audio attenuator headphone to line

[tg]

I want to make a simple audio attenuator by soldering a couple of resistors
into a cable, similar to here:
http://www.epanorama.net/circuits/speaker_to_line.html
this page talks about attenuating speaker level down to line level with 10k
and 1k but I want to attenuate headphone level down to line level. I haven't
done this before and want to get it right so can anyone advise on the
correct resistor values to use?

 

[Fred McKenzie]

I want to make a simple audio attenuator by soldering a couple of resistors
into a cable, similar to here:
http://www.epanorama.net/circuits/speaker_to_line.html
this page talks about attenuating speaker level down to line level with 10k
and 1k but I want to attenuate headphone level down to line level. I haven't
done this before and want to get it right so can anyone advise on the
correct resistor values to use?

My recollection is that "line level" is related to the level that would
drive a telephone earpiece, and be generated by a telephone's carbon
microphone. In other words, line level is not greatly different from
headphone level.

Just as anyone would adjust a volume control to set their personal
listening level, you would need to adjust the amplifier output for the
desired line level. The only network needed might be for impedance
matching to the line. If your headset amplifier has a very low output
impedance, a series resistor equal to the line impedance may be all that
is needed.

What kind of "line" are you working with? Some are balanced, but the
circuit you refer to is for an un-balanced line. For a balanced line
you may need an audio transformer.

Fred

 

[tg]

What kind of "line" are you working with? Some are balanced, but the

circuit you refer to is for an un-balanced line. For a balanced line
you may need an audio transformer.

the line input is a 1/4" TRS socket on an m-audio microtrack II.
http://www.m-audio.com/images/global/manuals/MT11_flyerUK_LR.pdf
Strangely enough I haven't been able to find any proper specs on the
microtrack but I know it commonly takes microphones and such. Headphone
output is too 'heavy' for a decent recording into this input so I need to
attenuate it.
I can't use any boxes or such because the headphone device and the
microtrack will be used on the move, often in the open, on foot, running on
batteries. Thus I have to integrate any attenuation into the cable. Thanks
for any further advice.

 

[Arfa Daily]

the line input is a 1/4" TRS socket on an m-audio microtrack II.
http://www.m-audio.com/images/global/manuals/MT11_flyerUK_LR.pdf
Strangely enough I haven't been able to find any proper specs on the
microtrack but I know it commonly takes microphones and such. Headphone
output is too 'heavy' for a decent recording into this input so I need to
attenuate it.
I can't use any boxes or such because the headphone device and the
microtrack will be used on the move, often in the open, on foot, running
on
batteries. Thus I have to integrate any attenuation into the cable. Thanks
for any further advice.

The resistor values you suggested give an attenuation of 10 : 1 which is
probably rather too much. OTOH, I'm surprised that you find a headphone
output too 'heavy' to feed a standard line level input. The output from the
headphone socket of an iPod, for instance, feeds a standard line level input
on an amplifier, without issue. I do it every day with a variety of
different amplifiers, as I use my iPod as a source of test music for
amplifiers after repair. Even if the output from the headphone socket does
seem a little OTT to drive the recorder's line input, you can reduce it by
turning down the volume control on the source device.

If, however, you still want to externally attenuate the headphone signal,
prior to driving it into the recorder, then a ratio of 2 : 1 might be more
appropriate, so just use a couple of equal value resistors . You're never
going to match the impedances properly, as the output of the source device's
headphone socket, is likely to be somewhere between a few ohms, and 32 ohms.
The line input on the recorder will likely be around 47k ohms. Just use two
1k resistors. If that doesn't give enough attenuation, double up on the
'top' resistor to say 2k2.

Only thing that might make all of that wrong, is if the input that you are
trying to use on the recorder, is not a 'line level' input. I say that
because you talk about the device "commonly taking microphones". A
microphone input is probably anything up to 100 times more sensitive than a
line level input. If this is the case, then you might need an attenuator of
50 : 1 or more. In which case, try 47k for the top resistor, and 1k for the
bottom one.

Arfa

 

[David Nebenzahl]

I want to make a simple audio attenuator by soldering a couple of resistors
into a cable, similar to here:
http://www.epanorama.net/circuits/speaker_to_line.html
this page talks about attenuating speaker level down to line level with 10k
and 1k but I want to attenuate headphone level down to line level. I haven't
done this before and want to get it right so can anyone advise on the
correct resistor values to use?

According to that propaganda sheet, the Micro Track II will accept input
from "studio monitors (and/or headphones)". So can't you just plug it
directly into the headphone output?

(Not sure what they mean by "and/or" here. I've always held that this
usage ("and/or") is needlessly confusing and should never be used, as
"or" as it's commonly understood is not an exclusive or, so it means
one, the other, or both.)

 

[Fred McKenzie]

http://www.m-audio.com/images/global/manuals/MT11_flyerUK_LR.pdf

TG-

At the bottom of Key Features, a note reads: "For information on using
dynamic mics with the MicroTrack II recorder, please visit the
MicroTrack II product page on m-audio.com." This type of microphone
apparently uses one of your 1/4" TRS inputs.

I went to the web site and found the recorder's User Guide. Under
Recording, it mentions that you should "2. Turn down the input gain of
MicroTrack using the [LEVELS] buttons on the front panel." I think this
may be enough to solve your problem of the headphone output being too
'heavy'.

Fred

 

[tg]

thanks for all the replies here. I tried a few resistor combinations (from
arfa's response) and what worked best in the end was a 22k resistor on the
positive and a 47k resistor linking the positive and the negative. I made a
cable with this setup and was able to get nice clean recordings from the
headphone socket at normal headphone volume.

 

[Arfa Daily]

thanks for all the replies here. I tried a few resistor combinations (from
arfa's response) and what worked best in the end was a 22k resistor on the
positive and a 47k resistor linking the positive and the negative. I made
a cable with this setup and was able to get nice clean recordings from the
headphone socket at normal headphone volume.

I'm glad what I said helped you to get a result that you were pleased with,
but I'm a little confused. Are you sure that the resistor values that you've
stated are correct, and the bottom one wasn't 4.7k rather than 47k ? As
stated, the attenuation provided would be very small - in example numbers,
1v in, around 0.7v out. With the bottom resistor at 4.7k, the attenuation
would be something over 4 : 1, which seems more realistic ?

Arfa

 

[tg]

I'm glad what I said helped you to get a result that you were pleased
with, but I'm a little confused. Are you sure that the resistor values
that you've stated are correct, and the bottom one wasn't 4.7k rather than
47k ? <snip>

nope, just checked and the bottom resistor is 47K.
in your previous post you did say 'a ratio of 2 : 1 might be more
appropriate,' and you were right, this - as it turned out - is a 2:1 ratio.

 

[Arfa Daily]

nope, just checked and the bottom resistor is 47K.
in your previous post you did say 'a ratio of 2 : 1 might be more
appropriate,' and you were right, this - as it turned out - is a 2:1
ratio.

Not quite. As stated that your series resistor is the lower value of 22k,
and the shunt one is the higher value of 47k, this is a 1 : 2 ratio ...

Still, if it does the job that you were looking for, not worth getting
bogged down in maths and definitions

Arfa