Ok, 2 things, one a little off topic. I was looking at the model number on my lm3875 and touched the metal tab which was a kinda metallic white and it left a very noticable fingerprint. so what is that white stuff?
otherwise. i've got my plan down to using hopefully a transformer with 48Vct (7A) and 24Vct (3A) ouptuts. i planned to use the 48Vct with an amp using 2 lm3875T (for midrange, 80hz - 1800hz) and 2 lm3886 chips (for bass, to 80hz). the impedance of each speaker is 8ohms nominal, but the single subwoofer will be on a bridged load. the 24Vct i wanted to use to power the lm1875 chips for my tweeters, and also at some point it would be regualted to +-15V or +-12V or +-18V for powering opamps and such.
now my major concern is that the lm3886 chips will go into protect mode? or will they not? i am thinking of adding a capacitvie multiplier fitler just to drop the voltage a little to prevent the protection from kicking in, or do i not have to?
otherwise. i've got my plan down to using hopefully a transformer with 48Vct (7A) and 24Vct (3A) ouptuts. i planned to use the 48Vct with an amp using 2 lm3875T (for midrange, 80hz - 1800hz) and 2 lm3886 chips (for bass, to 80hz). the impedance of each speaker is 8ohms nominal, but the single subwoofer will be on a bridged load. the 24Vct i wanted to use to power the lm1875 chips for my tweeters, and also at some point it would be regualted to +-15V or +-12V or +-18V for powering opamps and such.
now my major concern is that the lm3886 chips will go into protect mode? or will they not? i am thinking of adding a capacitvie multiplier fitler just to drop the voltage a little to prevent the protection from kicking in, or do i not have to?
TOOTHPASTE.
Hi,
Probably heat conductive paste as used between semiconductor and heatsinks or a chassis.
Can't quite recall the exact composition but I think it's something like molybdenum grease.
Nothing to loose sleep over anyway,😉
Hi,
Probably heat conductive paste as used between semiconductor and heatsinks or a chassis.
Can't quite recall the exact composition but I think it's something like molybdenum grease.
Nothing to loose sleep over anyway,😉
A lot of old transistors have this on them. I believe it to be an oxide of some sort or on the T0-220 packs with the metal tab, will have it too. I also think it is an oxide to protect the metal from corrosion when bolted to a dissimular metal such as aluminum.
I repair amps with LM3886's every day and I'll tell you only once......... Put a series capacitor before your tweeter..... If the chip fails, it will put the rail voltage on it and blow it too...... Costly mistake. We have more JBL "Eon" powered monitor speaker boxes with shorted chips (on the tweeters) and open circuit Horn (tweeter) diaphram coils......... PROTECT YOUR TWEETERS!!!!!
With respect,
Chris
I repair amps with LM3886's every day and I'll tell you only once......... Put a series capacitor before your tweeter..... If the chip fails, it will put the rail voltage on it and blow it too...... Costly mistake. We have more JBL "Eon" powered monitor speaker boxes with shorted chips (on the tweeters) and open circuit Horn (tweeter) diaphram coils......... PROTECT YOUR TWEETERS!!!!!
With respect,
Chris
good, i had planned to put a cap on the output and possibly even an inductor (in parellel with the speaker) to get a 2nd order network and block out any 60hz or lower stuff, though i may just go for a simple filter cap.
I have the same problem with a TDA7250 and TIP147/142 transistors. At +/- 38V and RL=4 ohm the amp goes into standby if i raise the volume over a certain limit.
How can you lower the voltage of the power supply ???
Thanks in advance.
"I have the same problem with a TDA7250 and TIP147/142 transistors. At +/- 38V and RL=4 ohm the amp goes into standby if i raise the volume over a certain limit. "
-so the chip works and is protecting itself noramlly? i was worried the idle voltage would shut the chip off, so i wouldn't be able to turn the volume up to anything...
as for the solution to your problem, an impedance matching transfromer is a solution, though i don't know if i'd use it.
thats also why i wanted to use the capacitvie multiplier filter, to drop a little bit of voltage.
-so the chip works and is protecting itself noramlly? i was worried the idle voltage would shut the chip off, so i wouldn't be able to turn the volume up to anything...
as for the solution to your problem, an impedance matching transfromer is a solution, though i don't know if i'd use it.
thats also why i wanted to use the capacitvie multiplier filter, to drop a little bit of voltage.
Look at other power crossover values 2uF 2.2, 4.7 etc. I'd put a non-polar electrolytic and a high voltage, say 300V for high power, 160V for 50 to 100W. The lower the value, the more midrange frequencies will creep in.
Chris
Chris
3886 & others
Don't use more than 30-30 dc for bridging! 28-28 is better, since some minimum impedances can creep in. You can regulate down that 35-35 DC you'll be getting, but it'll be a pain. Better to locate a torroid that'll do 30-30 (I can't)
than to use the Apex beastie, whichis large and clunky. 30- 30 is fine for 3876's all day,too. I don't really know 3875's, but they are all so cheap---
A wall wart (say 22AC) is actually more convenient for O-PAMPS, when it comes to doing the wiring, and better than dropping the main amp rails. Can you do a votage doubler circuit? They are very covenient!
Don't use more than 30-30 dc for bridging! 28-28 is better, since some minimum impedances can creep in. You can regulate down that 35-35 DC you'll be getting, but it'll be a pain. Better to locate a torroid that'll do 30-30 (I can't)
than to use the Apex beastie, whichis large and clunky. 30- 30 is fine for 3876's all day,too. I don't really know 3875's, but they are all so cheap---
A wall wart (say 22AC) is actually more convenient for O-PAMPS, when it comes to doing the wiring, and better than dropping the main amp rails. Can you do a votage doubler circuit? They are very covenient!
tweeters
Oh- on protecting bi-amped tweeters, I think a 28-33u is about right, and I'd use polypropylene exclusively. Costs a few bucks.....
Oh- on protecting bi-amped tweeters, I think a 28-33u is about right, and I'd use polypropylene exclusively. Costs a few bucks.....
hmm. i'll have to ask around school about this one. i've already placed my orders and don't want to place any more. and i think the caps to protect the tweeters are more expensive then the tweeters themselves! (which were choosen mainly for the low Fs to match a 6.5" mid-woofer)
Sorry guys,
I didn't know what kind of system you were building. I guess I'm accustomed to seeing 40-70.00 horn tweeters blow so a 6.00 capacitor is nothing. I really don't know how much JBL gets for the horn diaphrams but I'll bet our cost (shop) is over 100.00. For my personal home tweeters, I bought Seas Excel tweeters, on sale, for 65.00 so again, a 6.00 capacitor doesn't cost much to protect the investment. Again, sorry, I didn't know what kind of parts you are using. MCM also sells a "tweeter protector" I think it is just a MOV that acts like a very small resistor until its rating is exceeded and then goes very high in resistance as to attenuate power levels that exceed its power rating. I don't know how well they work but I installed them into a set of PA speakers and had no troubles with them. I don't know how they will handle DC though. I'd assume they will burn up.
Well, good luck with your project!
Chris
I didn't know what kind of system you were building. I guess I'm accustomed to seeing 40-70.00 horn tweeters blow so a 6.00 capacitor is nothing. I really don't know how much JBL gets for the horn diaphrams but I'll bet our cost (shop) is over 100.00. For my personal home tweeters, I bought Seas Excel tweeters, on sale, for 65.00 so again, a 6.00 capacitor doesn't cost much to protect the investment. Again, sorry, I didn't know what kind of parts you are using. MCM also sells a "tweeter protector" I think it is just a MOV that acts like a very small resistor until its rating is exceeded and then goes very high in resistance as to attenuate power levels that exceed its power rating. I don't know how well they work but I installed them into a set of PA speakers and had no troubles with them. I don't know how they will handle DC though. I'd assume they will burn up.
Well, good luck with your project!
Chris
yeah, next semester there's going to be 3 computers (all of which could almost be classified as servers in terms of noise...) 2 refrigerators, and to make things even better, the lights buzz... oh and of course the AC/heating. there's only so much precision that can be had in such an enviroment!
http://sound.westhost.com/project15.htm
"The only real thing to worry about is the degree of filtering needed! We must assume that at least 3 Volts will be lost across the capacitance-multiplier filter, to ensure that the DC input (including ripple component) always exceeds the output voltage. "
-this is the line i noticed.
or could you just get a lot of diodes?
"The only real thing to worry about is the degree of filtering needed! We must assume that at least 3 Volts will be lost across the capacitance-multiplier filter, to ensure that the DC input (including ripple component) always exceeds the output voltage. "
-this is the line i noticed.
or could you just get a lot of diodes?
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