I'm using a Pro-Ject Phono Box MKII phono pre-amp with an M-Audio2496
sound card to copy vinyl to CD.
The output level of the MKII is too high for the sound card input and
the card clips.
Is there a commercially available line level pad of, say 5 - 10 dB,
that I could use between the two devices?
Can you tell me how to build a pad?
An adjustable pad would be great if it exists. (I didn't have this
problem when I was using my McIntosh preamp since I could adjust the
output level.)

Specs:

Pro-Ject MKII
Input impedance 47k ohms
Output voltage 300 mV @ 1kHz
Max. output 9.5 V (1kHz)

M-Audio 2496
Peak Analog Input Signal +2dBV
Input Impedance 10k ohms minimum

First check your sound card driver. I've had this problem and solved it by
rolling back to an earlier version of the sound card driver. The input
range that you can get a soundcard to accept is very much driver-dependent.
Try all the versions you can get hold of; the newest is not necessarily the
best (at least with Sound Blasters, which is where I ran into this
phenomenon).

I believe Radio Shack sells 20 dB pads built into RCA plug adapters.

If you want to build a pad, it's simple. For each channel, you need two
resistors (wattage does not matter since they're each handling far less than
1/10 watt). Here's how to wire it up (for one channel):
- Input ground to output ground.
- Input center pin to 22k resistor to output center pin.
- 4.7k resistor from output center pin to output ground.
That should give you 15 dB of attenuation. If you want less attenuation,
change the 22k resistor to 10k. If you want more attenuation, change the
22k resistor to 47k. Build all this in a shielded metal box with the shield
connected to the cable shields (signal ground).

Pro-Ject MKII
Input impedance 47k ohms
(irrelevant since we're connecting to its output; the output impedance of
any modern preamp is going to be quite low, like 1000 ohms or less, even
though it's designed to drive a 10k amplifier input)
Output voltage 300 mV @ 1kHz
Max. output 9.5 V (1kHz)
(those two seem to contradict each other, but the second one indicates that
it could indeed overdrive a sound card, even one with pro audio level
inputs)

M-Audio 2496
Peak Analog Input Signal +2dBV
(meaning it will take up to about 1.3 volts input)
Input Impedance 10k ohms minimum
(meaning its input impedance is at least 10k ohms and may be higher; that's
why we used a smaller resistor, 4.7k, on the output of the pad. Output
impedances should always be lower than the input impedance of the thing
being driven.)

Of course, if you believe one of the people who have posted on this group
recently, electronics has *nothing* to do with audio and you should just do
everything by ear.

Apparently Radio Shack has discontinued their handy attenuator, but you may
still find it at some stores. (It's red.) See also this:

http://www.partsexpress.com/pe/showd...number=266-234

Parts Express has a variety of these. They're used in custom home theater
installations to match up the volume of different non-adjustable sources, to
make it more convenient for the user.

he

http://www.electronicplus.com/conten...=AS&subcat=AM3

and he

http://www.partsexpress.com/pe/showd...number=266-234

Amazing what 2 hours of Googling will do.
Thanks

Thanks mc.
Found it before retrieving your reply.

On Sat, 11 Feb 2006 19:50:49 -0500, "mc"
wrote:

Apparently Radio Shack has discontinued their handy attenuator, but you may
still find it at some stores. (It's red.) See also this:

http://www.partsexpress.com/pe/showd...number=266-234

Parts Express has a variety of these. They're used in custom home theater
installations to match up the volume of different non-adjustable sources, to
make it more convenient for the user.

On Sat, 11 Feb 2006 19:38:44 -0500, "mc"
wrote:

First check your sound card driver. I've had this problem and solved it by
rolling back to an earlier version of the sound card driver. The input
range that you can get a soundcard to accept is very much driver-dependent.
Try all the versions you can get hold of; the newest is not necessarily the
best (at least with Sound Blasters, which is where I ran into this
phenomenon).

Generally, the soundcard doesn't get control of the signal until it is
digitised. So it is YOUR responsibility not to overload the input of
the AD converter. Do Soundblasters have a digitally-controlled
attenuator before the AD stage?

"Laurence Payne" wrote in message
...
On Sat, 11 Feb 2006 19:38:44 -0500, "mc"
wrote:

First check your sound card driver. I've had this problem and solved it
by
rolling back to an earlier version of the sound card driver. The input
range that you can get a soundcard to accept is very much
driver-dependent.
Try all the versions you can get hold of; the newest is not necessarily
the
best (at least with Sound Blasters, which is where I ran into this
phenomenon).

Generally, the soundcard doesn't get control of the signal until it is
digitised. So it is YOUR responsibility not to overload the input of
the AD converter. Do Soundblasters have a digitally-controlled
attenuator before the AD stage?

I don't know, but I had one that definitely wouldn't accept a pro-level
signal (1 V rms) until I changed drivers, and now it works perfectly. And
then I had another instance of a very similar problem.

Digitally controlled potentiometer chips do exist, of course; I don't know
if the Sound Blaster has one.

dh wrote:
he

http://www.electronicplus.com/conten...=AS&subcat=AM3

and he

http://www.partsexpress.com/pe/showd...number=266-234

Amazing what 2 hours of Googling will do.
Thanks

That's nice....

Now, what was the question?

jak

"jakdedert" wrote in message
...
dh wrote:
he

http://www.electronicplus.com/conten...=AS&subcat=AM3

and he

http://www.partsexpress.com/pe/showd...number=266-234

Amazing what 2 hours of Googling will do.
Thanks

That's nice....

Now, what was the question?

The output of his RIAA preamp is too hot for the input of his
sound card. Four 2-cent resistors or a $5 stereo pot would fix
the problem.

Richard Crowley wrote:

Now, what was the question?


The output of his RIAA preamp is too hot for the input of his
sound card. Four 2-cent resistors or a $5 stereo pot would fix
the problem.

That's what he thinks the problem is. The specs for his sound card
and preamp suggest otherwise.

--
Eiron

I have no spirit to play with you; your dearth of judgment renders you
tedious - Ben Jonson.

"Eiron" wrote in message

Richard Crowley wrote:

Now, what was the question?


The output of his RIAA preamp is too hot for the input
of his sound card. Four 2-cent resistors or a $5 stereo
pot would fix the problem.

That's what he thinks the problem is. The specs for his
sound card and preamp suggest otherwise.

Most modern sound cards use digital attenuators if there is any input
attenuator at all. They usually have limited input voltage dynamic range.
The usual limit is 1 volt rms for consumer cards, 2 volts for some, and up
to about 7 volts for some cards designed for audio production.

Analog attenuators are avoided because they cost money and have limited
performance. Modern sound cards have up to 120 dB dynamic range with 110 dB
being not that unusual any more. In contrast, AFAIK the best
digitally-controlled analog attenuator chip that was ever sold was probaby
the Crystal Semiconductor CS 3310, which had about 95 dB dynamic range. It
could attenuate 10-20 vrms signals with low distorion.

The output level of the MKII is too high for the sound card input

You may have software control over the input level range. All of the M-Audio
cards I've seen let you specify -10, "Consumer", or +4 levels. If you have
this feature in the Audiophile's Control Panel, set the inputs to +4 and the
distortion should go away. Without having to wire up anything.