Vintage Synth Repair

Hello to all.  My ARP SOLUS produces a "thump" whenever the envelope triggers.  It's not a 
mechanical noise...it's akin to tapping the end of a cable while it's plugged into an amp/
speaker.  I tried to troubleshoot by using the external audio input just to confirm that it 
wasn't the j-wire/bus bar contacts, but I can't get anything to trigger the solus (wurli, 
guitar, korg ms20 are what I tried).  I guess I need to preamplify.  Anybody dealt with 
"thumps" before?...the bad kind, that is!  Thanks--Stephen

Does it do that when the envelope controls both the filter and amp? 
When you say it sounds like a cable being tapped, do you hear a 60Hz 
hum for a second? Or is it more like turning off the power to 
something still plugged into an amp? If you turn off the ADSR, does 
it make those noises?
-Mike

--- In vintagesynthrepair@yahoogroups.com, "easterleggs" 
<milotoll@h...> wrote:
> 
> Hello to all.  My ARP SOLUS produces a "thump" whenever the 
envelope triggers.  It's not a 
> mechanical noise...it's akin to tapping the end of a cable while 
it's plugged into an amp/
> speaker.  I tried to troubleshoot by using the external audio input 
just to confirm that it 
> wasn't the j-wire/bus bar contacts, but I can't get anything to 
trigger the solus (wurli, 
> guitar, korg ms20 are what I tried).  I guess I need to 
preamplify.  Anybody dealt with 
> "thumps" before?...the bad kind, that is!  Thanks--Stephen

Another question for you more knowledgable than I:  Could the ARP "VCA thump" I've read 
about on the Omni also apply to the Solus?  If so, does this require a power supply repair 
or a VCA circuit trim pot adjustment?  My Solus makes a loud thump/pop every time fresh 
contact is made between J-wire and bus bar.  It is generally irrespective of ADSR or 
Resonance settings, though a very long attack will mitigate the pop slightly.  Any 
suggestions as to how to proceed with repair?  Thanks--Stephen Nichols