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Custom 1000 W quad channel amplifier build

Discussion in 'Amps and Cabs [BG]' started by Jeff Siddall, Dec 5, 2018.


  1. I built a custom fEARful 12/6/1 cab earlier this year, and now I need an amp. I was planning on buying some off-the-shelf class D amp but my long list requirements ended up eliminating everything on the market:
    1. 3-channels (or more) to provide active crossover of cabinet
    2. 1000-ish watts RMS into 8 ohms
    3. Rough power split of 75% LF, 20% MID, 5% HF
    4. Fit into 2U rack space
    5. Weigh < 20 lb
    6. Noise < 30 dBA
    7. Less than 14" deep
    8. Looks decent
    9. Moderately affordable
    10. Readily available replacement parts
    11. Easy to repair
    12. Remote control power
    90% of what is out there was out by item 1 and a little further down the list there was nothing left. So, I decided I should build a custom amp that meets all of my requirements.

    To be clear I am not building everything from scratch but rather combining off-the-shelf modules and wiring them up into the form factor I want. Even so, it will be on the edge of my ambition limit!

    So far I have purchased and tested all 4 amp modules and power supplies. Combined they really do put out 1000 W RMS clean power into 8 ohms as 760 W (2x380 W bridged) + 210 W + 30 W for minutes at a time. I have also replaced all the fans with Arctic Cooling thermal controlled versions so as of now all my requirements are met. Obviously number 8 in the list above is subjective but if I can manage to build this out of steel and maple it will look good to me at least.

    I have the chassis and wood started but am waiting for a lot of other misc parts. So far I have mainly just created a render of what I want it to look like and where all the components will go inside the box:

    Custom_Bass_Amplifier_Layout_v1.1_crop.

    Time will tell how long the real work takes.

    Updates:
    Rear Panel Progress
    Finished Rear Panel
    Finished Front Panel
     
    Last edited: Dec 20, 2018
  2. Wasnex

    Wasnex

    Dec 25, 2011
    Cool project :thumbsup:. I don't have the back ground to help with the amp design, but I do have experience with running active speakers. What will you use to form your active crossover networks? If you are using off the shelf processing, have you set up and run the speaker active so you have an idea of how much benefit you will gain? I suspect there will be improvement in performance unless you go to the effort of phase aligning all the drivers.

    I currently use a couple of KT DN9848E which has 4 inputs and 8 outputs. Each input and output has delay, parametric EQ, and compression. The outputs also have peak limiting and a range of selectable high pass filters, low pass filters, and all pass filters. It can be pretty challenging to dial in a system by ear with all these parameters. Ideally you will want a measurement suite like SMAART so you can visualize delay and phase errors. I haven't used SMAART myself, but I have observed technicians using it and mixed on the systems afterwards. Nice!

    Anyway, good luck and have fun!
     
    Pbassmanca likes this.
  3. Thanks!

    So far I just have a SUPER-X PRO CX2310 3-way. It has 24 db/octave filters that are supposedly phase aligned. My goal was simply to build something better than a passive crossover in the cab so I should have already achieved that. If I really wanted to tweak phase that closely then I could get a high end crossover/processor as you have done.

    I did hook up the rig using a 2-channel sound reinforcement amp and ran the fEARful in a 2-way config and was very happy with how that sounded. I also ran the LF driver alone with the bridged 760 W amp modules and literally shook the house. A box of screws vibrated off a shelf near the cab when I hit a low B :D
     
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  4. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Impressive number of fans!
     
  5. Ha, yes. Since your signature says "Product Development Engineer" I feel authorized to bore you with some details: The noise level of all 5 fans combined is just 29.5 dB. The two exhaust fans, which will be the source of most of the noise, have a combined SPL of 25.5 dB.

    The chassis should have a maximum heat load of 235 W. With the rated free air flow of the fans that can be extracted with a 7 C temperature rise.
     
    okcrum, Pbassmanca and agedhorse like this.
  6. ThisBass

    ThisBass

    Aug 29, 2012
    Germany
    I think its (at least) risky to power 750 Watt into a 3" VC woofer with an electric bass guitar. You should be knowledged of one or two things about some science electroacoustic wise and also acoustic science as well to be fine in any situation of real practice just to not "overstrain" the speaker thus not damage the device over time.

    Your rough power assumption of
    split of 75% LF, 20% MID, 5% HF

    tells that you are NOT experienced enough just to devide power density (and dynamic demands) for an electric bass guitar

    edit,
    you didn't tell us anything about the lowest tuning of your instrument, nothing known about your prefered music genre, your prefered sound setting, nothing is known about your effects used if there are any, nothing is known about your playing style such as you may play with fingers or if you just use a pic, nothing is known about your string damping techniques.

    Did I forget anything what's furthermore neccessary just to judge "individual" power strain to a cabinet?

    edit,
    we don't know if your 12" woofer is protected by a HPF which helps to suppress transient (sub) noise (no, its no sub Harmonics) which easily harms drivers to be pushed beyond Xlim with transient frequnecies below tuning.
    I have told this issue frequently on this form. Transient noise is a very different animal versus considerations of even and odd order Harmonics which are compoesed by playing a note on the instrument but, to the contrary its kinda of a natural "sub noise" which is very natural coming along with every stringed instrument.
     
    Last edited: Dec 5, 2018
    Pbassmanca likes this.
  7. Wasnex

    Wasnex

    Dec 25, 2011
    Supposedly the Greenboy crossovers are phase aligned as well. fEARful passive crossovers by greenboy

    I am an advocate of active, but the advantages are not as significant as they were years ago when you needed to extract every last watt of power for maximum SPL out of a Crown DC300...which was once considered a powerful amp. I think the time to use active today is when you want to tweak every parameter of the system alignment for maximum performance. So basically if your not down in the weeds looking to improve phase and subtle EQ issues, you might as well just get a big power amp that can overcome the power lost to the passive crossover. Still an interesting and fun project :thumbsup:.

    For the record I have two active crossovers, a biamp capable bass amp (GK 2000RB), and an old parametric EQ (Orban 672A) with separate HPF and LFP sections that can be configured as 12dB/octave crossover. I have had a lot of fun playing with these (and lot's of other pro sound gear) over the years, and typically use polarity and physical offset to try and account for phase issues when I don't have digital delay...it's so much nicer now that I have my own processors with electronic delay capabilities.
     
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  8. ThisBass

    ThisBass

    Aug 29, 2012
    Germany
    Such as things sometimes are used in the (misterious) HiFi world were costs is no limiting factor nothing at all, right?;)
     
    Pbassmanca likes this.
  9. Actually, those Eminence Kappalite 12" drivers are rated for 450 W continuous and 900 W program so 750 W of clean bass guitar is far from risky for this driver. Greenboy's maximum excursion chart claims the LF driver can take it's maximum power from 60 Hz up:

    fEARful™ FAQ

    Many users have had success with those levels of power so I am not too worried. Having said that, yes, I will also use a HPF to prevent over excursion due to excessively low frequencies.

    Also, my goal for this amp is to essentially match it to the capabilities of the cabinet's drivers. I didn't want an amp that was limited to a certain style of playing, or a certain type of instrument. Rather, the power splits I listed are simply those that allow the amp to deliver clean power to the realistic power limits of the individual drivers. Will I be running a continuous 1000 W into the cab with all drivers running at their maximum power? Absolutely not. But can I maximize the capabilities of the cabinet, regardless of the source material, using this amp? Yes, I believe I can.

    Understood, and those Greenboy crossovers are probably pretty good. However, they are expensive to build properly, they allow no control over crossover frequency, levels of the individual drivers, power limits on individual drivers, phase control etc. Fundamentally they seem inferior in nearly all respects to an active setup.

    I envy your processor for sure, and after I get this all running maybe I will decide that is the level of customization I want. Either way, the amp is going to meet my needs so that seems like the next step to getting to my "ultimate rig".
     
    Pbassmanca likes this.
  10. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Or where status is more important the accurate.
     
    Pbassmanca, Bim1959, DJ Bebop and 3 others like this.
  11. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    I strongly disagree, and I do have EXTENSIVE experience with the "LITE" platform from the very beginning of their production.
     
  12. I'm all ears. Please explain!
     
    Pbassmanca likes this.
  13. Wasnex

    Wasnex

    Dec 25, 2011
    Not from what I remember reading in HiFi related webpages. HiFi cork sniffers tend to look down on digital gear such as the KT DN9848E and favor analog, passive crossovers, or designs that use no crossovers at all. My perspective could be out of date since I haven't followed HiFi for many years.

    Plenty of more modest speaker processors have delay capabilities, DBX DriverRack for example. I have used DriveRacks with JBL VersArray rigs and the stock tunings include delay offsets between the woofer and horn in the mid/hi packs. Perhaps a sophisticated user might think to dial in some delay between the mid/hi packs and the subwoofer as well after the rig is set up....as I am sure you know, it's possible to deal with phase errors between drivers in a crude manner by tuning by ear.

    If you were putting together a multi-way system with fixed driver relationships like the OP's speaker, it probably wouldn't cost that much to have someone run a SMAART analysis and dial in your processor.
     
  14. Wasnex

    Wasnex

    Dec 25, 2011
    I think what you may be missing is the amount of engineering that went into the Greenboy crossovers to make his designs work as well as the do. Can the designs be improved, yes, but I suspect simply converting to active crossovers is unlikely to exceed the synergy of the originals. I am not saying your tri-amp rig won't sound good. But it may not actually sound better than an adequately powered passive rig that has superior engineering...but that wouldn't stop me from doing it since it sounds like a really fun project ;).
     
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  15. mmbongo

    mmbongo Dilly Dilly! Supporting Member

    Aug 5, 2009
    Carolinas
    lol, do you not know who you're talking to there?
     
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  16. ThisBass

    ThisBass

    Aug 29, 2012
    Germany
    At least THIS assumption you are just doing on your own disqualifies yourself from doing more of experiments with outcomes you never can predict by yourself.

    You can't get 750 Watt of clean bass guitar out of it. If any than there is really no more than 1/10 of this expected "clean" power available which in number derates your 750 Watt assumption down to (roughly) 75 Watt at best.




    Didn't read the specs but, bass players do really rarely (if any) play steady sinusiodal signals with their bass guitar instrument.
    Real world "practice" considerations needs some different considerations what's really going on under the hood.

    German language words "Papier ist geduldig"
    paper words are patient words
     
    Last edited: Dec 5, 2018
  17. Greyvagabond

    Greyvagabond Supporting Member

    Aug 17, 2007
    Los Angeles
    Mother of god, that thing will thump. Not sure what types of gigs you're playing where you need a 1,000 watts, but that thing is going to to awesome!
     
    Pbassmanca likes this.
  18. TrevorOfDoom

    TrevorOfDoom Supporting Member

    Jun 17, 2007
    Austin, TX
    I'm just gonna throw this out there:
    A Greenboy True 12/6/1 crossover runs about $45 on speakerhardware.com
    You're telling me your tri-amp fan-apalooza is gonna cost less than $45 to make?
    :eyebrow:

    I will echo the thoughts of a previous poster:
    Greenboy put a LOT of work into those cabs to make them the best they can be. Like all good speaker designs, the crossover is made to match the speakers and the cab. If one is changed, the whole thing changes.
    So I'm not sure how your tri-amp thing could possibly sound better than what Greenboy already designed.

    Of course, I'm willing to be wrong. And I love a good nerdy project, so I'll be watching this thread.
     
  19. TrevorOfDoom

    TrevorOfDoom Supporting Member

    Jun 17, 2007
    Austin, TX
    Greenboy's specs indicate that a properly built and cross-overed 12/6 should be able to handle ~500 watts, continuous.
    And I usually suggest not even looking at the Peak or Program wattage, as a speaker usually only gets to that power right before the speaker blows up.

    This thing seems like overkill.
    This isn't a '98 Honda Civic you're souping up, this is a Lamborghini. It's already there.
    But again, I'm curious what will come of this.
     
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  20. Wasnex

    Wasnex

    Dec 25, 2011
    Something you may not be aware of, if you change the output level of one of the drivers this shifts the effective crossover frequency and also can introduce phase error between the drivers as well. I can't say for sure, but this could be one reason why variable level controls were not included in these designs.
     

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