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Ampeg V4 External Master Volume

Discussion in 'Amps and Cabs [BG]' started by until.tomorrow, Feb 6, 2005.


  1. until.tomorrow

    until.tomorrow Guest

    May 5, 2003
    US - Milwaukee
    Has anyone here ever used one of these things? If so, How were the results?
    Also, I'm sure there is nothing to the circuit so if anyone had a schematic could you e-mail it to me gerkear@yahoo.com

    Thanks
     
  2. until.tomorrow

    until.tomorrow Guest

    May 5, 2003
    US - Milwaukee
    Also could a volume pedal be used in the ext amp plug on the back of the V4 instead to mimic the master volume control?
     
  3. If one were to mod the V4 circuit: (early V4 only)

    Replace R21 with a 100K pot with the wiper wired so the circuit sees 100K when the pot is up, but is down to 0 when the pot is down.

    Note the same effect can be had by plugging a pot into the external amp out. This way you don't deface the amp, a major point of concern.

    I don't do this myself, because this is primarily for guitarists who want to have the preamp section distorted but at lower volume level. For us bassists it's of little use: we need all the (clean) power we can get. Attenuating the circuit here doesn't add headroom.

    If you don't have a good copy of the V4 schematic PM me, I've scanned mine and I'll emial it to you. But it's a big file (1 meg).
     
  4. until.tomorrow

    until.tomorrow Guest

    May 5, 2003
    US - Milwaukee
    I wouldn't want to deface my amp so I was originally planning on just wiring something up to plug into the ext amp out. Is the pot you use for that also 100k?
     
  5. I'd guess a pretty big pot, since it would be in parallel with R21. Maybe 1 meg or so, so it's effect would be minimal when attenuation isn't needed. (There may be a 10K resistor across the wiper also, so the pot goes from 10K to 1 meg....) It's been a while since I read up on this mod.

    At one time Fliptops sold a master volume unit, supposedly it looked like the external reverb footswitch that was optional for these amps. They may still have them I don't know.
     
  6. mikeyvr6

    mikeyvr6 Supporting Member

    Feb 19, 2002
    Plymouth, Wisconsin
    You mean something like this?
     
  7. The 0x

    The 0x

    Aug 24, 2003
    Timonium, MD
    What if a bassist WANTS overdrive?
     
  8. good point...but the V4 is only 100 watts to begin with....so cranking up the existing volume will send the amp into "overdrive" at relatively mildly ear-splitting levels with the bass. With a guitar, this would be painfully loud.
     
  9. Joe Beets

    Joe Beets Guest

    Nov 21, 2004
    I had a B25 once, it went into overdrive as soon as the drummer started banging on his drums. Had to get rid of it. :meh:
     
  10. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    Phooey... I once saw one of those in a junk bin at a now defunct music store for $1....

    Such a device would be useful only if the preamp had enough gain to distort in the first place. IIRC, Ampegs of that era were known for being pretty clean all the way up.

    Perhaps the best mod would be a post-phase inverter tube master volume control with a dual-ganged pot so you (try to) overdrive the phase inverter tube too...

    I have an old Craig Anderton article on this somewhere...I'll try to remember to dig it out.
     
  11. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    Do you have a V4 (with reverb) or a V4B (no reverb)? If you have a V4, the Reverb circuit could be tapped into for some gain...
     
  12. until.tomorrow

    until.tomorrow Guest

    May 5, 2003
    US - Milwaukee
    I have a V4 (with reverb)
     
  13. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    If the reverb tank in connected with RCA plugs and cable, perhaps one of these things would work...

    http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=41418&item=3780972779&rd=1&ssPageName=WDVW

    They also made one with a slide potentiometer on it to allow the user to balance the level of distortion and still use the reverb (the one shown above eliminates the reverb).

    I'll take a look at a V4 schematic and see if there are any other easy mods...

    I don't recall if we confirmed that your goal is to achieve an overdriven tone at less than full volume or something else entirely...
     
  14. until.tomorrow

    until.tomorrow Guest

    May 5, 2003
    US - Milwaukee
    Yes that was the planned goal. I started off using a Dallas Rangemaster that I built. When it is activated the bass drops out. If I adjust the controls to account for that, the clean "channel" sounds too bassy then.

    Could you use a volume pedal in the ext amp jack? As I recall my friend had a Music Man tube amp and used this setup to get (guitar) distortion.
     
  15. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    The volume pedal trick should work. I presume that he just plugged the cable into the output jack of the volume pedal...correct?

    The official Ampeg device that I saw had a mono phone plug on it so it would do essentially the same thing as the output of a passive volume pedal. The key word here is "passive" as you want a volume pedal that is just a potentiometer controlled by the foot.

    Just remember that you're completely at the mercy of the taper of the potentiometer of the pedal and that it might be difficult to control the exact volume that you want.

    Have fun!!!
     
  16. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    BTW, here's the schematic for the V4's preamp...the proposed pedal would progressively short the preamp output to ground leaving the output of the preamp (pin 3 of V3) across the series combination of the 0.47 uF cap and 10K ohm resistor...

    http://members.aol.com/portaflex/schems/v4preamp.gif
     
  17. until.tomorrow

    until.tomorrow Guest

    May 5, 2003
    US - Milwaukee
    Yes and also the volume pedal's restance would be in parallel with the 100k ohm resistor.

    Are you saying it would act as a short when the Resistance of the volume pedal would be 0 ohm? (shortest path or less resistive path is always the best...current is lazy)
     
  18. Yes the volume pot would short the output to ground. This is a tube output, not SS, so this is OK.
     
  19. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    You're not really shorting out the output of the tube. With the external amp output shorted to ground, the tube still sees the series combination of the 0.47 uF cap and 10K ohm resistor as a load.

    At 0 ohms on the volume pedal, no signal will get to the poweramp.