MUFF WIGGLER Forum Index
 FAQ & Terms of UseFAQ & Terms Of Use   Wiggler RadioMW Radio   Muff Wiggler TwitterTwitter   Support the site @ PatreonPatreon 
 SearchSearch   RegisterSign up   Log inLog in 
WIGGLING 'LITE' IN GUEST MODE

Q107 SVF + MOTM 730 Pulse Divider = noise
MUFF WIGGLER Forum Index -> 5U Format Modules  
Author Q107 SVF + MOTM 730 Pulse Divider = noise
jonat8han
Hi,

Anyone else got a Q107 & a MOTM 730 on the same power supply? I'm getting a faint pulse tone (at around middle C - I haven't measured the exact frequency) out of the Q107 with nothing plugged into it. I've traced this back to the MOTM 730 Pulse Divider. If I disconnect the 730, the tone goes away. If I power up the system with *only* the 730 & Q107, I get the tone. The tone seems to be passed through the Q107 as I can filter it.

Some more specifics:

The modules are not connected. The extent of my "patch" to reproduce this is lowpass out (though all outs work) from the Q107 to my soundcard input.

No other modules are producing this tone (that I can find)

the tone's pulsewidth (but not frequency) is changeable via the 730's Init Div knob.

The modules are about 3-4 feet away from each other in the cabinet.

I'm using an MOTM-995 adapter board from a dotcom QPS-1 power supply & dotcom power harness to power the 730.

I have a lot of other MOTM format modules, but the 730 is the only one that takes +5v. Though, I used to have a 650 and didn't notice this problem with it.


Any ideas?
SynthBaron
The Q107 doesn't use the +5V rail. May be grounding issue.

I recall having bleed through problems in the past with the Q107, so this may be something inherent to the design.
JohnLRice
I think I encountered something similar once (no Q107 here though), but I forgot about it. I'll see if I can reproduce it later.
jonat8han
I actually tried cutting the +5v wire on a dotcom power connector & connecting the Q107 that way. no luck, though.

also, I've tried the whole rig with a ground-lift - same problem.
Girts
have you tried to change the Q107 location from the PSU?
I had all sorts of oscillations and clock signals coming through Q107 until I placed it away from PSU as far as possible and then Q107 was much quieter. That was before I had 730, though.However, my 650 produced nasty oscillating tone in various frequencies depending of the LCD brightness. I decided to put 650 and 730 on separate PSU and now everything is fine.
jonat8han
It's pretty far away from the power supply (2-3 feet) but if I disconnect the 730, the Q107 doesn't produce any noise.

maybe a separate power supply is the key, though. bummer. seems like a waste for one module ...
russma
Simple solution really.

Send the 730 to me.

That is all.


Guinness ftw!
jonat8han
just leave it patched up to your phone line so when I need subdivisions, I dial you up
Just me
You could try to additionally filiter the power supply at the MOTM module to prevent it from bleeding back into the power buss.
jonat8han
can you give me an example of what I'd need to do that?
Spiked Lunch
My Q107 is quite noisy too, I don't get any bleed but I do get mains hum from it. It's kinda quiet so 99% of the time not an issue but I wish it wasn't there Rage!
doctorvague
jonat8han wrote:
Hi,

Anyone else got a Q107 & a MOTM 730 on the same power supply? I'm getting a faint pulse tone (at around middle C - I haven't measured the exact frequency) out of the Q107 with nothing plugged into it. I've traced this back to the MOTM 730 Pulse Divider. If I disconnect the 730, the tone goes away. If I power up the system with *only* the 730 & Q107, I get the tone. The tone seems to be passed through the Q107 as I can filter it.


Interesting. I'm having a very similar problem with my Modcan digital delay producing a faint background tone like that around the same pitch too, even with all controls zero'd out both sides produce the same tone. It's not 60 cycle hum. Unfortunately there's no way to really troubleshoot without yanking my whole system and disconnecting every module, etc. I don't have a 730 but I do have a 650 at the other end of the cabinet. I did try pulling the Modcan as far out of the cabinet as I could and proximity didn't seem to have an effect, so the next thing to try would be a process of elimination to see if something is dirtying the power supply rails or ground. I guess I could scope the supply rails, i hadn't thought of that. How would you scope a 'dirty ground'? Not sure about that one... I did scope the Modcan output to see what the tone looked like but that didn't give any clues. Bruce didn't have any ideas other than send it in for repair. He hadn't heard of this problem before.

What makes a dirty ground and how do you deal with it? Extra filter caps? Where do you put them? Perhaps they could be kluged onto the power cable to the Modcan at the connector? I've read where LED's can dirty the ground but don't really understand much about this issue, TBH. Would running a direct separate ground wire help? If there's noise on the power rails that's a different issue than a dirty ground, yes-no? I have way more questions than answers on this one...
russma
jonat8han wrote:
just leave it patched up to your phone line so when I need subdivisions, I dial you up


Hey now...that's interesting!...


hmmm.....

thumbs up
cornutt
The MOTM-995 supports separate analog and digital grounds. Possibly, connecting it to the QPS-1 via the Dotcom power harness is leaving the digital ground floating. You might want to try connecting a wire between the two ground terminals (the +/-15V ground and the +5V ground) on the 995. I think there's also a jumper on the MOTM-730 that straps the two grounds together; you might want to try removing that once you have them tied together at the 995.
SynthBaron
I'm looking at my 995 right now, and all the grounds are connected.
cornutt
SynthBaron wrote:
I'm looking at my 995 right now, and all the grounds are connected.


Hmm. I may have misspoke. I'll go look at one closely tonight. I've got one still in the bag, so it'll be easy to check.
SynthBaron
It may be seperate on the MOTM distro board, but since DotCom has no seperate digital ground there's no reason not to connect them.
kindredlost
The Q107 is notorious for bleed through hum. I get it from oscillators. No placement will eliminate it.

I've even sent mine back for testing. Tested good.

Fortunately, the levels are relatively low so any sufficient signal through the filter will mask out any hum. (or so I've found) I find it to be rather unimportant now. It has never interfered with a project yet.

Just saying.
Just me
The only times I get ANY hum out of my Q107 is when it is ground looping through my Voyager's VX-351. I've been very happy with how quiet the whole synth is.
jonat8han
Just pulled out my continuity tester, and it seems like all three ground pins on the MOTM 6-pin connector are connected on my 995 board ...

also, there don't seem to be any jumpers on the 730 ...

maybe should I try removing the ground for the +5v on the cable going to the 730?

I wish I knew more about this.

any other ideas? maybe if I were powering dotcom modules from an motm supply with separate grounds this wouldn't be happening?
MUFF WIGGLER Forum Index -> 5U Format Modules  
Page 1 of 1
Powered by phpBB © phpBB Group