(preamp question)v1~v4 what does that mean?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by dico0325, Oct 9, 2005.

  1. dico0325

    dico0325 Member

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    Hi, I've been here for a while, great forum.

    I got a voodoolab guitar preamp, the clean channel sound funny and unstable, sometimes it produce high compress or clipped and distorted sound even in extreme low gain setting, it's currently using 4 Sovtek 12ax7wb, after I change the order of the tubes randomly and the sound improved abit, sound much normal now, so I am thinking replacing the tubes, but I don't know anything about tubes, I've read alot of post in here and got some general idea of it, but I still have some questions, please help.

    1. there are four sockets labeled v1 through v4, as I check the old post here and saw some people talking about v1 and v2, at first I didn't know what they are talking about, does every preamps have these, can some one explain to me what's the meaning of them.

    2. can I install different tubes in the pre? like two JJ's and two Sovtek, or I should put 4 same tubes in it?

    3. the current sound of the voodoolab pre works for me, but I would like to make it more open sounding if it's possible, can anyone recommand some tubes where I should start looking?

    thanks in advance!
     
  2. John Phillips

    John Phillips Member

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    V1 etc refers to the position of the tube in the circuit, and/or their physical position on the chassis, which are normally fairly similar. Usually the lower the number, the closer the tube is to the start of the signal chain (the input of the amp), and the higher the number the closer to the power stage - eg in a typical Fender BF/SF 6-preamp-tube amp, V1 and V2 are the first gain stages for each channel, and V6 is the phase inverter. The power tubes are numbered too, but their 'order' doesn't matter.

    In most amps, the lower numbers are more critical, both to tone (because a bad tube here messes up the tone, and the subsequent ones simply amplify the bad tone) and for noise or microphonics, since noise generated in them is also amplified by the following stages. You'll frequently find that a tube which is too noisy or even squeals in V1 or V2 is perfectly OK later in the amp.

    In multi-channel amps it can be more complicated, and tubes are not necessarily in the 'logical' order and may only apply to one channel - eg in the Mesa Maverick, V1 and V4 only operate on the clean channel, V2 only on the dirty, but V3 is shared between both as half of it is used for the FX loop.

    There is no reason why you have to use the same type of tubes in all the positions.

    If you want to open up the tone of your preamp, get rid of the Sovteks immediately - they're notoriously lifeless and murky-sounding, and in my experience do tend to go noisy and have other problems.

    I would replace them all with NOS RCAs or GEs - some of the cheapest old-stock types, very clear and detailed but still warm and rich, and with good life expectancy (especially in a preamp, they'll probably last decades). I did exactly that with my Mesa Formula preamp - which came with Sovteks, I fitted GEs - and it made a HUGE difference to the tone. It didn't change the fundamental character, it just let you actually hear it properly.
     
  3. dico0325

    dico0325 Member

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    thanks John, great infos.

    anyone using the voodoolab pre? I search the manual and voodoolab site but can't find any info about the tubes.....
     
  4. R3deemed

    R3deemed Member

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    I, too, have a Voodoo Lab preamp. It's decent, but for the price I should be madly in love with it.

    I'm not.

    Anyway, I got rid of the stock tubes and replaced them with 4 JJ 12AX7 ECC83Ss. This created a way too saturated distorted sound, so I replaced V1 and V4 with 12AT7s. This helped a bunch.

    I might just try John's advice.

    BTW, I love the cleans (for the most part). I can't say I've experienced the same trouble you are. Is your unit new? Are you sure there's nothing wrong with it?

    I e-mailed Digital Music and got a response. Unfortunately I no longer have the e-mail, and I can't remember which positions control which functions on the preamp. E-mail them. I'm confident that they will respond.
     
  5. dico0325

    dico0325 Member

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    bpd_103, the pre I own is the only one my local dealer has, or I might say the last one in the whole country, so I can only keep it or return it.

    I can get a great clean tone connect the preamp out into a H&k Tour Reverb FX return, but not so good on a AVT100 or with the pre's cab sim, when the gain go beyond 3 o'clock you start to hear some compress and distorted sound mainly on lower frequency especially if I'm use my 50th strat's neck pickup, there's no second unit here for me to compare, I know some amps sound like this so I really can't tell it's defected or it's the clean channel's character.
    before I swap tubes order in the pre, the distorted sound very obvious and bad, almost sound like a mic pre didn't warm up properly, and the dealer didn't stock any tubes, so I am thinking getting some tubes and try for myself.
     
  6. R3deemed

    R3deemed Member

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    It just sounds not right to me, but it may have something to do with the set up. Does the dealer at least have a power amp/speaker cab you can run into make sure it's at least working properly? Maybe get their take on it as well.

    Back to your original question, I think the V1 and V4 ran the distorted channel(s) and V2 & V3 ran the clean, but I could be wrong.

    John, where would I buy the tubes you mentioned? I took a brief look on eBay and they look to be around $50 a pair. Is that what I could expect to spend?
     
  7. John Phillips

    John Phillips Member

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    I'd probably go to KCA or Lord Valve. That way you get a warranty. I'm not sure they're asking a lot more than $25 a go for those kind of tubes anyway... not all NOS are expensive.

    It's fairly easy to find out which tube does what BTW - just pull one and find out what still works :). Sometimes you may that one is used in two different places at once (because a 12A*7 is a dual triode), so it isn't always conclusive, but if you pull (say) V2 and the clean channel is still working you know at least that V2 only applies to the dirty channel. Once you've done that you'll have a better idea of which tubes might be worth substituting with different types. 12AT7, 12AY7 and 5751 all give somewhat less gain; 12AU7 gives a lot less. Most of them are cheaper than equivalent 12AX7s too.
     
  8. dico0325

    dico0325 Member

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    john, so I can remove all the tubes and power it up without causing any damage? can I swap tubes when power is on?
     
  9. dico0325

    dico0325 Member

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    I ordered some tubes and they came in today...

    Ei ECC83/12AX7
    RFT ECC83/12AX7
    Electro-harmonix 12AX7EH
    Philips/miniwatt 12AT7WA Mullard

    I really like the RFT, I put them on v1 & v4 which affect all channels, it solved the problem I have(but others don't, because RFT is more expensive??), now I got a very tight lows and the top really open up, but best of all is the super sweet mids, absolutely beautiful.

    I put EH on v2 & v3 which affect the od and dist channels, EH sound as sweet as RFT but with less hi end, but that's enough for me, RFT is a little too bright for the dist channels.

    compare the sound I have now, the sovtek 12AX7wa is really weak sounding, less gain and blur the dist channel.
    the Ei is better than the stock Sovtek 12AX7wa but not much, the 12AT7WA is just for testing, I don't like it.

    test tubes was really fun, but I need to save some money to get more to try, this could become costly hobby.......
     
  10. Sunstone Recordings

    Sunstone Recordings Member

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    Hi, I really need some help here... I have an Orange AD30 Twin Channel Combo, and I really don't know what each of the V positions directly effect. Can anyone help me? I found one schematic of this amp and it's as easy to read as an upside down dictionary.
     

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