Author Topic: low rent output expansion  (Read 1024 times)

Offline widdly

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low rent output expansion
« on: February 28, 2020, 09:12:16 pm »
For any cheapskate hacker types, I've found these cheap dac's on ebay that support the i2s format used by the mv8000 ..

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You need to set the jumper on the dac to LFS.  The ebay auction says that the data and bclk pins are swapped but I found that is not case.

You can connect four of these via a 34pin IDC cable to the mv8800.  Refer to the op1 service note p.58 for the pinout.
Each DAC board needs five connections  They connect to the following pins on the mv1 op1 34pin expansion cable...
BCK -> pin 19
DATA -> pin 20,21,22 or 23 (channels 1/2 3/4 5/6 7/8)
LRCK  -> pin 18
GND -> pin 31
Vcc  -> pin 33

The output level is standard  -10dBV line level.  The RCA connectors are easy to desolder so you can connect 1/4" sockets.  The audio quality sounds great.  With a little bit of hacking around you can build an 8 channel output board for well under $100.

« Last Edit: March 02, 2020, 03:01:50 pm by widdly »

Offline keefaz

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Re: low rent output expansion
« Reply #1 on: February 29, 2020, 06:35:41 am »
Interesting, you connect the various digital signals in serial or in parallel?

Offline widdly

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Re: low rent output expansion
« Reply #2 on: March 01, 2020, 03:38:29 pm »
In parallel.  All the BCLK connect together, all the LRCLK connect together, and each DAC gets a separate DATA connection.  The clocks probably should be buffered but it works ok without.

Here is the current state of mine.  I still need to do a bit of drilling and make a bracket.  I think I will add the extra midi ports as well.

« Last Edit: March 01, 2020, 03:46:19 pm by widdly »

Offline keefaz

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Re: low rent output expansion
« Reply #3 on: March 07, 2020, 04:47:15 pm »
Nice job, I like the fact you use MV input to check the MV individual outputs sound ;D

Offline keefaz

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Re: low rent output expansion
« Reply #4 on: March 07, 2020, 05:16:03 pm »
I was thinking, you can make cheap balanced outputs, using a 470 ohms resistor to ground and to the TRS jack ring (eg duplicate the same resistance at opamp output, if I read correctly the value on PCB from ebay picture)

(Oh yes, you would have to change the TS output jacks to TRS obviously)

Like this:
« Last Edit: March 07, 2020, 05:17:45 pm by keefaz »

Offline widdly

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Re: low rent output expansion
« Reply #5 on: March 09, 2020, 07:50:10 pm »
I was thinking to test this I'll need to get some speakers and cables and another power board...then I thought I can just loop those outputs right back into MV   ;D

You TRS idea wouldn't really be balanced so there wouldn't be any noise cancellation.  A proper balanced output could be done fairly easily with a couple of opamps something like here..









Offline keefaz

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Re: low rent output expansion
« Reply #6 on: March 10, 2020, 05:56:32 am »
It's impedance balanced, meaning it will work if connected to a balanced input (rejected common noise)
It's not ideal but it works (balanced input is differential, it will substract potential same way between +V and -V or +V and 0V). Now cable carrying this signal will radiate more than with true balanced signal (no cancelling phase), and signal will be 6dB less, but for relatively short cables connected to balanced input in controlled environment it works fine.

Offline widdly

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Re: low rent output expansion
« Reply #7 on: March 11, 2020, 04:38:44 pm »
Thanks for the insight, I had not come across impedance balancing before.

This article is helpful if anyone else is unfamiliar with it.....

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