[Kristian Domke]

Hi,

I have some (3) old active monitor speakers with simple 1/4" mono
inputs. Because of the known benefits I would like to add symetric inputs.

Is there a way with a not too expensive curcuit? All I found seraching
the web were ballancing amplifiers, but as I understand it, this would
be the wrong direction, wouldn't it?

Thanks!

Kristian

[Laurence Payne]

On Thu, 27 Sep 2007 19:56:07 +0200, Kristian Domke
wrote:

Hi,

I have some (3) old active monitor speakers with simple 1/4" mono
inputs. Because of the known benefits I would like to add symetric inputs.

Is there a way with a not too expensive curcuit? All I found seraching
the web were ballancing amplifiers, but as I understand it, this would
be the wrong direction, wouldn't it?

What are these "known benefits"? Have you a problem that you feel it
might solve? If not, I doubt you'll hear any improvement.

[Kristian Domke]

Laurence Payne schrieb:
On Thu, 27 Sep 2007 19:56:07 +0200, Kristian Domke
wrote:

Hi,

I have some (3) old active monitor speakers with simple 1/4" mono
inputs. Because of the known benefits I would like to add symetric inputs.

Is there a way with a not too expensive curcuit? All I found seraching
the web were ballancing amplifiers, but as I understand it, this would
be the wrong direction, wouldn't it?

What are these "known benefits"? Have you a problem that you feel it
might solve? If not, I doubt you'll hear any improvement.

Well the monitors are used in an live environment, and sometimes they
catch 50Hz from AC, via the cabling. I hope to make the connection more
robust against these effects. (I know, that symetric is not always
better then not)

[Scott Dorsey]

Kristian Domke wrote:

I have some (3) old active monitor speakers with simple 1/4" mono
inputs. Because of the known benefits I would like to add symetric inputs.

Are you sure they are not 1/4" TRS? What are they?

Is there a way with a not too expensive curcuit? All I found seraching
the web were ballancing amplifiers, but as I understand it, this would
be the wrong direction, wouldn't it?

The easiest way is to use a transformer. The cheapest way is to use one
of the balanced line receiver chips from Burr-Brown or Analog Devices...
but if you use the chip you will need bipolar power to drive it. So it
comes down to what kind of power you can steal from the the monitor power
supplies.

Are these by any chance 1960's Sennheiser designs?
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Kristian Domke]

Scott Dorsey schrieb:
Kristian Domke wrote:
I have some (3) old active monitor speakers with simple 1/4" mono
inputs. Because of the known benefits I would like to add symetric inputs.

Are you sure they are not 1/4" TRS? What are they?

I dont have them here, but I am quite sure. As far as I know just 1/4" TS.


Is there a way with a not too expensive curcuit? All I found seraching
the web were ballancing amplifiers, but as I understand it, this would
be the wrong direction, wouldn't it?

The easiest way is to use a transformer. The cheapest way is to use one
of the balanced line receiver chips from Burr-Brown or Analog Devices...
but if you use the chip you will need bipolar power to drive it. So it
comes down to what kind of power you can steal from the the monitor power
supplies.

Are these by any chance 1960's Sennheiser designs?

They are from the 1960s, but they are from the German Democratic
Republic. Maybe they are Sennheiser clones, but I have never seen one of
those, so I cannot tell.

Kristian

[Mike Rivers]

On Sep 27, 1:56 pm, Kristian Domke wrote:

I have some (3) old active monitor speakers with simple 1/4" mono
inputs. Because of the known benefits I would like to add symetric inputs.

What do you "know" about the benefits? Do you have a problem with them
now? If so what's the problem. I'll bet it isn't that they're not
balanced.

Is there a way with a not too expensive curcuit?

No. An electronically balanced input circuit isn't difficult to build
and doesn't involve expensive parts. But to integrate it into the
speakers after the fact would be difficult (and therefore expensive to
have someone else do it). Transformers are expensive. The reason why
they use unbalanced inputs is to save money - often quite a lot of
money. Pay me now, pay me later, or forget it because it doesn't
matter anyway.

[Mike Rivers]

On Sep 27, 4:04 pm, Kristian Domke wrote:

They are from the 1960s, but they are from the German Democratic
Republic.

My gut feeling is that just balancing the inputs isn't going to solve
your problem. But considering that the alternative is buying new, more
modern speakers, I'd suggest that you try a transformer and see if
that helps.

The Ebtech Hum Elimiator will do the trick, and you can probably find
one fairly easily over there in 50 Hz land. It's not too bad as long
as you don't push a lot of level through it. A 1960s unbalanced input
is probably a pretty low level device. Buy one from a real dealer and
make sure you can return it for a refund if it doesn't solve your
problem. A real dealer will understand.

http://www.ebtechaudio.com/he-2des.html

[Scott Dorsey]

Kristian Domke wrote:

They are from the 1960s, but they are from the German Democratic
Republic. Maybe they are Sennheiser clones, but I have never seen one of
those, so I cannot tell.

If they are from the 1960s, you almost certainly have unipolar supplies
in there, so your hardest part is going to be figuring out how to derive
+/-15V from whatever you have inside there.

I'd go the transformer route if it were me, and wherever you got the
speakers from probably has some nice 1:1 transformers lying around.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Chris Hornbeck]

On Thu, 27 Sep 2007 20:52:35 +0200, Kristian Domke
wrote:

Well the monitors are used in an live environment, and sometimes they
catch 50Hz from AC, via the cabling. I hope to make the connection more
robust against these effects. (I know, that symetric is not always
better then not)

One important factor is often overlooked: bring the monitors'
AC power cords (via extension cords, as short as possible, and
if necessary) back to the *same* AC outlet as your other sound
reinforcement electronics.

This might seem like a silly waste of effort, but if you research
the topic "ground loop" it will fall into place. Non-symmetrical,
or as it's called in America "unbalanced", connections are
especially sensitive to ground loop issues.

Live sound venues are almost guaranteed to be a nightmare (on a
good night), so armouring yourself behind a wall of the known
and predictable is The First Step.

All the best fortune,

Chris Hornbeck