Hi everybody,
I went to a local surplus store, called American Science and Surplus (www.sciplus.com i think) and couldn't pass up a $12 subwoofer I saw there. It is an 8-inch 50W sub made my LA Sound. I then built a nice bandpass box for it, and connected it to my sub amp I built with an LM3886. It sounded great, deep, tight and no distortion. Yes, it distorted when the amp did, but other than that, it was great sounding. Now, I want to build a new amp for it. I want to use 2 LM1875 in bridged mode, to get around 50W or so. Can the LM1875 drive a 4-ohm speaker in bridged mode? If so, about how much wattage can it put out?
Since the heatsink would be mounted to the aluminum backplate, the chips must be insulated. I have these blue rubber like things from a heatsink from a computer ps with both a 7905 and a 7912 on it. This thing is for insulating it, right? I would prefer though, to just get the insulated version of the chip. Is there a power output reduction when using the insulated version of the chip? I would prefer using the insulated version also because I wouldn't have to buy special screws that don't conduct.
Finally, can somebody direct me to a good bridged circuit?
Thank you, Mike
I went to a local surplus store, called American Science and Surplus (www.sciplus.com i think) and couldn't pass up a $12 subwoofer I saw there. It is an 8-inch 50W sub made my LA Sound. I then built a nice bandpass box for it, and connected it to my sub amp I built with an LM3886. It sounded great, deep, tight and no distortion. Yes, it distorted when the amp did, but other than that, it was great sounding. Now, I want to build a new amp for it. I want to use 2 LM1875 in bridged mode, to get around 50W or so. Can the LM1875 drive a 4-ohm speaker in bridged mode? If so, about how much wattage can it put out?
Since the heatsink would be mounted to the aluminum backplate, the chips must be insulated. I have these blue rubber like things from a heatsink from a computer ps with both a 7905 and a 7912 on it. This thing is for insulating it, right? I would prefer though, to just get the insulated version of the chip. Is there a power output reduction when using the insulated version of the chip? I would prefer using the insulated version also because I wouldn't have to buy special screws that don't conduct.
Finally, can somebody direct me to a good bridged circuit?
Thank you, Mike
I looked at the datasheet. These chips can put out 4A of current. Wouldn't they power a 2-ohm speaker fine? It's sort of like the 3886. It has no problems with a 2-ohm load. I have ran 2 4-ohm sub speakers in parallel off of a 3886 and it had no problems with it. Would it work, just putting out more heat?
Does the insulated version of the chip lose power like the insulated 3886 does?
This is a low powered chip. I can't see it needing fancy mounting brakets. All it should need is a screw- it works on my 3886 amp which puts out much more heat.
Has anybody experimented with bridged 1875s and could tell me how they work into a 4-ohm speaker? A schematic would also be appreciated. If not, what is a good, simple chip to use for this that can put out about 50W.
I tried this speaker with a 100W amp and it started to burn and smell with the volume up so I want to keep the power output not too much above 50W. What size fuse would I need to protect the speaker? And where would I place it? Inline with the speaker wire?
Thanks, Mike
Does the insulated version of the chip lose power like the insulated 3886 does?
This is a low powered chip. I can't see it needing fancy mounting brakets. All it should need is a screw- it works on my 3886 amp which puts out much more heat.
Has anybody experimented with bridged 1875s and could tell me how they work into a 4-ohm speaker? A schematic would also be appreciated. If not, what is a good, simple chip to use for this that can put out about 50W.
I tried this speaker with a 100W amp and it started to burn and smell with the volume up so I want to keep the power output not too much above 50W. What size fuse would I need to protect the speaker? And where would I place it? Inline with the speaker wire?
Thanks, Mike
Look at the power dissipation curves on the datasheet. You'll find that the chip will dissipate a lot of power when driving a low impedance with a fairly high power supply. Neither the 3886 nor the 1875 are rated for driving a 2-ohm load. If you want more power, use the proper amp.soundNERD said:
But go ahead and try it, maybe we'll hear another spectacular tale of how the gainclone blew, taking a speaker with it.
There have been a few stories posted here about chip amps blowing and taking out the speaker, yes by putting DC on the output.
Look closely at pg. 4 of the datasheet at http://cache.national.com/ds/LM/LM1875.pdf .
There are other chips out there. How about this one (consider wiring two in parallel instead of briding them into a 4-ohm load):
http://cache.national.com/ds/LM/LM4780.pdf
Look closely at pg. 4 of the datasheet at http://cache.national.com/ds/LM/LM1875.pdf .
There are other chips out there. How about this one (consider wiring two in parallel instead of briding them into a 4-ohm load):
http://cache.national.com/ds/LM/LM4780.pdf
djk,
How would I connect the 3886 to get 200W into a 2ohm load? How much power could it put out with +-24V? I really want under 100W, since that is the max rating of the speaker.
If I were to use a single 3886 but also use the MJ15003/4, would I get more power into 4-ohm speaker?
I have decided on a 3886, and last night ordered 5 samples of the insulated version. Where can I find a good, simple circuit for it? If the schematic comes with a PCB design that would be good also.
Thanks, Mike
How would I connect the 3886 to get 200W into a 2ohm load? How much power could it put out with +-24V? I really want under 100W, since that is the max rating of the speaker.
If I were to use a single 3886 but also use the MJ15003/4, would I get more power into 4-ohm speaker?
I have decided on a 3886, and last night ordered 5 samples of the insulated version. Where can I find a good, simple circuit for it? If the schematic comes with a PCB design that would be good also.
Thanks, Mike
"If I were to use a single 3886 but also use the MJ15003/4, would I get more power into 4-ohm speaker?"
Boosted LM3886/MJ15003/04 on ±40V is 200W/2R, or 100W/4R
Boosted LM1875/MJ15003/04 on ±28V is 100W/2R, or 50W/4R
Basic scheme in bridged mode:
http://www.mif.pg.gda.pl/homepages/tom/files/simp200W.gif
Boosted LM3886/MJ15003/04 on ±40V is 200W/2R, or 100W/4R
Boosted LM1875/MJ15003/04 on ±28V is 100W/2R, or 50W/4R
Basic scheme in bridged mode:
http://www.mif.pg.gda.pl/homepages/tom/files/simp200W.gif
Sorry, I thought you said a bridged 3886 with the transistors would do 200W into 2-ohms.
Which one in the schematic is the 03 and which is the 04? Will the transistors run hot and require heatsinks? Also, where do I get them at?
Also, do they boost voltage or current so I would have to change the mute resistor?
If I were to use the same schematic you pointed me to for the 3886, how much power would I get with a 4-ohm speaker?
Finally, do I connect them to the 3886? just as in the schematic?
Thanks if you can answer any of my questions, Im new to this idea and don't know how it works.
-Mike
Which one in the schematic is the 03 and which is the 04? Will the transistors run hot and require heatsinks? Also, where do I get them at?
Also, do they boost voltage or current so I would have to change the mute resistor?
If I were to use the same schematic you pointed me to for the 3886, how much power would I get with a 4-ohm speaker?
Finally, do I connect them to the 3886? just as in the schematic?
Thanks if you can answer any of my questions, Im new to this idea and don't know how it works.
-Mike
"OK, I got some samples of the transistors ordered this morning. What is better to use in my case, inverting or non-inverting? I am going to draw up a schematic to be "approved" by everybody."
Doesn't matter.
"Sorry, I thought you said a bridged 3886 with the transistors would do 200W into 2-ohms."
A bridged 3886 can swing 160V peak-to-peak, you figure it out.
"Which one in the schematic is the 03 and which is the 04?"
Look at the data sheets and figure it out.
"Will the transistors run hot and require heatsinks?"
Go look at a commercial 400W amp and see how much they use.
"Also, where do I get them at?"
http://search.ebay.com/search/searc...erty=MetaEndSort&category0=12576&BasicSearch=
"Also, do they boost voltage or current so I would have to change the mute resistor?"
Read the instructions for the 3886 chip.
"If I were to use the same schematic you pointed me to for the 3886, how much power would I get with a 4-ohm speaker?"
400W/4R from an unregulated 80V supply.
"Finally, do I connect them to the 3886? just as in the schematic?"
Is this a trick question?
Doesn't matter.
"Sorry, I thought you said a bridged 3886 with the transistors would do 200W into 2-ohms."
A bridged 3886 can swing 160V peak-to-peak, you figure it out.
"Which one in the schematic is the 03 and which is the 04?"
Look at the data sheets and figure it out.
"Will the transistors run hot and require heatsinks?"
Go look at a commercial 400W amp and see how much they use.
"Also, where do I get them at?"
http://search.ebay.com/search/searc...erty=MetaEndSort&category0=12576&BasicSearch=
"Also, do they boost voltage or current so I would have to change the mute resistor?"
Read the instructions for the 3886 chip.
"If I were to use the same schematic you pointed me to for the 3886, how much power would I get with a 4-ohm speaker?"
400W/4R from an unregulated 80V supply.
"Finally, do I connect them to the 3886? just as in the schematic?"
Is this a trick question?
Sorry, most of those questions came from quickly looking at the scehmatic you provided. I was unsure if I would connect them the same way for the 3886 as I would for the TDA2030, so no, it isn't a trick question.
Call this a stupid question, but isn't there a large risk of DC on the output if for some reason the transistor were to fail?
What "commercial amp" are you talking about. Its common knowledge that the 3886 gets warm, but i know transistors don't always get hot, only when operating certain ways. So, do I need a heatsink is a yes or no question.
I thought that inverting/non-inverting made a difference in sound quality is why I asked that.
Heres the schematic:
thanks!
Call this a stupid question, but isn't there a large risk of DC on the output if for some reason the transistor were to fail?
What "commercial amp" are you talking about. Its common knowledge that the 3886 gets warm, but i know transistors don't always get hot, only when operating certain ways. So, do I need a heatsink is a yes or no question.
I thought that inverting/non-inverting made a difference in sound quality is why I asked that.
Heres the schematic:
thanks!
Attachments
Yes. Add fuses, but they still may not blow fast enough. Try 5A fast blow to start.soundNERD said:
You need a very large heatsink because amplifiers are not 100% efficient. Look at any commercial 400W amp to get an idea of how big your heatsinks need to be.
I can't remember what the latest opinion is from the gainclone demigods, but it probably doesn't matter.
Your questions make me feel that this is probably not a good project for you yet. I strongly suggest you try a regular gainclone first, then build a bigger one. A 400W amp and its power supply are difficult to build properly and can be dangerous.
It would seem that a reply I just posted (thread 295208) would be more relevent to this thread !, to cut a long story short ,yes you can get 100W+(into 4R) by using four lm1875 and with very low distortion of about 0.005% all on about 27V. I will post the details of how to do it if theres enough interest (and hope that my employers dont' read this site !)
Jez.
Jez.
"yes you can get 100W+(into 4R) by using four lm1875 and with very low distortion of about 0.005% all on about 27V"
Dying to hear the details, I mean 100W/4R is 28.3V, that's pretty good from a 27V supply.
Or did you mean a ±27V supply?
Running four LM1875 in parallel/bridge mode with all the DC servos required to get 100W/4R is a waste of time and money.
One LM3886 driving a pair of outputs in the supply leads is much simpler, and costs less too.
Circlotron's 'Afterburner' circuit is good too.
Dying to hear the details, I mean 100W/4R is 28.3V, that's pretty good from a 27V supply.
Or did you mean a ±27V supply?
Running four LM1875 in parallel/bridge mode with all the DC servos required to get 100W/4R is a waste of time and money.
One LM3886 driving a pair of outputs in the supply leads is much simpler, and costs less too.
Circlotron's 'Afterburner' circuit is good too.
oops !,
I built this some months ago at work,my memory has played tricks on me!,it was into a 2R load of a 100 volt line transformer via bipolar coupling caps. I did,however ,try it into a 4R resistive load just to see what it might be like as a hi-fi amp, it was then that I was surprised to see such good THD figures at 25W.
Jez.
PS Quite new to site, could any one reccomend a thread with the circuit of this gainclone i'm reading so much about ?, or does' "gainclone" simply refer to any hi-fi amp made with an IC ?.
I built this some months ago at work,my memory has played tricks on me!,it was into a 2R load of a 100 volt line transformer via bipolar coupling caps. I did,however ,try it into a 4R resistive load just to see what it might be like as a hi-fi amp, it was then that I was surprised to see such good THD figures at 25W.
Jez.
PS Quite new to site, could any one reccomend a thread with the circuit of this gainclone i'm reading so much about ?, or does' "gainclone" simply refer to any hi-fi amp made with an IC ?.
Yes, a gainclone is an amp made with a chip. How it got it's name I described here: (about the only thing I was right on on the site. I am fixing it, so please don't point out how wrong the other information is):
www.electronet.5u.com/audio.htm
There is also a site called the Decible Dungean, made by a member of this site. I don't know the link though.
-Mike
www.electronet.5u.com/audio.htm
There is also a site called the Decible Dungean, made by a member of this site. I don't know the link though.
-Mike
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