Soundlab MkII - eg bleed

amongstmyselves · Posted: Mon May 30, 2016 8:37 pm Post subject: Soundlab MkII - eg bleed

Hi all,

I'm having a small issue with bleed coming from both envelope generators. With modulation levels to either VCOs turned down I still get a small amount of pitch modulation.

Anyone else had this issue ? Is it just the way the unit operates ?

Cheers,

Steve

elmegil · Posted: Tue May 31, 2016 7:41 am Post subject:

Definitely not "just the way it operates".

Sounds like maybe bad grounding? Check your solder joints....

amongstmyselves · Posted: Tue May 31, 2016 3:56 pm Post subject:

thanks for that elmegil. At least I now know that there shouldn't be any bleed.

I thought that grounding could be the issue. Due to custom case I was trying to avoid having to access the board as requires removing all the wires Crying or Very sad

At least the connections are all plugged.

Cheers,

Steve

bence · Joined: Jan 12, 2013 Posts: 17 Location: Budapest, Hungary

hi!
did you solve this?

mine also behaves similarly, with the EG-s set to Gate mode there's a small and constant pitch drop (max 20 cents maybe) during the attack and sustain stages (independent of attack and decay times). affects both vcos and the vcf too.
with both EGs set to Gate mode and both in the attack/sustain stage the pitch drop is around twice as large.
i suspect bad decoupling caps and/or too high current somewhere around the EG section...or bad wiring. will have to check it.

is your problem similar?

amongstmyselves · Posted: Wed Jun 22, 2016 5:16 pm Post subject:

Sounds very similar to my issue.

No I have not solved it. I was hesitant to spend lots of time with the wiring. My unit is a little more complex as I have a Theremin and Echo Rockit in the unit.

One thing I did notice is that I get a definite voltage drop on the power line going into the unit when this happens. I tried doing more power regulation closer to the boards as my power supply is in a separate unit with a couple of metres of cable on it. This did make it less obvious but not enough to modify the unit.

At this stage I am considering the unit working with this small caveat. If I don't use the EGs in a sound I can simply switch them off as I have a middle position on the EG repeat source switch which is off. I can't remember if this was part of the original design ?

All the best with it. If you do manage to find a solution please share.

Steve.

elmegil · Posted: Wed Jun 22, 2016 5:56 pm Post subject:

What are y'all using for power supply?

amongstmyselves · Posted: Wed Jun 22, 2016 6:10 pm Post subject:

MFOS Adjustable LM317/LM337 1.5A Supply with a 12-0-12vac 20VA toroid transformer which is 0.8A for each rail. Should be heaps.

Oops. Just had a look at the power supply as I couldn't remember the transformer size and one of the 10000uF caps is leaking. Not good. Don't think this is cause of the problem though.

bence · Joined: Jan 12, 2013 Posts: 17 Location: Budapest, Hungary

i'm using an external 12vac adapter with something like Ray's wallwart psu on a small perfboard: 2 diodes, 3x3300uF per rail, 7812/7912 with small heatsinks.
the supply wiring for the front panel and for the pcb are separated at the psu board, so even if the EG circuit on the pcb draws high current it shouldn't cause supply voltage drop on the front panel - that is if the psu is all right. have to check that too.

also can check this: connect the wipers of all pitch pots (X14,15,27,28/vco/ and X2,11/vcf/) to gnd and see if the pitch drop still happens.
if it does then a possible workaround could be to create a stable voltage for the pitch pots with a pair of low current regulators (say 78L09, 79L09). however with a good psu and separate supply routing this shouldn't be necessary.

mine is a bit messy inside and not so easy to work on, but gonna investigate this once i have the time.

amongstmyselves · Posted: Thu Jun 23, 2016 4:27 pm Post subject:

Hmm. Good idea Bence. I'll give that a try soon.

Steve