DIY Rack Mount Minidsp Balanced 2x4 Enclosure - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 58 Old 07-17-2014, 06:55 AM - Thread Starter
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DIY Rack Mount Minidsp Balanced 2x4 Enclosure

Parts are coming in this week for my latest DIY project. Mounting the Minidsp into a rackmount enclosure.

Parts:













Tools:
I used a step drill bit from Harbor Freight:
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Last edited by NicksHitachi; 07-21-2014 at 09:11 AM.
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post #2 of 58 Old 07-17-2014, 06:56 AM - Thread Starter
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Assembly:










Here is how i handled grounding the shield(pin1) on each input and output:

One short jumper wire from pin1 to body pin.



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Last edited by NicksHitachi; 07-22-2014 at 04:22 AM.
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post #3 of 58 Old 07-17-2014, 06:56 AM - Thread Starter
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Interconnects:

For relevant reading Look At:

Rane Sound System Interconnection

Deailing with Legacy Pin 1 Problems

For my application I used this cable strategy:

AVR>>>



>>>Minidsp>>>




>>>Pro Amp
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post #4 of 58 Old 07-17-2014, 06:56 AM - Thread Starter
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.....
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post #5 of 58 Old 07-17-2014, 09:21 AM
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Nice. There are a few similar projects scattered across the web and miniDSP forum.

I considered this also, but then got lazy and just used a DCX2496. I like being able to change settings without a PC sometimes.
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post #6 of 58 Old 07-17-2014, 09:51 AM - Thread Starter
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I hear that on the ability without PC....

Yeah there are several scattered about, just setting up shop in case I have any questions along the way. Any links to other projects would be appreciated.

I also found this:

minidsp box/case thread
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post #7 of 58 Old 07-17-2014, 10:33 AM
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post #8 of 58 Old 07-17-2014, 10:42 AM
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Check out this app note by Bruno Putzeys (PDF) about proper wiring of pin 1 of the XLR. In it, he says, among other things:

Quote:
Originally Posted by Bruno Putzeys
In the past, confused designers believed that pin 1 was an audio connection. So they wired it to the circuit board. This caused lots of problems. Fortunately, manufacturers have largely cleaned up their act in the past 20 years.
Unfortunately, miniDSP are among the ones who haven't cleaned up their act, as their packaged boxes wire pin 1 to the board. Having a DIY box is a great way to get rid of this problem.
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post #9 of 58 Old 07-17-2014, 10:45 AM - Thread Starter
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Quote:
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link to the rackmount enclosure?
Clicky on picky
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post #10 of 58 Old 07-17-2014, 10:51 AM - Thread Starter
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Quote:
Originally Posted by andyc56 View Post
Check out this app note by Bruno Putzeys (PDF) about proper wiring of pin 1 of the XLR. In it, he says, among other things:



Unfortunately, miniDSP are among the ones who haven't cleaned up their act, as their packaged boxes wire pin 1 to the board. Having a DIY box is a great way to get rid of this problem.
Interesting, please elaborate.

So they wire the drain wire to (-)?

I assume my pro amps have the drain wired to ground?

Should every balanced component have the drain wire tied to ground?
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post #11 of 58 Old 07-17-2014, 11:07 AM
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Quote:
Originally Posted by Nick****achi View Post
Interesting, please elaborate.

So they wire the drain wire to (-)?

I assume my pro amps have the drain wired to ground?

Should every balanced component have the drain wire tied to ground?
Only pins 2 and 3 of the connector should go to the PC board. Pin 1 should go to the chassis only, and not to any other pins. The cable shield connects to pin 1. Some XLR chassis connectors have pin 1 internally connected to the conductive housing, in which case no wire would be needed to connect pin 1 to the chassis. That's the best approach I think.

This technique is part of the AES48 standard, based on a 1995 AES article by Neil Muncy.

The idea is that 60 Hz ground loop currents are unavoidable in non-trivial systems. When a collection of interconnected balanced components are wired this way, these 60 Hz currents circulate harmlessly through the chassis of each one and not through the circuit board. Muncy did a number of tests with a "hummer" circuit that injected large 60 Hz hum currents into the shield and measured the resulting hum on the output signal. Systems wired per his approach exhibit very high measured immunity to these hum currents.
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post #12 of 58 Old 07-17-2014, 11:19 AM - Thread Starter
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Sounds like i should rethink my power connection and go with a standard IEC three prong so i can shunt the drain pin(1) to ground...... Right?
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post #13 of 58 Old 07-17-2014, 11:31 AM
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The XLR wiring technique works to prevent hum whether or not you have the chassis connected to the safety ground of the home wiring system. However, for safety reasons it's a good idea to connect the chassis to safety ground. Certain types of power supply failures can cause the chassis to become electrically "hot" with risk of electrocution in the absence of a safety ground. With the safety ground setup, such a failure ends up either blowing an internal fuse or the breaker in your home.

Edit: Here's an illustration of the recommended approach (AES48).

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post #14 of 58 Old 07-17-2014, 11:34 AM
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Nick! Why have I never seen this before. You been hiding this from me ?

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post #15 of 58 Old 07-17-2014, 11:50 AM - Thread Starter
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Quote:
Originally Posted by andyc56 View Post
The XLR wiring technique works to prevent hum whether or not you have the chassis connected to the safety ground of the home wiring system. However, for safety reasons it's a good idea to connect the chassis to safety ground. Certain types of power supply failures can cause the chassis to become electrically "hot" with risk of electrocution in the absence of a safety ground. With the safety ground setup, such a failure ends up either blowing an internal fuse or the breaker in your home.
Ok good to know. I can add the three prong later maybe. Voltage to the case is like <12V so isnt the danger pretty minimal? Im powering the minidsp with a wall wart so step down occurs outside the case.

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Nick! Why have I never seen this before. You been hiding this from me ?
LOL, not hiding, its part of my rack renovation.... Might as well do it all at once.

I got speakers to build too but saving them for last
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post #16 of 58 Old 07-17-2014, 12:03 PM
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Quote:
Originally Posted by Nick****achi View Post
Ok good to know. I can add the three prong later maybe. Voltage to the case is like <12V so isnt the danger pretty minimal? Im powering the minidsp with a wall wart so step down occurs outside the case.
That sounds plenty safe. I've added an illustration of the wiring technique from Muncy's original article to my post above, so if you go that way, you would just omit the connection from home wiring safety ground to case. But the circuit card ground and the power supply zero volt side still connect to the case.
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post #17 of 58 Old 07-17-2014, 12:25 PM - Thread Starter
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Quote:
Originally Posted by andyc56 View Post
That sounds plenty safe. I've added an illustration of the wiring technique from Muncy's original article to my post above, so if you go that way, you would just omit the connection from home wiring safety ground to case. But the circuit card ground and the power supply zero volt side still connect to the case.
OK, so the zero side of the ~12VDC connects to case also, I understand that.

What is the "circuit card ground?"
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post #18 of 58 Old 07-17-2014, 12:40 PM
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Quote:
Originally Posted by Nick****achi View Post
OK, so the zero side of the ~12VDC connects to case also, I understand that.

What is the "circuit card ground?"
In the balanced miniDSP kit user manual, it's anything labeled "ground" in the table on page 5, also including the zero volt side of the power supply. So if the zero volt side of the power supply is connected to the case and also to the miniDSP power supply connector, that should do it.
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post #19 of 58 Old 07-18-2014, 04:07 AM
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This is so confusing to me, lol. I have always wondered which XLR cables needs to be moddified, and whether or not you have to do this for all pro-amp or all of the MiniDsp's?

What I am understanding based on the list, is that if you have a balanced cable connecting to the MiniDsp 2 by 4 balanced with advanced plug in, or any other type of balanced cable connecting to a pro-amp, then you would need to chop off one of the ends of an XLR cable and snip pin one, then connect the left over wires back to the original connector then plug into amp or MiniDsp?
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post #20 of 58 Old 07-18-2014, 04:25 AM - Thread Starter
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It depends on how the "pro amp" handles grounding of pin 1.

Assuming your pro amp follows correct spec, it sounds to me that your drain wire(s) connected to the minidsp should be connected to the zero wire of the power supply.

Snipping the drain wire essentially makes it an unbalanced wire with a fancy connector.

Ill have to ohm out my cables and connectors to see if pin 1 is connected to the outer body which would skip the step of connecting it to the chassis.
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post #21 of 58 Old 07-18-2014, 06:51 AM
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Quote:
Originally Posted by Nick****achi View Post
It depends on how the "pro amp" handles grounding of pin 1.

Assuming your pro amp follows correct spec, it sounds to me that your drain wire(s) connected to the minidsp should be connected to the zero wire of the power supply.

Snipping the drain wire essentially makes it an unbalanced wire with a fancy connector.

Ill have to ohm out my cables and connectors to see if pin 1 is connected to the outer body which would skip the step of connecting it to the chassis.

For additional information, for anyone interested, Google "pin 1 problem".
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post #22 of 58 Old 07-18-2014, 07:06 AM
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u should also put a rectifier between ground and earth like so How to Wire-up a Power Amp.pdf
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post #23 of 58 Old 07-18-2014, 07:21 AM - Thread Starter
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u should also put a rectifier between ground and earth like so How to Wire-up a Power Amp.pdf
The bridge and resistor work as a DC blocker on the earth ground in that position right? Keeping forward grounds from oscillating? Or am I mis-interpreting?

For this exercise I'm just going to use the two prong power supply. The case only holds 12V so I'm not too concerned with shorts to the case that need an seperate earth ground.

My plan is to connect the (-) of the 12V power supply to the chassis and also the drain wires of all the XLRs to the chassis(star grounded of course). Sound right?
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post #24 of 58 Old 07-18-2014, 07:24 AM
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Quote:
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u should also put a rectifier between ground and earth like so How to Wire-up a Power Amp.pdf
Those recommendations are for an unbalanced system only.
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post #25 of 58 Old 07-18-2014, 07:32 AM
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Quote:
Originally Posted by Nick****achi View Post
My plan is to connect the (-) of the 12V power supply to the chassis and also the drain wires of all the XLRs to the chassis(star grounded of course). Sound right?
If pin 1 is not internally connected to the housing, it gets wired to the chassis with the shortest wire possible. It need not go to the same ground lug that the power supply connects to. In fact, it should not do that, as that would make the wire too long.

The rectifier approach is a good one for power amps with unbalanced inputs, but it's inappropriate for this situation.
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Quote:
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Those recommendations are for an unbalanced system only.
yeah i shouldn't post so early in the morning
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post #27 of 58 Old 07-18-2014, 10:16 AM
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yeah i shouldn't post so early in the morning
It's a very good document that I hadn't seen before, from Bonsai (Andrew) over at diyaudio.com. He is a bright guy and has made many very good designs.

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post #28 of 58 Old 07-20-2014, 06:07 PM - Thread Starter
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Making slow progress:



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post #29 of 58 Old 07-21-2014, 06:50 AM - Thread Starter
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post #30 of 58 Old 07-21-2014, 06:56 AM
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What are you using the mini DSP for ? You bought the cased one and not just the board ?

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