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Old 4th September 2008, 09:50 AM   #1
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Default Looking for a project :)

Hi! I'm looking to build myself a stereo system! Pretty much, I'm a broke high school student (barely a senior) looking for some loud, sweet sound at low cost. I have a real appreciation for DIY stuff, as it's usually sturdier, you can tweak it all you want, it's frequently cheaper, and it impresses people, so I though I'd build myself something.

I know at many other forums I've seen people bite at the ambitious and sometimes unrealistic newbie. I am totally inexperienced when it comes to stereo gear, but I have experience in other electronics. I've built many solid state guitar effects boxes, and I've built a tube amp from scratch, and fixed up another amp. So while I'm not a total newbie, forgive me for any stupid questions.

I was planning to build a solid state amp, as even though I'm less experienced in this, it's more efficient, modern, and I can do it for cheaper. Here are some of my first questions:

How many watts should I aim for? I have experience with this when it comes to instrument amplifiers, but that's different because they're narrower frequency bands, and of course quality of reproduction (distortion, etc.) isn't necessarily considered a bad thing, at all. Do I have to worry about usable headroom with solid state? (For amps I have more experience with tube systems.) Generally, it just boils down to me wondering how many watts I need to properly fill a reasonably sized room with sound.

And once that is figured out, is there any favorite circuit around here? I don't care too much about nitpickety audiophile quality, but I do want good sound, with a solid bass. Is there any recommended simple pre and post amp that's reached general consensus as being pretty good for its worth?

Thanks! Sorry for an overly long post.
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Old 4th September 2008, 12:40 PM   #2
AndrewT is offline AndrewT  Scotland
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you can buy ready assembled music machines from the Far East far cheaper than anything you can build yourself.
The main difference, the ones you build yourself have a chance of sounding good.
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Old 4th September 2008, 01:01 PM   #3
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Aside from the fact that AndrewT is right (however depressing it might be), there are some decent designs out there for DIY'ers. If you can scrounge up the power supply materials, case and heatsinks (the expensive parts), the cost of the actual circuit components is quite small.

I would first consider the projects on Rod Elliott's page. Particularly P3A and P101. They are well designed, and there are hundreds (if not thousands) of satisfied builders of each. I personally built the P3A (about 8 of them plus 3 prototypes) and learned alot from the project. Definitely buy Rod's PCBs if you attempt either of these projects, as the time and money required to prototype your own boards (and fix your mistakes) will be far greater than the cost of the boards. Plus if you buy the boards you get access to detailed help information on the secure portion of Rod's pages.

The second project I would consider is the Symasym amp which can be learned about by searching for that name on this forum or on google. I haven't built one, but many on this forum have and the feedback seems to be good (what a terrible pun!). The biggest advantage of this amp (in my mind) is that the PCB artwork is freely available, reducing the cost somewhat.

Finally, a chipamp amplifier is another option which should be considered. You sound like you want to be more involved in the learning process than what a typical chipamp build requires, but one can't deny that they make a great little amplifier.

Good luck with your project, we'll be here to answer any questions.

-David
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Old 4th September 2008, 01:25 PM   #4
jaycee is offline jaycee  United Kingdom
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Cheapest and easiest is a Gainclone. However the expensive parts are the case, heatsinks and power supply parts. It's good if you can get a suitable dead amp to gut for parts.
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Old 4th September 2008, 01:53 PM   #5
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Thanks for all the replies guys.

Maybe I was unclear on quite how cheap I wanted to be. :P Counting a good case, heatsink, etc. the cost can rack up, but I was planning scrounge.

How much will stuff really cost?

I was thinking of getting the heatsink and case from a Goodwill take-apart. It seems like this would be viable as both the heatsink and case are pretty non-specific parts.

Transformer is a bit more finicky, but I thought I'd be cheap and go with a generic EI Hammond or something for 30 bucks. If noise were an issue I'd mount it in an isolated power supply unit or something.

I already have pretty much all the passive components I need. I just probably will need a few of the higher wattage resistors probably. And I'll need the silicon, as I don't think I have any in my parts bin.

I'm hoping with 30 bucks for the transformer and say 10-20 for Goodwill take aparts, I can keep the price down low. Say no more than 10 dollars in other components. And of course, I will have have a good sounding, sturdy amp setup.

Honestly though, if a Chinese setup still sounds that much cheaper for reliability and and sound for the price, let me know, as I'm (really) broke and need to spend each dollar to its utmost.

Thanks!
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Old 4th September 2008, 02:15 PM   #6
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The best deal for the money is working (or repairable) used equipment by a long shot. I have no doubt that in a city like Portland that you can find something local at a garage sale, thrift store or even on the internet (say on local craigslist or even local pickup on ebay).

If you intend to build your own nonetheless and want to do this project for the pure challenge of it, then you are on the right track; although I wouldn't spend $30 on a hammond transformer (if $30 can even get you an appropriate hammond, they are pricey) when you are likely to find one in the amp you salvage.

The silicon for a two channel amp project can easily reach $20 for even a project like the P3A. Higher power projects will obviously require more silicon and will increase in price.

I'm not trying to discourage you from building your own amp. It's a great project and a great way to learn. I'm just not going to tell you that it will be something that it is not (less expensive).

Here's a thought, the 25W per channel accurian amps used to be clearanced at radio shack for around $15 + shipping. Surely someone out there has an extra one to sell to you. There are many threads out there describing this amp.

-David
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Old 4th September 2008, 02:33 PM   #7
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It's the "loud" part that will bring up the cost, and make a working older thriftstore find a better return for the money, allowing for some upgrades as budget allows. For an inexpensive first SS amp there is a Velleman kit that includes heatsink, PS on the board, it's only 15WPC though and the transformer could be Radio Shack or scrouned. I forget the Velleman kit number, but I built one in a nice homemade case with homemade single driver speakers. Sounds pretty good, but not "loud". The kit can be found at Parts Express website as well as many others. Good luck!
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Old 4th September 2008, 03:10 PM   #8
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Hmm, well if it really is as pricey as you guys make it sound, I may hold off until a bit later, when I have a bit more money to spend. Thanks for all the replies though, and if anybody else has anything to offer up, please do post.

I think I may take the route of scrounging something old, and then maybe regutting it when I have the cash.

If I want to take that approach, what's the best way to tell if something is appropriate for my needs building a p3a? That seems like a well documented and well received build, so I think I'll go with that. What's the likelyhood that the parts (transformer namely) from a scrounger will have a fitting transformer? What should I look for to see if it does?

Thanks!
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Old 4th September 2008, 03:35 PM   #9
AndrewT is offline AndrewT  Scotland
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an amplifier, or a transformer from an amplifier, specified to produce 50W to 70W into two 8ohm channels would suit your needs.
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Old 4th September 2008, 04:09 PM   #10
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You can tell alot by looking at the original amp topology. If it has one output device per rail per speaker, it's probably going to have similar transformer requirements as the P3A. Most of the newer, integrated chip amp style receivers have higher voltage transformers than the P3A requires. You will want to look for discrete output devices, and two per speaker output (one NPN one PNP).

The original amp power rating will also tell you a lot about the transformer voltage. If it is similar in power to the P3A project (60W-80W per channel) then the voltages will probably be ok for the P3A amp.

If you have the fortune of seeing a voltage specification on the transformers (highly unlikely), then you will want to look for +/- 25V (for use with 4 or 8 ohm speaker) or +/-30V (8 ohm speakers only). If the voltage is given in VCT (center tapped) you will want 50VCT or 60VCT respectively. A little under the above rating would be acceptable ( I use a 48VCT transformer ), but you should under no circumstances exceed the 60VCT (+/-30V) rating.

The P101 project can take higher voltage transformers, up to around 80VCT (+/- 40V), which should be compatible with most transformers you find in modern equipment.

I have a mid 90's technics receiver in front of me for example. Not the kind of amp you would choose for your project, but the transformer on it puts out +/-32.4V, too high for the P3A but acceptable for the P101.

-David
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