Interfacing piano keyboard to PC

Thread Starter

waltsar

Joined Nov 10, 2012
19
I've been tasked (by my grandson) to help connect a vintage piano keyboard to his laptop. It's an 80's Casio with an analog output (line out). Is there a relatively low-cost device to do this? I've considered making a 100:1 divider to reduce the line out (about 1 volt) down to 1 mv (mic in) - I believe the mic input to a typical PC has a built-in A to D converter. If I get any positive answers to these questions I'll have lots of additional questions about input, output jacks, cables, audio software, etc.
 

Ya’akov

Joined Jan 27, 2019
9,069
Welcome to AAC.

What you need is a pad, which is a specialized voltage divider to deal with impedance matching. You will need about 35dB of attenuation to go from the expected line level output of -10dBV of the keyboard (about 316mV) to the expected mic level input of about -40dBV (about 10mV).

The pad also needs to match the line out 10㏀ impedance with the mic input expecting somewhere around 200Ω from an electret condenser microphone.

This article is an excellent source of information of various versions of pads. The L pad is the simplest and most common option for this application. If you have stereo out, you will need two pads with a common 0V.

You will also need to block DC with a capacitor since the mic input could be trying to power an electret mic expected at the other end of the cable. This should be chosen carefully as it can effect the frequency response.

Does this happen to be a CZ-01?
 

MisterBill2

Joined Jan 23, 2018
18,167
I just had to do a similar connection a week ago: feeding a laptop computer audio output to an installed sound system that only had a microphone input available. "Y" had good advice, but in my case total isolation of the commons with a transformer was needed because somehow the buzz on the mains power, from all of the light dimmers, was present on the computer signal common, and getting into the sound system input, which was a balanced XLR connection. So in addition to the attenuation a small, even tiny, audio transformer should be used to isolate the commons side of the signal path as well.Then there can be none of the "ground loop" problems.
 

Thread Starter

waltsar

Joined Nov 10, 2012
19
Welcome to AAC.

What you need is a pad, which is a specialized voltage divider to deal with impedance matching. You will need about 35dB of attenuation to go from the expected line level output of -10dBV of the keyboard (about 316mV) to the expected mic level input of about -40dBV (about 10mV).

The pad also needs to match the line out 10㏀ impedance with the mic input expecting somewhere around 200Ω from an electret condenser microphone.

This article is an excellent source of information of various versions of pads. The L pad is the simplest and most common option for this application. If you have stereo out, you will need two pads with a common 0V.

You will also need to block DC with a capacitor since the mic input could be trying to power an electret mic expected at the other end of the cable. This should be chosen carefully as it can effect the frequency response.

Does this happen to be a CZ-01?
Thanks for the reply - much appreciated. The cable with L pad sounds like it would do the job perfectly. The keyboard is a Casio CT-607.
 

Thread Starter

waltsar

Joined Nov 10, 2012
19
I just had to do a similar connection a week ago: feeding a laptop computer audio output to an installed sound system that only had a microphone input available. "Y" had good advice, but in my case total isolation of the commons with a transformer was needed because somehow the buzz on the mains power, from all of the light dimmers, was present on the computer signal common, and getting into the sound system input, which was a balanced XLR connection. So in addition to the attenuation a small, even tiny, audio transformer should be used to isolate the commons side of the signal path as well.Then there can be none of the "ground loop" problems.
Thanks for the reply - Much appreciated.
 

MisterBill2

Joined Jan 23, 2018
18,167
None of my current laptops have a line in or out. Evidently there was not enough demand for that function, so it was deleted. All in the name of increased profits for the seller.
 
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