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Chip Amps Amplifiers based on integrated circuits

Neurochrome LM3886DR Build
Neurochrome LM3886DR Build
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Old 23rd August 2016, 11:07 PM   #11
dreadnoughtstrength is offline dreadnoughtstrength  Australia
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Quote:
Originally Posted by tomchr View Post
Cool! Nice work!



Math is Pout = Vout^2/(2*Rload) with Vout in volt, peak.

or: Pout = Vout^2/Rload with Vout in volt, RMS.

Tom
That's about what I figured; close enough to 50w!

Knocked this box up in Solidworks, but the guy helping me CNC said it's not 'sexy' enough (he's a crazy German engineer haha), so we're redesigning. Still undecided if I add a preamp and some other bits and pieces in or not, I'd love matching PSU/amp boxes but running a preamp with that just complicates umbilical wiring.
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Old 24th August 2016, 02:39 AM   #12
tomchr is offline tomchr  Canada
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I'd shy away from umbilical cords. Using such cords increase the supply impedance which will degrade performance. There's no need to keep the amp and supply separate.

Tom
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MOD686: Up to 240W/8Ω, <0.00025% THD. MOD86: 40W/8Ω, 0.000054% THD. HP-1: 3W/20Ω, -130dBc THD, 128dB DNR.
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Old 24th August 2016, 03:01 AM   #13
jwicaksana is offline jwicaksana  Indonesia
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Nice build!
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Old 25th August 2016, 10:49 PM   #14
chrisb is online now chrisb
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Quote:
Originally Posted by tomchr View Post
I'd shy away from umbilical cords. Using such cords increase the supply impedance which will degrade performance. There's no need to keep the amp and supply separate.

Tom

The little prototype of yours we played with last week was a tidy compact build with no detectable noise, and I think you've sold me on the Speakon connectors, and use of balanced inputs when available. I was already a convert to SMPS for lower rail voltage circuits.
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Old 25th August 2016, 11:39 PM   #15
Bare is offline Bare  Canada
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Clearly you haven't yet had an SMPS.. Fail.. taking out your amp.
Not to worry, there's good prognosis for enjoying that singular pleasure.
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Old 26th August 2016, 12:59 AM   #16
tomchr is offline tomchr  Canada
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Chris and I spent a bit last Thursday listening to my LM3886DR + SMPS-86 amp. No blown speakers here. The combo also performed well during my testing.
I've tested the SMPS-86 with my Modulus-86 as well. Same stellar performance. About a year ago, I tested my Modulus-86 on a SMPS300RE from Connex. Worked great!

While it sounds like you had a rather bad experience, I think your experience is an isolated case and should not be generalized to switch mode power supplies in general.

Tom
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MOD686: Up to 240W/8Ω, <0.00025% THD. MOD86: 40W/8Ω, 0.000054% THD. HP-1: 3W/20Ω, -130dBc THD, 128dB DNR.
Neurochrome : : Audio - www.neurochrome.com - Engineering : : Done : : Right
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Old 26th August 2016, 09:13 AM   #17
AndrewT is offline AndrewT  Scotland
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I have not yet built any power amplifier with an SMPS as the PSU.
I do have a lot of user experience of mains transformers and mains to DC SMPS.
I have NEVER had a mains transformer failure.
I have had dozens of mains SMPS failures.
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Old 26th August 2016, 08:21 PM   #18
tomchr is offline tomchr  Canada
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I've had mains transformers fail. I haven't personally experienced an SMPS failure. See. This is the problem with basing design decisions on personal anecdotes. You don't get the full data set.

Considering the number of switching power supplies in service world wide, you will see some failures even if the failure rate is in the ppm. I think blanket statements like SMPS = BAD are based on emotions rather than facts.

The SMPS modules I use in my SMPS-86 are well designed and very rugged. They include protection against various fault conditions, including over-current and over-voltage. On top of that, I added surge protection and inrush current limiting.

Tom
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MOD686: Up to 240W/8Ω, <0.00025% THD. MOD86: 40W/8Ω, 0.000054% THD. HP-1: 3W/20Ω, -130dBc THD, 128dB DNR.
Neurochrome : : Audio - www.neurochrome.com - Engineering : : Done : : Right
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Old 28th August 2016, 10:41 PM   #19
TioFrancotirador is offline TioFrancotirador  Poland
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Hi tomchr,

While waiting for your PCB to come I am collecting the parts. I am curious of the function of 20k resistor + 47pF in parallel to another 20k resistor in feedback loop. Can you explain what is it for? Is it necessary? What is the downside of not having this RC network, leaving just this 20k resistor like in other designs.
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Old 28th August 2016, 10:50 PM   #20
tomchr is offline tomchr  Canada
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As described on page 8 in the LM3886 data sheet:
The cap across the inputs (Cc in the data sheet) prevent quasi-oscillation as the output voltage swings near the supply rails. This results in a cleaner output and slightly higher max output power. The drawback is that Cc causes some overshoot on the transient response.
Rf2 and Cf are introduced to combat this overshoot and keep the amplifier stable.

The three parts are necessary if you want good performance.

Tom
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MOD686: Up to 240W/8Ω, <0.00025% THD. MOD86: 40W/8Ω, 0.000054% THD. HP-1: 3W/20Ω, -130dBc THD, 128dB DNR.
Neurochrome : : Audio - www.neurochrome.com - Engineering : : Done : : Right
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