MDAC First Listen (part 00100010)
- Thread starter mnewbould
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JohnW
pfm member
Sorry Alan, due to the rear panel space I've had to use a mini XLR type
there is just no space on the MDAC2 rear panel for full size XLRs for the headphone and ADC inputs - the main Balanced audio outputs remain full sized The Mini XLR's are a much higher quality connector then standard Cannon /Neutric types - they remind me of the Swiss Lemo connectors.
The biggest issue I see with them (apart from being non standard) is the size off the cable entry - upto 5mm Dia... its going to be rather fine work soldering leads with them...
This is the cable end "Plugs" (3 Pole for the ADC inputs & 5 Pole for the Balanced headphone output)
http://www.soundplugtw.com/index.php?option=product&lang=en&task=pageinfo&id=34&belongid=9&index=4
I'll stock the connectors - and can arrange various cables..
I thought that you were going to use a *male* 5W socket on the MDAC2 - sure, the semi-standard of balanced headphones using 4W female big XLR on the source side is one thing, but with a custom connector, I was under the impression that using male 5W miniXLR on the source is more appropriate (considering the "common sense" of using male/female on other outputs/inputs).
What should we prepare for?
Thanks,
Jiri
PS: I based my presumption (maybe incorrectly) on
MiniXLR Female 5W
PPS: I don't mind either way, just pointing out this small discrepancy.
JohnW
pfm member
Jiri,
I've Emailed the company late Friday - lets see what's available in the PCB mounted type (I can buy 3W Male which is not helpful) for the ADC inputs I'd prefer to use 3W Female - and 5W Male for the Headphone output (On the MDAC2 PCB / rear Panel - reverse for the cable end).
I'd like to keep the correct engineering convention of:-
Male = Output Signal
Female = Input Signal
Not the messed up (why did they do it???) full sized XLR which uses Female XLRs for the output signal which just flys in the face of convention for no good reason - I've no doubt some amateurs started it!
Please don't start getting too concerned with the exact details until I've got clarifications from the vendor.
I've Emailed the company late Friday - lets see what's available in the PCB mounted type (I can buy 3W Male which is not helpful) for the ADC inputs I'd prefer to use 3W Female - and 5W Male for the Headphone output (On the MDAC2 PCB / rear Panel - reverse for the cable end).
I'd like to keep the correct engineering convention of:-
Male = Output Signal
Female = Input Signal
Not the messed up (why did they do it???) full sized XLR which uses Female XLRs for the output signal which just flys in the face of convention for no good reason - I've no doubt some amateurs started it!
Please don't start getting too concerned with the exact details until I've got clarifications from the vendor.
I agree, which is why I pointed out your link of PCB-mounted 5W miniXLR *female*, instead of male for balanced headphone *output*.
ADC inputs should indeed be 3W female, no confusion there.
Sorry, may be just a misunderstanding & mixing ADC into the balanced headphone discussion.
Jiri
JohnW
pfm member
This might be a far out question for most MDAC owners - but as I approach the start of ADC section, I'm thinking more about an inbuilt Phono gain stage (I guess most people would like to connect there turntable directly to the MDAC2 ADC input).
If there is a slight chance I'll have the space, I might be able to squeeze an inbuilt selectable Phone stage.
If its possible (remember a slight chance) - then it would offer selectable Line / MM /MC input Gain levels (selectable RIAA and Flat for Digital EQ).
What I'd like to know what input cartridge loadings (Capacitance and resistance) are commonly used for the MM / MC ?
47K for MM and 100 Ohms for MC seems common - but what input capacitance is "Normal" ?
I've looked at Phone stage design - I've even recently bought a unit from Ebay to serve as a lab bench reference design - but I'm surprised how poorly its designed leading me to think that while the MDAC2's internal Phone stage (if its possible) might not be the last word in performance it could be better then most say 1K GBP units - with no need to mess with an external unit...
If theres no space internal to the MDAC2, then at least I'll have a better understanding for the requirements of an simple external HQ unit.
If there is a slight chance I'll have the space, I might be able to squeeze an inbuilt selectable Phone stage.
If its possible (remember a slight chance) - then it would offer selectable Line / MM /MC input Gain levels (selectable RIAA and Flat for Digital EQ).
What I'd like to know what input cartridge loadings (Capacitance and resistance) are commonly used for the MM / MC ?
47K for MM and 100 Ohms for MC seems common - but what input capacitance is "Normal" ?
I've looked at Phone stage design - I've even recently bought a unit from Ebay to serve as a lab bench reference design - but I'm surprised how poorly its designed leading me to think that while the MDAC2's internal Phone stage (if its possible) might not be the last word in performance it could be better then most say 1K GBP units - with no need to mess with an external unit...
If theres no space internal to the MDAC2, then at least I'll have a better understanding for the requirements of an simple external HQ unit.
Wow John!! If you can squeeze a phono stage in there, that would be awesome!
if you have to make a trade off between MM and MC loading options, may I suggest MM please?
There are very high quality MM carts available today and the phono stage will still be compatible with MC carts via a SUT.
In my experience, 47K impedance and 100pF capacitance seem to be the most common settings, though the latter does vary between 100-300pF.
if you have to make a trade off between MM and MC loading options, may I suggest MM please?
There are very high quality MM carts available today and the phono stage will still be compatible with MC carts via a SUT.
In my experience, 47K impedance and 100pF capacitance seem to be the most common settings, though the latter does vary between 100-300pF.
Ah John this is a whole suject in its own right there is a good paper by Mr Hagerman on this on the web somewhere but for moving coils it can vary from 100ohms to around 560 for something like Linn carts the capacitance doesn't matter to much then theres the issue of sensitivity as well very low to high output.You will need to have some way of vaying the input resistance for MC.
MM is usually OK at 47K but the capacitance is more of an issue something like 50-470pf range so this may need to be variable as well.
Geoff
A phono stage would be amazing news. For what its worth, I'm using this cart http://www.goldring.co.uk/moving-magnet/cartridges/2500.htm
JohnW
pfm member
I'm thinking of selectable 550uV and 150uV input gain for MC & 2.3mV for MM, with the input impedance selectable between 47K & 100R (when 47K mode is selected, then external termination resistors can be added for customised loadings).
Ideally, I'd like to operate an MC cartridge as a pure current source - so it operates into Zero ohms - however the biggest problem I can foresee would be large gain variation between MC cartridges...
I don't have a turntable nor much experience with Phone stage design - but I can apply basic engineering common sense - looking at other MC / MM designs has not proved very inspiring thus far...
JohnW
pfm member
I was just posting that I believe MC should be operated with an I/V stage - it just seems to be begging for it
Are there any commercial MC I/V designs or is everyone just following the same old?
JohnW
pfm member
HQ turntables begs for a high rate DSD conversion - this means no digital filtering... hence the proposed selectable (shunt based)!!! RIAA EQ in the analogue domain.
JohnW
pfm member
Just please don't forget that some of us are going to use the ADC for something else than a TT setup.
Note I stated "SELECTABLE"
I would sooooooooooo love to have a selectable phono stage in my MDAC! That's the only thing keeping me from ditching my integrated in favour of a poweramp direct connection from my MDAC...
My vote goes for MM 47K 50pf, I use a lovely Ortofon 2M Black that likes low capacitance.
My vote goes for MM 47K 50pf, I use a lovely Ortofon 2M Black that likes low capacitance.
stellablues
pfm Member
Johnw,
would love an inbuilt phono preamp if the quality was there - as this is my intended use for the ADC input. Thinking about it, for low MC you need lots of gain and this can be where hum and shielding is very important. do you think the inside of the MDAC2 is quiet enough for a phono preamp? my current phono has been lined completely with copper foil and I keep it as far from my other components as possible.
I also favor MM with seperate step up transformers if needed.
my MM clearaudio virtuoso wood states:
Output voltage: (@ 1 kHz, 5 cm/s): ~ 3.6 mV
Coil impedance: (@ 1 kHz): 0.66 kOhm
Coil inductivity: 0.42 H
Loading impedance: 47 kW
Loading capacity: 100 pF
my other choice of the MC Denon DL103 is very low output Output voltage: 0.3mV (needs >60db gain)
Impedance: 40 ohms
Recommended input impedance: 80-150 ohms
would love an inbuilt phono preamp if the quality was there - as this is my intended use for the ADC input. Thinking about it, for low MC you need lots of gain and this can be where hum and shielding is very important. do you think the inside of the MDAC2 is quiet enough for a phono preamp? my current phono has been lined completely with copper foil and I keep it as far from my other components as possible.
I also favor MM with seperate step up transformers if needed.
my MM clearaudio virtuoso wood states:
Output voltage: (@ 1 kHz, 5 cm/s): ~ 3.6 mV
Coil impedance: (@ 1 kHz): 0.66 kOhm
Coil inductivity: 0.42 H
Loading impedance: 47 kW
Loading capacity: 100 pF
my other choice of the MC Denon DL103 is very low output Output voltage: 0.3mV (needs >60db gain)
Impedance: 40 ohms
Recommended input impedance: 80-150 ohms
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