.8V pre regulator and re-stabilizes it to +5V. The output of the 8.8V pre regulator serves as ground reference. The output of the post regulator is decoupled to GND by a 1uF SMD film cap (C11).

The negative common mode voltage regulators function similar. The -15V regulator has a -18.8V pre regulator and a -15V post regulator.

Note that all common mode regulators have separate plus and minus inputs that are connected to the main power supply using twisted pairs. The main power supply contains rectifiers, smoothing caps and common mode capacitance multipliers.

WS and DATA inputs are first attenuated by R23 ... R26. U2 and U3 perform synchronous reclocking. R19, R20, R40 and R41 perform I2S attenuation for the TDA1541A. The MK8 only has 2 I2S inputs, DATA and WS. Source BCK signal is not connected to the module.

Each synchronous reclocker has a separate RC power supply filter, R21, C8, R22, C9.

BCK is derived from the masterclock using a synchronous Johnson counter consisting of U4 and U5. R28 ... R30 reduce ground bounce. R5 and R16 form the BCK I2S attenuator.

Balanced DEM clock is now derived from U5 using R43, R44, R31 and R32 to inject the signal into the DEM oscillator circuit on the TDA1541A.

The masterclock is built around 2 lateral MOSFETs T11 and T12. Both crystals are matched high-Q versions.

Chokes N1 and N2 are now connected to a DC reference voltage generated by R6 and C21. This lifts the clock signal above GND so clock rectifiers are no longer required. The masterclock runs on approx. 2V. CLC filter consisting of C12, R3 and C20 offers extra filtering of the 5V masterclock supply.

I/V conversion is passive by generating a voltage across resistors R17 and R18. The TDA1541A output current is buffered by lateral MOSFETs T9 and T10 that serve as current buffers (grounded gate circuit). The DC bias level on the TDA1541A outputs is adjusted by integrating the output signal across the passive I/V resistor and feeding it back to the MOSFET gate. This is done by P3, P4, C16 and C18. R45 and R46 make sure the MOSFETs can't go out of conduction as the DAC output current approaches zero.

The bias current running through the I/V resistors equals 2mA, so the DC voltage at the outputs equals +4V. In order to provide DC-coupled outputs, two +4V reference voltages are added that now serve as output "GND". The DC voltage between this DC reference and the voltage on the I/V resistor now equals 0V.

R1 and R2 are mobius loops that are used for low level refinement.

The MK8 outputs can be directly coupled to RCA sockets without the need of an additional module like required with the MK7.
Attached Images
File Type: jpg TDA1541A-MK8.jpg (115.8 KB, 1139 views)
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Old 24th November 2011, 10:51 AM   #4009
regal is offline regal  United States
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Maybe wishfull thinking but these new power supplies seem it may be possible to integrate to an asych usb I2s output using the same clock for both transport and DAC ?
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Old 24th November 2011, 02:47 PM   #4010
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Hi John,

I find it interesting to follow the progression of circuit refinement from the earliest version of your DAC to the Mk8. While many engineers would probably find ways to add circuitry in an effort to "improve" performance, you continually find thoughtful and creative ways to distill the design down to it's essence. As Einstein reportedly said; everything should be as simple as possible, but not more simple.

I'm curious to know, which currently in production DAC chip would you choose to base a new DAC board design around if you could no longer obtain legitimate TDA1541x devices?
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Last edited by Ken Newton; 24th November 2011 at 02:53 PM.
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