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Old 10th August 2012, 12:28 PM   #1
pra3718 is offline pra3718  India
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Default LM1875 Bridge and stereo

"The amp will work with 2ohms if you don't push it too much. It will need good heatsinking though."

The above line right or wrong. I am going to try it. 12-0-12 5 Amp transformer is easy to buy. So I am going to power up 18-(+/-)VDC. Bridging with ESP's bridging adaptor. Any advices welcome...
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Old 10th August 2012, 05:16 PM   #2
pra3718 is offline pra3718  India
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With little updates.
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Old 19th August 2012, 10:09 PM   #3
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Default About LM1875

Hi,
I am really interested in LM1875 build and its performance. Don't go below 4ohms with LM1875. Better if you drive 8ohms speaker with it. I prefer 8ohms. Even 4 ohms will produce too much heat at around 18(+-) supply and prformance will dramatically change with voltages below 15 volts and above 20v. Think about how much heat will be produced at 2 ohms speaker load? LM1875 are designed for at least 4ohms speakers. On the other hand, using a high impedance load (8ohm speakers) will also give you a little increase in bass level as compared to other audio frequency notes (This sounds pleasant and its my personal experience. Your opinions are still reserved.). NOTE: Never operate LM1875 without the heat sinks even with no input signal condition. IC will get damage easily and soon.

I prefer 18-0-18 Transformer (GURU is the best) 5Amp with LM1875 Stereo build.And 8ohms Speaker.The choice is yours.

And, have you heard anything about ground loops? If you really wanna built a good, stable and trouble free completely silent and clean output power amplifier with no noise and hum. I suggest you to go with the vero board instead of any PCB. You cannot achieve 100% star grounding pattern with any PCB build. LM1875 is a low number components circuit design which can easily be build on a veroboard. A large veroboard for a stereo build which will cost you around 30Rs. The choice is again yours.

Thanks, let me know about your progress regarding this project. I wanna know about the performance of this working project soon.I have heard that this amplifier delivers the sound quality near to that of the Class A amplifier if configured and build properly.Infact,
i wanna build one myself but not getting a time with my daily buisy schedule.

Last edited by noddy55; 19th August 2012 at 10:19 PM.
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Old 19th August 2012, 11:18 PM   #4
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Quote:
Originally Posted by noddy55 View Post
...You cannot achieve 100% star grounding pattern with any PCB build...
Could you clarify? I'm fairly sure I've managed it once or twice.
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Old 20th August 2012, 02:54 AM   #5
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I am planning a similar build on proto board, first amp build (not counting cmoy on breadboard and proto board). Had a quick question about the caps attached to the +-Vcc. these need to be done on both the channels separately? Can I do this on the psu board itself or do i need to do this close to the ic. I understand I need to keep all the fb stuff close to the pins. any other useful tips for doing a p2p build. For now i am planning to use 15v 3a EI core trafo. I might run both 4 ohms or 8 ohms speakers in future.
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Old 20th August 2012, 03:06 AM   #6
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Yes, add those caps to each channel separately. Offhand, they will generally be valued at about 100uF and 100nF, and they should be located as close to the IC power pins as practical.
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Old 20th August 2012, 10:56 AM   #7
pra3718 is offline pra3718  India
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Thanks

Quote:
I suggest you to go with the vero board instead of any PCB. You cannot achieve 100% star grounding pattern with any PCB build.
At my beginning stage I have used lot-off veroboard. A good sound quality can be achieve with it. @gotte advised me for tracks should be insulated with ground. Even I have searched professional circuit build like this.

I did not get good advice where LM1875 can work well with 2R load. I have suspended this project.. If some expert member allow to build, I would start again..
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Old 20th August 2012, 12:22 PM   #8
AndrewT is online now AndrewT  Scotland
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For a 2ohms speaker load the amplifiers are effectively seeing a 1ohm speaker load.
If one accepts that a standard chipamp is OK into an 8ohms speaker load. Then the 1ohm loading would require 8 in parallel giving a 16chip BPA for your 2ohms speaker.
Is that worth trying when you could use an lme498xx chip and a couple (or maybe 3pr) of output pairs?
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Old 20th August 2012, 02:58 PM   #9
pra3718 is offline pra3718  India
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Quote:
For a 2ohms speaker load the amplifiers are effectively seeing a 1ohm speaker load.
Thanks AndrewT

Little confusion for me. I am going to try for LM1875 bridge for 4R Load with lower power supply. So each chip would see as 2R Load. Pls. correct me if I am wrong. Members are using LM1875 MONO with 4R load and my trial is LM1875 bridge with 4R Load.
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Old 20th August 2012, 05:02 PM   #10
AndrewT is online now AndrewT  Scotland
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then you must design for a 2ohms speaker load for each half of the amplifier.
That 2ohms loadings is worse than 1r0 resistive load.

You will need a lot of current capability.
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