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Old 4th January 2014, 05:05 PM   #401
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Quote:
Originally Posted by sevenup2278 View Post
I made a dual LM1875 PCB with onboard heatsink and powersupply.
I think this would be very nice as first time project
Good work!
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Old 5th January 2014, 02:31 AM   #402
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Quote:
Originally Posted by plgsekip View Post
Or will there be an improvement in "sonic performance" if I put the cap?
Yes that's the point. It is your opportunity to put a little cap (range 10u~470u) in the power circuit for better clarity, and probably without causing loud mids.
Peter of AudioSector sometimes puts an extra 10u on only the negative rail for a bit better clarity and tone.
Actually, I have done asymmetric decoupling once--One of my radios, which has a passive auto center power circuit, does have an extra little cap on one of its rails, and that worked fine.

EDIT: This post is not general purpose here--it is regarding one sample.
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Old 5th January 2014, 06:47 AM   #403
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Default Different power circuits for different chips.

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Originally Posted by availlyrics View Post
@danielwritesbac I agree with you,pair of 1000uf & 0.1uF from +/- rail to Gnd is highly recommended.
I don't do that with LM1875. . . because it isn't an LM3875. Different chips have different needs.

STK and most TDA amplifier board power caps in the range of 100u~270u
Panasonic's 150u is close to perfect. Nearby values work.

Overture series of tv-sound amplifiers, LM3875, LM3876, LM3886, LM4780 amplifier board power caps in the range of 1000u~2200u when the chip is used in non-inverting mode.
Panasonic's 1500u is close to perfect. See exact model at AudioSector.

LM1875 and LM675 amplifier board power caps in the range of 150u~470u
This is similar to many discrete amplifiers.
Panasonic's 270u is close to perfect. Nearby values work.
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Old 5th January 2014, 07:54 AM   #404
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Thanks Daniel!
I have actually followed the suggestion to remove the series output cap. Surprisingly, it sounds better! Now I understand that the series output cap was only needed for my other LM1875 which suffers mids distortion as you suggested (the implementation board from XY Hifi).

For my latest version of LM1875, the output cap is not needed to improve the sound. @availlyrics insisted and now I got his point! :-D Thanks.

Now I am going to change the circuit a little bit by removing the 1000 uF rail to rail cap, and installing 470uF per rail as (your 2013 version employs parallel 220uF). I hope it will help the clarity. I also need to limit the amount of components since I am going to do it point-to-point.

@danielwritesbac, do you have any tutorial on doing p2p for LM1875 as you did for TDA7294?

I also might reduce the gain... it's currently using 22k NFB, and 820R of NFB-Resistor. I probably use 22k and 1k.

BTW, has anyone done a microcap simulation for LM1875? I am interested in the .CIR file. Thank you.

Cheers!
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Quote:
Originally Posted by danielwritesbac View Post
Yes that's the point. It is your opportunity to put a little cap (range 10u~470u) in the power circuit for better clarity, and probably without causing loud mids.
EDIT: This post is not general purpose here--it is regarding one sample.
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Old 5th January 2014, 01:41 PM   #405
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Quote:
Originally Posted by plgsekip View Post
@danielwritesbac, do you have any tutorial on doing p2p for LM1875 as you did for TDA7294?
Actually I don't, so howabout the fun puzzle of an STK465 point to point instead?
With so many pins that the soldering will be more fun than LM1875's simple 5 pins.
Click the image to open in full size.
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Last edited by danielwritesbac; 5th January 2014 at 01:44 PM.
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Old 5th January 2014, 11:10 PM   #406
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I think I'll skip to TDA7294. I don't have this STK465 and I want to resurrect my old TDA7294 which to my ears sound - subjectively - better than LM1875. I have a pair of them and your post on P2P TDA7294 is challenging.



Still the same question, anyone done simulation on LM1875 using microcap or alike software?

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Originally Posted by danielwritesbac View Post
Actually I don't, so howabout the fun puzzle of an STK465 point to point instead?
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Old 6th January 2014, 05:03 AM   #407
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If you are looking for a spice model for the LM1875 chip itself, one did not exist for a long time but I believe that TI.com might now have one. However, if they do, I don't know how good it is, or if it works well (or at all) with anything other than the TINA simulator software. Do a search for "LM1875 spice model" and you should find the posts. You could also just search for a simulation model at ti.com.
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Old 6th January 2014, 09:58 PM   #408
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Hi gootee !
Thanks. I'll have a look.
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Old 7th January 2014, 06:03 AM   #409
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Quote:
Originally Posted by plgsekip View Post
Thanks Daniel!
I have actually followed the suggestion to remove the series output cap. Surprisingly, it sounds better! Now I understand that the series output cap was only needed for my other LM1875 which suffers mids distortion as you suggested (the implementation board from XY Hifi)....
I've purchased LM1875 locally from different shops, one LM1875(may be fake?) had problems with mids- I could hear audible distortion from my midrange spk. After swapping it with other LM1875 the problem was solved. My primary suspicion - problems with passives, gnd layout was isolated in this way. May be you can try swapping LM1875.

Quote:
For my latest version of LM1875, the output cap is not needed to improve the sound. @availlyrics insisted and now I got his point! :-D Thanks
You are most welcome!
BTW if you are going to use direct coupled design, build some sort of basic spk protection circuits like those based on UPC1237.
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Last edited by availlyrics; 7th January 2014 at 06:24 AM.
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Old 7th January 2014, 07:15 AM   #410
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Default Tone = Linearity

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Originally Posted by plgsekip View Post
my old TDA7294 which to my ears sound - subjectively - better than LM1875
The LM1875 resolves better but the old-production TDA7294 (and new-production TDA7293)'s tone is more palatable than LM1875.

To get a really great tone from the LM1875, you'd want to make a parallel amplifier. Paralleling increases the output linearity. When you begin with better linearity, you don't have to fight tone later.
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