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Messages - aruption

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31
Amplifier Discussion / Re: Hohner Pianet Amplifier Low Output
« on: April 15, 2018, 04:01:13 PM »
I was starting to figure that the problem might be in the transistors. I have two AD130s on order right now - those are the two labeled 5 and 6 in the diagram. 

By "bottom power transistor" you mean the one at the bottom of the schematic that is labeled 6 in the diagram, correct?  And that should read 15V on the emitter?  I got 8.5V on both the emitter and collector of that one with my DMM.

32
Amplifier Discussion / Re: Hohner Pianet Amplifier Low Output
« on: April 15, 2018, 02:11:48 PM »
All three volume controls I've tried do the exact same thing.  Seems unlikely to me that they would all have a break in the wafer at the same spot.  That's why I'm wondering if there's something else in the circuit that would cause this.

33
Amplifier Discussion / Hohner Pianet Amplifier Low Output
« on: April 15, 2018, 11:17:56 AM »
Not a guitar amp, but I'm hoping someone here might be able to help me out!

I've had a Hohner Pianet L for about a year now.  For those of you who aren't familiar with it, it's the first solid state electric piano that Hohner produced.  This particular model has built in speakers.  More info and schematics are here: http://hohner-pianet.com/hohner_pianet/pianet_L_LB.html

It's come a long way from when I bought it, when it made no sound at all.  All of the caps have been replaced as well as most of the resistors and the volume pot.  Mechanically, everything is in perfect shape.  The main problem I'm still fighting is a rather low volume output.  Compared to the other Hohner electric pianos I own (Pianet N and Cembalet N), this one just does not have the same volume.  It is very quiet until the volume pot reaches about 80%, then there is a sudden increase in volume AND distortion.  This volume level is closer to where I believe it should be, but the distortion doesn't seem right.  Overall, there is a buzzing in the background which isn't much worse than say the buzz from a Strat pickup.  The level of this buzz (and any other background noise) is affected by the volume pot in the same manner as the actual piano sound.  The output sounds the same through both the internal speakers and the output jack.  Also, I've tried three different volume pots now, all with the same results.

I've come to this forum because I'm hoping that someone with experience in SS amps in general might be able to help me out.  I've brought this up on other vintage keyboard forums, but haven't really gotten anywhere.

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