MDAC First Listen (part 00100010)

[GWM]

The other consideration on the phono stage is going balanced from the cart all the way to the ADC this would be an attractive approach just doing another meto stage seems a bit pointless given all the products out there.

 

[ChrisPa]

No step up transformer please. With so much sophistication in the rest of the electronics it seems so wrong.

(It feels a bit of a cop out - but then I'm not designing the electronics, so that's really not for me to say On the other hand, depends on whether this is a statement design or something being squeezed in the box)

It's my understanding, (but as I type, i mean swype, based on no evidence i have to hand whatsoever) that the current output of most MCs is about the same. It's the turns that are used to generate voltage. Would need to read more to justify that.

Understand your point about DSD and eq.

With regards commercial designs
- Aqvox PHONO 2 Ci
- mr-labs Versa
I'm sure there are others

I have (somewhere) a Jeremiah Braithwate esq (Stan Curtis) head amp from the late 70s/early 80s which I understand to be an I/V design

 

[ChrisPa]

PS. Whilst I understand your objective for a DSD phono stage, I'd still be extremely interested in a capacitor-less eq, with eq performed by DSP, even if that means more 'conventional' a to d

 

[jirij]

PS. Whilst I understand your objective for a DSD phono stage, I'd still be extremely interested in a capacitor-less eq, with eq performed by DSP, even if that means more 'conventional' a to d

The way I understood is that this will be possible for PCM if you bypass the builtin phono stage.

It would also be great to have the amplification part usable for ie. dynamic microphones, but I don't suppose this will be doable.

 

[JohnW]

I have (somewhere) a Jeremiah Braithwate esq (Stan Curtis) head amp from the late 70s/early 80s which I understand to be an I/V design

Do you mean this device?

http://lecsonaudio.com/?page_id=76

I love the name

Stan Curtis wrote regarding the Braithwaite connection:-

“Where did you get that? Jeramiah Braithwaite Esq. a good solid Yorkshire name."

"I designed them for Mike Harris to sell and we came up with the Jeremiah Braithwaite Esq name. Very old North Country."

You have to love it !

Funny you should mention Stan Curtis / Lecson as I've just bought a AC1 / AP1 as I've never forgotten the Amplifiers heat exchanger design which Allen Boothroyd’s original inspiration came from a visit to the Ely Cathedral- more specifically the heating radiators within the cathedral. Not to mention the incredible industrial design of the AC1 Pre Amplifier - you have to love the coloured sliders!!! This was designed during the heyday of the best of British HiFi IMO...

http://lecsonaudio.com/?page_id=56

I'm loosely thinking of using the same idea of 2 halves of a cylindrical extrusion for a future LakeWest power amplifier you know, once I've completed the MDAC2, VFET AMPs, Phono stage etc etc...

I'd be very interest in you could dig up the Pre-amplifier if its still around? (I understands its a tiny unit, probably last used years ago).... I'm really searching for a decent reference unit - and I/V mode with MC really seems the most sensible route...

Recently I bought a Deltec DPS50 (DPA) as it had well regarded measurement results (I need a Lab reference unit). Its based upon the Deltec OH32 Hybrid module - but in reality its pretty poor, based upon series feedback for the RIAA EQ - which in combination of the required lead compensation of the feedback network to insure stability around results in a rising frequency response above the audio band. The transient energy from the records surface noise will stimulate this rising HF response and make the unit sound "Brighter" - which is not desirable!

 

[JohnW]

The way I understood is that this will be possible for PCM if you bypass the builtin phono stage.

It would also be great to have the amplification part usable for ie. dynamic microphones, but I don't suppose this will be doable.

The RIAA EQ would be selectable so that it could be performed in the digital domain for PCM recordings - I'm not sure how much gain is required for a Microphone - but I'm guessing that even the MM's input gain would be too high?

 

[JohnW]

PS. Whilst I understand your objective for a DSD phono stage, I'd still be extremely interested in a capacitor-less eq, with eq performed by DSP, even if that means more 'conventional' a to d

Its always been intended that any Phono stage I design (internal or external) would have RIAA / Flat EQ so that we can performed the EQ in the digital domain.

In fact the increased resolution of Delta Sigma ADC's at LF results in an synergistic match with uncorrected RIAA signal from the LP - so it does make sense - but sadly PCM after Digital domain RIAA EQ, unless Dominik starts getting involved with 1 Bit processing (which we can perform with the FPGA).....

 

[JohnW]

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.

Its a valid point of concern - I'm not worried about Hum as the MDAC2 AC PSU is external, but the high level of Digital RF in close proximity to the high gain stage...

I second issue is where to put the Phono lead Ground terminal on the rear of the MDAC2 rear panel which is already packed!

 

[occamsrazor]

Sorry for the newbie questions.... I've read through some of the (667!) posts in this thread but am still not clear about a couple of things.....

1. Is this project still open for purchasing?

2. Am I correct in saying that what is being offered is a drop-in board to replace that in the Audiolab M-DAC? i.e. one needs an existing M-DAC unit already as the host - the "MDAC2" doesn't come with it?

Thanks....

 

[ti33er]

Sorry for this question too, but it may also serve as an answer for new people browsing due to the huge amount of Posts in this thread!

What would the ADC Analogue to Digital Converter be used for? There is already an AV Passthrough at Line-Level which could act as a PreAmp for other things, no?

1. Phono Stage for people wishing to add Room-EQ to their LP Records?

2. Old Tape Cassette recordings into Digital (yeuch) !?

3. ?

Many thanks

Paul

 

[Paolo Anziano]

John, I'd really love a phono stage squeezed inside the MDAC2 !!

 

[Bigbobby666]

John, I'd really love a phono stage squeezed inside the MDAC2 !!

agree... and glad that no one bought my MDAC when i put it up for sale

 

[Akasha]

Its always been intended that any Phono stage I design (internal or external) would have RIAA / Flat EQ so that we can performed the EQ in the digital domain.

.

I too really, really hope you will succeed overcome limited space, noise issues etc. on this one, it would be truly awesome

 

[jirij]

The RIAA EQ would be selectable so that it could be performed in the digital domain for PCM recordings - I'm not sure how much gain is required for a Microphone - but I'm guessing that even the MM's input gain would be too high?

My remark wasn't meant to be taken too seriously, since there's no "right" gain setting for all microphones.
I would prefer an external amp with selectable gain (cca 20-40dB) and a balanced "line" input for the ADC, just as originally planned. If the phono amplification section can't be bypassed (eg. just the RIAA EQ being switchable), I'll have to account for double-amp setup, I guess.

 

[EIffel]

ti33er,
As I understand it, the ADC offers the to broad benefits:
- It transforms the MDAC2 into a fully fledged preamp (albeit with one single analog input). The AV passthrough is much more limited (no volume or any other type of adjustment safe for converting a SE signal into a balanced one). Besides basic things such as volume control, it should also be capable of treating the signal in one form or another, such as room-EQ, etc. It could be used with tapes (reel-to-reel, cassettes), FM radio or other 'wierd' sources (SACD, gaming devices, etc.). This ability also means that one many no longer need a preamp at all, or that one can remove a preamp between the MDAC2 and one's amplifier(s)

- It offers a way to "digitize" an analogue signal -balanced or not-. This could be used to transfer LPs to hard disk, recording live music, testing and measuring analogue signals (room EQ, measurement of audio device...), with very good quality and a broad range of formats

All-in-all, for a small cost increment, it adds a lot of flexibility to the MDAC2...

 

[JohnW]

here is already an AV Passthrough at Line-Level which could act as a PreAmp for other things, no?

The AV "Passthrough at Line-Level" (AV Bypass) is just that, it simply routes the external signal connected to the MDAC2's AV bypass input to the power amplifiers when selected or when the MDAC2 is powered off - it has no level control (the volume level is controlled by the external source - e.g the AV system).

The AV input allows you to integrate the MDAC2 into a home AV system without compromising the HiFi set up

If you wanted to use external analogue line level inputs, then you would need some way of controlling the volume level of the analogue source - such as an active or passive pre-amplifier.

Using the ADC inputs (and presuming the ADC's are pretty transparent - which I'm hoping for), then we can perform level control in the digital domain

 

[JohnW]

My remark wasn't meant to be taken too seriously, since there's no "right" gain setting for all microphones.
I would prefer an external amp with selectable gain (cca 20-40dB) and a balanced "line" input for the ADC, just as originally planned. If the phono amplification section can't be bypassed (eg. just the RIAA EQ being switchable), I'll have to account for double-amp setup, I guess.

Jiri,

I keep stating that the MM /MC gain stage would be selectable (If I have the space to include it) - so you will still have the option for Line level ADC inputs

 

[JemHayward]

Another vote for built in phono stage, though I'd also be quite happy with an external unit. I use a Naim prefix built into my LP12 at present, so in essence, my turntable is a line level device at the moment. For some reason I find the idea of RIAA in the digital domain appealing, but thats probably because my electronics knowledge gets very flaky when it gets to filters! I use a DL103 so a decent amount of gain and 100ohms on the MC input would be about right for me. At present I'm running into 560 ohms and that seems to be fine as well. I don't think the loading of MCs makes a huge difference, but I've never been in a position to try out lots of different loading in quick succession. Incidentally, Jonathan Carr, the designer of the Lyra cartridges, was a fan of 47K loading for MC cartridges!

 

[Chronic]

Hi there, been a while since I've been on the forum, my M-DAC's been working lovely but will be buying a turntable over the Christmas period and wondering how I could connect it to the M-DAC, would this suffice to take phono out the Turntable and then optical or coax into the M-DAC?

Also, my remote control has become very unreliable, I changed the batteries but it's still unreliable, it's really necessary as I use my M-DAC as a preamp, does anyone know who I should contact? I sent IAG an email but not much happening yet

Also, is it worth me upgrading to vA.10, I don't have any issues with the current firmware (vA.06 I think) but custom labelling inputs would be nice for sure, any instructions available for how to do this after updating or is it self explanatory in the sub menus?

Many many thanks for any info

 

[JohnW]

Chronic,

You will need a Phono Pre-Amplifier with ADC - I believe Rega might make such a device - or wait a few months longer for the MDAC2 L3 )