Demeter compulator with a static/crackling noise

Discussion in 'Pickups & Electronics [BG]' started by Ray man, Feb 6, 2014.


  1. Ray man

    Ray man

    Joined:
    Nov 5, 2009
    Location:
    Staten Island NY
    It seems that the more it squishes the signal, the more crackling is audible. My guess is that it may be the compression pot. I can't be sure, but I think it gets worse depending on the position of the knob.
    Thats the best I can describe it. I tried cleaning it but no help, although it dosn't have the same kind of sound that a dirty pot makes.

    So far I've replaced the power supply, power jack, trimpot, stomp switch and the LED.

    Hmm...
  2. Ray man

    Ray man

    Joined:
    Nov 5, 2009
    Location:
    Staten Island NY
    Any ideas?
  3. SirMjac28

    SirMjac28 Patiently Waiting For The Next British Invasion Gold Supporting Member

    Joined:
    Aug 25, 2010
    Location:
    The Great Midwest
    Have you contacted Demeter? they have great customer service.
  4. bongomania

    bongomania Gold Supporting Member

    Joined:
    Oct 17, 2005
    Location:
    PDX, OR
    Disclosures:
    owner, OVNIFX and OVNILabs
    I'd guess there could be a bad solder joint around the opto element, or a failing capacitor near there. So I'd try re-flowing any dry-looking solder, and replacing caps one at a time to see if that helps.

    Or just contact Demeter. :) Actually their customer service is hit-or-miss, I've seen equal numbers of people proclaiming "excellent" CS and people saying Demeter ignored and failed them. But you can't win if you don't play, so call them.
  5. SirMjac28

    SirMjac28 Patiently Waiting For The Next British Invasion Gold Supporting Member

    Joined:
    Aug 25, 2010
    Location:
    The Great Midwest
    You're right Bongo I have to remember to say "my experience"instead of making a blanket statement because you never know who's going to answer the phone or ignore an email but I would definitely hit them up.
  6. Ray man

    Ray man

    Joined:
    Nov 5, 2009
    Location:
    Staten Island NY
    Ok, calling Demeter would be the next step, although I bet you guys could figure it out just as easy so I guess we can give it a shot.

    The solder joints look nice and shinny and nothing seems loose, messy, or bridged together, but I will check yet again.

    Would you rule out the comp pot?
  7. bongomania

    bongomania Gold Supporting Member

    Joined:
    Oct 17, 2005
    Location:
    PDX, OR
    Disclosures:
    owner, OVNIFX and OVNILabs
    Well I wouldn't rule anything out, on principle. But based on your description it might be more likely that the parts that the pot controls are at fault, not the pot itself.
  8. Ray man

    Ray man

    Joined:
    Nov 5, 2009
    Location:
    Staten Island NY
    Ok lets assume your right, I wouldn't know what part to look at since my knowledge stops here.
    I would have no problem changing it if you can point out what comes next.

    [​IMG]

    Otherwise I have to call Demeter, although I realy want to do it myself if possible.
  9. boomertech

    boomertech Supporting Member

    Joined:
    Apr 8, 2009
    Location:
    Syracuse, NY
    Disclosures:
    Designer/Owner of FEA Labs
    Have you always had this problem or did it just start?

    -Frank
  10. Ray man

    Ray man

    Joined:
    Nov 5, 2009
    Location:
    Staten Island NY
    Well, it's easy to miss unless pointed out, it could have always been there but I first noticed it while using headphones. It's a continual crusty/fizzy noise as the compression squeezes the decaying note.
  11. boomertech

    boomertech Supporting Member

    Joined:
    Apr 8, 2009
    Location:
    Syracuse, NY
    Disclosures:
    Designer/Owner of FEA Labs
    This circuit has no filtering in the compression control circuitry (AKA the sidechain). So I think what you are hearing is the bleed thru from the sidechain circuit on the virtual ground that also is connected to the audio path.

    You can try to lessen the fizz by slowing down the current driver for the LED in the VTL5C10 opto. You will need to connect a capacitor across pins 6&7 of the opamp on the left side of the board. I would start with a 0.01uF and increase the value as needed. This modification changes the opto’s control driver from an On-Off drive to a smoother ramping integrator drive to lessen the current spikes.

    -Frank
  12. Ray man

    Ray man

    Joined:
    Nov 5, 2009
    Location:
    Staten Island NY
    Is this just the way it was designed, or is it or is this a symptom of something failing? I might be able to live with it, unless it gets worse.

    The opamp is the little 8 legged black thing that looks like a robot bug? It will be a pain to solder on that, but I can manage.
    I'll take a trip to the shack tommorow for some caps.


    Why did Demeter not include this?
  13. boomertech

    boomertech Supporting Member

    Joined:
    Apr 8, 2009
    Location:
    Syracuse, NY
    Disclosures:
    Designer/Owner of FEA Labs
    I doubt something is failing, because there are only a few components in there that might fail… the majority of the components are resistors. From how you described the noise, the opamps (robot bugs) and opto appear to be functioning correctly. I have seen the same type of noise that you are describing in other circuits. In those circuits it has been bleed thru, component pickup or excessive current spikes on the internal power paths.

    If possible try soldering the cap on the back of the PCB instead of directly on the IC legs. There is also a 10K resistor from pin 6 to pin 7 that you can piggyback.

    The mod I have suggested isn’t something that Demeter forgot to add. I suspect that the lack of filtering is due to the opto he chose to use. The reaction of the light dependant resistor (LDR) in this opto is slow enough that technically you can get away with little to no filtering in the sidechain. This pedal was designed for guitar, so the noise that you hear with your bass may not be as audible with guitar frequencies.

    -Frank
  14. Ray man

    Ray man

    Joined:
    Nov 5, 2009
    Location:
    Staten Island NY
    I may just have to accept it. The solder side of the pcb has the pot mounted directly over the solder joints. It's so close that there are foam pads stuck to the back of the pot to keep it from shorting.

    Do other bass players have this noise with the compulator? I would assume so they since it's the same design. IOW if I tried a bunch of different compulators, wouldn't they behave the same?
  15. MR PC

    MR PC

    Joined:
    Dec 1, 2007
    Every piece of gig orientated Demeter gear I've owned has had solder joint problems. Don't know anything about his higher end studio pieces. My experience with customer service was always spotty. Great designs. I just ended up taking my problems to a local tech who went through and resoldered. In the case of my Tube DI, it was pretty much the whole thing. In the case of my Tube Bass 201 preamp, it was a faulty trim pot causing signal output failure. Service manager was a d*** on the phone both times. With the pedals, again,great designs. But faulty soldering with all 3 units I owned and really cheesy stomp switches.

    I hear the company has taken a turn for the better, sure hope so. Great designer.
  16. Ray man

    Ray man

    Joined:
    Nov 5, 2009
    Location:
    Staten Island NY
    Haha.
    I had like 2 or 3 different issues with my vtbp 201 including
    what you discribe. My attempts to fix it all failed, I just don't know enough to about it to diagnose and fix.

    But yeah this is the 2nd Demeter product to act up on me.

    Btw, Your right about the footswitch, it went bad with the quickness.
  17. MR PC

    MR PC

    Joined:
    Dec 1, 2007
    It's an easy fix on the 201, just have a tech remove the offending trim pot from the circuit board and have them install a regular sized one on the rear of the unit. It's a standard pot, nothing exotic. Voila', now you can adjust it easily, without taking the unit apart. Don't know why Demeter chose to hide it inside the unit. I believe we used one of the existing 1/4" output holes in the rear chassis for the installation, so no drilling necessary. Heck I've seen all kinds of variations on the original 201, including a factory built in Chorus box accessible from the rear panel.

    I'm really interested in the new Mini Amphead from Demeter, hoping the road test reviews are favorable.
  18. Ray man

    Ray man

    Joined:
    Nov 5, 2009
    Location:
    Staten Island NY
    It was easy to change the trimpot on my compulator, finding the right one was a pain.
    My 201 had more problems that were just beyond me.

    Having a standard pot through the 1/4 jack is a cool idea.

Share This Page