I have never built an amp before, but I am a vetern speaker builder by passion, and Electrical Engineering student by trade. I recently bought a pair of Acoustat Spectra 1100 ESL speakers, but my puny 50 WPC Sony amp can't drive them without straining. I would like to build a stereo amplifier with at least 100 WPC at 8 ohms. As I am in college, I must do this on a budget (less than $200). I don't know any particular designs, so I would need full schematics, PCB layout, power supply diagrams, wiring diagram, and parts list. Thanks in advance for your ideas and help...
I think $200 is going to be hard to find anything that would live up to your expectations.
One thing you should know is that DIY stuff generally costs more than store-built, for the same power level (although you get better performance).
Here's a link I suggested in another thread. Add to these modules the cost of a transformer, cabinet, wiring, connectors, etc. and you'll have a good idea of what it might cost.
The schematics you may run across don't give a good idea of the costs of such a project. Cabinet, transformer, capacitors and heatsinks are typically the majority of the cost.
Also, I would really recommend you not build a high-power amp from scratch as your first project. There are too many things that can go wrong.
http://www.audioxpress.com has several modules and a few new modules that might suit your needs. You'd have to get your own trans, enclosure, power supply. The newer modules have power supplies you can purchase.
OMP/MFs come w/ transformer. They are mono blocks. 115w for $139. These were reviewed in Audio Electronic magazine. They got a good review.
HY2005 120 Watts (150W rms max) Power Amp Module with Integral Power Supply 6 lbs. $104.99
But you might have to go slightly above $200 to get one these together too.
Start savin'!! ;)
[Edited by vdi_nenna on 09-22-2001 at 10:56 AM]
Electrostats are a hard thing to drive since the element is pure capacitive load. So you need a lot of power to drive them with the equalizing crossover. 200 Watts is normal for driving them and the amp should also be stable to drive a hard load like that. You prabable need more money then you have calculated.
Consider building an OTL tube amp. Tubes are reatively inexpensive, and moreover don't mind getting hot which means you don't need heatsinks ... Tubes were great for my Quad ESL 63's. A transistor amp for electrostatics needs a lot of current drive (power supply), but a tube amp can be quite puny by comparison. A good tranny amp will give you better bass, but you can't beat the tube IMHO (or limited experience ...)
Without output transformers you don't need that either ...
For cabinet, any old wooden frame + a metal sheet on top (dare I suggest 1.5mm Cu?). You won't get a cheaper cabinet anywhere.
So you need a power transformer. Perhaps you can get one of the surplus units from http://www.angela.com or better still find something in a junkyard for free.
Power chokes should also be possible to find at a junkyard for near no cost. Get the electrolytics new -- it will be worth it. Perhaps you could even go to a photofinisher and ask for used "one-time" cameras which contain high voltage photoflash capacitors. If you are not the lucky type, you might have to spend at least a quarter of your budget on caps alone.
Add high quality connectors (you can use el-cheapo's, but why bother) or better still hardwire your home-made speaker cables.
For preamp use a simple stereo potentiometer, perhaps $10-15 for a good one -- perhaps even connected in shunt mode.
You should probably use a coupling cap somewhere which would set you back about $10 for one good one.
Search for "Bruce Rosenblitz" or go directly to the master at http://www.tubecad.com for improvements on Bruce's open source designs + other stuff.
I can't offer any scematics off hand, but I am working on a design for a direct coupled 4 Ohm 100W RMS Using ECG 180 & 181 type outputs.TO-3 These are hi-current devices, 7A peak linear operation . (lower Vceo) ($15\pair)......... For an 8 Ohm load, 2N3055 & MJ2955 (I think) are cheaper, your peak current for 100W is someware around 5A. (higher Vceo) any more 'I' with 253055, saturation is garanteed. :D
"One thing you should know is that DIY stuff generally costs more than store-built"
Yup. However, there are ways to finesse that. The first thing is to understand what is expensive and what isn't. Transformers, power supply filter caps, heatsinks, connectors (RCA, binding posts, etc) and enclosures are where most of the cost goes.
You can reduce costs a lot if
A- you don't care what it looks like. Usable enclosures can be found by scrounging - giant cookie tins that you may have gotten from your aunt last Christmas, 20mm ammunrtion boxes from a surpluss store (also commonly available through white water rafting sources), dead 486 PCs - etc. You can even substitute nuts and bolt from the harware store for binding posts (look at the back of some old 70's recieveiers).
B- Find an electronics surplus shop.
C- Shamlessly beg friends and relatives for old electronics geat in the garage, basement, closet, and attick __ You are looking for primarily for a suitable heatsinks, transformer(s) and filter caps. An enclosure might turn up too. Maybe even power switches and fuse holders - but be sure the current rating is adequate.
D-Stick to something simple like the Prpject P3A at www.sound.au
E- Hardest of all is step away from your (our, my?) audiophillic midset: 5% resistors ARE OK most of the time, gold plate is nice but not neccessary, film and ceramic caps desoldered from an old VCR still function, etc. Instead, try the mindset that building a good sounding amp for next to nothing is a challenge - make it a goal instead of a limitation.
Check e-bay. Particularly for heatsinks and transformers.
Finally, (having had some less than fabulous experience with Sony gear) consider that perhaps you don't need more watts so much as better watts. My Sony (long gone) skimped on heatsinking and transformer VA rating - 4-ohm speakers killed it. I bet yours does too. The P3A, above, configured for a solid 50W@8ohms (70-80 @ 4?) will probably sound beter than the Sony. If it were me I would be looking for a 24-0-24 transformer with a max of 300VA and 14,000uF to 20,000uF of filter capacity -- this is certainly scroungable -- as far as collecting the "stuff", it's easier after that.
Why are you two guys replying to a THREE YEAR OLD POST?
I my case, because I'm a total bonehead that didn't notice the posting date!!!!!
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