Amplifier kits?

Discussion in 'Archived Threads 2001-2004' started by Jack*Mains, Jan 26, 2003.

  1. Jack*Mains

    Jack*Mains Stunt Coordinator

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    Hey, I've been looking around for a while into getting to build some DIY amps, and I would like to start by building a moderately powered (100W or so) subwoofer amplifier from a kit. The only problem is: all the kit's I've found are for full range amps. I would really rather not use a full range amp to power a subwoofer because: 1 - It is a waste and 2 - a cheap full range amp will probably sound a lot worse then a cheap amp designed to go from 10Hz to 100Hz.


    If you know any place where one could buy a subwoofer amp kit *Preferably in Canada,* please share the knowledge.

    Thanks.
     
  2. TimForman

    TimForman Supporting Actor

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    Is Seattle close to Canada?[​IMG] Adire Audio sells sub amp kits. Check out their website.
    Adire Audio
     
  3. Aaron_Smith

    Aaron_Smith Stunt Coordinator

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    I'm not sure if I agree about a full range amp sounding worse than an amp designed specifically for subwoofer use. Most subwoofer amps have very high distortion, even within their specified operating limits. Power is power, and clean power is the best- no matter what frequency range you're playing with.
    I have built the AKSA 55 watt kit, it's a beauty and they make a 100 watt version. They have a discussion forum over at Harmonic Discord. Rod Elliott also has some good designs and some pre-fab PCB's for sale. Both of the above suppliers are in Australia.
     
  4. Michael R Price

    Michael R Price Screenwriter

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    Jack,

    As far as I know, there isn't really such a thing as a DIY subwoofer amp. Sure, you will want to use a design known for good bass quality, whereas treble sweetness and other characteristics are not an issue. I don't really think it would be a waste to use a "full range" amp - after all, all amplifiers are really full range and the best subwoofers use separate amplifiers (example: Samson and QSC) that were probably designed to operate full range. And as for having lesser quality than a cheap sub-only amp... I wouldn't know, I've never heard of a sub-only amp.

    The designs you'll want to look for for a good subwoofer amplifier would probably be Class AB or Class D, with a good amount of feedback to increase the damping factor. And also a strong power supply that doesn't droop under load. Those considerations would probably be more important than the finer points of the circuit design, given that you won't be too concerned with soundstaging or anything.

    How much do you intend to spend? In this instance it may be a better choice to just buy a pre-made amplifier... especially if you are looking for a lower price. It's generally hard to find the components used in amplifiers at surplus prices. Unless you can find great deals, the heatsinks, transformer, capacitors, and everything else is going to add up. (At least in my experience, that is...)

    An option to consider would be building a bridged or parallel amplifier using the National Semiconductor LM3886 IC. I think if you parallel two of them you should be able to get 100W into 4 ohms... and they are very tolerant of low power supply capacitance. Besides that, AKSA and ESP kits come to mind.
     
  5. Ted_Polzin

    Ted_Polzin Stunt Coordinator

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    Elliot has a amp he says is a subwoofer amp at http://sound.westhost.com/project68.htm. It is probably better than a lot of commercial full range amps but it works well and can run in, true continuous 400 watt with an extra set of output devices or 300 watt occasional use with the regular set. From what you say the 300 watt (4 ohms) would be perfect.

    Ted
     
  6. TimForman

    TimForman Supporting Actor

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    I run my sub with an external high output pro-type amp (like a DJ amp). The THD is a little higher than good quality hi-fi stuff but at the lower frequencies (
     
  7. Jonathan M

    Jonathan M Second Unit

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    Hi Jack,

    I can confirm that Rod Elliotts 300W sub amp is a good one. Sounds fantastic with the DPL12 I'm driving (Small sealed 35 litre enclosure). I'm in the process of doing a quick it.write-up on it. Had a bit of "fun" with counterfeit output transistors, but once I got genuine parts, it works fantastically!

    Another option would be a bridged P3A amp from Rod. Make sure you only run it into an 8ohm load though!

    Michael -
    As for the power supply for a sub amp, I don't agree that it needs to be particularly stiff. Most sub signals (either LFE or combined LFE and low-passed signal) are VERY transient in nature. Most of the time the sub amp is not working hard at all. I have 6000uF per rail on my amp, and it works fine. Rod recommends 4700uF per rail at a minimum and suggests any more than 10000uF is a waste.

    Another cheap option, Jack, is to do the bridge-parallel implementation of the LM3875. That'll quite happily do 300W into 4 ohms and would be nice and easy to start with. Comes with pretty good protection circuitry too which is good for a first effort (You want your first one to survive that first power on!)

    Another cheap option Jack is to do the bridge-parallel implementation of the LM3875. That'll quite happily do 300W into 4 ohms and would be nice and easy to start with. Comes with pretty good protection circuitry too which is good for a first effort (You want your first one to survive that first power on!)
     
  8. Michael R Price

    Michael R Price Screenwriter

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    The LM3875, while it seems to sound better in hi-fi applications than the LM3886, is not as powerful. The LM3886 can handle more current and has more output into 4 ohms (68W rated from a single chip), so it should be a better choice for a sub amp.
     
  9. Scott Simonian

    Scott Simonian Screenwriter

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    I wish I could make my own amp. I would like to build one that is like that of the Cinepro amps. Ultra high dynamic capabilities. Class AB output, BIG, BIG caps. I want it all. That would be cool if I could make em mono or stereo blocks at a time.

    Anyone know how to build something like that?
     
  10. TimForman

    TimForman Supporting Actor

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    I'm on the same path. I decided it would be best to learn some basic electronics then start out with something small to hone my skills. I'm currently building the K50 25W mono amp that I got from Qkits.com. There's some really cool looking stuff at SealElectronics.com too. Another web site to check is velleman-kits.com.
     
  11. Michael R Price

    Michael R Price Screenwriter

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    Scott, I'm trying. [​IMG] I think I know how to built them now, after several stumbling blocks along the way, one channel is working and the other is awaiting parts. See the DIY symmetrical amplifier thread.

    Does having capacitors larger than soda cans count?
     
  12. Al Garay

    Al Garay Stunt Coordinator

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