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Audio output for Yamaha PSS-100 square wave keyboard!
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author Audio output for Yamaha PSS-100 square wave keyboard!
Hawk
Hi all, hoping to add a line level audio output to a Yamaha PSS-100, and improved volume control for the internal speaker as well. Fantastic sounding keyboard. I don't know how to go about this though, and I'm hoping someone here can help me. Soldering is no problem, done many mods over the years, but I'm an instruction follower and not an electrical engineer. If someone can help me, I'll take photos and document the process in this thread so others can follow help

I highlighted the amp on the circuit diagram, it is a TA7368P. You can find the datasheet here: TA7368P Datasheet Is it correct to think that I'll find line level audio at pin 1 of IC4? If so, do I need a capacitor or any sort of protection in-line before the output jack? The service manual is here to view the circuit diagram in high resolution: PSS-100 circuit diagram

Also, I'd like to add volume control for the built-in speaker since the panel volume control truncates the length of the sound and at the default volume (maximum) it is loud as hell!. I see that a person built an amp using the TA7368P here: TA Amp and used a trimmer resistor as volume control directly before the signal enters the amp. In the Yamaha circuit there is a 4.7K resistor directly before the signal enters the amp, would replacing this 4.7K resistor with a variable resistor be the appropriate way to add volume control? If so, what value of variable resistor should be used? If not, how would I accomplish the equivalent? Or, should should volume control for the speaker be done on the output side of the amp?

MikeDB
Run a separate 1uF capacitor from pin 15 of IC3 to the live side of the new output jack, and ground to the other side of the jack. Then probably a 10k resistor across the jack.
Hawk
Hi Mike, thanks for your reply. Is there a reason to get the signal from pin 15 of IC3 rather than pin 1 of IC4? It looks like the beep gets added after that + a cap and resistor before it gets to the amp, I don't know what the significance of those components are but I'm curious. Also, when you say a 10K resistor across the jack, do you mean a resistor bridging the ground and live? What does this do? I appreciate your help!!!
MikeDB
Yes -loading the input of IC4 may change the signal, probably reducing high frequencies. Connecting direct to IC3 (or more probably soldering to the correct end of the 2.2k resistor because it's easier) will give the original signal.

But yes you could try connecting at the line marked BEEP instead and see if this sounds better or worse.

The 10k across the jack reduces turn on or plug in pops.
Hawk
I see, I'll get out a breadboard and try both sources. Thank you very much for your help. I also want to be able to turn the internal speaker off when needed, would there be any ill effects if I cut the trace right before leg 1 of the amp and wire in a switch to disconnect it when needed? Will IC4 experience issues if it has nothing connected to the input?

Also, does anyone have any ideas for adding volume control for the internal speaker?
MikeDB
Here you go
[img]Picture file[/img]

C2 should be the 4700pF already there but I forgot to set the value. Anyway it should do all you need.
Hawk
Mike you are the king! Thank you for taking the time to do that for me, can't wait to open it up and do this mod. I wish this keyboard had a built in delay, then it would be perfect. I'll post pictures here of the mod, and I'll let you know if I have any questions

edit: Mike, if I'm reading this correctly the 4.7k resistor is removed and replaced with with the 10k variable resistor R1? This is extremely helpful. Also, do you think disconnecting the line running to leg 1 of IC4 in order to disable the internal speaker would be harmful to the amp? I'm assuming no, but want to be sure.
MikeDB
Hawk wrote:
Mike you are the king! Thank you for taking the time to do that for me, can't wait to open it up and do this mod. I wish this keyboard had a built in delay, then it would be perfect. I'll post pictures here of the mod, and I'll let you know if I have any questions

edit: Mike, if I'm reading this correctly the 4.7k resistor is removed and replaced with with the 10k variable resistor R1? This is extremely helpful. Also, do you think disconnecting the line running to leg 1 of IC4 in order to disable the internal speaker would be harmful to the amp? I'm assuming no, but want to be sure.


It should be ok. May cause a click but if you can live with that then fine
Hawk
Just got the parts in the mail for this project. I know it's veeeery simple in contrast to many projects on muff, but I still appreciate the help. I've been playing this PSS-100 pretty much every day, it's going to be great to hear it with some delay and reverb. I'll post some photos and a finished pic once I've got it all wrapped up.
jorg
"Beep" might be a signal that drives a beeper (piezo speaker) - so an output rather than input.
Hawk
The beep gets mixed in with the rest of the audio, it sounds when a button on the control panel is pressed. When you're using the voice variator controls, the beep stops sounding when you've reached the far range of that parameter. It's useful but it can be annoying if you want to modulate a parameter as you play. I don't think the beep is used in any of the percussion tracks, but I'll disconnect it temporarily when I open the keyboard to test and see.
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