plain Big caps on psu vs. carlosfm style Snubber - Page 2 - diyAudio
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Old 28th August 2008, 02:35 AM   #11
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Shiraz, Hope to hear from you soon!
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Old 28th August 2008, 07:42 AM   #12
Ted205 is offline Ted205  United Kingdom
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i'm using the 4780 in parrellel with 10000uf and snubber PSU and 2200uf || 10uf || 100nF at the chip. I've also used the zobel.

Sound is excellent, i can't fault the bass at all.
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Old 29th August 2008, 10:01 AM   #13
sangram is offline sangram  India
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I've used different kinds of approaches for building these things, and currently am running the following configurations:

1. 200VA+10,000uF/rail+LM4766, 6 ohm PSB speakers at work. Coupled with a little USB DAC, and uses relays on the output which may affect the output quality slightly, but unavoidable due to large turn-on thump by the DAC.

2. 220VA/ch+20,000uF/rail+LM3886 parallel, 4 ohm Dynaudio studio Monitors in my project studio

3. 440VA/ch+4,700uF/rail+LM4780 BPA, 8 ohm Sony in the living room

It's like making multiple dishes with rice, they all have it, but they're all a little different. The system with the 4700uF caps subjectively sounds the best to me, with the right mix of mids and lows.

That transformer is pretty heavily oversized for the kind of power output I use (90dB+ speakers), and the others use moderately-sized supplies with much heavier capacitance. The sound isn't as liquid as the main rig, but the speakers aren't of sufficiently high resolution either.

On rigs 1 and 2 I use 1208 ceramic X7R caps soldered directly to the chip pins for bypass, plus Panasonic FM 100uF at the supply pins, a centimeter or so away. Both are P2P (the 4780 is the Audiosector kit) and this helps me make changes quickly. Neither uses snubbers or zobels.

Of snubbers, I tried them in the 4780 amp, and I never tried them after that. They (I don't remember exactly though) did something nasty to the sound.

The next project is a 6-channels amp based on the LM4781 (I have the chips already). That's going to be a very complex P2P, but I'm going to do it anyway.
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Old 31st August 2008, 07:32 PM   #14
shiraz is offline shiraz  Denmark
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Which brings me to my first question, which I think was never really answered:
What's the difference between having different sized (from big to small) capacitors down each rail, as opposed to a snubberized PSU?

snagram:
On the 4780 rig, are the 4700 uf caps the only caps you've got between the PSU and the chip? And what do you have on the PSU? 10uf?
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Old 1st September 2008, 04:07 AM   #15
sangram is offline sangram  India
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Sorry should've been clearer. It's the Audiosector kit with 1500/0.1 on the amp board and 10uF on the supply board. The stock configuration was excellent, if slightly raspy in the midrange. 10,000uF (supply board only, the amp board is in stock configuration with 1500/0.1) killed the midrange. It didn't help much in the bass region either. Snubbers exaggerated the problem. I switched these to 4700uF and am now very, very happy. The amp board is still stock.

But my favorite colour is blue, yours may be red. So experimentation is the key to achieving your desired results. In general I see:

1. High-cap supplies improve bass heft at the expense of the midrange. My transformers are heavily oversized for my application and listening levels, so I never experienced a lack of bass, not even with the stock configuration. But in my other rigs, where the transformers are much weaker, caps help chips stand bass transients.

2. Snubbers are supposed to bring back some of the midrange magic into a high-cap supply, or some such thing. In my experience they made the midrange very grainy and raspy. I didn't like it at all. Anything else I say would be very subjective. I did experiment extensively over a month with values and locations, but never could find a happy medium.

3. It really, really helps to have sensitive speakers. Chips (unless stacked) can't take low-impedance loads well. And once you put an insensitive beast in front of a chipamp, you have to use large caps or the supply will buckle. A single LM3886 can't drive a 85dB speaker to reference level. Maybe to a normal listening level, but at (my) reference level SPiKE kicks in. Speakers are a big factor in your results, as is your taste and preferences.
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Old 2nd September 2008, 08:08 AM   #16
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Can someone measure the ripple on each rail of a plain Big cap supply and the so-called snubberized supply? It would be great if we can not only hear the difference, but also see the differences.

To measure the ripple, access to a scope is a must. However, test tone can be generated by a PC sound card. A high power resistor as dummy load is also needed.
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Old 2nd September 2008, 04:58 PM   #17
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by panson_hk
but also see the differences.

To measure the ripple, access to a scope is a must. However, test tone can be generated by a PC sound card.
Most DMMs set to AC mV will register an approximation of the ripple on the DC voltage.
All three of mine do. They each correspond to about one third of the ripple peak to peak shown on the scope.
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Old 2nd September 2008, 08:23 PM   #18
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Hi Andrew,

Correct me if I am wrong. I would like to see the ripple waveform. It consists of 100 Hz component as well as signal dependent component. We may also see something else.
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Old 2nd September 2008, 09:58 PM   #19
shiraz is offline shiraz  Denmark
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sangram:
Thanks for this. This is very informative for a greenhorn like myself.

My speakers are supposed to be 91db/w, so I'm hoping they're ok (despite not being so expensive).

I was just wondering about the 1500/0.1: Where did you put the 0.1 uf cap? On the pins of the 1500uf cap? Because as far as I can see, on the audiosector kit, there aren't any dedicated pads for an extra 100 nf cap there.
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Old 3rd September 2008, 05:08 AM   #20
sangram is offline sangram  India
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They're on the underside of the board, with the legs directly connected to the pins.
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