Building my first amp, having reservations

[cjv998]

Hi everyone, I've been looking around Rob Elliot's site for a few days now, and I've decided I want to build my own amp. Here are my criteria so far:

-cheap (I still want something that will impress me (a.k.a. sound considerably better than my Logitech Z-2300's and Audigy2ZS sound card I have on my computer now, even though I have a feeling that won't take much), but I don't want to spend an absurd amount on it; I'm a college student on a budget after all)

-PCB readily available (I don't want to have to mess with etching one and worrying about component layout and such)

-fairly easy to make (obviously, this is my first time building an amp, so I'm concerned about screwing something up; however, I do have some electronics experience. I'm going to be a senior in the Physics B.S. program, so I've taken a lab course in circuit construction along with a very theoretical course in electricity and magnetism)

I've considered the P3A on Elliot's site, but I heard (in another thread here, if I remember correctly) the average cost will be $(U.S.) 200 - 300. This is probably the upper limit I'd be willing to spend, or at least close to it. That being said, are there any more affordable alternatives to the P3A that will deliver similar sound quality, or would the P3A be a good choice?

By the way, I don't know what wattage I need, because I haven't picked out speakers yet; I could use suggestions here as well. I'm willing to build cabinets and such, if need be. I only want a set of stereo speakers (no surround sound or anything, probably won't even mess with a sub if I get speakers with decent bass response).

Thanks everyone! (PS: Sorry if this is in the wrong section, feel free to move it if so)

[David94114]

Try one of these:
http://www.audiosector.com/lm3875.shtml

go with the "classic kit" rather than the "premium" for a first project.

it's a less expensive solution than the ESP design you are considering; simple and easy to build, and high quality.

Also, if you have trouble, there are many people on this site who can help you.

Only caution - you don't want to use really low impedance speakers with it, but if you exercise some caution with the choice of speakers you should be fine.

[Hatti]

Hi,

David was a litle bit quicker, than me

This one´s realy simple. If you search for "gainclone" you find much more information about this.

Cheers, Hatti
I prefer tube amps.

[cjv998]

Thanks for the fast replies. I'll still need a power supply if I go with the gainclone David posted, obviously. Any suggestions here (I assume this will still be comprised of parts that are readily available on Digikey, or is there a better way to go about buying them)? Also, is it even worthwhile (read: more cost-effective ) to buy components or a kit for speakers, or would I be just as well off to buy standard pre-assembled home audio speakers that are commercially available?

[David94114]

For the power supply, search on this site in the chip amp section and you'll find lots of discussion about gainclone power supplies, or email Peter Daniels, whose site i referred you to in the prior post. It's very straightforward.

As for speaker building, there are some good kit options here too, ranging all across the price spectrum. Some good options are at www. partsexpress.com. Others are found by searching on this site. You can buy complete kits; you can also buy a pre-built cabinet, pick your own drivers, and work out your own crossover design. Or you can work with a tested, posted design, but not a kit. It all depends what you are up for. THat said, a big part of the reason for doing this is the fun and the challenge; if you are just looking at it as a money saver, and if you put a reasonable value on what your time is worth per hour, I'm not sure it's a great way to go.

[ssmith]

Originally posted by David94114
Try one of these:
http://www.audiosector.com/lm3875.shtml

go with the "classic kit" rather than the "premium" for a first project.

Speaking as another newcomer to diyaudio, I'd also recommend a kit like this -- good results are pretty much guaranteed and you'll end with an excellent amp for the money. The parts count is low and cheap, and it's a great way to get your head around the topology, design and construction of an amp without things getting too scary.

A good start is to download the pdf from the site mentioned and familiarise yourself with how it all fits together, then do plenty of reading here to fill in the gaps....

[cjv998]

Sorry to keep bugging everyone, but the specs on these transformers would be suitable, right? My only concern was the output (24VAC or 25VAC, or ~34V or ~35V rectified) is rated at 2.5 and 2.4 amps of current, respectively.

http://www.plitron.com/shopping/shopexd.asp?id=100
http://www.plitron.com/shopping/shopexd.asp?id=101

Anyway, it sounds like I'll want a 3 amp fuse for the mains line that goes to the primary on the transformer, and I'm looking into a stepped attenuator for volume control, or maybe I'll even just start with a potentiometer and see how that sounds, because $20 - $30 and several hours of soldering seems like a lot to invest into what essentially amounts to a volume knob.

Also, for speakers, I think I'm just going to pick up a pair of Paradigm Mini Monitors (a shop in town is an authorized Paradigm dealer, so I'm going to stop by over the weekend and have a listen). They seem to be great for bang-for-the-buck, from what I've read, they seem to have big enough woofers (6.5") to be acceptable without a sub for now, and they are supposed to work well at ~50V RMS (or a little higher even).

[David94114]

The following is from the online manual for the kit I suggested:

"Referencing the National datasheet LM3875.pdf, you can find the practical maximum rail voltage rating for the average impedance of your speaker. The Output Power vs. Supply Voltage chart on page 9 is a good indication of the maximum rail voltages for a given speaker that you will design to. When looking over the curves a speaker with a nominal impedance of 4 ohms tend toward 25V rails with a reasonable margin of safety, while voltages above 35V are still well within the range for 8 ohm speakers. This shows that transformers with 18-22V secondaries are well within reason for many common commercial and DIY speakers. A transformer with 25V transformer secondaries can also be successfully with less of a safety factor."

Note that the choice of supply voltage will depend on the mpedence of your speakers.

[sharpi31]

I can't praise Peter Daniel's kits enough!

Such a simple design, but such good sonics. Brilliant first project :-)

[cjv998]

What about an Alel Lundberg transformer from www.partsexpress.com?

http://www.partsexpress.com/pe/showd...number=122-625

I ask because it'll be $45 cheaper than the Plitron model ($55 shipped vs. $100), and for me, that's a big difference!