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-   -   8 Channel Amplifier for Linkwitz Orion Kit (http://www.diyaudio.com/forums/chip-amps/37451-8-channel-amplifier-linkwitz-orion-kit.html)

ngiachin 8th July 2004 07:08 PM

8 Channel Amplifier for Linkwitz Orion Kit
 
I was just wondering if I could get some expert opinions from the board here. I am not an electronics diyer, I have very limited experience in such, however I have access to close relatives that are electrical engineers. I am currently building an Orion kit and when finished will need 8 channels of amplification. I would like to do this in the least costly manor. I was considering using BrianGTs GC kits which I believe are 55wrms per channel, but I am not sure how I would configure the transformer(s) then. Would I be better off just buying two used Parasound 855a or B&K 5 channel amps than attempting to use the GC for amplification? I guess I am kinda asking someone to spell out for me if possible exactly how I would go about a 8channel gainclone. Thanks, and sorry about the newbieness.

Nik Giachino

Fenris 8th July 2004 09:44 PM

I'm doing a 8 amp gainclone (stereo with 3 way active crossover) for a set of line arrays right now as well as helping a friend with a 15 amp GC (5 channels, two way active XO, MTM speakers with one GC per driver) monster. It's pretty straight-forward, either build each of the 8 amps as a monoblock (more expensive) or use a single large power supply and wire them all up to that (usually less expensive, but can have issues of its own). Either way it will probably require a large chassis (think 19" rackmount type here). Brian's kits will simplify the process enormously, but it's still not trivial to DIY an amp yourself. So far I've finished 3 monoblock pairs, one single channel subwoofer amp, and a 5 channel amp all using gainclones and the most difficult part has always been running the wiring and case fabrication. Building the GC amps themselves is fairly easy, even using the point-to-point method.

ngiachin 9th July 2004 12:47 AM

Thank you for the reply. I would love to run all eight as monoblocks, but the cheapest 160va transformers I can find a 35 bucks...seems kinda expensive to put into a project I have so very little knowledge of...I wonder if I can find a diyer in the Milwaukee area to help me out...hrmm..that might be a good idea.

Variac 9th July 2004 01:00 AM

Making 8 gainclone channels is very little more work than making a pair.

Probably would be best to split it into 2 4 channel amps, If the crossover filters are separate for each channel. There is no problem having all 8 in one box also. Use Brian's kits to save money and time.

As Fenris said, all the work is making the boxes and wiring the
multi input switches, etc. Since you probably have a separate preamp, the amps are very simple. You can bolt multiple channels to one heatsink. If you order a good sized box for each channel,
your costs and effort will be little more than 2 monoblock powerblocks.

Even 2 channel amps often share one transformer. The simplest and cheapest is to use one transformer for say, 4 channels.
Get a 500 VA transformer and you'd be more than fine for 4.

You will discover that one big transformer is a lot cheaper than a bunch of smaller ones. Althought there is a theoretical advantage to individual transformers, I would think that at least the 2 bass amps per channel could share a say, 250- 320 VA transformer.
Then you could have separate 100-150 VA transformers for mid and tweeter, but I wouldn't stress over separating them. It's fine to use one for all 4 I'll bet.

Even though the amps are dead simple to make, you will have questions. We will be here to help you though! Costs are about $60 per channel not including the box.

I'd get rack mount boxes from Par-metals if you want to keep it simple. They are about $60-80 each.

A multi channel gainclone is perfect for your speakers.

mrlots2do 9th July 2004 02:25 AM

Quote:

Originally posted by Fenris
I'm doing a 8 amp gainclone (stereo with 3 way active crossover)

I'm also building an 8 channel BrianGT amp for two 3way WtmW mains and one 2way mtm center channel. I would be interested in your active Xover notes and schematics.

My mains will have 1 amp for 8ohm tweeter, 1 amp for 8 ohm mid and parallel amps for 2 parallel 8ohm woofers (4ohm load). Question though, do I need the parallel amps for the 2 parallel woofers?

Phil

ngiachin 9th July 2004 02:55 AM

Thank you so much for your responses...

I plan on taking your advice and running two four channel amps with seperate transformers for the high-mid and low channels. I believe in doing things that way that I can pretty much stick with the directions of brians reference material.

Any recommendations on where to purchase the transformers...I saw it looked like partsexpress had good prices on avel y23's but I am not sure about the transformer voltage ratings...I need between a 18v-22v right? Time to start learning.

Nik

sam9 9th July 2004 03:36 AM

Take a look at www.marchandelec.com. Look at the PM21 dual 65W amp. Four of these would give you 8 channels. This is a very straight-forward kit to build - it was my first. The easiest thing is to get it complete with parts, but you can buy just the PCBs if you desire and buy the parts separately - may or may not save some money - probably not.

This is an LM3886 based amplifier. It is not called a "gain clone" because that term was not invented at the time the PM21 appeared. Nonetheless, it fits the definition of a GC. Marchand was just a little ahead of the curve but doesn't get evough credit for that, IMO.

Power supply modules are also available from Marchand, but I suggest you e-mail Marchand asking his recomendation for a power supply suitable for 4 PM21 modules. Also ask about recomended heatsinking.

Four modules won't take up much space but since you are new to this, may I suggest you use an enclosure bigger than you think you need. With eight channels, that's a lot of wiring and confusion can be reduced by having lots of space to work in. In fact, you might consider two enclosures of two PM21's each just to keep ife simple.

Variac 9th July 2004 06:28 AM

Phil,

Using 2 amps (one for each bass driver) will give you more power for the bass, and the amps will be happy :D with the 8 ohm load. This is a nice way to in effect get twice the power for your woofers, that need it more than the midrange or tweeters.


Nik,

Linkwitz recommends using a separate amp per bass driver for
optimum results with his speaker also.

Although you can get some great deals by going for surplus stuff,
ordering the Avel transformers is easy, quick, and you get what you need, AND the biggest thing of all: A lot of us (including myself) have used them and can advise you how to hook them up
because we know the wire color scheme.

I used a 330VA with dual 25 volt outputs and it works great for 2 channels! Probably more than needed but it only costs about 5$ more than the 250VA model.

I'm not clear, for one side you are going to use one transformer for the 2 bass amps and another transformer for the mid and tweeter? ie 2 transformers and 4 amps per side? This sounds good to me! By splitting it 2 boxes each with 4 amps, you can put the amps right next to the speakers which is good.

Fenris 9th July 2004 03:30 PM

Quote:

Originally posted by mrlots2do

I'm also building an 8 channel BrianGT amp for two 3way WtmW mains and one 2way mtm center channel. I would be interested in your active Xover notes and schematics.

My mains will have 1 amp for 8ohm tweeter, 1 amp for 8 ohm mid and parallel amps for 2 parallel 8ohm woofers (4ohm load). Question though, do I need the parallel amps for the 2 parallel woofers?

Phil


My active XOs are based on Rod Elliot's schematics found here:
http://sound.westhost.com/project09.htm
but done in an extremely minimalist manner. No input buffers, no output buffers. Each lowpass section directly drives two GCs. I'm working off of memory here, but I think I used resistor values of 732 and 1474 ohms and capacitor values of .082 and .15 uF (it's what I had in my parts bin) for a crossover point of approximately 2000 Hz. Rod has a program you can download to easily calculate values. I used a piece of proto board approximately 4" x 6" with an "IC" pattern. I used OPA2132 dual op-amps, each functioning as a complete filter. Quad op-amps wouldn't have enough room around them for the passive components. I laid out the parts for one highpass and one lowpass until I found the best and most compact arrangement, and then repeated 4 more times. Actually, after soldering the first I found a better arrangement (slightly shorter lead lengths, less chance of short circuiting) and did the last 4 that way, but that's not a big deal. I also put a +12v and -12v limiter and filter caps on some spare real estate on the board. I'll try to take some pictures if you want.

For my 3-ways, I'm going to run 2 woofers off of two gainclones, each woofer with one GC. Much easier than paralelling everything, but it does double the number of wires to be run. I'm going to simply use a Neutrik 8 pole connector for an idiot-proof and compact connection between the speakers and amp (since the XO, amps, and speakers are all tailored for each other it doesn't have to be compatible with anything else).

ngiachin 9th July 2004 03:58 PM

Again, thanks everyone for the input. I will have to look into these different kits...there is the BrianGT GC, the LM3886 Marchandelec's, and the Elliot kits...difficult to pick without being able to hear the results...anyone able to compare any of these?


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