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Power amps

Discussion in 'Amps and Cabs [BG]' started by mlowe, Mar 27, 2005.

  1. In all the talk about amps and cabs. I've noticed that many of you hate the fact that amps are so heavy. Makes senses if you're the one lugging it to gigs.

    I've been spending many hours building a variety of power amps focused only on bass guitar. There are many reasons why I did this. One is that I've always been interested in electroincs so to pay about 3 grand here for something I can build very easily for $700 bucks means more money for a better bass. Better power amp too in some cases.

    The other reasons could be that most of the bass power amps are not as grunty as they could be. I know that sounds very bold but I mean that in terms of sound, not volume.

    I have just finished a 2 channel power amp that has the following specs but it is very heavy and the build is quite intense for the jo blow. (Safety issues etc)

    2 x 850W RMS @ 4 ohms, 450W @ 8ohms and damping factor greater than 300 when operated 8 phms. In has bal/unbal input, input sensitivity control and soft start etc. All the usual requirements for a nice bass amp. Under $1000 in parts.

    The main factor in building this amp was sound by means of headroom. Huge grunt turned down low sounds great.

    As this forum has had many posts about equipment weight it reminded me of a amplifier that I was looking at before I built this one.

    It was a digital class D type but at that time had a few criteria that didn't suite the bass amp. Mainly ability to bridge or operate in stereo with flexability etc.

    The same group here in Australia now has one or two that will do this. In fact the specs are incredible.

    This amp would be,
    Single channel
    750W RMS @ 8
    1400W RMS @ 4
    Weight would be very very light. And it's light. The transformer is the only heavy item in the whole amp. And it's even much smaller than the norm

    As this exact amp is about 96% effiecient as compared to the average class a,b being half that, there is almost no waste, no heat and they are now very low distortion. Are in the hifi grade for sure. Very robust.

    This amp has great damping factor specs, and can also be built with less power by only changing the transformer spec. The amp modules are the same. The above power rating would be the maximum safe continous operating.

    This amp can be built for around the $900-1000AUS so about $750 US for our friends in the US.

    Imagine picking it up and it only weighs about 8lbs. But it makes 1400W RMS. When you see the indside of the amp you will say NO WAY. I said the same. It's so simple.

    If any of you guys are interested, I was thinking it could be an DIY amp for people here that wish to build their own. It isn't about profit. Just aiding each other to build and improve this item. Eveyone involved chips in, and it makes it very easy for all.

    If you guys are interested please post a reply and I will go to the trouble of gathering all the information and post it here so you can read up for yourself. So far I can't see anything negative about this design and it's application as a great bass amp.

    I will be building one as soon as possible and would like to get some feedback from some players on their thoughts of its performance. The build of these amps is extremley simply. In fact with a kit form you could assemble it in a few hours.

  2. Wow, this sounds to good to be true.
  3. And most of the best designs so far come from, well, Sweden!
    I'm getting some photos as soon. I just need to get permission first before posting them.
  4. dood


    Dec 9, 2004
    This i've gotta see! I'm interested in Electronics, and this certainly sounds good!

  5. dude, im so there. ive been interested in making a tube amp kit for a long time but i have never had the time. i was planning on trying to do one this summer. let me know ASAP when you can get one together, and a parts list and directions and that sort of thing

    PM as soon as you have any more details, or start a new thread when this one dies :cool:

    actually im aslo interested in this other amp your talking about, but i doubt i would have the skills to build as i only have a little bit of electronics experiance. wieghts not a major concern of mine
  6. Cooool,

    Ok, the info for the analog amp is not problem. There is 2 good amp circuits for this.

    1. single module 400WRMS @ 4, 240 at 8, I love this amp module. It's so compact, beautiful design and so easy to build. AND VERY CHEAP. Don't let the low cost of building these fool you. They sound awesome.

    2. single module sym mosfet. 870WRMS at 4, 450 at 8. This is a monster. We often joke about using this as an arc welder. :smug:

    You can get the PCB's from aussieamplifiers.com they cost about $40-50 each. take a look, he calls them AV400 and AV800. I have built stereo versions of both and they live up to the test.

    I'm using the 400 x 2 as a mixer amp now and it has so much grunt it is never turned up but gee the headroom makes it so clean. Drum beats punch you right in the guts.

    The 800W jobs are just killer. The only issue is they are rather large. To fit 2 of these in a 3ru case you must fan cool them as I did. I used monitored fans so if they die it kills the amp as the final stage would fry for sure.

    As for the digital amps they are at


    At first you will read that they are advertising far lower power ratings. But, when you read the pdf tech sheet, you will also become a believer.

    They can be bridged. With only the mains transformer voltage changed they produce over 1400W RMS at 4 ohms and about 750 at 8ohms.

    The same company supplies power supplies and soft start circuits cheap as well.

    These little amps are only the size of a credit card each. If your in the US or UK you buggers are going to get even a better deal as your dollar and pound are stonger than our dollar.

    I think from the UK your only looking at about 500 pounds to build it.

    Take a look, it's very cool stuff. Don't fear about building those other ones, BUT your MUST BE VERY CAREFULL when you are handling huge amounts of capacitance (80,000uf per rail at 100V) it will take fingers off if your not carefull.

    Just take your time building them and execise safety. Always ask if you not sure and tripple check your work.

  7. lo-freq

    lo-freq aka UFO

    Jan 19, 2003
    DFW, Texas
    If you built a mono version of the #2 above, about how much would it cost and weigh?

    Side note:
    Class D amps (I've heard) are not easy to design that sound really good.
    Part of why I'm interested in the Lab.gruppen fP series, but dang, they are expensive.
  8. in the immortal words of cartman... KICK ASS DUDE!

    i have a feeling i may be trying to put one of these togther in the near future
  9. The 800 watt one weights a very rough 15-20Kg, about 40+ lbs.

    To be honest, I really only needed a single module. The reason I built it stereo is because after working out that the cost was not a huge amount more it made some sense.

    As the cabs I intened to use are both 8ohm, I could run a cab on each channel and the amp with run cooler. Or I can put both cabs on one channel and they again with get about 400w each.

    The beauty is that if a channel was to fail, hey there's a spare.

    Also my preamp is stereo so I could run a 15" and 4x10 and mix and blend etc.

    The cost of the transformer and power supply caps is the major cost of the amp. The transformer is about $230 here which is very good. The caps cost a bit but the more the better. I ran 8x 10,000uf 100v per channel. It would be even better with more but doesn't really need it. These caps here cost me about low $20 each!!! ouch.

    This is a really rough estimate but the single 800 costs about AU$700-800 to build and stereo add another $300-400.

    Take into account a commercial badd power amp with these specs are 1,000's of dollars. And if you build in a precision manner you'll get an amp that's just as good if not better.

    The only amp I've ever used that gives it a real run for it's money is one of the monster ampegs. That ampeg here is about 4 grand.

    A break down of parts is as such. Very rough estimate depending on were you buying your parts.

    All in AUS$

    PCB $50
    Caps $25 each x 8 = $200
    Transformer $250
    Power transistors 14 @ $6 each total $84
    Heatsink allow $40
    Case $100
    Misc components $40
    Connectors speakon, xlr and power etc $30
    Softstart kit $75


    These prices are rounded up too so you may find it's more like $750AU.

    Believe me, when you finish it and you power it up and it works. It's a great feeling. Flicking on the power switch the first time is a heart stopper but if you check your work over many times first you should be ok.

    I built the 400 first and it was simpler than the 800 which helped with experience first.

    Don't skimp on the quality of parts too. Buy the best transformer and the best caps you can afford. Within reason of course.

    You will find that the cost of the transformer to go "overkill" is not much.

    It needs a 1000VA for the 800W and to buy one thats say 1200 is only $20 more it's cheap insurance that it will deliver the goods. It also places a little less strain on the caps.

  10. This was very true in the past. Must agree. But these guys here in Australia have the kits already designed and built so all you have to do is wire them up inside your cabinet.

    As the are extremley efficient they put all the developed power out the speakers instead of heat. That means of course your power supply is not there to power you heater and amp but just your amp.

    The best thing about this is the amps are very small, very light and less expensive at the end of the day pew watt because you don't need a huge bank of quality capacitors that cost $25 each. Also the transformer is half the size which helps with the weight.

    You also don't need massive heat sinks and fans all over the place.

    These digitals also have output protection build in so go ahead and short out the output. No problem.

    I have noticed that they say you may need to turn off the protection is you run them bridged ofr they can pulse.

    Your right about the sound quality. They "were" a little average in this department but take a look at the thd figures now! They are up their in hifi grade now. Well and truly way good enough for musical instrument amplification. In fact thier specs are significantly better that most of the best bass amps.

    I've seen about 3 or 4 good designs of digital amps in this power range. One from Sweden, and a few from the US. They were a little rocket science but not anymore.

    Many power amplifiers that you see with 2000W RMS in a 2RU case are digital.

    Prior to building the 800w this one one of the reasons I stayed away from the digital. Now it's not a problem. If I was to build another now it would be a digital for sure.

    Easier, cheaper per watt, lighter, flexible and smaller.

    I honestly can give you one single reason why they are not as good or better.
  11. lo-freq

    lo-freq aka UFO

    Jan 19, 2003
    DFW, Texas
    Thanks for all the info.
  12. Hi Guys,

    I spoke to the guys today about the digital amp modules. They cleared a few things.

    They can be operted in stereo or bridge mode by using simple external circuit to switch. There is two versions 2.2 and 2.3 and then an SE version of both.

    The difference between ver 2.2 and 2.3 is audio quality. The SE version of each has significant power increase.

    So the 2.3SE wins. It is $375AU per module. As confirmed today 1400WRMS at 4, 750RMS at 8.

    Operating at this power level they will need a heatsink but it will be very minimal. No fans etc.

    The original weight I said is approx right. The only noticable weight is the transformer. The rest is almost lucky to be 2lbs or 1Kg.

    Still, I won't believe it until I can pick it up and plug it in and measure 1400W at the butt.

    They are very helpful and answered all my questions. They are willing to help in anyway with making a bass power amp success for us that would like to assemble one ourselves.

    I have agreed that I will build a prototype with their assistance.

    My suggestion to you is that as I am local to these guys, I will build one. Make everything template based and place all the info here for you to have. All I ask is that if any of you can see some way of improving it or adding something, share it and put it up here too.

    They asked me to send a detailed email with requirements. I was thinking of working out a few combos. There is almost no change in parts other than the transformer.

    Here's a suggestive list all figures are in RMS.

    A. 200 at 8, 380 at 4, per channel
    or 1400W at 4, 750 at 8 bridged mode using 58V

    B. Stereo only mode each channel 280 at 8, 540 at 4. using 69V

    The transformer to use at this stage is 1000VA thats 25% larger than required. I'm getting quoted $230 here to have it made with a 15v winding as well. This is to power some other circuits in the amp.

    Might be better to use a pcb mount seperate transformer for this part.

    Will have more info a day or two.
  13. Hi Guys,

    I have compiled an email with the remaining questions in relation to making this amp kit. I'm trying to get a list of materials and the places to get them from. The only component I'm asuming will be supplied localy is the transformer as the weight will make frieght far more, and local supply is not hard to get these anywhere. We can list the specs of windings so there's no confusion.

    I have since found that the designer of the modules is in Denmark. So if your in the USA for example it would make more sense to source these direct.

    They're at http://www.lcaudio.com/

    Check the tech document about bridging operation and it will show the incredible amount of grunt these thing can make without the weight or trying to imitate your heater.

    The other factors that I'm waiting on information for is exact power supply details to run these at full power bridged. As they are not class a a/b etc the power stage has fundemental differences in calculating the amount of capacitance required etc.

    There is a pdf tech document that shows the operation senarios. It is incredible how simple they have made it for the kit assembler.

  14. Transverz

    Transverz believer of the Low End Theory

    May 3, 2004
    Los Angeles, CA
    Really interesting! And I don't even understand half the stuff I've been reading! Luckily, I have some friends that are EE majors still in school so I might get some help. But I am very interested in building a 1U rack mounted power amp of about the power specs you mentioned. Sounds like fun!

    I will await the full list of materials needed. I'd also like to see or help out with making a step by step guide for a layperson like me to be able to understand :D .

    But the thought of being able to use an amp that *I* built with my own two hands sounds awesome. Or at least, built by my hands along with other hands who know what the heck their doing hehe...

    Good stuff! Thanks mlowe...best of luck!


  15. Hey I'm not sure about the 1RU size but let's see what the winders can do with the transformer. The amps that LC Audio are showing is based on the modules only operating in low power modes so they don't need physically large power supply transformers. I think they were using on 500 VA from memory. When in the mode I've discussed they draw more current.

    The indication at this stage is that it will need a 750VA transformer. From memory they were saying to use 1VA per watt at 8ohms. So that it makes 758W RMS at 8 would be 758VA. I'm looking at getting quotes on 1000VA as the cost and size is not that much more but just allows a little over spec.

    Given the simplicity of this home brew it's worth it. I'm not sure I could be bothered trying to build anything else like a good preamp when there are so many killer units already out there.

    I guess in a way it's also the case with power amps but then these power amps weigh in at about 8lbs (3.5Kg) and make 1400W.

    I just checked the cost of the modules in US$ and they are $243! each. Whoa. If your in the USA my bet is a QSC is a better option.

    Otherwise if you elsewhere, where a grunty amps costs the same as a small country. Yeh.

  16. Here's some pictures of the power amp modules. The two smaller modules are 400W RMS/4 per chan and the single module with the power stage in the center is 850W RMS/4 mono.

    The 800 sounds great. Very very punchy. Headroom to spare. Ample power supply helps control those cones.

    The caps near the power stage was to aid in damping which is now better than 400 and that was with only 10,000uf per supply rail. 40,000 is better. This module cost under US$140 to build! And that's finding the best components I could get. But, the power supply is 2/3 of the total build cost! All higher ratings than required. Voltage/temp/tol etc. The power stage uses IR transistors. About US$4 each x14.

    This module was built for only one thing in mind. Sound quality for bass guitar. Weight is bad. Cost effective? Here not too bad but in USA you could just buy heaps of great gear there for similar money so $ wise it's debatable at best.

    The 800 in stereo is a sight to see. It only just fits in a 3RU case. I mean it's a real tight fit. By the time the power supply, chunky heatsinks, fans and all those caps are in there even a roach would have trouble getting around in there without getting a buzz. The 2200VA transformer is big and very heavy.

    Just remember if you guys want to give building one of these a go be very careful. If your new to building gear I wouldn't suggest doing it on your own at first for safety reasons.

    Also, there is a little power mosfet transistor matching to do. If your not familiar with bias matching etc it's better to get some help and make sure all those ducks line up.

    The best thing I found building these amps was the knowledge gained. Now, to choose a commercial amp is no mean feat when you have a basic understanding of what counts and what doesn't.

    Then in the words of AC/DC you'll be thunderstruck.... :bassist:
  17. Just found out that the digital class d amp with 1400W can be built into a 1RU case without any compromises!!!!!

    The only negative is that it needs to run dual transformers which will increase cost but it also has th possitive side of redundency being that if one channel dies you could run the other by itself in mono instead of bridged mono.

    I think the 1RU will be the way to go. That sort of power in 1RU will freak dudes out. 1RU powering 2 410's at full power, what a sight. :bassist:
  18. remo


    Jan 15, 2005
    ha another melbournian!!! man I'd love to check this amp out sometime PM me!! I'm a photocopier techincian by trade and love electronics as well I'd be really keen to build my own amp...
  19. lo-freq

    lo-freq aka UFO

    Jan 19, 2003
    DFW, Texas
    Peavey make a 1400W 1RU power amp; I wonder if they use dual transformers.
  20. The class D amp sounds like a car amp. I never understood why you could by an amp for your car thats 2.5 inches high that will run 1200watts into 1-4ohms for like $450 but you couldnt get one for your bass or PA.