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Boost pedal between preamp & power amp?

Discussion in 'Amps and Cabs [BG]' started by Planet Boulder, Jun 25, 2004.


  1. Planet Boulder

    Planet Boulder Hey, this is a private residence...man Supporting Member

    Nov 10, 2001
    6,482 feet above sea level
    I once had impure thoughts. Oh, and I pluck my ear hair.
    I was messaging Bob Lee and he pointed me to RDL for some line amplifiers for the purpose of boosting the gain to account for sensitivity mismatches between a preamp and power amp of mine. I was also checking out the Ebtech line level shifter, which would allow me to alternate between +4db and -10db.

    Before dropping the bread on one of these (and thank you for your advice, btw, Bob!), I was wondering if there would be a problem with instead using a clean boost pedal between my preamp and power amp in order to boost the gain going into the power amp (without coloring the tone). I'm concerned about possible ohm issues and I just want to make sure I don't do something stupid.

    For reference, my setup includes an Ashly BP41->Trace Elliot RA500sx.

    Would this work?
    Thanks!
     
  2. Planet Boulder

    Planet Boulder Hey, this is a private residence...man Supporting Member

    Nov 10, 2001
    6,482 feet above sea level
    I once had impure thoughts. Oh, and I pluck my ear hair.
    Bump - just wondering if anyone might be able to help me out.
     
  3. Razor

    Razor

    Sep 22, 2002
    Dallas
    PB, I dunno if we're on the same page but...........I've got a boost pedal that Seymour Duncan makes, it basically gives me a "shot" of power when I need it and it's got a dial to adjust how much boost you want. It sits on my pedalboard in the chain. It's a very hot little gain box and they can be had for around 70 bucks. Dunno if this is what you're talking about though.
     
  4. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    Yes, you can put something to boost the signal in between the preamp and the amp.
     
  5. My bass in your

    My bass in your

    Nov 1, 2003
    Holland
    Boss LS-2
    Ibanez Phathed in Clean mode.
     
  6. One possible problem would be that footpedals are designed to work with guitar output voltages and their output is less than 9 volts peak to peak, since they are often powered by a 9 volt battery.

    They may be overloaded if asked to take a larger preamp signal and boost it.

    As a general principle, footpedal effects go between the bass and the preamp input. Rack effects etc. go between the preamp output or the fx send and the amp input, or fx return.
     
  7. Planet Boulder

    Planet Boulder Hey, this is a private residence...man Supporting Member

    Nov 10, 2001
    6,482 feet above sea level
    I once had impure thoughts. Oh, and I pluck my ear hair.
    Good deal - thanks for the replies, all!
     
  8. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    Actually, according to Ashly's specs at http://www.ashly.com/spec-sheets/retired/old-prod.htm, with a BP-41, you shouldn't need any extra boost. So with your setup, I wouldn't recommend it.

    If you cannot get high enough levels with the BP-41, there is something wrong with it or perhaps your bass.
     
  9. Planet Boulder

    Planet Boulder Hey, this is a private residence...man Supporting Member

    Nov 10, 2001
    6,482 feet above sea level
    I once had impure thoughts. Oh, and I pluck my ear hair.
    Bob - you're right. I actually mis-typed. My Ashly is my main Preamp and it is plenty loud.

    My issue actually exists with my Acoustic 360 preamp.

    Sorry for the confusion - I must've had the Ashly on my mind. :D
     
  10. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    I used to suggest the Ebtech Line Shifter when ever someone had a low output preamp.

    The frequency response of those things is pretty bad IIRC so I don't know if it would be a good choice.

    Personally, I'd look for a schematic of your preamp and see if there is a quick mod that you can do to increase the output level.

    The other alternative is to buy a QSC power amp with custom input sensitivity like I did (for my output challenged Pearce BC-1).
     
  11. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    Just read your last post...how about running the 360 into the Ashly's FX return (assuming that it has one) and use it as a gain boost?
     
  12. Planet Boulder

    Planet Boulder Hey, this is a private residence...man Supporting Member

    Nov 10, 2001
    6,482 feet above sea level
    I once had impure thoughts. Oh, and I pluck my ear hair.
    That's a possibility, but the Ashly would still color the tone more than I'd like.
     
  13. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    I just looked at the 360 preamp's schematic. There seems to be a output level control that may be internal to the 360 preamp.

    I owned a 360 for a little while and don't remember whether or not there is a trim pot on the circuit board or a full sized pot that is adjustable on the inside only. The schematic shows a value of 50Kohms.

    Perhaps if you pull the (unplugged) 360 out of its case to look inside, you might see the control and then be able to crank the output level up.

    Good luck!
     
  14. 4Mal

    4Mal Supporting Member

    Jun 2, 2002
    Columbia River Gorge
    I might be more inclined to add in a compressor offering a bunch of gain, You don't have to run the compressor portion of course. Maybe less color than the Ashley ?
     
  15. Planet Boulder

    Planet Boulder Hey, this is a private residence...man Supporting Member

    Nov 10, 2001
    6,482 feet above sea level
    I once had impure thoughts. Oh, and I pluck my ear hair.
    Billy - thanks, man! I may just crack 'er open and check it out. :D

    4Mal - I was actually thinking similarly, using my Bass Compactor pedal between the two.
     
  16. Rock&Roll

    Rock&Roll

    Jul 21, 2002
    USA
    Just heads here. I've done this with my 360 head. I understand why you'd want to do it as well. The 360 head seems to have a little lower output than other pre-amps. I think this is something proprietary to the 360/361 combination so that it works best with the amp it was designed to drive. Never the less, it still sounds great with other power amps. It just seems you have to crank the voume more with other amps.

    But.....honestly, I fried a fulltone fatboost pedal in about 5 minutes by doing this. So I havn't done that since. That's just what happened to me though...........who knows.
     
  17. 4Mal

    4Mal Supporting Member

    Jun 2, 2002
    Columbia River Gorge
    That is why I was thinking a rack mount compressor. The Bass compactor is designed for instrument level input where the rack gear stuff is usually line level. It isn't the end all compressor but maybe a 3630 (50 to 75 bucks used) would do the trick.
     
  18. PB, as a test I put a Boss Bass EQ pedal between Fishman Pro EQ/Preamp and a Carvin DCM1000 amp. Both are 9 volt powered. The Fish has shown itself to be a little low in output to fully power the Carvin. With the Boss pedal used only as a boost I got a noticeable increase in volume (note: I also noticed that some of the "sparkle" of the sound disappeared when running through the pedal, even in bypass mode).



    The Ebtech passive unit advertises a +/- 1dB response 10Hz -40kHz. This seems pretty big (particularly in comparison to the freq response of a good power amp), but I wonder if it is really noticeable? OTOH, the RDL mono unit (STA-1M) claims +/- .25 dB, 10 Hz to 20 kHz. But it requires a seperate power unit and some wiring by the user.

    scratching my head and pondering pluses and minuses :meh:
     
  19. Passinwind

    Passinwind I Know Nothing Supporting Member

    One thing that bugs me about using a pedal as a line booster is that most of them have unbalanced outputs. The possible extra noise is rarely an issue given a short cable run, but the 6dB signal drop as compared to a balanced run seems to make a case for a different solution, no?

    When I'm faced with this problem, my first solution is usually to insert a parametric EQ in line. My Ashly has useful high and low cuts, 15dB of flat gain available, and most of the time I can benefit from at least a little tweak of the EQ. Each band is individually switchable, so unwanted coloration is not much of a problem, IME. Downsides: cost, weight, rack space usage. I've used my Symetrix 525 comp as a booster from time to time. It cost me $40, and sounds pretty good as a comp too.
     
  20. Planet Boulder

    Planet Boulder Hey, this is a private residence...man Supporting Member

    Nov 10, 2001
    6,482 feet above sea level
    I once had impure thoughts. Oh, and I pluck my ear hair.
    Man - these are great replies and points, all! Many thanks again...