MDAC first listen (part VI)
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PhilCTTE
Senior mumbler
Hi John,
I really hope the MITX will support Alac files, I'm dead set on buying it, but as my whole library is Apple Lossless if it doesn't support this format I'll have to stick with my Mac...
Is there any news on the MPax? Pretty please John, give us the MPax
Its upto the user to install the media software to cope with what ever format you need, be it Itune,s Jriver etc. The MITX will be blank I've assumed
sam_cat
C'est Crounchifique!
As its a pc you should be able to install whatever OS/software you want..
OpenELEC/XBMC supports ALAC (along with plenty of other formats:http://en.wikipedia.org/wiki/XBMC)
Sam
OpenELEC/XBMC supports ALAC (along with plenty of other formats:http://en.wikipedia.org/wiki/XBMC)
Sam
GroupDelay
Member
Jo Sharp:
Careful with this modification. C3 is there for a reason. It is to balance the DC bias currents on the input pair of transistors (through the 27K=24K+3K). As these are not JFETs this will be a significant voltage.
Firstly it will add >>100mV of DC on the speaker outputs. This may not be a big issue (crackling when connecting speaker cables, not suitable for active speakers, switch on thump). However anything plugged into it which uses muting relays which open for muting will cause a Huge crack out of the speakers (amp gain x DC, so could be several volts). I guess the MDAC does this, from the conversations about output/headphones relays.
I'm surprised to see an audio designer with John's following on here recommending this. He appears too careful about his appearance here online to give such advice. Maybe power amps are not his area.
There are ways of designing this in, but don't go ripping out parts without knowing how the design works. Try different capacitors of varying type and quality by all means, or bypass them with polypropelene ones. But don't short out C3 unless you like unpleasent noises...
Careful with this modification. C3 is there for a reason. It is to balance the DC bias currents on the input pair of transistors (through the 27K=24K+3K). As these are not JFETs this will be a significant voltage.
Firstly it will add >>100mV of DC on the speaker outputs. This may not be a big issue (crackling when connecting speaker cables, not suitable for active speakers, switch on thump). However anything plugged into it which uses muting relays which open for muting will cause a Huge crack out of the speakers (amp gain x DC, so could be several volts). I guess the MDAC does this, from the conversations about output/headphones relays.
I'm surprised to see an audio designer with John's following on here recommending this. He appears too careful about his appearance here online to give such advice. Maybe power amps are not his area.
There are ways of designing this in, but don't go ripping out parts without knowing how the design works. Try different capacitors of varying type and quality by all means, or bypass them with polypropelene ones. But don't short out C3 unless you like unpleasent noises...
Phil,
Adrian's excellent SBT Async USB mod is now so easy to install and so stable that it's a complete no-brainer... I'd urge you to try it.
Bit-perfect + Async USB (effectively clock locked) + Galvanic USB Isolator + silent streaming device = perfect data delivery to the DAC. As far as SQ goes, I fail to see where there is room for improvement regardless of budget.
It's probably safe to assume that anyone playing digital music files has already got a PC in their house, so for most people buying an SBT this is not going to be an additional requirement. You just need to get a network connection up and running from that PC to the SBT (whether the music is on the PC's local HDD or external HDD - it doesnt matter).
Assuming your SBT isn't faulty, then if you were having problems streaming Hi-def this would have to be a problem with the NAS or the network. Did you ever try streaming from your laptop to the SBT or running over a wired connectoion? I'd be surprised if this didn't cure the problem.
There's clearly a hobbyist element to your motivation for building a dedicated media PC, which I fully understand and I wouldn't dream of knocking you for, but I have to disagree with your comments on the sound quality and convenience of the SBT. Mine is doing a wonderful job
bitperfect plus noise
Did you try disabling the volume on the Touch in the settings with the 100% fix? At first I sued the volume on the Touch as it was convenient but had a hiss, I then disabled it and it completely solved the issue.
gh0st
pfm Member
@soundcheck's Touch Toolbox 3.0 software mod works alongside Triode's Async plugin, and can lock out the volume at 100% at the OS level, besides other things like disable unnecessary services and devices (WLAN radio, screen etc).
I use the above setup through a usb hub, but no isolator (although my SBT does have a very quiet PSU, not the default wallwart), and I can report no extraneous noise.
PhilCTTE
Senior mumbler
Yes did this. Thanks.
Phil,
Adrian's excellent SBT Async USB mod is now so easy to install and so stable that it's a complete no-brainer... I'd urge you to try it.
Bit-perfect + Async USB (effectively clock locked) + Galvanic USB Isolator + silent streaming device = perfect data delivery to the DAC. As far as SQ goes, I fail to see where there is room for improvement regardless of budget.
It's probably safe to assume that anyone playing digital music files has already got a PC in their house, so for most people buying an SBT this is not going to be an additional requirement. You just need to get a network connection up and running from that PC to the SBT (whether the music is on the PC's local HDD or external HDD - it doesnt matter).
Assuming your SBT isn't faulty, then if you were having problems streaming Hi-def this would have to be a problem with the NAS or the network. Did you ever try streaming from your laptop to the SBT or running over a wired connectoion? I'd be surprised if this didn't cure the problem.
There's clearly a hobbyist element to your motivation for building a dedicated media PC, which I fully understand and I wouldn't dream of knocking you for, but I have to disagree with your comments on the sound quality and convenience of the SBT. Mine is doing a wonderful job
Well unfortunately as mentioned ... this USB mod came out just after I'd sold my SBT. Spdif only !. So all SQ comparisons were stock SBT without server via optical digital out to MDAC compared to Laptop USB > Isolator to MDAC.
If what you are saying that the SBT via USB improves the SQ from what I heard then I may rethink my strategy.
Regards streaming hires via SBT, my network is fine as I have many other devices working happily, my NAS is a basic WD and does not have the processing power to run LMS. So it was going to be an expense to either purchase a NAS £300+ (1 to 2TB) such as the QNAP's , Synolgy Thecus etc...
True I do have a laptop , but its a multi use one, so I would have to get a spare or a headless pc for serving duties.
Stock SBT with no LMS server does not work with hires. And as I was not getting the SQ from the SBT I thought I'd wait for MITX.
With the MITX what you are getting in addtion is clock locked USB 192 optical convertor with built in galvanic isolation . Plus the flexibility of choosing software and other apps, rather than being tied into whats on offer from the 3rd party apps of the Logitech arena.
I guess it all boiled down to SQ to pursue the SBT further.
This USB mod may well tip the balance back to its favour.
HELP!!
I have ha the MDAC for quite a while working perfectly straight into my Power amp
Today for the first time I wanted to see how it would perform with y pre amp back in the system.
I disabled the pre amp facility and I can't seem to get any sound out of my speakers.....
Can Anyone help?
I have ha the MDAC for quite a while working perfectly straight into my Power amp
Today for the first time I wanted to see how it would perform with y pre amp back in the system.
I disabled the pre amp facility and I can't seem to get any sound out of my speakers.....
Can Anyone help?
Cereal Killer
432
Why would you want to use a USB to SPDIF optical converter? i though the MDAC was designed around being an Async USB DAC?
You can also buy similar barebones computers which have optical SPDIF out direct from the motherboard.
Richard Kimber
pfm Member
As far as the official Audiolab version is concerned, I had an email from Audiolab support saying they expected it to be available early next week, and they would email me when it's available.
Not quite, as the USB to SPDIF adapter which JohnW has written about would be clock locked to the MDAC. This should have the same benefits, in terms of jitter and galvanic isolation as Async USB + Galvanic isolator, while adding support for higher sampling frequencies (up to 192kHz).
The optical SPDIF outs on motherboards are built to a very low price point, so, even excluding the clock locking features, John's design is also likely to work better.
Cereal Killer
432
I can't see the point of it! ... If the MDAC has issues handeling USB 'noise' then surely the DAC is at fault.
Well saying that I had a similar issue with a laptop. it was creating a slight hum. My DAC's linear PSU has a 'GND/LIFT' option and using this sorted the issue.
Also with the Shuttle, as per my link, Its totally silent via USB on both.
Well saying that I had a similar issue with a laptop. it was creating a slight hum. My DAC's linear PSU has a 'GND/LIFT' option and using this sorted the issue.
Also with the Shuttle, as per my link, Its totally silent via USB on both.
Spacey,
Horses for courses, but this future gizmo adds a few features to the MDAC, which some may find helpful:
- A second Async USB inputs (This may be a world first... ideal for PC + SBT?)
- 192kHz Async USB capability (the MDAC only supports 96kHz by default)
I don't think the MDAC is more prone than other equivalent devices to USB electrical noise, but the design of this second USB input should take away this risk (and protect one's stereo in the unlikely event of a power surge on the USB out of the source component).
Horses for courses, but this future gizmo adds a few features to the MDAC, which some may find helpful:
- A second Async USB inputs (This may be a world first... ideal for PC + SBT?)
- 192kHz Async USB capability (the MDAC only supports 96kHz by default)
I don't think the MDAC is more prone than other equivalent devices to USB electrical noise, but the design of this second USB input should take away this risk (and protect one's stereo in the unlikely event of a power surge on the USB out of the source component).
JohnW
pfm member
As I said each to there own – but I’m pretty blasé about details like this, I don’t care about a few little pops and thumps when changing inputs if the end result is better sound quality.
Being easily distracted while working on the BDAC’s PCB layout I’ve just spent 15 minutes making a spice model of the NCC series amps – interesting as I have recently been designing our MAMP so “Spice Model” comparisons can be informative.
For a nice change I had all the transistors models in the spice library and used “Real” device models – not “generic” spice models – so the models should be very close to reality.
The NCC topology is a basic “text book” amplifier circuit, the final SQ will be strongly determined by its construction and component choices rather then design – that’s where the mysteries and the skill of the Black Art come into play
DC Offset results with “perfect” matched input transistors:
NCC with coupling capacitor (so in standard form) -27.2mV
NCC with input coupling capacitor bypassed, with no Input device connected -19.4mV (Lower due to the extra 100K Pre-Cap now also paralleled to Ground).
NCC with input coupling capacitor bypassed, MDAC powered off (MDAC internally terminates to 10K) 1.9mV
NCC with input coupling capacitor bypassed, MDAC powered on (Modeled as an effective 5 ohms source impedance which should take into consideration MDAC output impedance, connector and cable resistances) 12.9mV
A significant portion of the NCC inherent DC offset is caused by the imbalance in Diff pair tail currents, 649uA (TR1) over 494uA (TR2), while the input bias current is 1.6uA - the resultant output offset levels are still small IMO and of no real concern.
So, in fact the DC offset (without taking into consideration MDAC’s offset which may still causing a slight Pop sound when un-muting) is LOWER when the NCC input cap is removed while connected to MDAC, with only an 11mV difference in output offset at the speaker terminals between muted and unmated states.
NCC standard (with Cap fitted) -27.2mV
Offset at speaker when MDAC powered off: 1.9mV (Cap Bypassed)
Offset at speakers with MDAC powered on 12.9mV (Cap Bypassed)
Pls. note that these results do not take into consideration the amplifiers “inherent” offset due to imperfect input device matching. Unbalanced input device will magnify the differences – it would have been nice to see a trimmer across the Emitters of TR1 / TR2 to null the inherent offset.
In all cases the input offset is low as not to be a concern, in my experience and now confirmed by simulation results the input bias current is low so as not to pose a concern – in fact DC offset levels are LOWER in the case of NCC with the MDAC as an input source impedance in both Muted and Unmuted states...
As I say each to there own...
John
JohnW
pfm member
Try Pressing and HOLDING BOTH Sel Up and Down during power up, until power-up is completed. This will Reset the MDAC.
John
JohnW
pfm member
We are looking into Quad2fan's reported issue with USB... Nothing yet...
JohnW
pfm member
Hi Spacey,
The USB to SPDIF optical converter allows to clock-lock the PC and offer optical isolation
There would be two optical links, one for the Data, second for the Clock link.
sq225917
Bit of this, bit of that
ha ha ha, you've been owned. Well done for shouting your mouth off and giving us all a laugh- kinda back fired on you didn't it.
John_73
pfm Member
Hi John.
Checked the usb buffer display and the indicator bar length alters regularly between approx. 1/5 full to just over halfway full. This is on a late 2009 Mac mini, 4GB ram running Windows7 via Bootcamp (in other words not an emulated windows), and using Foobar2000 with wasapi plug-in.
Will hopefully get around to checking the usb buffer reading on the Mac proper running Lion and iTunes with and without the bitperfect add-on tomorrow. Also use Audirvana often too and had the same random issues with these 'static' sounding pops with all.
John
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