M-Box Upgrade

[just.sounds]

Hello i have got a nice DIY project idea but i thought that maybe some of you have tried a similar thing

I have an m-box that I want to upgrade and put in a new case
The analog part is easily replaced with a soldering iron and some endurance (i want to build in some better pre amps with more gain and a monitor volume control)

But the real question is do any of you have any experience with replacing the converters and keep the buss powering intact?
some scematics would also help lots!

greetz!

 

[rodabod]

This sounds like a nice idea to me.

I'd start by searching on the net for A/D converter data sheets - AKM branded or whatever. Have you checked the brand of the ones in the M-Box? You'll be able to find out somewhere.

You may want to upgrade the clocks as well.

Keep an eye on current draw - the USB bus can only provide so much.

 

[pucho812]

wow. thats a tall order for your first post. let me be the first to welcome you to the diy family. As for your request and having been someone deeply involved with digistuff, it's going to be dificult to do. I am sure the analog section can be upgraded or replaced but the digi section is a no go. remember the mbox is an all in one unit designed to run off USB buss power as well as transfer info to and from the computer. i wouldn't mess with that. IMO you would be better off building a 2 chnnel pre with an a/d in it.

 

[just.sounds]

that was my backup plan to build the whole shebang in a new case and connect it with the spdif and find a way to clock it all nice and smooth

 

[just.sounds]

It is problematic when you want to stay moblile with digidesign/pro tools
and really rather used a mini me or a metric halo uln2
But I like challenges and this is one i think!

 

[12afael]

the preamp of this box is a focusrite design.
why you only conect the new preamp on the line input?

time ago thought about build a sound card with a ti chip with usb, spdif , analog/digital and digital/analog converters(but 16bits... ) . the power supply of the mbox is some that I want to see . it work with the usb supply. I would like to know how they get dual rail supply for the preamp.

if you can take photos, it would be cool.

 

[featherpillow]

I would like to know how they get dual rail supply for the preamp.

There are circuits that will give you a negative rail off of a positive supply. You could ask Ted F for some details. I'm pretty sure he designed the Joe Meek VC5, and that uses a transistor tied to the positive regulator to generate the negative rail. Also, Maxim makes IC's that will generate negative rails from positive supplies.

Or, they may be powering the preamp circuit from a single-sided rail, and using a voltage divider to generate a reference voltage for the opamp's input to force the negative swing.

 

[12afael]

Also, Maxim makes IC's that will generate negative rails from positive supplies.

yes, I know that. I just want to see how the supply of the mbox is being implemented. 5 volts from the usb port and I don´t remember how much current can drive . two preamps , panthom power , all the digital stuff , some leds, I think it work on the limit .

Or, they may be powering the preamp circuit from a single-sided rail, and using a voltage divider to generate a reference voltage for the opamp's input to force the negative swing.

I feel that is not very pro. the current on the voltage divider maybe could add noise in the input.

 

[drunton]

Quote:
Or, they may be powering the preamp circuit from a single-sided rail, and using a voltage divider to generate a reference voltage for the opamp's input to force the negative swing.


A lot of stuff out there uses this method. I opened up my M-audio FW1814 and that seems to be what they do. Plus, I bought a Presonus Digital option card - the one for the eureka. This is what they do.

By the way, my idea is to use this Preesonus digital card as a cheap AD. Got one on ebay - uses 5V. It has the "2nd" input already configured with a 1/4 TRS in. Then just need to build the interface for the "primary" input that usually comes from the Eureka - just some simple signal conditioning.

It's a pretty easy card to wire up - 4 wires - +5V, GNDx2 , Signal In. voila - dual 192khz SPDIF converter

 

[buschfsu]

anyone seen what the preamp ics are in this? are there any drop in repacements? burr browns or AD?

 

[JLM Audio]

A good noise floor improvement for Mbox and Mbox 2 which don't have the new versions dc power connector is to cut the +5v wire in the USB cable and connect in a external 5v 1Amp supply that powers the Mbox only.

 

[Rochey]

The converter chips in the Mbox, 002, and 002R are the AKM 5383 (ADC) and 4383 (DAC), 110dB decent and very inexpensive: http://www.asahi-kasei.co.jp/akm/en/product/ak5383/ak5383.html

As a converter "upgrade" you might consider hooking up a PCM4202 Evaluation module to it. The Eval module has an S/PDIF output that you could bring straight into the MBOX.

You will need some gain from line level into the Eval board to compensate for the attentuation that's used on the analaogue front end. Either that, or bypass the boards front end completely.

That way, you could get a very clean 118dB ADC.
In fact, wait 3 monthsor so, and you should be able to get a 123dB ADC! (PCM422x)

ideally, you'd use a green pre or something as a front end, however, you'd need a circuit to convert the line level out of the green pre to 0 to 5V range of the ADC, along with a bias of 2.5V.
It's not the hardest thing in the world to do... just another task :wink:

 

[Rochey]

[quote author="JLM Audio"]A good noise floor improvement for Mbox and Mbox 2 which don't have the new versions dc power connector is to cut the +5v wire in the USB cable and connect in a external 5v 1Amp supply that powers the Mbox only.[/quote]

This would make quite a difference... I'm told that the USB 5V is typically very very dirty. As that 5V is used a reference throughout the system (i.e. things like your converters might be running from it) then having a flat and stable 5V is very very important.

 

[buschfsu]

the opamps in the mic pres are njm2122 (jrc).

I am considering swapping with opa2134s. anyone done this?

 

[redear]

As a converter "upgrade" you might consider hooking up a PCM4202 Evaluation module to it. The Eval module has an S/PDIF output that you could bring straight into the MBOX.

I could not tell by the spec sheet wich out would serve as the s/pdif

ideally, you'd use a green pre or something as a front end, however, you'd need a circuit to convert the line level out of the green pre to 0 to 5V range of the ADC, along with a bias of 2.5V.
It's not the hardest thing in the world to do... just another task :wink:

would one of the buffer schems on the info sheet for the Eval do this? I have an M-box and dont like it much but cant afford an upgrade right now. It also has a dead chanel now so I cant do 2 chanels at once these days anyway...