help with selection of high power amplifier kit for dj/sound reinforcement use

[ogp]

Hi, I am relatively new to the arena of diy amplifiers and such. I was looking at possibly purchasing a kit since I have never built one before. I do have some experience soldering, but not on reading schematics, although I don't think it would be very difficult to learn. So, I was looking into getting a kit for a high power amplifier that I could use for DJ/Sound reinforcement use. This would be subject to long periods of high output, so I would like something that would last. I would also like something that sounds comparable to commercial products. Does anyone have any suggestions? Most of the amps I have found seem to be class A whereas I probably need a class D amp. I have found a few things from hobbytron.com that velleman makes. The ones that caught my eye were this one http://www.hobbytron.net/vk4020.html and this one http://www.hobbytron.net/vk4010.html. Has anyone built either of these units? What about some of the kits from marchandelec.com? I need a stereo amp to drive two speakers (four would be nice) and put out at least 100 watts, although I think somewhere around 200 or 300 would be better. Any help/suggestions are greatly appreciated. Thanks.

Dave

 

[paulb]

Dave,
Something like the ILP modules (see http://www.audioxpress.com/bksprods/kits/ki-hy2000.htm) might be worth looking at. Note that even if it says "power supply included" you still need a transformer.

 

[ogp]

so if I got one of the modules that came with a power supply, would the only things I need be a transformer and a case? and then just wire up some rca inputs and speaker binding posts? Also, could you tell me exactly what the difference is between the OMP/MF modules and the ones you pointed me to? Thanks.

Dave

[Edited by ogp on 09-21-2001 at 04:20 PM]

 

[paulb]

I haven't used the ILP modules from AudioXpress, so I can't say exactly what you would need. I'm sure they come with an application note; perhaps you could find the ILP web site or send an inquiry to AudioXpress.
Fuses, man, you gotta have fuses too. At least:
- one for the AC input
- one for each speaker output
- maybe one each in the + and - DC power rails
I'm not familiar with the OMP/MF modules.

 

[Helix]

SPK output fuses

I wouldn't put any speaker output fuses, they apper to have enough output protection.

 

[AKSA]

You might like to consider an AB kit from http://www.printedelectronics.com called the AKSA.

 

[ogp]

Do you think the AKSA would be powerful enough for my application?

 

[AKSA]

How much power do you need? This is a vexing question, as it is related to ego and other subjective issues.

The AKSA is 100W into 8 ohms, but is extremely punchy in the bass and sounds like about 150W when compared to many other amps, such as Rotels.

A great deal of perceived power can be gained by careful choice of bass driver, too. An 87/wattdB driver produces half the subjective bass of a 93dB/watt, and with improving driver technology it's no longer difficult finding such beasts.

Generally, with amps, the more power they produce, the tighter must be the stability margins, since stability is intimately related to rail voltage. Ensuring an amp is stable generally means throwing it in irons to slow it down, and this has marked effect on the sonics across the entire music spectrum. Very large (cf. 500W and up) amps run high rail voltages - I have seen 125V rails on some Pro audio types - and ensuring stability at this levels is a horrendous challenge, usually resulting in a powerful but leaden sound. (One can hardly expect a Jumbo jet to exhibit the dynamics of a military fighter!!)

Thus there are rewards in keeping the rail voltage as low as possible, and this is the reason less power will sound better than more, so long as the drivers can generate the SPL.

Hugh

 

[djk]

The amps and speakers need to be examined as a system.But let us look at an amp first.The Velleman kit was examined by Audio Amateur and found to have oscillation problems.The most common amps for DJ/PA in the USA over the last 20 years or so are of the Peavey CS800/BGW 750 variety.Class AB output stages with five pair of outputs running on +/- 80V and capable of 400 watts at 4 ohms.If you bi-amp your speakers two amps powered with +/- 40V will be able to play the same volume level.Each amp will need only one pair of outputs and be much easier as a DIY project.An electronic crossover will be needed.The system should take the form of a pair of two way satellites and a subwoofer.The mid-high box can be quite small as it need only respond down to 100hz and are generally mounted on a tripod type stand.A pair of 10s or 12s and a horn are what you need here.The subwoofer will be quite large and go on the floor.A single 15 in a bandpass box will work here.Buy three of these amp cards http://sound.westhost.com/project3a.htm and two of these crossover cards http://sound.westhost.com/project09.htm The total cost delivered in USA is $82.80 for all five boards and documentation http://sound.westhost.com/purchase.htm One amp card will drive the mid and high for the left channel and another for the right channel.The third card will be bridged and drive the subwoofer.The two crossover cards are to be configured with 100h and 1.2khz for the crossover points.Two 30+30 (60VCT) 200~400VA transformers will be required.The crossover will 'steal' its power from one of these.Suggested drivers are all Eminence: four Alpha 10, two per box will give 103dB/2.83V and go down to 100hz.A pair of MD2001 will be 105dB/2.83V and go down to 1.2Khz on the correct horn.A single Kappa 15LF (not the pro series) will be 101dB/2.83V and go down to 40hz in a bandpass box.All the drivers and horns should cost less than $300.The bass should play 101dB + 23dB (amplifier power rating) = 124dB, the mids 103dB + 17dB = 120dB for one side + 3dB for stereo = 123dB, and the highs 105dB + 17dB = 122dB .This is for single tone sine wave.On program material expect another 8~10dB, or about 130dB .At a typical listening distance of 30 feet this will be about 110dB on peaks.With dynamic program material this will be about 95dB average before clipping (loud) and with some compression could be able to reach 105dB (very loud).

 

[ogp]

wow, djk, that was an extremely detailed post. Thanks a lot. Would the amplifiers and crossovers be difficult to build for someone who doesn't really have any experience? You sound as if you have built this very system. If so, do you have any documentation or anything as to your speaker designs? Also, I was looking around on partsexpress for the drivers and they seem to be much more than the stated $300. And I couldn't find a MD2001, is the MD2001S-8 the same thing? Has it been a while since you bought these speakers, or do you have a cheaper place to purchase them? Thanks again for all your help.

Dave

 

[djk]

I build two or three good sized sound systems a year.I buy my woofers in 100 lot direct from Eminence so I do get a little better price than the average guy does.When I need a small quantity I buy from either Image Communications or a distributor I won't name as they only sell to shops.Parts Express and MCM are very expensive.The part number on the compression driver varies epending on whether it is the original or type II diaphragm (the original is smoother, the type II has more high end above 10Khz) 2001/2002, 8 or 16 ohms, and bolt on or screw on.A XXX2002S-16 would be a type II diaphragm 16 ohms with a screw on mount.The main question I would have is what kind of a time frame do you have for completion? It is going to take you probably two or three weekends to build and finish off the speaker cabinets (paint or carpet, corners, handles, grills, jacks, etc).All the amplifier and crossover boards could be stuffed in a weekend.But I would allow six weeks to acquire all the parts and finish mounting them in a chassis and test everthing out.Do you have this kind of time?

 

[ogp]

yea....there is no real rush...I just wanted to build some dedicated sound equipment that I could use for house parties and such. I am trying to design the speakers in WinISD, but am unable to figure out how to add the tweeter to the woofers. I can only get two woofers in the program. Is the tweeter not a big deal? Or am I just doing something wrong? Or is there some other program that I should use which is better?

Dave

 

[ogp]

bandpass

djk, when you suggest a bandpass box, are you suggesting a 4th order or a 6th order bandpass?

 

[djk]

"djk, when you suggest a bandpass box, are you suggesting a 4th order or a 6th order bandpass?" I was thinking of a 6th order type.I do have a design for a 4th order type that is 104dB/2.83V but it doesn't quite go high enough for this system.

 

[Super]

OGP: You do not really have to factor in the tweeter when determining box calculations, because every tweeter is basically in its own enclosure. However, I would suggest sealing off the tweeter inside the enclosure (i.e another mini-enclosure)so that the waves coming from the bass drivers don't interfere with the tweeter.

 

[GRollins]

Nearly all tweeters are enclosed. You can do anything you want behind them. My ribbons, for instance, are not, but they are the exception rather than the rule.
Most mid-range units need to be enclosed in a special space of their own, though.

Grey