Logitech Z130 Hack: Gain Modification

The Logitech Z130 is based on a BT2025BH stereo amplifier chip. The gain is set to 36 dB using a 100 ohm resistor along with a 100 uF capacitor. The gain was modified by placing a jumper across the 100 ohm resistor to get the chip's maximum gain of 46 dB

I tested this with the volume turned down. The increased gain had a more noticeable effect at higher volumes, but it was still not enough for my purposes.

The goal is to use this amplifier with an electric piano. I found that it would not put out enough sound to act as a monitor speaker even with everything turned up.

Category:

Science & Technology

Tags:

• logitech
• z130
• hack
• gain
• modification
• diy
• computer
• speaker
• amplifier
• Sound
• Do It Yourself
• Audio

[Caleb6543]

@RDELAPLAZA We could defeat the connection that cuts out the piano speakers. I don't mind hacking some inexpensive computer speakers, but I'd rather not mess with an expensive piano.

[Caleb6543]

@RDELAPLAZA The piano is a Yamaha YDP-135. It only has one MIDI output and two headphone outputs. We can feed one headphone output into the building sound system, but then the piano speakers cut out so the pianist can't hear what she is playing very well. She could wear headphones, but then she couldn't hear what is going on around her. We may end up getting a keyboard monitor, but I'd like to try this approach. :-)

[RDELAPLAZA]

@Caleb6543 Your piano probably has ways to get the signal out of it.

1st.- will be the signal out, destined to be fed to a regular instrument amplifier

kind of low level.

2nd.- will be the headphones signal out, coming from the audio amp that feeds the instrument (piano) speakers - this signal should be a lot higher and you will be able to adjust it with the volume control - Use this one -

Then it's possible that anything of what I said is applicable.. he he

let us know

[Caleb6543]

@RDELAPLAZA I understand what you are saying, but the 5 Watts should be plenty loud for what I want to do with it. If I send it a strong signal from my boom box, it will put out a lot of sound. The problem is that the piano sends out a weak signal so the speakers never end up putting out anything near the 5 Watts. My father had a good suggestion; put two computer speakers in series with one being fed by the earphone jack of the other. :-)

[RDELAPLAZA]

You want it to sound LOUDER...

you will need more WATTS or MORE POWER.

This thing is limited to 5 watts.

More gain is going to STOP at the output stage... as simple as that.

Then you will need BIGGER Speakers able to withstand that power.

If it were NOT like that...

You could provide a rock concert sound level for a 150000 people stadium with your gadget

... just raising the gain as much as you wanted...

I think I made my point, you can do only so much with 5 watts

is it not ?

[Caleb6543]

@definitionofis If I turn up the volume on the radio I was using as a test signal, the speakers can get plenty loud. I'm just not sure why the signal from the electric piano is so weak. I don't think the pre-amp would have to have a huge gain; perhaps 20 dB or so. For grins, I might just try using a single transistor amplifier. I'm not terribly worried about distortion because the speakers are just to be used as monitors.

[definitionofis]

Maybe the power output end needs the bigger potential, not the pre-amp end. I guess you can tell when the sound gets distorted by a pre-amp. Can you tell ahead of time by feeding in a bigger signal?