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Tech advice needed please

Discussion in 'Amps and Cabs [BG]' started by PattyT, Oct 29, 2018.

  1. Hi guys,

    I've recently become a dad and as such am fairly poor monetarily.
    The local original music scene is forthcoming with gigs but they all pay really poorly and I need something I can gig with that's a bit louder than my peavey 112 solid state.

    I've been looking into diy options and have found some promising ideas.

    There are several class d solid state mono amplifier boards around with 200w rms (effectively my target wattage) for under 20bucks in component form.
    I have a ton of stuff lying around and simply need a diy head to use with a free EA 210 cab I got off a mate.

    I'll be replacing the speakers and wiring in the 210 cab with somethin gf like the deletion 10" drivers that are recommended for ampeg replacements.

    I'm competent with the wiring but need to work out power supply and input impedance.

    Power supply wise I'm planning on using a 500w computer psu I have lying around which can give me the 12v and 10a I need for the amp circuit and am wondering if any diy-ers in here have done the same with any suggestions for me.
    Bonus with this is that the computer psu also has 5v dc so I can run some led's in the case I make so make it look sweet.

    Input impedance is my real issue.
    I have no idea what a nominal input impedance would be for a regular bass amp and my searches have been inconclusive so far.
    I just need to know whether I need to run a preamp as well or if I'll get away with just the mono block.

    Any help would be muchly appreciated and ill try and get a build thread up for those interested when i finally get it done

  2. agedhorse

    agedhorse SUSPENDED Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Ummm, a 12V, 10A power supply is only 120 watts, computer power supplies are generally tightly limited, and I don't know of any class D boards that deliver a real 200 watts RMS with a 12V input.

    Perhaps you would be better off looking for a working used amp so you don't throw your money away. That's what it looks like you are planning on doing, even though you don't realize it...
  3. sawzalot

    sawzalot Supporting Member

    Oct 18, 2007
    Even though it's fun to think about, things like this can become much more costly than originally planned. I'd go with a decent used commercial bass head. Supply might be tight down under, but hopefully you can find something.
    Munjibunga and alaskaleftybass like this.
  4. Congrats on the new baby.
    I recall those days, faintly. Lots of expenses, little to no fun money.
    If you have all the pieces on hand and just want to experiment, while understanding that your Peavey will likely still work better than what you might throw together for free or on the cheap, by all means experiment away.

    Sans possible power supply issues to drive your 200 watt amp, it sounds like you need a preamp to put ahead of the amplifier? An outboard bass preamp can get pretty pricey. But if you have an effects loop on your Peavey and everything else works well, you can take the effects OUT (aka SEND) and that may drive your DIY amp. Then you don’t need to be concerned with the input impedance.

    If you really do need the info though, you want the input to be upwards of several hundred KOhms to a Meg.

    I must add caution though because from your OP, you don’t sound as if you have yet acquired the necessary knowledge to understand how this stuff works. If you have to sink any money into this, and you need a giggable amp, you are likely headed down the wrong road doing a DIY. I know you are on a tight budget right now, but if you end up throwing good money after bad, then things will get even tighter.

    If you can put a little away, and that will be tough, I know. You might be able to find a better amp and even trade in your Peavey or sell it to help offset the cost.

    Anyway, being a Dad to a newborn is going to be full time job on top of whatever else occupies your time.
    Can’t offer any more amp advice. Take the time you have with the youngen and make the best of it.

    Good luck and good health to the baby.
  5. pcake

    pcake Supporting Member

    Sep 20, 2011
    Los Angeleez
    just because you want something to work a certain way (and i get it - i do) doesn't mean that it will. pretty sure this project will be one of those times.
    Munjibunga and Rumbledore like this.
  6. G'day Pat, if Agedhorse says you are barking up the wrong tree it's a pretty safe bet to look for another tree.

    Replacing bass speakers with bass speakers is no guarantee of success with the cab either.

    Gumtree, look out.
    Rebel Rocker and G-Z like this.
  7. Sorry, I didn't mention it in the op, I plan to use 2 of these amp modules.
    The power supply I have is a modular thermaltake unit good for 500w with 2x 12v 10a circuits and also a few 5v circuits I plan to use for some sick lighting

    The power side works out fine mathematically (I've got power to spare on this psu)
  8. Too right! Used heads are almost as expensive as new ones! Not even classifieds around here have decent cheap ones unfortunately
  9. T
    Cheers mate
    I've been doing a ton of research and am definitely still learning about the specific circuitry but I am also a qualified low voltage technician so am grasping it all very quick.
    Old Garage-Bander likes this.
  10. Thanks for the feedback.

    In regards to the celestions I'm looking at using I have the spec sheets for the original speakers and the celestions and the celestions have better theoretical efficiency in the enclosure I have with some different porting which I'm also working on
  11. JimChjones


    Aug 6, 2017
    SE England
    I was considering this recently, and the conclusions I reluctantly came to was that the power amp side was a relatively small part of the equation, and because available preamps are all pretty fully featured there was no way to save money over the commercial low end of the range class Ds.

    In your position I would keep an eye open for a cheap secondhand powered monitor to use as a slave amp. Where I am they are frequently available very cheaply. You could then, if you needed, upgrade the cabinet and speaker at your leisure if you felt you needed to or just transplant the amp into the 2x10.
  12. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    Some players would sell their first born for the perfect rig. I can see why you wouldn't want to do that.

    Patching together a good amp isn't as easy as making a baby but it too, can get expensive by the time all the parts have been delivered and assembled. Connecting two computer power supply outputs to stack the voltages has it's perils.

    Adopting an amp can be a far more cost effective solution. It’s safer than building a monster.

    frankenstein monster.
    Last edited: Oct 30, 2018
    Munjibunga and alaskaleftybass like this.
  13. Pick up a used peavey 15. They're cheap new, they're half priced or less used. 300 for a new Max15, probably get a older combo for less than 100. They're cheap, they rock, they last.
  14. I'm also going to recommend you look for an old Peavey head from the late 70's/early 80's. As long as it's lived indoors and been run every once in a while, it will serve you well.
    Bim1959, Skillet, Rumbledore and 2 others like this.
  15. DocTT


    Apr 22, 2018
    Be careful with those inexpensive board amps. The 200 watt rating may be at a very high distortion level rating, like 10%. Also, while it may operate at 12vdc, the maximum output is likely to need a much higher input (40-60vdc), and that claimed 200watt maximum may be at 2 ohm. An 8-ohm load may only get 50 watt or less, even with 60v input. Verify the rating is RMS, not peak. Finally, bass signals are much more stressful on amp than typical full-time audio; they need to generate a lot of current to move a lot of air, and IMO, there just won't be enough current available, particularly at 12vdc. you can count on a very distorted output. And at $20? Don't see it. Get a bass amp. Or, use a bass pre amp into a PA amp. Used PA amps are cheap.
    pcake and agedhorse like this.
  16. agedhorse

    agedhorse SUSPENDED Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Unless there is a boost converter as part of the preamp, 12 volts isn't going to get you anywhere near 200 watts, even at 4 ohms BTL.
  17. If those $20-$50 amp boards worked good for bass amplification there would be an active club on TalkBass proud of their cheap homemade amp heads, but there is not which tells me them boards are not.
    Munjibunga and alaskaleftybass like this.
  18. voided3


    Nov 11, 2008
    Three things that I am surprised have not been mentioned yet:
    1. What is your total budget for an amp head, if you had to put a price on it?
    2. Have you considered making a head case for your Peavey combo's amp section to drive the EA cabinet, as long as the speaker impedance is compatible?
    3. Used Fender Rumble head!
    I like the suggestion of a used powered PA head, too. Powered PA speakers have dominated the local gigging scene for a while now so I'd imagine these are relatively easy to come by at a small price.
  19. DocTT


    Apr 22, 2018
    That $20 board is also not likely to have clipping protection. As soon as maximum output is exceeded, you'll start passing square waves. The top and bottom of square waves are DC, and that's a primary cause of blown drivers.
  20. byacey


    May 16, 2008
    Alberta, Canada
    Much of the power rating on that supply is for the 5 volt supplies, which isn't of much use in your application. Even the 12 volt rail doesn't lend itself well towards linear output designs. Should it have a separate -12 volt supply capable of 10A, it would still be a relatively low power amp. I think the advice given to save up your money to put towards a used amp is good advice.
    agedhorse likes this.

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