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MDAC First Listen (part 00101100)

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If the Detox PCB is gold plated then contact problem is no issue, correct?

Gold is the least reactive finish as such I'd prefer Gold plating - but the final decision is left to cost and vendors capabilities in China.

The Chassis parts need to be plated with a conductive layer close on the Anodic index to prevent corrosion in humid environment. With Gold plated boards we are looking into nickel-copper alloys on the chassis interface areas, if its not possible then just bare Aluminium with Tin plated PCBs.

Without an electrolyte, Galvanic corrosion is not such a major concern - but its something to be aware off (and could be a concern in high humidity environments if consideration is not made to the Anodic index potential difference).

As I said earlier, being a designer you really need to have a very broad knowledge base... :( its hard work!
 
Yes, they add "Wire conductive gaskets" recessed into the "Walls" which in combination with the screws guarantee 100% screening under all conditions and tolerances (just like cylinder head gaskets).

With the Detox's current construction any gap is hopefully going to be tiny - so the leakage wavelength will be well above any practical concern.

The Detox budget sets limits to how far I can go - but I'd like to believe its already many orders better then any other competing design in this regards.

John I would say you are aiming for F1 standards of performance here so should be best in class no pressure intended.:p
 
Hi John,

the "teasing" with the Detox PCB worked .... :)
I'm also in for that project. Installment payed.

Stephan
 
Hi John, a commercial question: Once the development and production is complete, and all of us have our shiny new units, what's next? Will there be a full commercial marketing strategy? Will you be selling the design rights to a major supplier?

Are we all investors in this start-up and looking forwad to a dividend down the line? :)

Cheers,

David
 
David
I think your dividend takes the form of the price differential between what you will pay and the price of a unit produced commercially, should that happen.
 
Hi John, a commercial question: Once the development and production is complete, and all of us have our shiny new units, what's next? Will there be a full commercial marketing strategy? Will you be selling the design rights to a major supplier?

Are we all investors in this start-up and looking forwad to a dividend down the line? :)

Cheers,

David

Is this a serious question really!
 
After putting 4 years of my life into developing the design (and counting) and the significant amount of my own resources - to read this is could be rather sad, so instead I take it as light hearted joke :)
 
The FDAC Analogue board design is progressing - slowly, but it is progressing....

https://dl.dropboxusercontent.com/u/86116171/FDAC Analogue Spin II A01abbbb.jpg

Once I've crack the High Power MOSFET Class A section layout then the design will start taking shape, keen to get building the Detox PCB :) ...Maybe by the end of the coming week....
I seem to remember a while ago a discussion about mosfets or not as there was a DR trade off (8dB, I can't remember). You were only going to use the mosfets if they sounded better. Possibly two versions...

Was it this part of the circuit? I think you said it was in the analogue input stage but IIRC it was not the adc input but the dac output.
 
The current PCB section I'm working on is the MOSFST ClassA output stage (These are the large TO220 power devices) - no change here the FDAC has always had a MOSFET output stage.

On the first two generations of MDAC2 prototype PCB's the output MOSFET's where mounted on an aluminium bar which served as there heatsink - but the thermal dissipation limits of the "small bar" limited the ClassA standing current. With the change to the Full Width Chassis - I'm using the think Aluminium Chassis as the heatsink which allows greater thermal dissipation = Greater ClassA standing current.

The MOSFET's you are referring to are used on the DAC's Analogue input stage - basically trading off Dynamic range for better RF performance - the ESS DAC being a switched array outputs significant RF energy which is broadband and above the effectiveness of the passive RC filtering due to the internal parasitics of the Film capacitors - so the Analogue stage has to be "RF tolerant". The MOSFET devices are vastly superior to Bipolar transistors in this regards.

All FDAC"s will be built with the MOSFET input devices, but I can rework them at extra cost here in Czech Rep. if someone wants a "Measurement" version.

With the MOSFET's input stage the prototype measured 127dB Awtd Dynamic range - this is pretty much up with the very best - with the BiPolars the prototype measured 133dB to 134dB.

The rework adds cost as x16 tiny dual SMD devices need to be replaced by hand.
 
John
You have made a judgement call about the trade off and obviously you have concluded that the Mosfets are the better option as regards SQ. You are far better placed to make that judgement than me so I'm happy to go with whatever you think.
 
Yes the difference between 127dB and 134dB is only a matter of "Technical superiority" sonically you cannot hear the dynamic range difference - but the RF non-linearity of the input devices can be heard as a Sibilance / Hardness / Brightness.
 
... - but the RF non-linearity of the input devices can be heard as a Sibilance / Hardness / Brightness.

EEEYEUCH!!! ...that's what I'm trying to get away from, harsh treble :-D

Please please John, make it go away

MOSFETS MOSFETS MOSFETS....!
 
Yes the difference between 127dB and 134dB is only a matter of "Technical superiority" sonically you cannot hear the dynamic range difference - but the RF non-linearity of the input devices can be heard as a Sibilance / Hardness / Brightness.
Hmmm. What do reckon the dynamic range of the output stage is?
 
Sorry I'm not sure I understand the exact question as I've already answered - the Dynamic range is ~127dB with MOSFETs and ~134dB with Transistors - but you do appreciate that these are both extreme results? These result are due to the dynamic range of the analogue stage.

So its a choice between the best dynamic range results or best sonic results, and as I listen with my ears and not by numbers I would always choose the best sounding version :)
 
Sorry I'm not sure I understand the exact question as I've already answered - the Dynamic range is ~127dB with MOSFETs and ~134dB with Transistors - but you do appreciate that these are both extreme results? These result are due to the dynamic range of the analogue stage.
Sorry I wasn't sure whether that was the figure for the complete system or just for one part. I was wondering whether the difference between mosfets and transistors in the input stage would be swamped by noise downstream.
 
The results are for the total system - limited by the MOSFET junction noise or Resistor Thermal noise in case of the transistors. Each channel has a total of 16 paralleled Transistors or Mosfets to reduce there individual noise contribution.
 
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