What better sound quality build after LM3875 and Class D 2020? - diyAudio
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Old 9th August 2015, 04:47 PM   #1
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Default What better sound quality build after LM3875 and Class D 2020?

Hi All,
What better sound quality build would you recommend after:

LM3875 - really happy with this, it was my first build

Class D 2020 - Sound was so so, not better than LM3875

I dont have massive power requirements, maybe around 50W max? I tend to listen on low-moderate volume and speakers are 8Ohm @ 90db sensitivity..

What can i bulid that is better sounding than what I have above?
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Old 9th August 2015, 05:26 PM   #2
wdecho is offline wdecho  United States
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The 3875 is a very good amp. After I built mine I went to 3 different Pass Lab builds. The latest offering (F6) is my favorite right now. Pass Labs on this forum and the store has the boards.
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Old 9th August 2015, 06:43 PM   #3
dewardh is offline dewardh  United States
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Well . . . on the chip amp side you started near the top. A Modulus-86 would be a “better” amp, but you might not hear much, if any, difference.

On the Class D side either a IRS2092 based amp or the lower power TDA8932 would be improvements on the 2020, and will sound as good as a good LM3875/LM3886 amp.

Nothing is going to sound any better . . .
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Old 9th August 2015, 08:28 PM   #4
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thanks guys
LM3875 is quite nice

wdecho, i tried dabbling into Pass Labs previously BUT the jfet and matching etc etc was a bit of unobtanium for me. Also, as a beginner I wish there was a KIT instead of having to source the parts randomly!

May I ask how you went about with your F6 build?
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Old 9th August 2015, 11:23 PM   #5
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Build another LM3875, feed it with inverted signal i.e. 'bridged'. Then use a step down transformer (2:1 turns ratio) on the new bridged amp.

@dewardh - TDA8932 didn't sound as good in the treble as a well decoupled chipamp to me. Bass was superior though.
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Old 10th August 2015, 12:24 AM   #6
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Quote:
Originally Posted by abraxalito View Post
Build another LM3875, feed it with inverted signal i.e. 'bridged'. Then use a step down transformer (2:1 turns ratio) on the new bridged amp.
Hi abraxalito, what does this approach do to the sound quality of LM3875? I am not that versed with electronics, so please can you explain a bit more?
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Old 10th August 2015, 12:35 AM   #7
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Happy to have a go at answering your question, the answer might be a little long-winded

In my experience with chipamps the PSRR is what limits the sound quality ultimately, once all possible care is taken with layout issues. PSRR is EE-speak for how sensitive an amp is to its power supply, it stands for 'power supply rejection ratio'. No matter which chipamp I've tried it has always been possible to improve the sound by adding more caps (once the supply is regulated) to the supplies. More caps means the operation of the amp itself results in less power supply noise.

There is a limit though to how many caps one can get close enough to a chipamp, so I've been exploring other ways to get around the PSRR weakness. It turns out that when a chipamp feeds a lighter load its PSRR is improved. The transformer gives the bridged amp 4X as light a load - so an 8ohm speaker turns into a 32ohm one.

The subjective difference I noticed is that the soundstage depth improved and so did dynamics. The amp with the trafo sounds more 'tubey'.
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Old 10th August 2015, 12:43 AM   #8
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thanks for the explanation abraxalito, I learnt something in the process
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Old 10th August 2015, 12:54 AM   #9
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Very pleased to hear that There are a few more details about this on my blog if you'd like to learn even more....
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Old 10th August 2015, 03:14 AM   #10
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The lower distortion of Modulus 86 is really audible. It doesn't sound like 3875. I have a 3875 amp too, but mod86 is another world. It makes 30W, enough for my 87dB 7ohm min speakers. It has very low distortion all the way to max power.
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