Plugging into effect return??

Discussion in 'Amps and Cabs [BG]' started by eunchang, Jul 7, 2004.

  1. eunchang


    May 12, 2004
    Seoul, Korea
    Hey. I got some question.

    I read from BP a couple months ago that Mike Pope said he plugged into effect return to bypass WW's preamp section. If Mike Pope does it, there should be reason, I thought.

    Since then, I often tried plugging into effect return when I play doublebass(equipped with Underwood pickup and signal goes through Sadowsky outboard pre/DI). I noticed that output volume was quite shy, but sound was very pleasing.

    Today, I plugged my electric bass into the return jack(at this time church's Workingman's 15), I was surprised. The sound was amazing!! Exactly what I was looking for!! No harsh treble, but still punch. With the bass's onboard EQ, I could easily get the sound I wanted. :)

    So please educate me. What did make the difference?? Impedence level?? Or just bypassing the preamp section??

    On my way back home I was keep thinking like,

    what if I get a big enough powered monitor(if there is any) and use it with DI


    if having two preamps between the pickup to poweramp(one from the bass, the other from the amp) makes so much coloration(right english word??) of my bass sound, I should be able to get a decent sound when I used passive mode.

    However, it wasn't the case from today's experience. There was so much difference between going passive->using preamp from the combo amp and going active->plugging into efx return.


    what if just have a power amp and a cab?? Using only onboard preamp's EQ??
  2. Eric Moesle

    Eric Moesle Supporting Member

    Sep 21, 2001
    Columbus OH
    There's no "wrong" way to find your tone. If doing an unorthodox setup gets you the tone you identify with, then do it.

    Secondly, Mike Pope uses a custom-tinkered and highly complex preamp in his bass, which itself serves as a preamp prior to hitting the actual amp. Bypassing the amp's tone section doesn't mean he's going straight clean, it just means he's already coloring his tone with the preamp on the bass itself and avoiding coloring the tone a second time with the amp.
  3. There is only one issue with the idea of running active to power amp. The gain from the active circuits cannot drive a power amp to full potential.

    I do something of this nature myself but I added a rack mount EQ with input and output gain to make up for the low signal. When set flat it's just a signal boost.
  4. eunchang


    May 12, 2004
    Seoul, Korea
    Thanks guys.

    I was wondering like,

    why the sound was so different between flat EQing and bypassing preamp plugging into efx return.

    Also, I noticed a good amount of volume dropped, so I guess impedence level was higher, I mean using the efx return..I don't know.

    I like the sound but the volume was not enough..that is my issue now. Any thoughts??
  5. The volume drop you experienced was caused by the lack of preamp gain. That is the primary function of a preamp. Today most preamps (whether it's built in or rack mount) inherently color the tone simply by passing through their circuitry. There are, however, small companies out there that are producing "colorless" rackmount preamps. These small companies get a lot of money for their product, however, due to their high cost of manufacture and extensive research.

    You can use various pedals or rack mount gear to boost your signal the way a preamp would. I stated in my earlier post that I use a rack mount EQ (JBL SPP-GE, which is made by rane for JBL). Anything with an input and/or output gain knob can potentially serve the purpose or boosting signal to the power amp.
  6. eunchang


    May 12, 2004
    Seoul, Korea
    Can you name a couple of "colorless" preamps for me?? U5, Demeter kind of amps?? Is that the reason many studio players use mic preamp rather than bass amp?? However, I didn't see many of them use mic pre in live, though.
  7. jokerjkny


    Jan 19, 2002
    NY / NJ / PA
    yup, the Avalon U5 is your best bet. allows my Sadowsky's to sound their best unencumbered by an overly coloring preamp. another cool idea is to get an EA iAMP800. has a complete EQ bypass switch, that again, sounds great for letting my Sadowsky's shine thru.
  8. 4Mal

    4Mal Supporting Member

    Jun 2, 2002
    Columbia River Gorge
    The ART Tube Series stuff is great for this. I've been using their Tube Channel mic pre for about a year. The thing rocks, very clear and uncolored. I picked up one of their Tube EQ's (same EQ as in the Tube Channel) and it has enough gain to take my passive fretless to very loud through my Crown.

    I have no idea how the low-end ART stuff is but their rackable more 'pro' stuff works really well.
  9. thepontif


    Apr 24, 2004
    Designer Fodera Guitars/Michael Pope Design, Inc., Trickfish Amplification
    Ok, here's the poop.
    The input impedance of a Walter Woods effects receive is 1 million ohms. That's the same as the preamp input. If you plug a passive Fender Jazz bass into the FX receive of the WW amp, you can drive the amp to full power. There are two reasons for this:

    1) The 1Megohm impedance doesn't require very much "energy" from the passive pickups. That means that the voltage won't get eaten up and turned into current (voltage, in a front end, is the only real component in loudness). This is called "loading" and it tends to make the bass sound terrible. Dark and unresponsive.

    2) The master volume control is actually a variable gain buffer. So the stage that you're plugging into is actually a very rudimentary preamp that does nothing but boost once you get up to about the number 6 on the control.

    You don't get any EQ, but you get tons of power and a nice clean signal path.

    The preamp in my bass is no big deal. It's an 18V preamp with a 3 band eq at fequency centers that work for me. Not exactly the same as Fodera's, but I have specific needs...human, male needs...


    Anyway, with that preamp I've driven Crown Power Base amps to clipping, but by adjusting the input sensitivity switch inside the back panel of the amp.

    I'm guessing, but I'd think the input impedance of a power amp section or FX receive on most commercially available amps could be anywhere from 600 ohms to 50000 ohms. I'd say 1k to 10k is an accurate next "narrowing down" of those numbers.

    Remember, the higher the number, the less energy is required to drive the input to the voltage that is being produced by the preamp.

    Most preamps would probably be able to drive a 10k load pretty well. You'll reduce the life of your batteries somewhat, but the energy has to come from somewhere.

    So if you add a single gain stage after your preamp...a single op amp with a heafty output can drive almost any amp, any low level load, all day long.

    The next thing is to increase the supply voltage to the preamp...
    Most op amps (which is what the majority of preamps are built around) can be powered with up to 36V. The catch is usually in the electrolytic capacitors in the preamp (the little "can" looking things. They're usually black or dark blue...sometimes other colors though). They are generally either 16V, 25V, 35V, or 50V. In a 9V preamp, the caps will never see greater than 9V, so a 16V cap is fine. Higher voltage caps are ok. If you change them to 35V (usually slightly bigger physically but fittable) you can put 3 batteries in your bass and get a 27V supply. That's that much more energy you can get into the amp...more available headroom. With the buffer you could easily drive almost anything, and if you balanced the output too, you'd really be styling.

    These are things that can be implemented relatively easily and get a LOT of the fat out of the signal path.

    The other thing (that I did in my hotel room when I was out with Chick) is to add a pre eq, pre volume output to the bass and send it to a DI. I was able to vary my eq on the bass without affecting the sound in the house.

    That got long...sorry guys.
  10. thepontif


    Apr 24, 2004
    Designer Fodera Guitars/Michael Pope Design, Inc., Trickfish Amplification

    The sound was different because of a number of factors. The obvious one weren't plugged in to the same stuff. The next obvious one is, there was less gain. The least obvious one is that the fx return was possibly "loading" the output of the bass. Not just reducing the level, but squashing and malforming it.

    If the sound is good and you like it, you just need another gain stage. I could build you one if you want. You'd need to contact me through my web site. There are some available on the market, but they tend to do more to hurt than help.
  11. just an idea for boosting your volume....know those pickup boosters? the ones that are supposed to add like 26 decibals tops to your signal and supposedly give you this fuller pickup tone and bigger feeling? maybe if you put that in the fx loop with your bass you wouldn't have to worry about blowing a couple hundred bux on a new preamp. i might be right, might be wrong, someone correct me if i am.
  12. thepontif


    Apr 24, 2004
    Designer Fodera Guitars/Michael Pope Design, Inc., Trickfish Amplification
    I'm sure that would "work" but how are they powered? If it's a 9V deal then you'll only get probably +/- 2.5V effectively and when you do the math to get it to RMS it's only about +/- 1.75Vrms with very little available current. You won't drive a power amp with that but it might help a little. There are better solutions that I could make for a couple hundred bucks and change that would really give you exactly what you want and nothing beyond what you need. Just really clean, transparent gain.
    There are all kinds of shortcuts and money saving tricks in audio, but at a certain level of application they become false economy. Doing things the right way is always the best way when you get right down to it. The ideal amp is a straight wire with gain. That means that what comes out is the same as what goes in, just bigger. That's not going to happen with PU boosters.
  13. Tim__x


    Aug 13, 2002
    Alberta, Canada
    I don't mean to make you lose buisness Pontif. But a good quality pickup booster will work fine for this application. With good design and rail to rail opamps it's not hard to get 8v peak-peak (5.65v RMS) output with a 9v battery.
  14. thepontif


    Apr 24, 2004
    Designer Fodera Guitars/Michael Pope Design, Inc., Trickfish Amplification
    Well, if the load isn't too deep I guess that could be true. What rail to rail op amp is going to give you nice sounding audio operation without killing your batteries in a hurry? OPA134 is 4 mils quiescent your battery is dead in 150 hours. LF442 is low power, but no where near rail to rail and very little drive current available...lousy slew rate too. TL082 sounds like crap and isn't rail to rail either. A PU booster is OK...but there's no arguing that it's the best solution. It's not likely to get within a volt of the either rail and even that's optimistic. Not that it can't be done...but I'd be surprised if the components in a device designed to cut corners don't serve the same purpose for it's manufacturer.
    How much does a PU booster cost?
    I'll bet the op amps in them cost about 20 cents in quantity...a truly good audio grade op amp sells for $3.00 or more in quantity. Like the Linear Tech 1013 dual chip. 3 dollar op amps come in custom low volume stuff, and in really expensive stuff.
    The parts in a PU booster are designed to boost millivolts to volts. If you're running the output of a Sadowsky preamp into it (which can get pretty hot), you're not likely to get much more gain from the booster except the little bit that it might be able to squeeze out if it can get closer to the rails than the first preamp. If the Sadowsky's not cutting it, the PU booster probably won't either. A 9V preamp won't produce more than 9V (single ended) no matter WHAT you put in. Likewise, no matter how many 9V preamps you put in a row, at the end you won't have more than 9V.
    A PU booster may HELP, but it's not the right tool for the job. I believe in using the right tool for the job. It always yields the best and most consistant, predictable result.
  15. RAM


    May 10, 2000
    Chicago, IL
    Glockenklang and Read Purity both come to mind.