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NAD: The BEST Amp I've Ever Heard!! Kustom KXB500

Discussion in 'Amps and Cabs [BG]' started by Low Class, Aug 3, 2014.


  1. MarkA

    MarkA In the doghouse. Supporting Member

    Sep 26, 2008
    Update on the Kustom: Noticed the volume level fluctuating once or twice -- thought it might be a late-manifesting effect of the aforementioned "toast". Didn't take it in to a tech, but I did pop the top and couldn't find anything burned, burst, or discolored. Thought it might have to do with the much-earlier-mentioned ribbon-cable issue some have encountered with the amp (namely that the connection might have been dirty or slightly corroded, but that unplugging and plugging in the cables seemed to address the issue). Unplugged all of the ribbon cables and cleaned the prongs of the contacts with a cotton swab lightly sprayed with DeOxit D5. Plugged them back in. (Cleaned the pots while I was at it -- volume had become slightly scratchy.) The amp has worked flawlessly since (this was a month or more ago).

    There is still a bit of slowly ebbing, residual doubt regarding the amp but, from everything I can see, it's working fine and seems set to continue doing so.
     
    R&B likes this.
  2. barrybass33

    barrybass33 Supporting Member

    Jan 7, 2008
    westchester new york.
    Going to sell my Kustom KXB 500

    Amp is in great condition....
    If any one is intersted just pm me....
     
  3. Treebeard

    Treebeard

    Jun 5, 2016
    Cary, NC
    Bear Light Symphony, TimepeaceNC Band
    Anybody got some RACK EARS for a kxb they want to get rid of hit me up!
     
  4. shrigg

    shrigg Joy Decision Bassist/BL, AudioKinesis Beta Tester Supporting Member

    Sep 7, 2007
    Traverse City, MI
    I'll look. Here's my KXB500 in action:

    live video
     
  5. Teacher

    Teacher

    May 3, 2012
    Just bought one finally, awaiting delivery!
     
    R&B, Sanchan, Relsom and 1 other person like this.
  6. Teacher

    Teacher

    May 3, 2012
    Ummmm....anyone have any idea what the heck this means? Some hotrodding outfit or something???? 20191111_185711.jpg 20191111_185655.jpg 20191111_185655.jpg 20191111_185655.jpg
     
  7. MarkA

    MarkA In the doghouse. Supporting Member

    Sep 26, 2008
    Sanchan likes this.
  8. Teacher

    Teacher

    May 3, 2012
    Some gut shots. Anything look weird to anybody? I don't see any obvious (to me) signs of work, but I'm no amp tech. 20191112_134909.jpg 20191112_134923.jpg 20191112_134945.jpg 20191112_134952.jpg
     
    Sanchan likes this.
  9. figuredbass

    figuredbass Supporting Member

    Jul 11, 2007
    NYC vicinity
    Thanks for the clear pictures! There are definitely some mods that have been done to this amp. The front panel says "OPA2134/HF Boost" (high frequency boost?) that could be a "bright" switch or treble enhancement mod. OPA2134 is an op amp, obviously used to "upgrade" the original RC4558 used in IC3. (IC3 = integrated circuit #3. In this case IC3 is an audio "op amp" = operational amplifier.)

    Pics #1 & #4 show one of the dis-connectable connectors glued solid, possibly done in an attempt to stabilize it against an intermittent connection that might have been happening there. In pic #2 there is definitely a mod - the blue resistor connected in series with the diode that's glued to the circuit board in a blob of sealant/adhesive. I don't know what the purpose of this mod is though. It's in the vicinity of the IC4 op amp, which is normally used for the clipping indicator and tuner out. In pic #3 the input op amp (IC3), originally an RC4558, has been replaced with an OPA2134. While the OPA2134 is an excellent opamp, it's not exactly a drop-in replacement here without also reversing the polarity of the electrolytic coupling capacitors around it, due to the fact that the DC offsets often reverse when a going from a bipolar (4558) op amp to a FET (2134) op amp in some circuits. I ran into this very issue when I upgraded the 4558s in my own KXB500, so rather than change the caps' polarities, I simply swapped the RC4558s with OP275s (yes, I know many people hate those; I love them for certain things, like upgrading 4558s:)). The other issue with replacing a 4558 with a 2134 is that the 2134 draws more than twice the power than the 4558. I doubt that would be an issue here because in your pictures it looks like only IC3 was swapped, but swapping many of them out could run the risk of over-taxing the power supply of the ICEpower 125ASX2 power amp module.

    I hope this has been helpful!
     
    MarkA and Teacher like this.
  10. Teacher

    Teacher

    May 3, 2012
    Thanks, man! No, I have no idea what that means, but I do appreciate your awesome input! So what might that mean for my sound?
     
  11. figuredbass

    figuredbass Supporting Member

    Jul 11, 2007
    NYC vicinity
    I wish I could give you more info, but I'm not certain what any change in sound would be, if any. The only clue is "HF Boost" written on the panel, but it's impossible to say if it's an actual treble boost ("bright") permanently put into the amp or if it's has been removed and put back into stock condition prior to selling the amp. Sorry I can't offer more help on that. I do know for a fact that the KXB500 is a perfectly flat, clean amp with the tone controls set at noon (zero internal voicings), so you could A/B it against another amp you're certain also has a flat response to hear if there is any noticeable tonal change.
     
  12. Teacher

    Teacher

    May 3, 2012
    I could only compare it against my '68 200s and my Hartke B9p, so that's a no go. But it doesn't sound particularly bright to me. At any rate, it is definitely a lovely little amp. Who knows? Some day, if I find another at a good price, I may pick it up and a/b them.
     
    figuredbass likes this.
  13. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Those pictures show a hack job on soldering a couple of replacement ICs. Workmanship like that would have me very concerned that the rest of the work and the thought process behind the work is equally defective.
     
    noeinstein likes this.
  14. Meaculpa

    Meaculpa

    May 18, 2019
    You're right. Gk has that and "gk sound" added... what you looking for is called Hartke.
     
  15. BogeyBass

    BogeyBass Inactive

    Sep 14, 2010
    oh boy
    opamp " upgrades"

    what opamp is best for Metal ?

    id only guess its same ultra rare inline package that got discontinued in the 90s of course lol
     
  16. shrigg

    shrigg Joy Decision Bassist/BL, AudioKinesis Beta Tester Supporting Member

    Sep 7, 2007
    Traverse City, MI
    MarkA likes this.
  17. MarkA

    MarkA In the doghouse. Supporting Member

    Sep 26, 2008
    Thanks for posting this.

    Not that this amp needs a manual for basic operation (indeed, I'm not certain that I've ever read mine -- maybe at some point), but, in skimming this, I learned a thing or two (like how the mute function and effects loop can be controlled via footswitch).

    An interesting (to me) note on the Gain control -- from the manual:

    Gain: Adjust this control clockwise as required to increase the amount of preamp gain. If your bass has powerful or active pickups, you may need to reduce Gain to avoid unwanted distortion. Alternately, if your bass has low-output, vintage-style pickups, you may need to turn the Gain control up. Start with this control set at 12:00 to determine if further adjustment is required. In general, set the Gain control as high as possible without generating audio distortion, unless of course you desire it.
    Setting the gain control "as high as possible without distortion" (or close) is how I've generally proceeded with solid-state amps -- at least to start. In most cases, I find that this gives me the most detailed and open sound. I also pay attention to the dynamic feel. Solid state front ends (unless they're specifically designed to emulate a tube, etc.) tend to be more linear in their response than a tube front end, but there still seems to be a sweet spot (or multiple sweet spots, depending on your goal) with regard to gain-staging, even if the effects are more subtle.

    Anyway, I was in the habit of running the Gain pretty high (2 o'clock-ish -- maybe even a bit higher, sometimes) with the KXB and my passive bass. I might have been getting a tiny bit of harmonic distortion but, if so, it was subtle and more perceived as a little extra brightness/edge than as distortion per se. I found, though, that dialing the Gain back some (still past noon) and dialing up the Master to compensate made the amp feel more dynamic and responsive -- palpably so, particularly when playing with a drummer.

    Below a certain point, there was no dynamic advantage and the sound became dull.

    Nothing groundbreaking here -- I'd just gotten into a habit of setting the amp a certain way. Once I used my ears again and started over, I found that that wasn't the best way (at least for me).
     
  18. shrigg

    shrigg Joy Decision Bassist/BL, AudioKinesis Beta Tester Supporting Member

    Sep 7, 2007
    Traverse City, MI
    Yeah, I usually am around 1:00 on the gain and I really like the way the amp responds with my P Bass (with SPB-1's). I run it that way with an always-on Catalinbread RAH in my Joy Decision band and I get a really great Hooky pushed Hiwatt tone. Even for non-pushed use I leave it around 1:00 because it seems there is a little "extra" life in the amp compared with lower settings. Kind of like the Drive control on the TH500 which I like right at 9:00.
     
  19. shrigg

    shrigg Joy Decision Bassist/BL, AudioKinesis Beta Tester Supporting Member

    Sep 7, 2007
    Traverse City, MI
    PS: The main reason I was looking at the manual was to try and see if there was an integral HPF in the KXB500... Seems not, but does anyone know for sure?
     
  20. MarkA

    MarkA In the doghouse. Supporting Member

    Sep 26, 2008
    I suspect that there is one -- most (not all) modern amps seem to have some form of protection from at least very deep sub lows. Too, played side-by-side with some other amps which I know do extend quite low (the Eich T-900 I used to have, for one) the Kustom sounds, feels, and looks (less cone movement) like it has less going on in the very deep lows.

    Exactly what it's got going on to effect that, though, I can't say.
     

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