Hello,

I just an Altec 15356a line transformer (black 8 pin can). I'd like to
use it inside an analog synth to conver from hi impedance to low
inpediance and output to an xlr jack on the back. Essentially I'd like
to hook it up so that there's a D.I. box already inside the synth.

Is this a passive device? It seems to be. I have the base to use it as
a standalone device, so I am assuming it needs no power.

Anyone who's used this transforer for a passive D.I. box, please let
me know the proper wiring. I can't seem to figure out how to wiring it
correctly.

Signal flow: Unbalanced, high impedence input to balanced
low-impedence output.

Please help, I heard these were great and it will fit nicely into my
synth.

Basically I'm not sure what the diagram on the thing is about.

The primary/input side has options for 600 ohm or 150 ohm. The
secondary/output is 600 ohm.

The words CONN. and STRAP are used. What does strap mean? Jump a wire
from pin to pin? Does CONN. denote input and output connections?

Please help, I am confused.

Thanks.

Servin

Servin wrote:

I just an Altec 15356a line transformer (black 8 pin can). I'd like to
use it inside an analog synth to conver from hi impedance to low
inpediance and output to an xlr jack on the back. Essentially I'd like
to hook it up so that there's a D.I. box already inside the synth.

Is this a passive device? It seems to be. I have the base to use it as
a standalone device, so I am assuming it needs no power.

Right. It's a transformer. I think it's one that is designed as an
input transformer rather than an output transformer, so it might be a
little more touchy about loading than a proper output transformer. Try
it and see.

Anyone who's used this transforer for a passive D.I. box, please let
me know the proper wiring. I can't seem to figure out how to wiring it
correctly.

Signal flow: Unbalanced, high impedence input to balanced
low-impedence output.

Please help, I heard these were great and it will fit nicely into my
synth.

Basically I'm not sure what the diagram on the thing is about.

The diagram on the side is what's inside. There are two windings on the
primary. You can put them in series for 600 ohm, or you can wire them
in parallel for 150 ohm.

A transformer is just some coils of wire around an iron core. Current in
one wire induces magnetic fields in the core, which induces current in
the other coils.

The primary/input side has options for 600 ohm or 150 ohm. The
secondary/output is 600 ohm.

The words CONN. and STRAP are used. What does strap mean? Jump a wire
from pin to pin? Does CONN. denote input and output connections?

Precisely.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

"Scott Dorsey" wrote in message
...
Servin wrote:

I just an Altec 15356a line transformer (black 8 pin can). I'd like to
use it inside an analog synth to conver from hi impedance to low
inpediance and output to an xlr jack on the back. Essentially I'd like
to hook it up so that there's a D.I. box already inside the synth.

Is this a passive device? It seems to be. I have the base to use it as
a standalone device, so I am assuming it needs no power.

Right. It's a transformer. I think it's one that is designed as an
input transformer rather than an output transformer, so it might be a
little more touchy about loading than a proper output transformer. Try
it and see.

Anyone who's used this transforer for a passive D.I. box, please let
me know the proper wiring. I can't seem to figure out how to wiring it
correctly.

Signal flow: Unbalanced, high impedence input to balanced
low-impedence output.

Please help, I heard these were great and it will fit nicely into my
synth.

Basically I'm not sure what the diagram on the thing is about.

The diagram on the side is what's inside. There are two windings on the
primary. You can put them in series for 600 ohm, or you can wire them
in parallel for 150 ohm.

A transformer is just some coils of wire around an iron core. Current in
one wire induces magnetic fields in the core, which induces current in
the other coils.

The primary/input side has options for 600 ohm or 150 ohm. The
secondary/output is 600 ohm.

What Scott said. But let me add some things about impedance. You said in
your post that you want to use the transformer to turn the "high-impedance"
output of your synth into a low-impedance output, and also that you wanted
to make it the equivalent of a DI output. First of all, those aren't
necessarily the same, and second of all, this transformer won't do what you
think it'll do.

If your synthesizer is typical, its output is unbalanced (comes out on a
2-conductor jack, probably 1/4") and line level. There are several common
line levels, and without knowing what synth you have I can't know what level
yours uses, but there's a good chance it's the "prosumer" level of -10dBV,
nominal. It probably, however, has a low output impedance already; it's
referred to as "high-impedance" only in the sense that it's intended to go
into a high-impedance input on a mixer or guitar amp.

Most passive DI boxes contain a stepdown transformer -- one with a lot more
turns on the primary side (input) than the secondary side (output). These
step the incoming signal down to microphone level, sending out a balanced,
mic level, low-impedance signal that can travel long distances (like from a
stage to a mixing console). You feed the signal into a microphone preamp or
mic input on your console, and you're there.

Unfortunately, this transformer won't do that. If you wire the primary for
600 ohms (series connection), you'll get an output that is balanced, but the
same level as your synthesizer's output. That's actually a useful signal,
provided the mixer or preamp you're feeding is set up to accept balanced
line-level signals. If it is, you're home free. Maybe.

The kicker is loading. As Scott mentioned, this transformer may want to be
loaded down with 600 ohms in order to respond properly. That was the
standard practice back in the day; it was called "impedance matching".
Modern equipment doesn't work this way; it uses a low output impedance
running into a higher input impedance, and a modern input transformer would
probably be loaded down with 10x the nominal impedance of its secondary --
in this case 6k or so. That would work fine; it'd be the same for your
synthesizer as running unbalanced into the line input of your mixer or
preamp, and it probably doesn't mind that. But loading the transformer with
600 ohms means the synth is also running into a 600-ohm load, and if it's a
prosumer-type synth it probably won't be happy with that, generating a lot
more distortion. And if you don't load the transformer with 600 ohms, you
may (may) get a big high-frequency peak in the frequency response, not a
good idea.

Wiring the primary for 150 ohms makes it a step-up transformer, and you'll
get more level at the output (6dB more, to be exact, excluding losses), an
output impedance that's 4x the synth's own output impedance, and a load on
the synth that's 1/4 the mixer's input impedance. Bad idea all around.

Having been the voice of doom, I'll now turn the page and say Try It. Hook
up the transformer with its input windings in series for 600 ohms, run the
synth into the input, run the output into your mixer's balanced line input
(if it has one), and see what you get. Don't go into the mic input. If it
sounds wonderful, or just sounds the same as it did running unbalanced,
you'll know I'm a worry-wart and you can proceed from there. If it doesn't,
though, you may want to investigate other routes. One of them might be using
the transformer backwards -- feeding signal into the secondary and out the
primary, with the latter wired for 150 ohms. That'll give you a 6dB stepdown
in level and a 4x stepdown in output impedance; see if that is low enough to
go into your mic inputs properly. Loading may get problematic this way too,
since Altec didn't design the transformer to be used this way, but it's
worth a try.

Peace,
Paul