1. Please take 30 seconds to register your free account to remove most ads, post topics, make friends, earn reward points at our store, and more!  
    TalkBass.com has been uniting the low end since 1998.  Join us! :)

GK 2001RBP is "not loud enough." Headroom, or...?

Discussion in 'Amps and Cabs [BG]' started by Anthony Fury, Dec 30, 2012.

  1. Anthony Fury

    Anthony Fury

    Jan 20, 2009
    Hey gang - I read through the FAQ and couldn't find anything like this, so here goes:

    Combo used to be:
    -Ampeg SVT Preamp
    -Crown PowerBase II Power Amp
    -Eden D410XLT

    It used to scream and was crystal clear.

    Combo is now the same except the Ampeg has been replaced with a GK 2001RBP. The only way I can get close to useable stage volume is to run without the -10dB pad and with the gain and master volumes cranked, which can't be right. I've tried:

    - Other basses with similar electronics / fresh batteries (no change)
    - Passive basses (no change)
    - Another D410XLT (no change)
    - Switching power amp channels (no change). Note: both channels of the Power Base II have attenuators, which I leave at 0 (all the way up) and only really touch them to troubleshoot / test.

    I have not tried another power amp altogether.

    Anyway, What can I check myself? I have a VOM and am not afraid to use it.

    Or has anyone else ever had a problem like this?

    Thank you in advance!
  2. RickenBoogie


    Jul 22, 2007
    Dallas, TX
    It may well be that the output of your preamp is not sufficient to drive the GK poweramp properly. Look at the input sensitivity specs on the GK vs the output of your preamp.
  3. Anthony Fury

    Anthony Fury

    Jan 20, 2009
    WOW man, I think you just saved Christmas, seriously!! I looked up the manual online and there's a 3-way switch hidden underneath a panel which sets input sensitivity and which I didn't know about. I'm trying this when I get home, thanks a million!!

  4. JimmyM


    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    I have to ask why use the Crown when you have a 1000w amp on the GK that you'll never be able to use fully with a 410.
  5. The 2001RBP is a 1RU preamp, easily confused with the 1000w 2001RB head.
  6. Indeed.
  7. Brad Johnson

    Brad Johnson Supporting Member

    Mar 8, 2000
    Gaithersburg, Md
    Yep... fairly rare too.
  8. JimmyM


    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    DOH! Sorry about that!
  9. GMSweet


    Oct 12, 2007
    New Hampshire
    I went through two 2001RBPs that only worked for a few hours before exhibiting similar problems. In my case, once the unit failed I could hear a rattling inside of the preamp. I eventually walked away from the GK since that was a common problem. I hope that isn't the case for you. Mine were brand new in the box when I bought then. If you Google the 2001RBP you will find similar stories.

  10. Anthony Fury

    Anthony Fury

    Jan 20, 2009
    Yes, thanks for clearing up. Sorry for not making it clearer.

    :meh: Yikes!

    So, first thing -

    I popped off that hidden plate on the Crown PBII and checked the switch. There are 3 settings: 0.775v, 1.4v, and "26dB." I've been doing my homework and have found some great TB threads, and, 0.775 is what I need (or my best shot, rather). It was set on 0.775 like it had been from the factory. I tried the other settings and everything just got quieter. The switch is inside the "works," and it definitely looks like 15 years of filtered grime is settled in there, so I wondered if the contacts were just dirty. I worked the switch back and forth a bunch but no change. (I think it's time anyway to pop it apart and clean it out!)

    Next, I tried a few things. The B "overdrive" channel of the RBP is much louder than the A channel, so I worked with that one. With the gain / level / master cranked to 11, I got it to squeak a little. I then tried using the "send" output for the effects instead, and it really began to kick. So, I put the VOM on the regular "Line Out" (with everything cranked) - the most I could get it to do was 0.08VAC. With the effects "send" output (and everything cranked), I got 0.2 - 0.25VAC. According to what I've read, I should be getting on the order of "whole" volts coming out of the Line Out at even modest levels.

    Edit: I am getting the same ~0.2VAC out of my old Seymour Duncan Live Wires at full blast (if you know what these are, please don't laugh/shun me too hard, haha)....I can actually plug straight into my Crown and play at a pretty menacing volume (though the driver excursion doesn't look very healthy).

    Based on the kindergarten schematic GK gives you, it looks like the problem exists somewhere in the "post" chain. I'm thinking it could maybe be something easy like an incorrect pot value / resistor from the factory? I know the circuit gets a little different in the RBP because of the bi-amp thing -for instance the tweeter function is totally abandoned in place- so maybe they forgot to iron something out in production. Thoughts??

    I got asked to work the Wanda Jackson show tonight, so R&D will have to resume tomorrow if I'm not completely out of it. *hiccup*
  11. 1958Bassman


    Oct 20, 2007
    Do you have the footswitch that's supposed to be used with this preamp? Does the Boost LED turn on?

    Post a photo of the controls.
  12. Anthony Fury

    Anthony Fury

    Jan 20, 2009
    Yes, I do. No, it doesn't because there isn't one. The 3 switches you get are A/B toggle, Tuner Mute, and Horn Cut which does nothing, because.......

    The entire Bi-amp part of this preamp is totally null & void, since it only has one Chain Out, a D.I. out and an FX loop. The 3 switches to the left, taken out by the flash are "-10dB pad," "A/B" and "Mute." At the right, the "Tweeter Hi-Cut," "Woofer Hi-Cut" and "Tweeter" knob do absolutely nothing. The "Woofer" knob is the main volume.

    This picture sucks, sorry in advance:


    Here are some better pictures of exactly what I'm working with (I love how every thread about these is a "for sale" thread, hahaha)

  13. GMSweet


    Oct 12, 2007
    New Hampshire

    Just so you have the details, here's what I went through with two units. The two I had had serial numbers that were only 33 units different, so it may have been a bad batch.

    I sent these notes to Brian at GK who then agreed to RMA the unit.

    • Problem appears to be at the input side. If I max out all tone controls on my bass ((J/MM bass with 18v Aguilar OB-3) and all EQ pots on the preamp, I get a faint signal out.
    • The clip light never comes on, even with the bass as hot as it goes.
    • The -14db pad switch has no affect
    • Channel B is slightly louder at max compared to channel A
    • I’ve tried the chain out and the DI out with no difference
    • Send out and tuner out show no real signal either
    • Multiple cable swaps have been tried.
    • Power light goes blue as expected. I even tried removing power for a few minutes to “reboot” the unit; no change.
    • My Ampeg SVP-PRO still works fine with the bass and all of the same cables

    I'm hoping that you have a different experience since you are getting signal out of the "send out" where I wasn't. For me the telling part was being unable to register a signal at the input stage... and the rattle inside of the unit. ;)

    If you want, I can PM you Brian's email address. Brian used to be on TB as well, but I haven't checked in a while.

  14. Um..... are those your usual settings?
  15. Brian is no longer with G-K but you can email jason@gallien.com. If you have a decent signal at the effects send I would suggest looping an instrument cable from effects send to return and trying the normal output again. Sounds like a dirty effects return jack.
  16. pickles

    pickles Gold Supporting Member

    Mar 23, 2000
    Ventura, CA
    Why are you replacing the ampeg with the gk? Why not just get a 1001rb-2 or mb500 for a Gk sound?
  17. JimmyM


    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    I want to hear more about Wanda! Only did one show with her but I loved her and I love all her old music, even some of the cheesy country stuff ;)
  18. GregC

    GregC Johnny and Joe Gold Supporting Member

    Jan 19, 2007
    My fiancee and I were up front at that show last nigt. Were you backing Wanda on the upright last night? If so, strong work! I thought the band was all Nashville guys.
    It was a great show, Jimmy, she did a really nice career retrospective set sampling the early rockabilly days, the country stuff and cuts from her two recent albums produced (respectively) by Jack White and Justin Townes Earle. She had the audience in the palm of her hand, and reached out during one song and clasped my hand and then my fiancee's--we just plain loved her. Man, I hope I can play an hour and 15-minute set with half that much joie de vivre when I'm 75.

    The bonus was, the Dirt Daubers (an offshoot of Mark/dukeorock's Shackshakers) opened up and had a burlesque act on stage at one point. A great night for sure.
  19. JimmyM


    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    Ya, the Dirt Daubers are quite cool. That's a pretty long set out of Wanda, though. When I worked with her, she did the 5 biggest songs and left, but then again, she was one act out of 12 on that show and wasn't headlining ;)
  20. Anthony Fury

    Anthony Fury

    Jan 20, 2009
    GMSweet: thanks for the input and the advice / email address!

    Jimi: HAHA, no, that was just a pic of how it was in the middle of me horsing around with it.

    B-string: that is an excellent idea. I will try that today. And thank you for the email also.

    Pickles: the Ampeg is long gone (actually sold on here a couple of years back) because for the life of me, I couldn't get ONE sound I liked out of it.

    JimmyM: The show was pretty amazing, I think. When she broke into "Heartbreak Hotel," I seriously got goosebumps. She used to date Elvis! And the Dirt Daubers were awesome / very nice people as well (shared the merch table with them).

    Greg: Are you from Chicago? I WISH I'd been asked to back her up, haha. I was actually the merch guy for her, sitting all the way in back like a butthead. And even then I thought the show was awesome.

    Back to my silly pre-amp, I'm taking it to a grown-up for help today, haha. I'm fairly certain he can get this thing spurred into action, and when he does I'll share the details.