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(some facts) Epifani UL502 thread

Discussion in 'Amps and Cabs [BG]' started by D.A.R.K., Jul 18, 2007.

  1. D.A.R.K.

    D.A.R.K. Supporting Member

    Aug 20, 2003
    greetings, after doing a search on these i decided to start a new thread on the subject.
    i just spoke with the guys at epifani, and wanted to clear up a few things which were conflicting info-wise in the other threads.
    the 502 and 902 both have class d power amplifiers.
    the 902 has rail-switching technology, while the 502 has modulation
    tech which utilizes a transformer. that is why there is only a 2lb. difference in the amps, but a whopping 1,200 watt difference in power rating.
    i personally prefer the sound of the 502(i just ordered one:) )
    and according to epifani this amp has a bit more immediate "thump"
    to it, a bit more solid transient at a flat setting.
    both amps can achieve the same tone, however, with a bit of eq.
    the di in these amps has no problem with phantom.
    (the original run did, but they were recalled and fixed. that was 4 years ago now).
    you do have the option of a jensen transformer for the di, but the folks at epi don't feel it is necessary, as there are no noise issues which need to be solved, although the jensen would obviously offer a slightly different tone.
    they suggested putting the epi next to pres like avalon, etc. to see for myself...
    looking foreward to putting this amp though the paces, will do a review eventually with my ken smith md7 and nscr5m.
    i hope this post can clear up some questions folks might have about these amazing amps.
  2. D.A.R.K.

    D.A.R.K. Supporting Member

    Aug 20, 2003
    thinking further about this amp, the only thing i didn't test extensively
    was the limiter...would anyone care to elaborate on this function of the amp?
    and any recording experiences anyone might care to mention?
    on another note, i contacted epi via e-mail about the possibilty of
    having the passive input modded for active, but they are not doing that mod at this time. i did, however, give the passive channel a full workout with an 18volt active bass and had no issues with clipping or unwanted distortion.
    i was quite impressesd by how fast epi replied to my query...same day answer.
  3. MacGroove

    MacGroove Brother of the Groove with a 'Pocket Full of Funk'

    Oct 5, 2005
    That thump you quoted that Epi mentioned is do to the 502's modulation/transformer that the 902C does not have due to it's switchable power supply.

    Thank you for bringing everyone up to date.
  4. MacGroove

    MacGroove Brother of the Groove with a 'Pocket Full of Funk'

    Oct 5, 2005
    Here's some info I had posted some time ago on the types of power supplies on the Epi amps.

    UL502...........Class D power with modulation
    UL 902C........Class D with switchable power supply
    PS600...........Class D with switchable power supply

    At NAMM I had the chance to play through the PS600 and later was fortunate enough to play through the prototype
    UL902C. The switchable power supply Nick is using, well let's say it's industrial grade. Nick IMO will be setting a new standard for switchable power supply. I hope that the Joker will confirm and support the oooomph, backbone of the PS600 and UL902C he had a chance to play through at a recent GTG that Nick's new switchable power supply should not be compared to previous ones on the market.
  5. D.A.R.K.

    D.A.R.K. Supporting Member

    Aug 20, 2003
    thanks for the info macgroove!
    have you had a chance to really test out the limiter?
    i'm also wondering if it is in line with the di output...
    or just post for protecting the amp section.
    i'm hoping it is usable for recording purposes...
    on the 902 and power, having spoke to epi yesterday i'm pretty sure the quote on the tonal qualities of the amps is for the most recent versions,
    however they assured me both amps could easily be made to match eachother sonically with some minimal eq tweaks.
  6. Peter Parker

    Peter Parker Banned

    Jun 10, 2001
    What limiter are you talking about? My 502 doesn't have a limiter

  7. Hey Gary!

    It's my understanding that the PS600 is quite heavy and not a switching power supply design like the 902. Is this correct? The weight of the 600 is similar to the 502.

    I will again plead for Nick to put out 1/2 of the 902.. a single 900 watt monoblock head with the 902/502 preamp in a $1,500 10 pound package that is 'bagable' versus needing to be rack mounted.!

  8. MacGroove

    MacGroove Brother of the Groove with a 'Pocket Full of Funk'

    Oct 5, 2005
    There is no limiter on either the 502 or the 902. At first Nick had a limiter and the photo of the 502 w/limiter is still in his web site. There is however, to my understanding, a built in limiter.

    Any yes the tone of 902 can with a little bit of an adjustment dial in the same tones but I do here a difference in the fact that the 502 has more oooomh where the 902 gets its ooomh from it's headroom when used with my UL410 S2. The extra watts allows the 1000 work more efficiently, so to speak.
  9. A couple of things. The 'passive/active' label used on many amps has NOTHING to do with whether a bass is active or passive. The passive input is the 'full volume' input and should be used at all times UNLESS you have a bass that has such high output that you need to use the 'modded' input, which is typically called 'active'. The mod is that this input is padded down in order to not be overdriven by basses with extreme output. Interestingly, the only bass I've ever had to use the 'active' (padded) input with is the passive Reverend instruments, which have huge output.

    Second, an 18 volt circuit in a bass preamp has nothing to do with increased output (i.e., a hot signal), but rather has to do with headroom (i.e., less likely to clip with a hot signal going into it). I've never heard of anyone clipping an on-board preamp, so the 18V thing is a little bit of marketing hoo-ha IMO and IME (maybe underwritten by battery manufacturers:D ).

    So again, 'modding' a passive input has already been done for you... it's called the 'active' input.

    I wish amp manufacturers would stop using this misleading shorthand and just call the inputs 'standard' and 'padded'.
  10. MacGroove

    MacGroove Brother of the Groove with a 'Pocket Full of Funk'

    Oct 5, 2005
    The weiight of the PS600 is 8 lbs. I tried it out at the 06' NAMM show and it was light as a feather like our WW's Ultra, I was told to keep its weight down it has the switchable power supple in it.

    You keep pluggin' away at Nick on the 1/2 the 902 system, I don't think he wants to hear it from me anymore. :D

    Good luck and OOOOOOHHHHH by the way not to derail this but I PM next week when I know for sure but yesterday I was at Stanford for test and spinal tap to check its fluid for any maligant cells and if there is none and they believe there is none, then the new 5mm tumor in my head can be taken care of with that Cyberknife laser treatment I had before. A simple in and out process. :hyper:

    Okay now back to are previous thread on the Epi 502 and 902.

  11. GREAT news!!!!!

    On the much less important issue of the design of the 600, that's what I thought also. However, there have been a number of posts about how heavy the PS600 is relative to class D/switching expectations, and the weight spec's have been taken off the Epi site for this head. I believe the weight of the PS600 as reviewed in Bass Player is listed at 16 pounds (about the same as the TF).

    Has Nick changed this design?
  12. MacGroove

    MacGroove Brother of the Groove with a 'Pocket Full of Funk'

    Oct 5, 2005
    My bad Ken, well sorta, the weight has changed, Nick just returned my call and the PS600 is using a heavier, more durable frame for the amp, Nick weighed it in at 13 lbs. now and still has the Class D/switchable power supply.
  13. Cool! Something seemed to be going on there. Kind of a strange deal to put a lightweight design in a heavy case. Between that and the no bridge-able 902 with no balance control, I think maybe Nick should stick to cabs:D
  14. bongomania

    bongomania Gold Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    A couple of things. ;)
    Actually my understanding (possibly mistaken?) was that some amp designs merely pad the "active" input as you described, but some others have an altogether different impedance between the two inputs, to accommodate the different output impedance between active and passive instruments.
    My understanding is again different- an 18V system is capable of increasing the gain of the pickup output by a higher amount before distortion. I have in fact distorted onboard preamps many times, on older basses such as a Kramer XL7 and a Gibson RD Artist; their preamps were not designed as "cleanly" as modern onboards like Bart etc. So it's not so just a question of how hot an input signal it can take from the pickups, but also how much it can amplify that signal without distorting itself (much like an overdrive pedal).
  15. David Wilson

    David Wilson Administrator Administrator Supporting Member

    Oct 14, 2002
    Lower Westchester, NY
    I guess from a marketing point of view, it probably didn't make too much sense to have the cheaper 600 be lighter than the more expensive 502 :)
    I don't know if that's why it was done, just speculating
  16. Bongo.... +1 that some heads have different input impedances on the 'hi and low' inputs (like AI... never heard a ton of difference between them... maybe a slight, slight difference in the low end). That's why I wish these companies would label these inputs accurately. Many a kid plugged his 'active' bass into the 'active' input thinking there was something 'special' about the input, when most of the amps just use a padded input as the 'active'. And, since most active basses have output that is well within the capabilities of the non-padded input, it makes sense to use a non-padded input when you can... one less capacitor or whatever to feed your signal through.

    Also, we aren't really disagreeing on the 18 volt thing... headroom as I said prior. However, my understanding is, this has nothing to do with output strength. For example, if you run the Ag pre that can be run 9 volt or 18 volt (I forget which one that is.. the OB-1?), Aguilar states that the strength/volume of the output won't change, just the headroom of the circuit (which I assume has to do with handling the INPUT to the preamp, not the output.

    However, I'm getting WAY beyond my knowledge base:eek: What I was trying to communicate was that a) 18 volt preamps does not mean a necessarily hot signal and b) I can't see any reason to 'mod' the passive input of an amp
  17. D.A.R.K.

    D.A.R.K. Supporting Member

    Aug 20, 2003
    great info guys, thanks!
    i suppose the limiter in question is due to the pics, i could swear there was one on the amp i demoed, but that would explain why i don't remember adjusting it.....(i'll call this the duh factor lol...i've tried out so many amps in the last week my brain is overloaded)
    this would also explain the lack of info on the site...
    -is there a defeat switch for the built in limiter?
    on the pre issue, i have had quite a few instruments with passive, 9volt and 18 volt pres. my personal experience is a much greater output from the 18 volt circuits, which has run me into plenty of overdrive issues with various pedals and pre amps.
    sounds like the aggie onboard is built like my smith 18 volt...
    designed to keep output to a reasonable level in order to work well with pedals etc. not so with my ns eub....
    the passive/active inputs in question are for the two different channels on the epi 502...
    i needed an amp which had two independent pres with their own eq,
    one to run my bg and the other to run my urb through.
    (hitting the low b arco with the bass dimed on my ns eub will overdrive most pres and pedals like mad)
    thus, my concern about the capability of the passive channel, and the possibility of modding it to match the active channel input. (i'm quite aware that it is just a pad)
    one channel is clearly marked passive,
    the other active.
    the passive channel has no pad switch option.
  18. bongomania

    bongomania Gold Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    The whole question of "is there a limiter" is a bit confounded when you put it like that... If there is a built-in limiter, then there is a limiter. Maybe you mean an earlier model had controls over its limiter? Or you're thinking of a limiter before the preamp, versus one between the preamp and power section, versus after the power section?

    Regarding modding the passive input for a pad, that's easy if you have basic electronics skills. All you need is an additional resistor right after the input jack. The value would have to be determined by experimentation. One way to do that is to put a pot (maybe 500K) in line between your bass signal and the passive input; play through it, and dial it back until your signal is attenuated the amount you want; measure the resistance of the pot at that point; and get a resistor of that value.
  19. Per the limiter question, I assume there is some sort of OUTPUT limiting. Most modern SS amps have some sort of limiting device used as a protection against power amp clipping. However, this is very different from an input limiter or compressor. Some amps, like the Eden WT line and the Thunderfunk have simple input limiters (in additional to output limiting) that can be controlled by the level of the input gain control. This type of limiter is typically used to reduce peaks being sent into the preamp. Other amps, like the Mesa MPulse600, the EBS TD and HD amps, have full featured compressors, that provide separate controls and act as both limiters and compressors.

    I believe the Epifani amps only have output limiting, which is purely a 'safety' device and would never even be noticed unless the amp was pushed beyond its safely rated output.

    As far as modifying the passive input, we seem to be talking in circles here. Of course it wouldn't be a problem to change the 'passive' input of an amp into a padded input. My point was why would you want to do that, especially since many amps, like the Epi502 already have a padded input (called in many cases 'active')?
  20. Per your 9volt/18volt experience, the output differences you are noticing are not due to 9 versus 18, but rather how the individual pre outputs are set. Many pre's actually have a gain control in the circuit, and you can adjust the output to match the input level of your amp. Some basses, like the Alleva-Copollo and FBass, have the output levels of their pre's set quite low, so that the active volume is the same as the passive volume when the tone controls are set 'flat'. Other basses, like the Celinder (9 volt) and MTD (18volt) have variable gain controls and can be set to very low are very high output levels. Others again, like the Sadowsky (9volt) are set very hot and cannot be adjusted.

    I believe the Smith (both 9volt and 18volt circuits) have output gain controls, but am not sure.

    Edit: Here is what Ken Smith has to say about this on his site:

    The New Smith BMT 18 volt Circuit was designed for Multi venue application. The 9 volt BT Circuit has been in use since 1981, and the BMT Circuit since 1993. Since that time there has not been a single musician, studio or touring, who has called about a lack of headroom in the Circuit. Although the 18 volt Circuit does provide more headroom, it would take an extreme case where the Bass is overly boosted and played overly hard for it to peak over 9 volt range. For this reason, within the design of our 2004 model we have included the 18 volt feature. Rest assured there is no difference in volume between the 9 & 18 volt units that we have tested. The 6 position DIP switches are preset at the factory for what we believe is the optimum performance frequency for the Smith Bass.


    Finally, your situation is EXACTLY what the 502 input section is designed for... two separate channels, one with a non-padded input for your bass guitar, another with a padded (active) input for your hot output EUB. I'm very confused here... why would you want to modify the passive input with a pad?

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