I have an older pair of KEF bookshelf speakers (C1's I think), that I would like to turn into active speakers using chip amps. The main purpose of this project is to learn about chip amps and their power supplies, etc.
My requirements are as follows:
1) separate amp, power supply and input per speaker
2) 15 watts or ?? per speaker (looking for guidance on this)
3) compact components, as the speakers themselves are very small bookshelf type speakers
4) self contained within the speaker, preferably! No "outboard" components if at all possible. The idea is to stuff the chip amp and PS both inside each cabinet.
What chip amp/power supply combo do you guys recommend? Any and all feedback is welcome.
Thanks - Samer
My requirements are as follows:
1) separate amp, power supply and input per speaker
2) 15 watts or ?? per speaker (looking for guidance on this)
3) compact components, as the speakers themselves are very small bookshelf type speakers
4) self contained within the speaker, preferably! No "outboard" components if at all possible. The idea is to stuff the chip amp and PS both inside each cabinet.
What chip amp/power supply combo do you guys recommend? Any and all feedback is welcome.
Thanks - Samer
I wouldn't try and stuff everything inside, at least have the heatsinks on the back. For one this allows for better cooling and hence using a smaller heatsink, and secondly all this stuff would eat up space inside the boxes and weaken their bass response.
The LM1875 is fairly well regarded and documented. Kits are available if you want to go that route. A couple of 18-0-18VAC, 4A transformers will get you about 20 watts of audio per speaker. Vendors here will have all the materials you need.
I don't know the speakers. Maybe more power would be better.
I agree that it isn't the best design to stuff the amps in the speaker cabinets. I think I'd fit a small case to the bottom rear of each speaker. I'd also seriously consider having the dual supplies in a separate common enclosure, but preference & application could easily supercede that consideration (if any noise issues are dealt with).
I don't know the speakers. Maybe more power would be better.
I agree that it isn't the best design to stuff the amps in the speaker cabinets. I think I'd fit a small case to the bottom rear of each speaker. I'd also seriously consider having the dual supplies in a separate common enclosure, but preference & application could easily supercede that consideration (if any noise issues are dealt with).
TDA2050 IC and Radio Shack 12.6-0-12.6 2A transformer. You'll get 12 watts or more of clean power into 8 ohms. The transformer is $13. If you're building to learn, there's no point in spending excessive $$ on the project.
Buy your ICs from Digikey or one of the reputable sellers. The stuff on ebay has a good chance of being fakes.
Buy your ICs from Digikey or one of the reputable sellers. The stuff on ebay has a good chance of being fakes.
I'm doing this (with new DIY speakers, not existing ones) and I have found that LM3886 and TDA7293/TDA7294 chip amps will power most everything out there, if you use an active crossover to reduce losses. Base or completed PCBs can be purchased on Ebay or from other sellers like chipamp.com and so on.
If the speakers are small (less than 8-10 liters) then you can place the transformer in a separate enclosure outside the speakers and just have the rectifier and caps inside. I used Neutrik PowerCon and 16ga power cable to connect the two. I used this approach with a 4L or 5L speaker and, while it was a tight fit inside, it turned out great. It's speaker #6 in the first two pictures on this page:
Meet-Spring2010
-Charlie
If the speakers are small (less than 8-10 liters) then you can place the transformer in a separate enclosure outside the speakers and just have the rectifier and caps inside. I used Neutrik PowerCon and 16ga power cable to connect the two. I used this approach with a 4L or 5L speaker and, while it was a tight fit inside, it turned out great. It's speaker #6 in the first two pictures on this page:
Meet-Spring2010
-Charlie
Thank you for all who have answered so far. The speakers are the KEF 15's after all, not KEF 1 as I had thought. Their volume is between 6 and 7 liters and they are rated at 80w max power (4 ohm).
I like the idea of the LM3886 chip, which I think will easily drive the speakers as they are a little inefficient (85 dB) and I like the kit offered by chipamp.com
I looked at the different transformers that are available, and what's recommended for the kit is a 160VA supply between 18 and 22 volts. I would like to still install a separate PS in each speakers which makes this an expensive project, as toroidals with those specs aren't cheap. Can someone recommend a cheaper PS that will still do the amps justice?
Do you have any other recommendations?
I like the idea of the LM3886 chip, which I think will easily drive the speakers as they are a little inefficient (85 dB) and I like the kit offered by chipamp.com
I looked at the different transformers that are available, and what's recommended for the kit is a 160VA supply between 18 and 22 volts. I would like to still install a separate PS in each speakers which makes this an expensive project, as toroidals with those specs aren't cheap. Can someone recommend a cheaper PS that will still do the amps justice?
Do you have any other recommendations?
The chipamp stuff is very good. I've used these PS + amp boards from Ebay and they seem fine:
High Performance Audio 60Wx2 LM3886TF Power Panel+Power Amplifier Board DIY KIT | eBay
You can get reasonably priced toroids from Antek... or try ApexJr, which sells some inexpensive transformers that could work for you.
-Charlie
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If you need amplifiers and active crossovers take a look at the Linkwitz-Lab site. Not the cheapest, but you can learn a lot from.
Thanks for the tip on ApexJr Charlie! I already called him up and ordered 2 Toroidals and 2 LM3886's. The trannies were $19.95 each and the power amp chips (National Semi) were $4.50 each.
http://www.apexjr.com/images/Avemco2x10pt2.jpg
I just ordered the PCB's from chipamp.com without the components. I would like to purchase those separately from mouser or digikey. Is there a recommended list of "upgraded" components to buy, in order to improve the sound quality. Perhaps beefier caps,etc..
Samer,
Those don't seem to be the best transformers if you want to use one per speaker. The secondary voltage is about 22VAC (center tapped). This means about 11-0-11 volts AC on the secondary. When you rectify the AC to DC with a full bridge rectifier, you will get about 1.4 times the AC RMS voltage minus the diode voltage drop in the rectifier (typically 1.4V). So the DC rails will be 1.4*11 - 1.4 = 14 volts DC, and this is really too low to get the full performance out of the LM 3886 IC.
It's possible that you made the common mistake of confusing transformer secondary AC voltage with the DC voltage that the chip amp should be supplied with.
But, luckily for you, there is a simple solution! First you should purchase two more of the same transformers from ApexJr. Then, you should construct each of your two DC power supplies using the following circuit:
Ignore the 24V labels, as these are for different transformers that what you have.
If you use the above connections, you should get almost twice the DC voltage on the + and - rails, e.g. your rails will be about +/- 25VDC, which is fine for the LM3886 chip amps, when powering 4 ohms loads. You can expect about 50W into 4 ohms and about 25W into 8 ohms from these voltages, when using the LM 3886.
-Charlie
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