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VMP 4000e

Discussion in 'Pro Audio Equipment' started by miroslav, Oct 26, 2005.

  1. miroslav

    miroslav Active Member

    I just got a 4000.
    Only had a chance to give it a basic tryout.

    I'm really diggin' the Pad=0dB along with various combinations of the Deep/Flat and Air/Bright/Flat switches.
    Deep with Air...knocked me on my ass!
    My main vocal mic (ADK TT/CE)...all of a sudden went from great...to killer!

    But I have a few questions as to the discombobulated layout of the switches...or so it seems to me.
    Maybe down-under…you guys look at things a bit upside down! :wink:

    The Phantom switch has OFF in the up position and ON in the down position…???

    EQ switches...
    The LF switch goes from FLAT/up, DEEP/center and LO CUT /down…
    The HF switch goes from BRIGHT/up, FLAT/center and AIR/down

    …???

    With the PAD switch…-15dB/up, 0dB/center/-30dB/down…???

    I dunno’…is it just me, or does anyone else think that Up=On=More=HF…
    ...or at least have FLAT and 0dB in the center position on all the switches, not centered on one and up on the other!
    You got similar switches going in different directions to achieve similar results. :?

    Finally, the Phase switch has PHASE IN/up…PHASE OUT/down…and at first glance I didn’t know if the IN/OUT meant ON/OFF...or in-phase/out-of-phase..?
    Turned out, that it means:
    up/Phase in = 0 degrees
    down/Phase out = -180 degrees
    I always preferred Normal/Reversed.

    OK…so much for nitpicking about the controls.

    Oh...the fuse socket is kinda’ loose. And the shield plate between the trannys and caps...needs a second screw to hold it so that it doesn't pivot around.

    Also...you may want to consider another two brace points in the center of the main PCB...because pulling/pushing tubes out/in as you change them...really can flex the PCB if you are not careful to hold it with your other hand.

    Other than that...the unit looks like it could withstand the staircase drop test. :D
    Very clean wiring!
    I'm looking forward to really using this puppy on a lot of tracks, and I’m sure I’ll post back here again!
    That 0dB/Deep/Air setting is very organic/retro...absolutely balls out! 8)
     
  2. Markd102

    Markd102 Well-Known Member

    Well I don't know how it's done on your side of the globe, but here, all switches are up for off, down for on.
    So also the phase switch was obvious that up/off was normal in phase, and that switching it "on" was engaging the reverse.

    anyway, it was obvious to me :wink:
     
  3. David French

    David French Well-Known Member

    I think this really is a cultural difference. The poer supplies on the R0DE tube mics also have up for off, down for on. In the States, up for on is the norm. The switches on the Sebatron threw me for a bit when I first got mine, but honestly, with a sound like that, who cares? :D

    The one thing I would have changed is not having to go through 0dB to get to -15 from -30.
     
  4. miroslav

    miroslav Active Member

    Ok...so maybe things are reversed down under...
    ...up is off, down is on.

    But...that still doesn't account for the LF/HF switches.

    LF ----------- HF

    FLAT --------- BRIGHT
    DEEP -------- FLAT
    LOCUT ------- AIR

    Just can't find the logic there... :?


    And yes...the PAD should have been either:

    0
    -15
    -30

    ...or...the "down under" way... ;)

    -30
    -15
    0
     
  5. zemlin

    zemlin Well-Known Member

    I'll second that emotion ...

    I don't like having to go through 0dB to get from -15 to -30. I agree that the EQ switches seem illogical, but are less of an issue.
     
  6. Markd102

    Markd102 Well-Known Member

    I agree. But I'm sure Seb has a valid reason......?
     
  7. Sebatron

    Sebatron Well-Known Member

    Yes.
    That PAD switch works around a negative feedback loop. As you know , with negative feedback in this configuration a straight short ( or maximum neg feedback ) would result in the least amount of gain ….
    The Toggle Switch is configured such that a straight short can only be obtained in the upper or lower switch positions …. not in the centre off position…..
    So basically that means the 0db spot has to be in the middle as that position requires the switch to be open circuit or maximum gain or minimum/zero negative feedback.
    That left me with just two other choices … where to put –15db ….Up top seemed most appropriate…

    The Deep/flat/lo-cut switch is a similar type in which the Capacitor of the passive RC equalizaton network is either shorted across ( switch in lowest pos… lo-cut ) or has a ‘ softening resistor at the flat position switched in …. This can only be done in either the Top or Bottom positions for the switch.
    Having the three way switch in the middle is an open circuit which doesn’t bridge anything across that cap …. Hence ‘ Deep ‘ occurs here…..
    We could get around this by adding some switching circuitry like FETS or Opto-Couplers or even relays.But this would compromise the audio signal.
     
  8. miroslav

    miroslav Active Member

    Ahh...Sebatron explains!

    Well there it is then....logical reasons for the somewhat "illogical" layout. :)

    No...don't add anything to the circuit just to fix the switch layout.

    It only takes a little getting use to...but it's quite workable.
    It kinda' makes you stop and think for a second when setting up the channels...and that's always better than just memorizing positions. :cool:

    PS

    Sebatron

    I'm the guy that emailed you a week or so ago about the warranty transfer thing.
    As you can see...I ended up buying the "almost new" 4000e anyway.

    I was a bit cautious...but the guy who sold it to me seemed very honest...and the unit does look like it's hardly been out of the box!

    I don't forsee and problems that would even require warranty service. The unit id solid...and sounds killer!
    All in all...I think I got a great deal on a 4-channel pre! 8)
     
  9. miroslav

    miroslav Active Member

    OK...I've had a chance to use the 4000e on some guitar tracks.

    What I noticed was that with the Pad at 0dB...and moderate levels from the amp/cab...the 4000e was breaking up on some peaks...and I therefore ended up switching the Pad to -15dB for one guitar track...and on another track, where I used the clean channel of the amp at a slightly higher output level...I had to go to -30dB to lose that high-end break-up.

    I was using a Traynor YCV40WR with an extension cabinet. I had a Sennheiser e609 on the combo speaker, right up against the grille...and I had a GT AM62 tube mic on the extension cab...about 12" away.
    Each mic fed one channel of the 4000e.
    At the 0dB setting...both mics on both channels showed signs of break-up on peaks.
    I switched channels on the 4000e...same thing.

    I then tried a different pre just to make sure it wasn't the guitar/amp/cab/mic combinations...there was no distortion.
    That's when I changed the Pad to -15 and/or -30 on the 4000e...and it cleaned things up right away.

    I know pres and tubes will have a threshold where they will distort if the input is too hot...but the amp level really wasn't LOUD...it was a moderate level...you could stand in front of the amp without cringing. :)
    I believe it may just be the JJ tubes that are breaking up...so I have some other tubes on the way and I will see if there is any difference.

    When I first tired the 4000e...with a nice ADK TT/CE tube mic...vocals were fantastic...especially at the 0dB setting!
    Of course, the guitar amp WAS putting out a good deal more level than my vocals...so maybe this is not unusual for the 4000e...?

    I have an older ART MPA tube pre...and I can literally smash it with input signal...it will just get "fuzzy"...but it doesn't have the high end, harsh break-up that the 4000e exhibited.

    Once I adjusted the Pad on the 4000e…I was able to get some nice guitar tracks…so that’s what counts.

    I’ll be working with it some more....
     
  10. Matt_Trix

    Matt_Trix Guest

    Hmm, with a hot signal coming into my 2000e and the pad set to 0db I can barely turn the gain knob above 0 before the output signal becomes so hot as to be useless. In other words, yeah there'd be breakup if I cranked it much but at that stage you're WAY beyond "normal" tube distortion. At 0db you're driving the tubes hard at pretty much any gain level as far as I can tell, that's what that pad switch does, control how hard you hit the tubes.

    Do you have VU meters on your VMP? Are you sure your signal isn't very loud in real RMS voltage terms? I'd rather suspect that your input signal doesn't sound "loud" but is pushing alot of voltage through.

    I normally use the 0db pad for really smashing a bass sound, I'd never use it on drums for example.. but of course, if it sounds right.. Bear in mind, that the signal coming out of the VMP with a 0db pad and bit of output gain is so hot that you need a great (read: expensive) analog compressor on the other side for it to be at all useable.

    My 2c. I'm sure Seb will jump in and set us straight anyway.

    Matt
     
  11. Markd102

    Markd102 Well-Known Member

    It's very rare for mine to go above -15. Only on very quiets sources.
     
  12. miroslav

    miroslav Active Member

    Well...I'm jusy tryin' to see what kind of flaver I can get out of the tube...that's why 0dB seemed like a good place to start.

    Yeah...at 0dB...I can't really turn the output knob much past 2 without redlining my other gear...
    ...but, even when I was holding the output level at a good point...I did notice that on peaks, there was occasional distortion happening at the input of the 4000e...which leads me to believe the tube just wasn't able to handle it...???
     
  13. miroslav

    miroslav Active Member

    It's been 3 months or so, since I got the 4000e...and I'm starting to dail it in finally.
    It’s taken some experimentation with sources/mics to get the desired tones…but it’s coming around nicely.
    I have about 2 dozen tubes I picked up on eBay...so I've been trying them out...looking for the right tone/noise combination.

    One thing that happened yesterday as I was putting the unit back into the rack, having just swapped out some tubes...
    ...as one of the protruding screws from the base of the unit, on the right/front side (where the power supplies are) lightly scrapped across the top of another unit in the rack...some sparks flew!!! :shock:

    I had just turned it on, to warm up the tubes, and was going to screw it back into the rack ears.

    Hmmm...THAT'S NOT NORMAL...I thought!
    So I pulled the unit back out, and found it was one of the 4 support screws that hold up the front power supply PCB.
    When I removed the screws and flipped over the PCB...one of the two yellow wires that go through the PCB and are soldered underneath...had been pinched by the left/front screw & support post...and the outside casing had been chewed off, exposing the wire....which was brining it to chassis ground as it touched the screw/post.

    OK...easy fix...I removed the exposed section and I re-soldered the wire to it's PCB point.

    But...now I am wondering if up to this point...while using the unit...
    ...could there have been any damage caused to any of the other components...and could that have been the reason I've blown two tubes in the # 3 channel already...???
    It appears that is where the tubes get their power from...via the ribbon connector...so I'm wondering if the short could have possibly contributed to the early demise of the # 3 channel tubes...?

    Anyway...after fixing it...the unit appears to be functioning fine...and the tubes I'm trying out right now (2 GE, 1 Magnavox, 1 Sylvania) all sound quite good...
    ...but I will see if the # 3 channel causes any more tubes to go in the near future.

    Oh...not to be nit-picky...but speaking about those screws.
    The top/bottom covers should be placed about a 1/8"-1/4" below the outside edges...so that all those screws in the top and bottpom covers don't protrude beyond the outer lines of the unit...and end up rubbing against the other gear above and below the 4000e.
    The screws just stick out WAY too much...making it difficult for the unit to slide in/out easy...which is tough if you do not have the extra rack space to leave empty slots above and below the 4000e.

    And...the screws/hols that hold the cover in place...are very poorly machined.
    After only removing the cover a few times...almost none of the screws tighten down properly...they just "float" in the holes.
    I think a better thread on the holes, and the use of a fine-thread screw instead of a wide-thread screw might help that situtation.
    I'm going to just replace the screws with a better fitting combintaion...but I just thought I would mention it... :wink:
     
  14. Matt_Trix

    Matt_Trix Guest

    Hi!

    Sorry, I can't help you with the tech stuff as I haven't even looked at the Seb internals yet. Haven't had time to play with tube changes yet either but I would love to hear some samples or even just your feedback about various tubes in the Seb.

    Matt

     
  15. miroslav

    miroslav Active Member

    I'm only on my third tube-swap...

    The JJ's seemed a bit harsh at first, though having re-dailed my source/mic combinations...
    ...on the next swap, I might try them again.

    I had 4 white lable GE tubes in there for awhile...until one of them started fizzing out...and now I have 1 white lable GE, 1 orange lable GE, a triple mica Magnavox and a triple mica (I believe) Sylvania.
    These are all used tubes I get on eBay.

    I have a Precise 111 tube tester...so I check them all out and then put them in the units for a listening test.

    Of the four I have in there now...the 2 triple mica tubes seem to be the quietest.
    I only put them in yesterday...so I'll be trying them out during some recording in the next couple of days...and I'll come up with some opinions about their respective "flavors".

    It's all subjective...unless you have an obvious noisy/fizzy tube! :)
     
  16. Markd102

    Markd102 Well-Known Member

    I actually came to the conclusion that this was done deliberately so you leave some ventilation space around the unit. could be wrong though.
    And I have room in my rack so it's never really bothered me.
     
  17. miroslav

    miroslav Active Member

    Deliberately...?

    Hmmm...I doubt it.

    A 19" audio rack has specific dimensions and the screw holes are drilled at specific intervals.
    Audio gear has to conform to those specs...otherwise, it doesn't fit right...it doesn't "play well" with the other gear in the rack. :lol:

    Sure...some manufactures (most) will always tell you to leave the spaces above/below empty...so their unit can vent...
    ...but that's not always possible...and if you have to place units next to each other...their screws should NOT get in the way, and dig/rub into the other units!
    So far...the 4000e has scratched the crap out of the other two units above/below...but it's only on their tops/bottoms...so it's not visible.

    There are also the units that come with rubber legs, for placing on the table...but when you try them in a rack...they also don't fit in with other gear. On some, the legs screw off...but on others they are glued on...a PITA.

    But...getting back to the 4000e screws...they still don't screw in properly...and you will see...after you remove the cover a few times...the holes become quickly stripped...and then the screws just float around.
    That was a machining SNAFU...either the holes or the screws weren’t done right.

    While I’m on a roll… ;)

    It would be better if the cover were just the top…with no sides. It sure would make it easier to remove…but with the U shaped cover…you have completely pull the unit all the way out of the rack, in order to swap tubes.
    If it was just the top…you could remove the unit above the 4000e…then remove it’s top…and swap tubes. The 4000e would never move…and those protruding screws would not scratch up the other gear as much.

    I don’t mean to be complaining…it’s just some overall observations on possible ways to improve on things for the future. :cool:
     
  18. Sebatron

    Sebatron Well-Known Member

    Thanks Mirorslav for your feedback.Down here in the Sebatron Dungeon youse spirit is spoken of very highly.

    We do try and discourage users from stacking the vmp series preamps directly on top of another unit because , as has been stated , of heat dissapation and EMF induced noise.
    Down here we hate too much conformity and decided to approach the cabinet as its own entity ,, whereas we could have chosen a generic style cabinet that would save us a few burgers if you know what I mean.
    The distinctive ‘ ~S~’ comes at its own expense and it was decided to have a wrap around lid at the time so that the unit could be operated from the sides whilist being lit….. i.e in operating mode …..

    8)
     

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