After building speakers for a while i thought i would have a go at a chip amp as my first project.
Being a natural bower-bird and skin-flint type i have a heap of old stuff floating around here, i have a good supply of heatsinks and cabinets won't be a problem( at least if I use old computer cases ) but using the Jaycar chip-amp kit using the cheapest possible parts
http://www.jaycar.com.au/productVie...&pageNumber=&priceMin=&priceMax=&SUBCATID=557
How far can you push the rail voltage?? I ask this question because I have on the bench a 28-0-28 CT transformer, but when I multiply by 1.4142 I get 39.6V, 5 volts more than the recomended 35V.
Is there any cheap, easy and reliable way of using this Transformer?? I have lots of transformers here but this is the smallest (amps die but trannies live for-ever)
Being a natural bower-bird and skin-flint type i have a heap of old stuff floating around here, i have a good supply of heatsinks and cabinets won't be a problem( at least if I use old computer cases ) but using the Jaycar chip-amp kit using the cheapest possible parts
http://www.jaycar.com.au/productVie...&pageNumber=&priceMin=&priceMax=&SUBCATID=557
How far can you push the rail voltage?? I ask this question because I have on the bench a 28-0-28 CT transformer, but when I multiply by 1.4142 I get 39.6V, 5 volts more than the recomended 35V.
Is there any cheap, easy and reliable way of using this Transformer?? I have lots of transformers here but this is the smallest (amps die but trannies live for-ever)
That kit appears to use the LM3876 chip (based on the picture), so the max rail voltages you can safely use are +/-42V. With mains fluctuations it would be safer to find a transformer that will give you +/-35V rails after rectification (one with ~25VAC secondaries). There's nothing barring you from using a lower voltage transformer either. I'm personally using trasformers with 18VAC secondaries on my LM3875 amps and they work great and the chips stay quite cool.
This one is a fairly old unit, I just checked it; it is rated 28-0-28 at 240V input our nominal voltage has changed to 230 would this drop in nominal voltage make much difference to the rated output??
Thanx ttan98, I did look for those at Jaycar when I bought the kit but Jaycar are becoming like Tandy/DickSmith more gadgets than gear
Thanx ttan98, I did look for those at Jaycar when I bought the kit but Jaycar are becoming like Tandy/DickSmith more gadgets than gear
Nominal mains voltage here is 230 volts but I have measured as low as 218 and as high as 252! In other words, don't assume your voltage stays the same. I have run LM3386 amps at +/-38 volts with no problem but I wouldn't go any higher.
It also depends on your speakers. My main speaker sounds much better with +/-27 volt rails
To sum up, you could try it but you are taking a risk, and it probably won't sound its best!
Hi Moon,
connect your transformer and measure the secondary voltage.
Phone your supply company and ask what their range of supply voltages are.
Calculate the worst case voltage from your transformer.
If the offload DC voltage is over +-42Vdc (>30.2Vac) then you are sailing close to the wind, particularly if you adopt my philosophy of +-20mF per 8ohm speaker.
connect your transformer and measure the secondary voltage.
Phone your supply company and ask what their range of supply voltages are.
Calculate the worst case voltage from your transformer.
If the offload DC voltage is over +-42Vdc (>30.2Vac) then you are sailing close to the wind, particularly if you adopt my philosophy of +-20mF per 8ohm speaker.
Wonderful bunch in this site, thanx all for helping.
I am goint to go with the tranny I have here and if it blows the chip I have only lost $AU 20-, while I know i should follow the advice and get a slightly smaller transformer the temtation to save a few dollers ( well $ 42.95 actually) is too strong.
I checked with my power company ans fluctuations of 12% are apparently quite common, I assume this wil cause the chip to run very hot so no mica or silicon pad, silver heat paste and isolating the heatsink seems to be the option.
I have a big slab of acrylic ( Perspex) here for mounting purposes and if I use a chimney arrangement the heat sink should be around 0.6 C/W.
Iam making the assumption that the reservoir caps (10,000uF 100V ) are still OK, this is too big but they are fairly new 3yrs old and came out of an old amp that died a little while ago as did the heat sinks and this amp was rated 200W OVERKILL?
I am goint to go with the tranny I have here and if it blows the chip I have only lost $AU 20-, while I know i should follow the advice and get a slightly smaller transformer the temtation to save a few dollers ( well $ 42.95 actually) is too strong.
I checked with my power company ans fluctuations of 12% are apparently quite common, I assume this wil cause the chip to run very hot so no mica or silicon pad, silver heat paste and isolating the heatsink seems to be the option.
I have a big slab of acrylic ( Perspex) here for mounting purposes and if I use a chimney arrangement the heat sink should be around 0.6 C/W.
Iam making the assumption that the reservoir caps (10,000uF 100V ) are still OK, this is too big but they are fairly new 3yrs old and came out of an old amp that died a little while ago as did the heat sinks and this amp was rated 200W OVERKILL?
just a thought here, but if chinmey style heat sinks are so much more efficient than any other type, why is it we have to make up our own??
I would not have thought it was that difficult to extrude an internally finned tube.
I was thinking of this as i was fiddling with various bits of aluminium and old heatsinks and looked at my old Kenwood monoblock, LM 7 while not exactly small the heatsink is so efficient it has to be a quarter the size of a comparable standard style with fins on one side and a smooth solid on the obverse.
Are cast heatsinks more effective than extrusions? and what is more important Mass, area or orientation??
I would not have thought it was that difficult to extrude an internally finned tube.
I was thinking of this as i was fiddling with various bits of aluminium and old heatsinks and looked at my old Kenwood monoblock, LM 7 while not exactly small the heatsink is so efficient it has to be a quarter the size of a comparable standard style with fins on one side and a smooth solid on the obverse.
Are cast heatsinks more effective than extrusions? and what is more important Mass, area or orientation??
Just used the calculator on ESP Rod Elliots websitehttp://sound.westhost.com/download.htm#hsink
and my fabricated heatsink is aproximately 1.4 degrees C per watt, this should be good enough.
I have the case from an old computer power supply to enclose the old transformer for RF sheilding and earthing, I just need to get a switch and mains fuse holder and a couple of heatsink brackets then I will start soldering
and my fabricated heatsink is aproximately 1.4 degrees C per watt, this should be good enough.
I have the case from an old computer power supply to enclose the old transformer for RF sheilding and earthing, I just need to get a switch and mains fuse holder and a couple of heatsink brackets then I will start soldering
OK here is link to my newly created file
Picture of fabricated heatsink
http://farm3.static.flickr.com/2253/2112222636_6d21900539_m.jpg
Picture of fabricated heatsink
http://farm3.static.flickr.com/2253/2112222636_6d21900539_m.jpg
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