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Old 3rd March 2011, 07:48 PM   #11
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Old 5th March 2011, 03:22 PM   #12
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Quote:
Originally Posted by AndrewT View Post
No !
both chipamps can and do work very well without an opamp in front.
Do not add extra components that are not required.
I've been running an LM3875 in true dual mono, 2x 120VA, 18-0-18v for a couple of years now. I use a passive attenuator (Alps 50k dual Log/47k metal film shunt). It needs to be cranked up a little to make it sound (subjectively) nice, but it is very detailed and uncoloured.

Although I am in the process of building an active line level pre which I intend to try in place of my passive.
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Old 5th March 2011, 03:29 PM   #13
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Originally Posted by zebra100 View Post
It needs to be cranked up a little to make it sound (subjectively) nice....
I'd guess that's a sign of having a noisy ground. At high volumes, the signal applied to the chip is mainly the input signal itself but at low volumes, the attenuation is greater and hence more ground noise gets fed into the amp.
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Old 6th March 2011, 10:34 AM   #14
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Originally Posted by abraxalito View Post
I'd guess that's a sign of having a noisy ground. At high volumes, the signal applied to the chip is mainly the input signal itself but at low volumes, the attenuation is greater and hence more ground noise gets fed into the amp.
It sounds a little coloured at low volume (slightly warm). I'm guessing it is more of an impedence issue. The amp is silent with no source playing, even at high volume settings.
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Old 6th March 2011, 11:51 AM   #15
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Originally Posted by zebra100 View Post
The amp is silent with no source playing, even at high volume settings.
Yes - sorry I didn't make it clear that I meant the noise on the ground will be RF - not directly audible but making its presence felt when music is playing.
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Old 22nd October 2011, 05:34 PM   #16
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Default Kits?

If you're comparing the two chipamp.com products, then I would ask:
Would you be willing to do without 4db worth of power that is only noise? If so, buy LM1875 kit and play music without noise.
However, if power is paramount, despite sporadic clipping sounding noise from the Spike circuit, then buy LM3886 kit. . . and maybe a baxandall to go with.

There are actually ways to play LM3886 without so much spike noise, and here they are:
Decibel Dungeon Buffered Inverting designs
MyRef
Nested LM3886
Parallel amp, PA100, PA150
Bridged Parallel amp BPA200, BPA300
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Old 22nd October 2011, 06:06 PM   #17
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Originally Posted by Rullknufs View Post
By the way. I heard some guy talking about not using capacitors since it "slowed down" the mids and highs and that it was better to simply use a larger transformer.. . .
That seems mixed up. Let's separate the two issues.

Its better to use a larger than necessary transformer instead of a smaller than necessary transformer. Current handling affects bass response.

The capacitors directly at the amplifier board will have an effect on the proportion of mid-range output, the heat output, and sometimes the clarity. But, you really don't want a blast of only mids and highs (insufficient capacitance) because that's just another way to say disproportionately poor bass response.

National Semiconductor, the maker of both chips, in their AN1192 document, recommends 470uF caps at the amplifier chip in addition to a real power supply board. With parallel and solo chips, the speaker return/ground is directed to the 0v tap upon the power supply board. Their approach provides a nicely level response with non-inverting LM1875 and some of their other chips. And, it works well for Parallel LM3886, Parallel LM4780. Conversely, there are other amplifiers, like TDA7294 and many of STK that could use 220uF (at the amplifier board, and in addition to a real power board), if design permits.

So now I can answer the original question:
If you started out with a too-small [amperage] transformer, then all of the possible power cap options would be wrong. That's the "cost effective" mass market, poorer quality, retail amp sound. But it is because of a too-small transformer. The issue isn't directly related to capacitor choices at all.
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Old 23rd October 2011, 01:33 AM   #18
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The primary difference is use is the LM1875's lower voltage and current output transistors give more high end definition while LM3886... higher power, louder.
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Old 23rd October 2011, 09:30 AM   #19
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Can you please explain to us all what specific parameters of lower voltage and current output transistors give rise to the higher definition sound?

I think you may have discovered an entirely new area of transistor physics previously unknown to science.
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Old 23rd October 2011, 09:48 AM   #20
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^ actually that's common knowledge, the tradeoff made and scientifically based. If you don't know, I suggest you gain experience because swapping them in /same amp, it is pretty easy to hear the difference and I am not one to tout voodoo parts swaps. All else being equal, smaller transistor dies are faster.

Last edited by !; 23rd October 2011 at 09:51 AM.
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