MOTM

Does anyone have plans for a small bi-directional direct box. I'm 
building a modular system to do processing with, mostly, and I'm really 
scared of unwanted noise (I hate it, clients hate it, we all hate it, 
if I want noise I'll patch it in, or hire a cabbie to sit outside the 
studio and chat with his dispatcher). I'm sure we all have the problem 
of coming out of our patchbays and into filters, envelope followers, 
whatever and then returning our output back to our mixer. There has got 
to be a simple fix for this. All I've seen is a DL connectorized piece 
of glorious overkill by Purple Audio (the 1176 cloners). I'm imagining 
something much simpler. Terminate one end at a patch row, the other a 
bank of jacks, 6-8 of them, unbalanced goes in or out at the synth, 
patchrows are balanced, maybe 2U wide. How have y'all addressed this 
problem?

[Sorry to be so slow responding, been kinda busy lately with the "day job"...]

I have been on a similar quest for awhile now.  I have some longish cable runs in my
studio and it would be nice to balance them out with a box that had 8-16 unbalanced
signals in and balanced outputs.  I thought I had found "just the thing" in the MAM
DI-16.  It is a passive 1U rack mount box that has 16 inputs and 16 outputs.  It was
very difficult to figure out if it was balanced or not from the information on the
web so I got my hands on one and opened it up.  As expected, it is just 16 small
transformers connected between 16 sets of TRS jacks.  Unfortunately, the
transformers only operate on the "tip" signal and don't do anything for the "ring"
signal.  So, it doesn't truly balance the signals on the way out but it will get rid
of ground loops by decoupling the input and output and that may be just enough in
many situations.  I see from the tiny circuit boards, that it would be possible to
add a second transformer to handle the "ring" signal and truly balance the output. 
Perhaps that's a project for later...

It doesn't seem like building such a box would be too difficult of a DIY project. 
You just have to find the right audio transformers.  There are many commercial
single/dual channel direct boxes out there with a wide range in cost.  You might
check the sweetwater web site for a few models.

Eric


--- pow333@... wrote:
> Does anyone have plans for a small bi-directional direct box. I'm 
> building a modular system to do processing with, mostly, and I'm really 
> scared of unwanted noise (I hate it, clients hate it, we all hate it, 
> if I want noise I'll patch it in, or hire a cabbie to sit outside the 
> studio and chat with his dispatcher). I'm sure we all have the problem 
> of coming out of our patchbays and into filters, envelope followers, 
> whatever and then returning our output back to our mixer. There has got 
> to be a simple fix for this. All I've seen is a DL connectorized piece 
> of glorious overkill by Purple Audio (the 1176 cloners). I'm imagining 
> something much simpler. Terminate one end at a patch row, the other a 
> bank of jacks, 6-8 of them, unbalanced goes in or out at the synth, 
> patchrows are balanced, maybe 2U wide. How have y'all addressed this 
> problem?


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Finding the right transformer is the key. It's very difficult and 
expensive to get one that performs superbly in the audio range. 
That's where your 'wide range of cost' comes it. It's such a hard 
thing to do, that many solutions just use active electronics instead 
of passive transformers.

Moe

--- In motm@y..., alt-mode <alt_mode@y...> wrote:
> I see from the tiny circuit boards, that it would be possible to
> add a second transformer to handle the "ring" signal and truly 
balance the output. 
> Perhaps that's a project for later...
> 
> It doesn't seem like building such a box would be too difficult of 
a DIY project. 
> You just have to find the right audio transformers.  There are many 
commercial
> single/dual channel direct boxes out there with a wide range in 
cost.  You might
> check the sweetwater web site for a few models.

In a message dated 2/3/01 8:15:14 PM, mate_stubb@... writes:

<< Finding the right transformer is the key. It's very difficult and 
expensive to get one that performs superbly in the audio range. >>

Very easy:

http://www.jensentransformers.com/

But I agree about the expensive part.

Ivan

I see from the tiny circuit boards, that it would be possible to
> add a second transformer to handle the "ring" signal and truly balance the
output.
> Perhaps that's a project for later...

I guess you won't need any extra transformers, just connect the "GND" side
to "ring" rather than sleeve and that's it. (A mono plug will automatically
connect ring and sleve then.)
I've never seen this box myself - I wonder why it would not be connected
like this from the start. I'll ask Stefan about it next time I meet him.

JH.

Perhaps check out the Analog Devices SSM 2143 Balanced line Receiver and SSM
2142 Balanced line Driver separately or in combination. I have started
experimenting with these recently with good success. Common Mode rejection is
very high and the audio specs are quite good. I just picked up a batch of 2143
from allied for about $3.50 each. I will report more later as things progress.
Charles.

Please do.  As I sit here mulling over ideas for my DIY tube preamp / soft
overdrive, inputs optimized for guitar and balanced mic in are on the list.
Maybe that SSM2143 is better (certainly cheaper) than the transformer I was
considering.
Larry H

----- Original Message -----
From: Charles Stella <cstella@...>
To: <motm@yahoogroups.com>
Sent: Sunday, February 04, 2001 6:20 PM
Subject: Re: [motm] Re: Balanced/Unbalanced


Perhaps check out the Analog Devices SSM 2143 Balanced line Receiver and SSM
2142 Balanced line Driver separately or in combination. I have started
experimenting with these recently with good success. Common Mode rejection
is
very high and the audio specs are quite good. I just picked up a batch of
2143
from allied for about $3.50 each. I will report more later as things
progress.
Charles.

Hi all,

I think if you are building a little prototype board then the SSM parts
make good sense. They are small, 8 pin DILs, and they provide good
performance for line level balanced applications. If you are designing a
PCB, then I think the op-amp designs are the way to go. They are cheaper
and all parts are easily available. At Soundcraft we were constantly
being pushed to use the SSM parts by AD reps, but in reality, the op-amp
approach is always the one to go for. Cheaper and no single source
problems.

Transformers are also very good, but they do colour the sound somewhat.
They have been said to improve the sound, but we get into the subjective
area of audiophiles here. They do of course provide the only real way to
get isolation, with the exception of fibre optics.

If we are dealing with line level signals and we don't need tens of
volts of isolation then the electronic balanced system is excellent.
Even the single op-amp input circuit is good enough for most actively
driven line level signals.

If I were to be building a universal input/output module, then I would
go for electronically balanced inputs. With the option of adding
transformers if you wanted. The mic amp could be somthing similar to
that used on Yamaha desks... nice and cheap but with excellent
performance. Standard four op-amp EBOS on the output.

Regards,

Tony Allgood  Penrith, Cumbria, England

Oakley Modular Synth and TB3030:
www.techrepairs.freeserve.co.uk/projects.htm
My music: www.mp3.com/taklamakan