audio impedance matching/volume control

[tgsimmons]

I've got a low power (50 mw), 16 ohm differential (sp+, sp-) audio output from a Winbond ChipCorder that I want to feed to a single input audio amplifier with a 20-40K input impedance (Hitachi HA1318). I also need to control the volume in the process. What's the best method of doing this?

[viveguy]

A small transformer and a potentiometer would be the easiest. You can find small,inexpensive transformers at Mouser (mouser.com). You can also find solutions at epanorama.net. Click on the audio links heading.

[Externet]

Hi.
Use a potentiometer of any value, connecting its extreme terminals to the balanced outputs of the 50mW amplifier and the wiper terminal to the Hitachi input.
The balanced source should be useable unbalanced, so connect the ground of the Hitachi input to any of the extreme terminals of the potentiometer.
Miguel

[Ron H]

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by Externet:
Hi.
Use a potentiometer of any value, connecting its extreme terminals to the balanced outputs of the 50mW amplifier and the wiper terminal to the Hitachi input.
The balanced source should be useable unbalanced, so connect the ground of the Hitachi input to any of the extreme terminals of the potentiometer.
Miguel<hr></blockquote>
Don't do this if the ChipCorder and the Hitachi have a common ground, or you'll short out one of the ChipCorder outputs, which the datasheet specifically warns against. I found this text in both datasheets I looked at:
***********************
SP +, SP- (Speaker +/-)
This is the speaker differential output circuit. It is designed to drive an 8Ω speaker connected across the speaker pins up to a maximum of 23.5 mW RMS power. This stage has two selectable gains, 1.32 and 1.6, which can be chosen through the configuration registers. These pins are biased to approximately 1.2 VDC and, if used single-ended, must be capacitively coupled to their load. Do NOT ground the unused pin.
******************************
If the ChipCorder is battery powered, or has an isolated power supply, it should be OK.<p>[ June 30, 2004: Message edited by: RonH ]</p>