Vintage Synth Repair

Hey guys,

I figured you all have run into this problem before and I haven't yet.

I have an SH101 that I've been running off of batteries because when i plug in a power supply it creates a very loud hum. I went in and replaced the two caps that were nearest the power jack with no success. 

Any other ideas? I have the schematics now and I'm gonna take a closer look at this supply, but I'd appreciate any inpute.

Thanks,
Johnny

--- In vintagesynthrepair@yahoogroups.com, Philip <eggwheatis@...> wrote:
>
> SH-101's are supposed to run on regulated supplies like the Boss PSA...if you run it on the unregulated version (ACA?) or any other unregulated supply it will hum badly.
> 
> Phil.
> 
> 
> 
> 
> 
> 
> 
> 
> Most wall-warts have crappy filtering and/or regulation.
Find one that's spec'd for the Synth
>

Above all, remember that SH-101's power connector is wired opposite of
nearly everything else on earth. Some of the Radio Shack
multi-wall-wart adapters will let you reverse the polarity in addition
to changing the voltage. There have been hundreds of SH-101s trashed
from people just hooking up a regular DC wall wart to it's backwards
DC input.

I'm pasting this in it's entirety from
http://www.guerillasofsoul.com/chad/sh101/101mod.txt  Sometimes things
from 15 years ago slip through the cracks on the web. At the very end
are some notes that 15vdc is better. I have an SH-101 and a variable
DC power supply, but have not tried this.

****************************************************************************************

Voltage Controlled Amplifier/Filter Input:

you will need: a screwdriver
               a soldering iron + solder
               one 1/4" phone jack
               some scrap wire
               1uF capacitor (not totally necessary)

what to do:    open up the back of the sh.101 with a screwdriver. the middle
               screws are of smaller threads and must go back in the same
               place, so if all else fails, remember these two.

               bore a hole (i used a soldering iron) into a open spot on the
               uppper portion of the sh.101--mine is right beside the battery
               cover to the left. this is where you will want to have your 1/4"
               phone jack to be stationed...from here you should solder the
               negative side of your jack to the ground trace of the lower
               breadboard (scratch off the green coating and solder directly to
               the copper board.)

               use some of the scrap wire to connect the positive side of the
               jack to the capacitor. from the free end of your capacitor, you
               should solder another wire to connect it to the right hand side
               of the resistor R109. (are one oh nine...haha) it is located
               under the "VCF width."

               you don't HAVE to use the 1uF capacitor, but it suppresses the
               fat clunk you would get if it wasn't there. my sh.101 is noisy
               enough as it is...

 Frequency Modulation input:

               do the exact same thing as above, yet you should: replace the
               capacitor with a potentiometer. bore two more holes in the unit
               (more of that nasty smell!) and place the pot and the jack out
               near the other jack on the unit. the positive end of the jack
               should be going through the right lead of the pot, then out
               through the center lead of the pot, then connect a jumper wire
               to the left side of the resistor R107, directly below R109. the
               negative side of the jack should also go to the ground. got it?


MORE FUN THINGS with a Roland SH.101:

               take the output and send it back through the FM input. sounds
               great when you twiddle the potentiometer as well as the ENV
               filter in unison. hold....

               send a CV output to go back into the gate input, and vice versa.

               send a CV signal (from a tb.303, perhaps?) into the CV in of the
               sh.101 and plug the jack in and out, and twiddle it around. it
               changes voltages and makes it sound like your signal is ....
               "liquified.."

               send only a gate signal into the sh.101 and listen (esp with a
               tb.303... ahh...)

my friend andy has two more mods, but i can never get in touch with him. we
play with his band this sunday, so maybe we will get in touch.


sines
--
  /\    /\    _________________s i n e w a v e___________________    /\    /\
 /  \  /  \  /    todd sines: tsines@...-state.edu   \  /  \  /  \
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Date: Thu, 8 Apr 93 03:38:23 -0400
From: jna@... (mail)
Subject: Re:  finally, the sh.101 mods.

Some comments about the SH-101 mods, from a guy who doesn't even own one:

SI> ....breadboard (scratch off the green coating and solder
SI> directly to the copper board)

DON'T DO THIS.

Copper oxidies over time, causing RESISTANCE in the circuit. That's why it's
sprayed green. Follow the ground plane to a component that is soldered into
the board. Melt some of the solder and use this for ground.

SI>  don't HAVE to use the 1uF capacitor, but it suppresses the
SI>  fat clunk you would get if it wasn't there. my sh.101 is noisy
SI>  enough as it is...

the 1uF cap acts as a noise filter / decoupling capacitor.
Use it.




Solution:

APPLY HEAVY CAPACITANCE TO THE DC SIDE OF A WALLWART FEEDING AN SH-101.
   470uf.....mild improvement
 1,000uf.....acceptable improvement
10,000uf.....equivalent to lab test bench supply

You can mount the capacitor in the 101 or on the cable feeding the 101
from the wall wart transformer. Note the 101's center pin on it's DC
jack is - while the sleeve is +


Finally I experimented with the variable power supply and found the 101
to be quiet at 15Vdc in. 9V is much noisier.
At 15V the 101 draws only 150mA.

On 5/27/09, Scott <painintheamp@...> wrote:
> --- In vintagesynthrepair@yahoogroups.com, Philip <eggwheatis@...> wrote:
>>
>> SH-101's are supposed to run on regulated supplies like the Boss PSA...if
>> you run it on the unregulated version (ACA?) or any other unregulated
>> supply it will hum badly.
>>
>> Phil.
>>
>>
>>
>>
>>
>>
>>
>>
>> Most wall-warts have crappy filtering and/or regulation.
> Find one that's spec'd for the Synth
>>
>
>
>