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Ampeg SVT3PRO & Epifani ULs Query

Discussion in 'Amps and Cabs [BG]' started by g4ui83tp2, Feb 17, 2005.


  1. Two unconnected (I think) queries about my current stack which I'm sure the more technically minded of you will have no problem in understanding and answering.

    I'm using an Ampeg SVT3PRO and am connecting it to two Epifani UL cabs, the 2x10 and 1x15.

    Both cabs are rated (according to the script on their back panels) as 500W and 8 ohms.

    The SVT3PRO outputs are rated as 275W @ 8 ohms, 450W @ 4 ohms, and 4 ohm minimum load.

    The SVT has a single Speakon jack output and two 1/4 inch speaker output jacks.

    The Epifani UL cabs have one pair of Speakon 'Input/Output' jacks and one pair of 1/4 inch 'Input/Output' jacks.

    My first query is what is the difference, if any, between connecting the cabinets separately with two 1/4 inch speaker leads, one to each of the two 1/4 inch outputs on the amp, and connecting one cabinet to the single Speakon output of the amp and then daisy chaining the other from the Speakon output from the first? Is this equivalent to connecting in series or in parallel, or have I misunderstood the nature of the SVT outputs?

    Any info on sound quality, risk to equipment (e.g. overloading) etc. would be useful.

    My second query is unrelated but may 'interact' with the first. It is, why, when I play at relatively high volume levels (gain and master at about one o'clock) the bullet tweeters in the Epifani cabs seem to create a relatively high frequency rattle or 'tinkling sound'? The sound goes away if I turn the tweeter adjustment on the rear of the cabs right down so I assume it is these that are producing this noise.

    I first noticed this when using the stack in a well damped sound room, but having been sensitized to it I can now hear it whenever playing at gig level volumes. Does this indicate something wrong with the tweeters or is this 'just one of those things' that will have to be tolerated if the tweeters are switched on?

    Thanks in anticipation, G4
     
  2. inazone

    inazone

    Apr 20, 2003
    Colorado
    Just a thought, but I dont think there is a difference in how you want to hook up your cabs. If it was me, I would just use the 1/4" jacks to each cab.

    About the tweeter, Ive had that problem twice. Once was a battery in the bass, just change it. The other was a preamp tube going bad. Get a new tube and go one by one untill you find the bad tube.
    You might be under powering the cabs a bit and getting the distorted sound but I would try the battery and tube first.
     
  3. jokerjkny

    jokerjkny

    Jan 19, 2002
    NY / NJ / PA
    like Ina said,

    there are many variables. best to check out what's what methodically. try the battery, try using a different bass, check the tubes, check your connections, check how low your bass' action is, and see if the strings are to blame.

    i.e. with the tubes, try tapping on them gently while in use. they shouldnt make too much noise, but if they do, a good time to swap 'em out.

    and no extraneous noise from your rig should ever be tolerated.
     
  4. Many thanks for the responses guys. The bass I'm using has passive pickups (Villex) and a good action adjustment (it's a Modulus Q4). I have also used that bass with a wide range of other kit, SWR, Ashdown, Marshall, Epifani amps, Behringer, Euphonic Audio, etc. so I'm reasonably confident that the bass is OK. I have tried other basses with active pickups (Barts, Seymour Duncan, Wal) on the stack and get the same effect, so I think I've excluded the battery issue both ways.

    I'm also pretty confident in the connections as the noise happens with both the Speakon and 1/4 inch connections and I'm using a new Planet Waves cable to connect the instrument.

    I'm interested in the tube explanation. The SVT-3 PRO claims to have 4 x 12AX7 (I assume in the pre-amp section) and 1 x 12AU7 (I assume in the power-amp tube gain section). However the amp seems sealed against user inspection or access so I guess it'll be a matter of taking it to an Ampeg servicer to check it out.

    Thanks again for the input, G4
     
  5. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    All the outputs are equivalent. Use any of them you want, so long as the loading stays at or above the minimum load.

    One 12AX7 and a 12AU7 are used in the power amp, the balance are in the preamp.

    The rattling noise may indeed be a tube issue. Tubes can be microphonic, or they can get that way after being toted around in a unit for a while.

    If you rap on the unit case sharply while it is on, and you hear the rattle noise, then it may well be a tube problem. There is a fan in the unit, and the fan can vibrate a susceptible tube enough to make a noise. I'd suspect the tubes in the power amp, because most of the preamp tubes would likely make more audible noise.

    It can also be a tweeter problem, that isn't unknown. But in that case, the noise is usually fairly obviously related to what you are playing at that moment.

    If you have a new unit, and you suspect a tube problem, I'd hustle back to get it taken care of, because tubes (and speakers) don't have the same warrranty coverage as the basic unit. There is an earlier time limit on them.
     
  6. Jerrold, many thanks for the insider input on this problem. I'll try out the Speakon daisy chaining option for connecting the cabs for a while as I always feel a little safer with 'locked' connections. I haven't so far been able to detect a difference in the sound produced that way so as long as I'm not increasing the risk of damaging kit this seems a good solution.

    Back to the tubes. Thanks for clarifying the configuration. When I next get the unit out of the rack I'll try a bit of tapping. Unfortunately this is a second user unit, but I got it at The Bass Gallery in London where Martin and Alex are always very helpful so I'm sure they'll put me onto the right track in getting replacements fitted if required. Other than this little 'tinkling' issue I have found the amp both reliable and versatile (I did A/B it with the Epifani UL500 head but found the latter a little less powerful and slightly 'muddy' in comparison, but then I am using a passive bass).

    Thanks again for your valuable input, G4
     
  7. Here's a bit of an update on the Ampeg SVT3PRO tubes. Having taken the head from the rack (4 Allen Key bolts) and taken the lid from the head (13 cross head screws) I found that the preamp had 3 Sovtek 12AX7WA tubes and the power amp has 1 Sovtek 12AX7WA and 1 Sovtek 12AU7 tubes. All the tubes were seated well and retained by plastic padding fixed under the lid. Pulling them out and giving them a little shake resulted in slight noise (a bit like a blown light bulb) from the first preamp tube and both the power amp tubes. Not a very scientific test, but I thought I might try some alternatives anyway and also see if the noise disappears from the speaker sound.

    I had no idea how much 'stuff' there is out there about tubes, but after completing my Ph.D. in audiophile tube mania :)hmm:) I ordered a couple of JAN-PhilipsECG 12AX7WA tubes (17 GBP each!) and a JAN-PhilipsECG 12AU7 (12.50 GBP). Some people seem to like these, they don't appear to be that different from the Sovteks (although they cost twice as much), but they are much less expensive than the Mullards, Telefunkens, and Amperexs which seem to be regarded as the acme of valves.

    So the next move is to do some swapping out and A/B-ing with the new valves, first to see if I can eliminate the 'tinkling' sound from the tweeters at high volume, and second to see if I can tell the difference between these valves in various positions. The beginning of another education I suspect :eyebrow: .

    Will post an update on the results when they arrive.

    G4
     
  8. Many thanks for the help guys ~ I now seem to have fixed the tweeter 'tinkling' noise and it was one of the pre-amp valves as Inazone fortold.

    I first started up the SVT3PRO with the original valves (but top open for quick changes), turned the tweeters on the cabs right up, and turned the treble up on the amp which generated a really clear tinkling rattle. I changed the Sovtek 7025/12AX7WA in the power amp stage with a JAN-PhilipsECG 12AX7WA first, followed by the Electro-Harmonix 12AU7A/ECC82EH (not Sovtek as previously stated, but still made in Russia) with the JAN-PhilipsECG 5814A. No change to the tinkling, more on sound difference later.

    I changed the 3 preamp Sovteck 7025/12AX7WA valves in turn with the other new JAN-PhilipsECG 12AX7WA from right to left looking at the front of the amp. Not until the final one (extreme left of the unit) did the tweeter noise 'magically' disappear. Interestingly this was the only 12AX7 in the amp with a GT Groove Tubes label painted over the Sovtek markings, it was also one of the valves which 'rattled' when shaken. I did try putting the Sovtek 12AX7 from the power amp section in this position, but the tinkling came back just as bad. Maybe both are equally damaged or this is a microphonics effect which exists in the Sovtek valves but not in the Philips.

    Anyway, thanks for the advice, and the valve check worked in the end. So, I've left all three JAN-PhilipsECG replacement valves in the amp.

    As to sound difference between the valves, I can only detect what I hear as a slightly more 'creamy' quality to the sound after the changes to the power amp valves. The main change for the pre-amp is the absence of the tinkling when the amp is driven, which is a great relief.

    The beginning of another technical chapter for me, no doubt hours of fun to come.

    G4