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MOTU 24ao

Connecting Hauptwerk to MIDI organs, sequencers, ...
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JohnNicholson

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MOTU 24ao

PostTue Aug 31, 2021 10:39 am

On the recommendation of people here, I have bought a Motu 24ao to split the optical signal from my PC into a multi-channel system of speakers, to create a more three dimensional sound. But I am not clear how to connect the amps to the back of the Motu24ao. I have written to Motu and had ambiguous reply. The manual is very vague about the rear end connections so it seems that they expect anyone using this equipment to be familiar with line level sound connections.

The rear of the Motu has a row of six twelve pin sockets, each with a single pin, numbered in groups of three from 24 to 1. I have used Phoenix connectors with screw blocks to attach the connecting lines to the input of stereo amplifiers.

They are grouped in threes to give 24 three wire channels, marked on the chassis G + - . But to me the symbols + and – relate to Direct Current, not to an oscillating audio signal. I am not clear whether to wire each group as either ...

A) with every numbered channel group of three pins providing a stereo signal using the – and + as the signal line for Left and Right, and taking the G as the return. This would give me 24 stereo channels (48 speakers).

Or …

B) with every numbered channel group of three pins provides a mono signal between the + and – pins and the ground is connected to any braided shield over the line signal. This would give me 24 mono channels, (24 speakers). (In fact, none of my line connections have a braided shield – and I would have thought this form of screening only applies to very high frequency signals such as the cable from a TV aerial to the TV receiver).

I would like to make contact with anyone who is already familiar with audio line level connections. To therm the answer to this may be obvious! I am novice to audio technology, but I am experienced in the software side of the project and also the organ building needed to build and set up the console. I expect I will also need help connecting the Motu to the PC.

The amps I am using in my experimental organ are TPA7498E 2 * 60 watt 15 – 34 volts. They are not expensive and seem to give plenty of power, and they will actually run on 12 volts DC. I have a car stereo bass boost amp for the deeper pedal organ stops, driving two 20" Ambassador speakers that were thrown out of school 60 years ago. I plan to run the whole organ from a heavy duty car battery which will be re-charged from mains when the organ is not playing.

I would appreciate views and advice.
Many thanks!
John Nicholson (North Wales UK)
biopoweruk@hotmail.com
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engrssc

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Re: MOTU 24ao

PostTue Aug 31, 2021 11:15 am

I am not familiar with the amps you mentioned. Most likely unbalanced input? The designations on the MOTU 24ao output terminals marked + and - are audio polarity designations, nothing to do with DC as in a power supply etc. For an unbalanced input to the MOTU 24ao, you connect the - to G which is the shield (screen). The "hot" (or center) wire is the + terminal.

Routing the output from the computer is done with a Routing Tab software program available from MOTU.

https://motu.com/techsupport/technotes/avbrouting

That should get you started.

Rgds,
Ed
Last edited by engrssc on Tue Aug 31, 2021 11:17 am, edited 1 time in total.
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mnailor

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Re: MOTU 24ao

PostTue Aug 31, 2021 11:15 am

Apologies for not directly answering your question, but I use three 8 channel snakes DB25 to TRS on my 24Ao to make it simple. There are DB25 to XLR and TRS snakes available. For example, see sweetwater.com under Products/Accessories/Snakes, then pick your connectors.
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IainStinson

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Re: MOTU 24ao

PostTue Aug 31, 2021 11:20 am

Hi John

I have a MOTU 24AO and connected it to my amps using the Phoenix Connectors.

(My connection to the computer is via the USB connection.)

There are six groups of connectors and each group has four (mono) audio outputs. They audio outputs are balanced outputs with three connections per audio output.

If you are connecting to a balanced input you use the three connectors (G to the cable ground and + and - to the signal inputs of the balanced input).

If you are connecting to an unbalanced input (which is what my amps provide), you connect the - to the negative input of the amp and the + to the positive input of the amp. You leave the ground output from the MOTU not connected. (This is the advice I got from MOTU support). It works fine. (Think old fashioned "hifi" amp inputs with red(+) and black(-) connecting cables.)

I found the connectors a bit fiddly, but they do work.

Hope this helps.

I note others have added a reply whilst I typed. I did not use the snake cables as I thought they were a little expensive (but they are more convenient). MOTU advise that I left the G unconnected, Ed's comments suggest connecting the G not the - (negative): I think either works, I chose to stick with the answer from MOTU.

Iain
Last edited by IainStinson on Tue Aug 31, 2021 11:23 am, edited 1 time in total.
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engrssc

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Re: MOTU 24ao

PostTue Aug 31, 2021 11:23 am

What mnailor is referring to for using balanced inputs/outputs.

What is the difference between balanced or unbalanced?

https://motu.com/techsupport/technotes/what-is-the-difference-between-balanced-or-unbalanced

Rgds,
Ed
Last edited by engrssc on Tue Aug 31, 2021 1:33 pm, edited 2 times in total.
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engrssc

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Re: MOTU 24ao

PostTue Aug 31, 2021 11:37 am

IainStinson wrote: MOTU advise that I left the G unconnected, Ed's comments suggest connecting the G not the - (negative): I think either works, I chose to stick with the answer from MOTU.


Not quite. What I said was to connect the - to the G terminal. This works with many cheaper single ended amps. With some the connections as Iain mentioned may work. Unbalanced is more prone to noise and hum. A balanced connection cancels these problems out but the amp input needs to be able (designed) to accept a balanced signal.

This solution also came from MOTU Tech Support which sorta solved a troublesome installation located near an AM radio transmitter site. For a better solution, we converted the system to use balanced audio.

Rgds,
Ed
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jkinkennon

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Re: MOTU 24ao

PostWed Sep 01, 2021 10:58 pm

I will not use unbalanced audio cables unless there is no alternative. It isn't worth the grief of unexpected hum and noise. Stick with TRS phone jacks and XLR connectors on shielded twisted pairs and most audio transmission issues will simply disappear.

This is essential reading for proper cabling: https://www.ranecommercial.com/kb_artic ... ticle=2107

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