Yes you can. The 1875's tab is connected to the - supply. You can mount them without an insulator on a single heatsink.
They don't need a huge heatsink. I used 1 about 4 inches wide, 1 inch deep and 1.5 inches tall with 14 fins. It barely got warm at all, but I was just running the chips in stereo.
But why bridge the 1875? Just get a chip such as the 3875 (56W) or the 3886 (68W) and use it in single mode. You'll get more power. Also, the lm1875 (just like almost every other chip amp can only drive an 8-ohm speaker at 40W in bridge mode (no 4-ohm). 3875 is better for 8-ohm loads also with 56W. The 3886 is designed to produce 68W into a 4-ohm.
Which chip to choose depends on the space you have (for heatsink size), the power you want and the load you are driving.
They don't need a huge heatsink. I used 1 about 4 inches wide, 1 inch deep and 1.5 inches tall with 14 fins. It barely got warm at all, but I was just running the chips in stereo.
But why bridge the 1875? Just get a chip such as the 3875 (56W) or the 3886 (68W) and use it in single mode. You'll get more power. Also, the lm1875 (just like almost every other chip amp can only drive an 8-ohm speaker at 40W in bridge mode (no 4-ohm). 3875 is better for 8-ohm loads also with 56W. The 3886 is designed to produce 68W into a 4-ohm.
Which chip to choose depends on the space you have (for heatsink size), the power you want and the load you are driving.
soundNERD said:
I got 4 ohm speaker, now i'm ready to test my bridge LM1875 but i got some problem.... When i test the output (only supply is present) I get some DC reading around 20V and one of the chip is disipates to much heat..
I used the schematic proded by the wegsite of sam electronics
can someone examine it? and give me some thought
Attachments
When an amp is in bridged mode, each sees the speaker as half its real impedence. Anotherwords, they each see it as 2-ohm which is too low to drive with a bridged configuration of the 1875.
I'm working on some schematics for single, bridge and parallel on my website if you don't mind waiting a week or so.
When you tested the chip. did you have anything connected besides the power? No speaker or input, right?
Did you check for shorts and stuff?
And, are you using a split supply (+ , gnd , and -)?
I'm working on some schematics for single, bridge and parallel on my website if you don't mind waiting a week or so.
When you tested the chip. did you have anything connected besides the power? No speaker or input, right?
Did you check for shorts and stuff?
And, are you using a split supply (+ , gnd , and -)?
First of all, bridging into 4 ohms is a no-no. You should build a parallel amp. The results will be much better.
The heat is being generated because one of your chips is oscillating. With no load connected, they should run cool.
The problem with this schematic is that it is not designed to be used with the LM1875. It may work fine for some other chip amps, but it will not work with the National ones. The circuit is not fundamentally flawed, but it makes some assumptions about the op-amps (chip amps) used that are not necessarily true.
The most erroneous of these assumptions is that the op-amp are stable at unity gain (gain = 1 or -1). The national chip amps are generally stable only with gain of 10 (or -10) and higher. If you look at the circuit, you will see that the second opamp, IC2, gets its input from the output of IC1 (via R5), and it operates as an inverting amp with a gain of -1.
Trying to fix the circuit is a moot point since you should not use a bridge amp with a 4 ohm load anyway. There are a couple of active threads here dealing with parallel amps. Check them out.
I'm willing to wait soundnerd..thankssoundNERD said:
right!..
I did, several times...
Yup!... i got 25-0-25 PSU
I really wish i could find other chips, such as LM3875 or LM3876
so that i dont have to bridge them to gain power coz i only have 50 watts speaker..
Before i begun to buid an OP amp i did check the abailability of the chip in local store, yes.. and STK40XX series is abailable but it is very expensive. SKT40XX is raging 100w higher output, i got only 50w monitor.
About the 100W chip, it will have no problem with the 50W speaker. As long as you don't crank it you will have no problems.
And I have the schematic and pcb for the single operation in eagle format here:
http://electronet.5u.com/schematics/eagle/
The bridge, parallel and the actual html pages are coming soon.
-Mike
And I have the schematic and pcb for the single operation in eagle format here:
http://electronet.5u.com/schematics/eagle/
The bridge, parallel and the actual html pages are coming soon.
-Mike
bridged LM3886s
I know that this is kinda off topic, but I bridged 2 LM3886s. My power supply is 25-0-25, and I have 2 subs with dual 6 ohm voice coils. I had all the coils wired in parallel, which gave me a 1.5 ohm load. I ran that off the 2 LM3886s with almost no problems. The chips did get hot quickly, and the ps voltage was dropping to 15v on each rail when the bass hit. Other than that, each chip had no problem driving a 0.5 ohm load.
Can someone explain why the chips can't drive a 4 ohm or lower load in bridged mode?
I know that this is kinda off topic, but I bridged 2 LM3886s. My power supply is 25-0-25, and I have 2 subs with dual 6 ohm voice coils. I had all the coils wired in parallel, which gave me a 1.5 ohm load. I ran that off the 2 LM3886s with almost no problems. The chips did get hot quickly, and the ps voltage was dropping to 15v on each rail when the bass hit. Other than that, each chip had no problem driving a 0.5 ohm load.
Can someone explain why the chips can't drive a 4 ohm or lower load in bridged mode?
Actually STK40XX series is my fist choice to buid 100w amp, but as i mentioned it is too expensive so i decided to shift into cheep one.soundNERD said:
As i serch the net for other chip amp the LM3886,LM3875,LM3876 are the one whos qualified for my needs but none of them are available in local market(but if u can send me one of them i'll be glad)
the LM1875 is the only chip i can get.. I'm thinking.. what 'bout TDA chip? do u think this chip are good to use? did u tested it?pls give me some feed back about this chip?
Nice.. but i cant view it!.. I should wait for html page to come up!
hi JhonDoe ,
you can get free samples from www.ti.com , you can request for OPA541, Opa549...as you know these chips are probably assembled at their Baguio Plant...
good luck!!!
you can get free samples from www.ti.com , you can request for OPA541, Opa549...as you know these chips are probably assembled at their Baguio Plant...
good luck!!!
If you want to get to view those before I get them into a standard image format, you would need Eagle:
www.cadsoftusa.com
-Mike
www.cadsoftusa.com
-Mike
I desided to bridge LM1875 to much more power than a single chip my question is..... Can I mount the 2 chips in one heatsink(w/out mica insulator) I mean the chip is direct mount in HS?
How much the size of the HS for this chips(the Ideal size)?
asking the questions in post1 raises the suspicion you should not be trying to design a bridged amplifier.
The problems you are having in post5 confirm that you should never have started considering designing a bridged amplifier.
Get real. Learn to assemble a simple non-inverting AC coupled single chipamp and learn from there how and why it works. Then you might be ready to consider a bridged design project.
National tell you so.
Go and read the datasheet.
The first clue is the 7Apk maximum output current, although typically they suggest 11Apk for some of their production. That is when the chipamp is cold. It is even less when it is warm and atrocious when hot.
The other clues are spread around in propensity.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.