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drfrink24 4th August 2003 05:59 PM

Newbie DIY Amplifier Kits, suggestions
Hello all.

I'm looking for some suggestions on a good DIY first project SS amplifier.

I'm looking at staying under $500 for a 4 ohm stable amplifier, to drive some Adire 281's (ported) that I've recently built.

I'd also like the ability to bridge the design, for future bi-amping possibilities.

I'd like to work with a kit, since this will be my first DIY electronic project.

I've read many posts, but, still looking for that "magic post", where someone fufills the big requirements:

1. Sounds good
2. under $500
3. Easy to build
4. Includes DETAILED instructions
5. Powerfull enough to drive the 281's

Thanks all!

5th element 5th August 2003 10:29 AM

Im not 100% sure that all this can be achieved, I mean I guess it can be but usually a first time project is simple and not vastly powerful. Im guessing that the adire would benafit from a serious amount of wallop hurled at its windings. Well as construction goes with an amplifier its all pretty straight forward. I'd recommend reading one of serveral books first to get a feel for it. I've read and would recommend Randy Slones High-Power Audio Amplifier Construction Manual. This book will provide you with a great variety of information and all the info needed on how to construct amplifiers. It has within it 12 designs most of which have PCB artwork with then to enable easy fabrication of your own PCB's. PCB's are not hard to make, following the walkthru in the book you can turn out a PCB for an amp no problem, first try.

I had done electronics work before I built my first amp but nothing as adventurous as an amp. I built one of the more simpler but in no ways less talented amps in the book and the design sounds simply wonderful. But what I can say is that some of the more complicated, more powerful designs would not have really been more difficult to complete, so as things go for a big sub, I'd recommend design 11.8 in the aforementioned book which pumps out 250 watts into 4 ohms. Alternately you could build two/four amps for driving you mains speakers instead as a first project such as design 11.4. This is the one that I built and it really sounds fantastic.

As far as your criteria go

1) The 11.4 can sound wonderful, im going to build a 11.8 in the future too but am sure that that will also sound brilliant. I say can sound because if you really botch everything up this will compromise sound quality, but from what I have heard slones amps are fairly tollerable in this respect, especially with component quality.

2) Price - I built four of the 11.4 designs for biamping, they all shared the same case and powersupply. The case was an old computer case so I didnt have to pay for that and it all came to about 300. I am now rebuilding the case and heatsinking. I've just been delivered the heatsinks now this very minute from Conrad heatsinks in Australia. These are very good quality and cost far less then me purchasing here in the UK including the p&p by airmail. So in other words you can build one channel for the adire for under $500 no problem.

3) Easy to build depends on the person but if your OK at DIY in other respects, can brandish a soldering iron with some dexterity and skill, then you should have no problem making an amp.

4) Amp construction is fairly self explanitory really and the bits which are not im sure folk here would be more then happy to help with.

5) Powerful enough...... that depends upon the SPL you want to through outta the Adire. But I would assume 250 watts into it would be enough.

Hope that helps Matt

drfrink24 5th August 2003 01:12 PM

Thanks for the feedback. I think I will have to invest in the book you are suggesting.

I think the Adires do chew up their fair share of power.

Kilentra 5th August 2003 05:12 PM

I'm using Adire Kit281s vented as well. They definitely do need a strong amplifier to sound their best. The project you are asking for does exist, with one exception - it is not so easy to build. I have built Anthony Holton's symmetrical amplifier... it's good for at least 400 watts (the power rails on mine are too high by accident, so I don't know the real output). The cost for the project is about $400. Budget $100 for surplus heatsinks, $100 for a nice big transformer, and $150 for the electronic parts (I'll give you a list of digikey numbers and such). Mr. Holton sells PCBs for about $55. If you're really crazy he also has a design for an 800 watt amplifier. The sym amp was my second DIY amplifier.

Here's the catch. As with all high power amplifiers, this one is dangerous to work with (+/-75 volts DC), and it is not as stable electrically and thermally as one would want. It is important that you build everything exactly correct, or the result may not be what you want. I have had at least 6 failures, thermal runaway, blowing transistors from over-voltage, and maybe oscillation too caused by inappropriate attention to details (wiring and mounting of the bias transistor; adequately checking all parts).

Additionally, Mr. Holton seems to not provide any support. Since about a year ago he hasn't visited the forum or answered any e-mails. I was not aware of anyone else building one of these amplifiers, but now that I have, I would be happy to help anyone who decides to try it. If you have any questions feel free to e-mail me.

Of course there may be other options (like Slone's) but I haven't seen any other good high power amplifier designs published. The sym amp sounds pretty darn good, but bi-amping is a good idea with the 281s. (I have a Pass Zen amp for that purpose.)

drfrink24 5th August 2003 05:34 PM

Thanks for the feedback. I just ordered both of Mr. Sloans books. After I read them, I make the decision if this is for me or not.

On a side note, how do you like your 281's?

I cannot say I'm absolutley in love with mine, because I haven't been able to really verify how good they can sound with the proper equipment.

I have noticed that many sounds are "smeared". I may be using the wrong terminology, but, it seems that given the higher the frequency sounds, the soundstage and music location changes. It might be the recordings though, or the smallish room they are in.

I have many sound treatments, plus, acostic ceiling tiles, so, I'm trying to make the best of it.

Kilentra 5th August 2003 09:49 PM

I haven't really found them 'smeared' at all, in fact to me the high frequency sounds are so precise that they don't really seem "life size." The highs are also slightly edgy or distorted although they take on a much more realistic "shimmery" quality with the Zen Class A amp, so it's probably not just the speakers' fault. There is a resonance in the upper midrange that causes some slowness in certain sounds, and I'm still not sure if it causes harshness or not (working on improving my equipment). Many have said the 281 is too bright or harsh. I enjoy the relatively bright/clear/exciting sound and I'm working on making it as pleasant as possible given the limitations in the drivers (the biggest of which is woofer breakup at 2.2KHz). But in general it sounds really good. Especially at night when I can relax, and there's less power line noise... my amplifiers have no pi-filter or regulation, and CD player supply is just 7805/7815/7915 for now.

Are you listening with the tweeters to the inside or outside? And, what's your current amplifier?

drfrink24 5th August 2003 09:59 PM

Original Question:

Are you listening with the tweeters to the inside or outside? And, what's your current amplifier?

The tweeters are on the inside, but, I've thought about swapping them.

I'm currently using a Sony TA-N55ES amplifier.

Is there actually a L and R speaker config. with MTM speakers? Does it affect near or far field listening?

Greg Erskine 5th August 2003 10:57 PM

Hi drfrink24,

Hope I'm not leading you up the garden path 'cause I know nothing about 281's, but in the last year or so I have built 3 or 4 amps that are rated at or below 60 watts. I have found these more than adequate to drive my inefficient 84db speakers. I was actually quite surprised at how loud these amps can go.

So here are my recommendations:

1. Aspen AKSA 55 (you probably want the 100watt)
2. Elliott P3A (60 to 100 watts)
3. Inverted Gainclone using LM3875
4. Non-inverted Gainclone using LM1875 (not powerful enough)

The AKSA is a complete kit excluding cabinet, switch, plug, and transformers. This kit offers excellent sound using reasonably good components. The PCB is the best I've seen. Backup service is the best I have ever experienced. Easy to make because of the large tracks and pads on the PCB.

Elliott's P3A is only a PCB, you have to buy all the parts. Good support via email. The PCB has some fine tracks so building is a little more difficult than the AKSA but still not that hard.

The gainclone, you will need to source everything. It is extremely cheap and is a good place to start learning the ropes. Good community support. No PCB required as point to point wiring is recommended.

My LM3875 gainclone is only using 17VDC rails (recommended max 35VDC) and still has sufficent volume for me. I will be upgrading to 30VDC rails soon.

Kilentra 5th August 2003 11:15 PM

That might be something to change. I had the tweeters on the inside at first, because I thought it would reduce reflections from side boundaries. I put them on the outside and the treble sounds bigger and clearer. This is because of the off-axis response peculiarity of the speaker, there are more problems in the midrange when you move off axis on the side the tweeter is. The Audioxpress review goes into this a little bit.

The amplifier should be fine, I doubt it would cause any serious defects in the sound.

Also, did you check the correct polarity of the drivers? Some kits including mine were shipped with mismarked crossover causing the tweeter and woofers to be out of phase. This would cause a 7-10db dip in the upper midrange and probably a lot of off-axis problems.

drfrink24 6th August 2003 12:17 AM

In response to Grege:

Yes, the ASKA 100 is my leading canidate for my choice. Seems a pretty well constructed kit, but still leaves room for DIY aspects.

I am a little hesitant, however, to start down the path with such an expensive choice. If memory serves me correct, the components, transformers and caps end up putting the kit at nearly $800 (US) in parts alone.

In repsonse to Kilentra:

I'll try swapping the positions of the speakers, but I'm fairly certain that the polarity is correct, because the crossover wires to the tweeter has a smaller clip than the other one, so, you can only wire it one way. I think they did this to adress this problem.

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