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Pre-amp to Power amp question

Discussion in 'Amps and Cabs [BG]' started by Matthew_84, Jun 2, 2012.

  1. For the last couple of months, my rig has been an MXR 10-band graphic EQ, and ART Tube Mic Preamp, and a Crown Drivecore XLS1000 power amp. The Crown is in bridged mode and the attenuators are fully open; the MXR and the input of the ART Tube MP are setup with the gain to be just below the point where the clip light on the ART TubeMP (after the input stage) turns orange, and I adjust my overall volume with the output knob on the ART TubeMP. I've done it this way to try and get as much headroom as I can.

    This morning, I've realized that I may want something to add a bit of tubey grit to my Warwick bass. I had a VT Bass Deluxe in the past, but wasn't too fond of it, but the Tech 21 Sansamp RPM seems to be voiced very much to my liking, and all of its features seem perfect for me. It has a 120V power supply, so I'm not as worried about it driving the Crown then I was with the VT Bass, even though the Crown needs a pretty hot signal.

    I guess what all this info is about is that I don't quite know if this unit will give me as much headroom as I had before, or if it would even be greater?

    Plus I'm getting kind of annoyed with the 10 band EQ. I have a passive fretless jazz, where I like the upper mids and treble accentuated; a passive P Bass where I want the low mids and bass accentuated, and now an active Warwick Rockbass with similar settings as the fretless (and the rest I can adjust with the onboard preamp), but I have to adjust the gain, and I'd like to add more grit if I needed to. I like things clean and simple, and kind of cringe of the idea of a pedal board, and I'm not one for a bunch of effects. So the Tech 21 RPM seems perfect, but I feel like if I went from the passive P Bass, with hardly any drive, and then switched it into Active mode and pumped up the drive that I may lose some headroom, and I feel like maybe I get better control over that with my current setup, but the again, it could that stupid clip light on the ART TubeMP making me believe that, and adding some sort of fuzz pedal would certainly throw that all out of whack.

    Sorry for rambling, I'll stop now. I'll likely just get the RPM, but if anyone has read this and feels like I'm a little misinformed about headroom and pre-amps and power amps and such, I would love some guidance, because I don't really know if what I'm doing is right. Thanks
  2. bongomania

    bongomania Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    One thing is that the supply voltage of a preamp unfortunately doesn't tell you anything about its output levels. It certainly has the potential from 120V, but the actual output could still be low.

    Some more info here: http://www.ovnilab.com/articles/preamp.shtml#power
  3. Thanks Bongo,

    So far I found this, and John seems pretty upfront in regards to the different preamp outputs and has this to say about the RPM; "It has very low noise and plenty of output to drive any power amp." But yeah, I can't find any ratings so far.
  4. Floyd Eye

    Floyd Eye Inactive

    Feb 21, 2010
    St. Louis
    I don't know about the RPM, but RBI drives a 1000 watt power amp beautifully.

    My rig is insanely loud.
  5. Thanks, which power amp do you use it with?
  6. tabdog


    Feb 9, 2011
    My son took over my setup.

    It is a Crown XLS 202. It runs at 500 or
    600 watts bridged at 8ohm into a Genz
    Benz 4X10 cab.

    I can run it with a $65 Hartke Bass
    Attack stomp box as seen in this photo.
    The Hartke is really simple, but works
    well. It will work off one 9 volt battery
    or a 120V power supply.


    It's so loud, it makes the acoustic
    paint rain down from the whole

    I have a DigiTech BP8 tube preamp
    that produce a multitude of sonic


    The SansAmp RPM should be a really
    good choice.

    I got one of those ART Tube MP
    preamps collecting dust in a closet.
    I tried using it for instruments, but
    that's a vocal preamp and I fail to
    see how you can get a lot of head
    room with that thing. But then,
    there's a lot I fail to see, OldDog.jpg

  7. Jim C

    Jim C I believe in the trilogy; Fender, Stingray, + G&L Supporting Member

    Nov 29, 2008
    Bethesda, MD
    Read Bonog's article
    The Crown XLS series needs something like 1.5 V output from the preamp to drive to full power
    Don't know about the Sansamp stuff but a SVP-CL only puts out .775 V

    To get full power the pre amp output must be = or greater than what the power amp needs for full power delivery
  8. Floyd Eye

    Floyd Eye Inactive

    Feb 21, 2010
    St. Louis

    Power section of a Carvin RL1000.
  9. chuck norriss

    chuck norriss Inactive

    Jan 20, 2011
    If you're asking for product suggestions I recommend looking into the ADA MB-1. Super diverse & can handle multiple basses at different output levels. It may suit you.
  10. The Crown XLS needs 1.4 Vrms.

    In one of the VT Bass threads, the Tech21 rep posted this:

    "I asked our engineering dept to test the VT Bass Deluxe. They put it on on the bench and ran it to its maximum output with a clean preamp signal. We used an 80mV signal which is the approximate output of our Fender Roadworn Jazz bass. You can get about 100mV if you really slap it. We ran the 1/4" output with the boost engaged into our meter with a 10kOhm resistor across the input to equal the input of the Crown Drivecore unbalanced input.

    The Crown's specs are 1.4Vrms for full rated output.
    We measured:
    2.3V RMS,
    7.5 dBV
    9.5 dBm."

    I don't know where the knobs on the VT Bass were placed for this test though.

    I did ask him about the RPM directly and he did say that it had more output than the VT Bass Deluxe, but wasn't specific.
  11. cableguy


    Jun 4, 2009
    North Bend, WA
    I had the VT deluxe and the RPM. Tech 21 rack gear has way more output as it should.
  12. tech21nyc

    tech21nyc Commercial User

    Aug 17, 2010
    Manufacturer: Tech 21
    Output for the RPM or RBI:

    I'm not sure what the OP is looking to accomplish exactly. I have the Art Tube MP as well as the Groove Tubes Brick preamp DI. They are both nice units but are really designed to be more like older analog recording gear. They provide tube "warmth." Our products are designed to emulate vintage tube amplifiers.

    The Art Tube MP has more than enough output to drive a power amplifier.

    I guess the question is, do you want the sound of a vintage tube amp or the sound of vintage recording gear?
  13. Nicely put.

    So I guess when the drive is up and the blend is full, then the output voltage would even be greater than this? Also, aside from the difference between balanced and unbalanced, is there anything different between the XLR out and the 1/4" out? Do they have the same output levels?

    I will likely be buying one of these units, but just need to wait a couple of months to be able to afford it. I'm really looking forward to it though, I will likely splurge on it impulsively before then.
  14. lsimy


    Apr 18, 2003
    Virginia, USA
    I have this setup almost identically with exception to using an XLS 1500 DriveCore. The RPM is enough to drive the Crown however RPM's IME break-up quick at the input so be prepared for it to get gritty fairly quick.

    Of all of the amps I have had, I keep coming back to this setup. It's fairly light and running a biamp cab (LDS 210+115 no tweeter) it rocks. The preamp gain has to no higher than say 10:00 before it starts to break-up.
  15. Sorry, but when you say "break-up" it doesn't sound like a good thing to me. It sounds like the signal gets broken up into segments or oscillates or something like that.

    By "break-up" do you just mean a tube clipping sound? Like something musically pleasing if you're looking for that grit? I do want a bit of grit (less then Geddy Lee's tone), some of the time, although I wouldn't want it for the majority of the time. I *believe* the RBI is voiced more for a Geddy tone, but I do want this because I think it will be warmer when I don't want grit and I like the parametric mid control.
  16. lsimy


    Apr 18, 2003
    Virginia, USA
    Break-up meaning a desirable overdrive if that is what you are going for. I think the RBI has less preamp gain than the RPM however I'm sure others on here can chime in with more info. I chose the RPM for the parametric mid. You can wind up 2-3k and get a great SVT-style sound.
  17. tech21nyc

    tech21nyc Commercial User

    Aug 17, 2010
    Manufacturer: Tech 21
    The XLR and 1/4" outs have the same amount of output though it can be difficult to compare. Usually when you run into an XLR input on a board you are going through a mic channel with a preamp vs a line channel so be aware of that. That's why we have the pad on the XLR out, so you don't overload a mic input. You have separate controls for the XLR and 1/4" levels.

    As far as break-up goes we get back into vintage tube amp vs vintage recording gear. As you have noticed with the Tube MP if you put the volume at 1/2 to 3/4 there is nowhere near the amount of overdrive that you would get by putting an Ampeg B-15, SVT, Fender Bassman etc to the same setting. Part of the reason that players think their tone gets too squashed with our SansAmp products is in part due to this misunderstanding. There is also the fact that because we are emulating a tube amp in its entirety in pedal form, the overdrive and distortion characteristics are not "volume dependent" as they are on a vintage tube amp. For instance if you took an Ampeg SVT and put the cab in an isolated room and started setting the volume control at 1/2 to full up (without being exposed to the volume) you would be quite surprised by the result.

    With the RPM or RBI there is an input pad and more than ample output so getting a loud clean tone even with the blend full up is not an issue. Just be judicious with the drive and don't be afraid to turn up the level to compensate.
    GeeWeezy likes this.
  18. I use the Crown XLS1500 Drivecore with the Sanamp RBI and it does/will get loud. I've been able to dial in a great tone close to how Geddy Lee sounds on Rush in Rio. Needless to say after having this setup I'll never buy a "bass head" again
  19. So I finally succumbed to GAS. I really couldn't afford a new one for a while, but found a used one for about the same amount of cash that I will get when I sell my 10-band EQ and a Noise Gate pedal I have that I don't have much use for.

    This thing is great! I only was about to use it for an hour or so, and played a wide variety of songs and was able to dial in exactly every tone I wanted for every song... So much easier than the 10 Band EQ plus the tube sim really warms it up noticeably, and the drive sounds great to my ears. I had it at noon with the blend 100% and easily could have turned it up a couple of hours before it got to be too much for my tastes.

    I'm actually surprised there isn't much more info on these units on TB. The drive, blend, mid-shift knobs are really versatile. I really don't see me needing anything else for a while.

    I did find that plugging into the front input with the -20db engaged wasn't quite enough output to drive the poweramp with the blend knob at 0, but once I plugged into the rear input and disengaged the pad, I got way more output than I could ever use. So all in all I'm very happy with this purchase so far. Can't wait to really take it for a spin.

    Thanks everyone for your input,

  20. dangerouscello

    dangerouscello I wore a suit under this Supporting Member

    Apr 15, 2011
    I'm glad to hear you're enjoying the RPM. I have one on the way, and it is always nice to hear timely recommendations of a product you just bought!

    Just when I thought I had the amp setup I wanted..

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