MiniDsp 2x4 low gain problem - diyAudio
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Old 29th August 2014, 04:50 PM   #1
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Default MiniDsp 2x4 low gain problem

Has anyone investigated solutions to low output from this unit. I have not seen a schematic anywhere on this. I'm assuming that it has an opamp based analog out, somewhere in design ,that the gain could be adjusted with resistor changes.
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Old 2nd September 2014, 10:36 AM   #2
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It doesn't have output opamps unfortunately.
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Old 2nd September 2014, 10:42 PM   #3
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Yes I've done some research hence and found that out. Do you know i hear that the balanced design will solve this. I'm assuming though that requires a balanced input on the amp driven? You can't drive an unbalanced with balanced correct. one phase will be connected to signal ground. This is a major drawback to this DSP design. Low output makes it impractical.
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Old 3rd September 2014, 01:30 PM   #4
Julf is offline Julf  Europe
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Quote:
Originally Posted by Freecrowder View Post
Yes I've done some research hence and found that out. Do you know i hear that the balanced design will solve this. I'm assuming though that requires a balanced input on the amp driven? You can't drive an unbalanced with balanced correct. one phase will be connected to signal ground. This is a major drawback to this DSP design. Low output makes it impractical.
Absolutely no problem driving balanced with unbalanced - it is the other way that is trickier.

A balanced input is differential - it looks at the voltage difference between the non-inverting and inverting input. It doesn't care if one of those happens to be connected to earth/ground.
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Old 3rd September 2014, 09:09 PM   #5
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CharlieLaub designed gain stage boards for the minidsp. See posts #74 and #76 here:

4-channel gain stage with DC-servo for MiniDSP

Last edited by ltdf; 3rd September 2014 at 09:17 PM. Reason: 237
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Old 4th September 2014, 03:44 PM   #6
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More recently I have designed a board (being fabbed right now) that employs a 4-channel VCA for post-crossover volume control, including up to 12dB of boost, the output level of which is controlled by a single 0-5V DC signal. This lets you run the miniDSP board at "full signal" levels, and then do the volume control in the analog domain. Because it can provide gain as well as attenuation, this approach solves multiple problems at once. Once I get it built up I will do some tests for performance (e.g. distortion and noise, etc.). There are other solutions that are coming down the pipeline (not from me however) that can do the same thing using more contemporary technology (digitally controlled volume ICs).
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