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Old 1st July 2005, 01:24 PM   #1
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Default Snuuber AND non-snubber ?

For the sake of reducing interconnect and allowing amplifiers to be located near speakers, I am considering the following for a bi-amp set up

per channel:
1 trafo with dual secondaries.
1 snubberised psu feeding LM3886 for bass
1 regular psu feeding LM3875 for mid+hi

Is it possible for each secondary to feed 2 bridges in parallel?
ie do the diodes isolate the 2 psus from each other?
or do you end up with both chips drawing from the snubber caps?
or does it just all go up in smoke?

or MUST I have 2 secondaries per psu?

TIA, Jim
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Old 1st July 2005, 01:42 PM   #2
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so you are going to have the power supply in the center and feed each of the amplifiers (adjacent to the speakers) -- from this one PS.

you should consider using at least #14 wire -- and for this purpose I have used a garden type extenstion cord -- I don't know how they are made in Europe -- in the U.S. they are 3 conductor white, black and green and available cheaply at Home Depot. Very flexible and easy to work with.

you should (must) decouple the power supply pins with 100nF caps AND decouple the amplifier power input pins with 100nF ceramic. Here's why -- A long cable run can pick up electromagnetic interference, radio frequency interference just as if it were an antenna You might also want to consider placing a 1uF line rated polypropylene capacitor from V+ to V- . You may also have to place a 220 pF ceramic or mica capacitor across the IN+ and IN- of the chipamp to reduce radio frequency interference.
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Old 1st July 2005, 03:33 PM   #3
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thanks for the reply, But.. no, that's not what I'm doing!

I'm just thinking of using a different chip for the mid/hi and low and using each chip with it's favoured(?) type of supply. I would like to get away with one transformer per channel (per box).
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Old 2nd July 2005, 06:34 AM   #4
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It should work fine, but dont you think, that if the snubber helps the sound it would be a good idea to use it for the mid/high which have to reproduce a lot more signal complexity, and a lot more of the audiable spectrum than the bass amp.
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Old 2nd July 2005, 09:27 AM   #5
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Quote:
Originally posted by neutron7
It should work fine, but dont you think, that if the snubber helps the sound it would be a good idea to use it for the mid/high which have to reproduce a lot more signal complexity, and a lot more of the audiable spectrum than the bass amp.

I think he thinks the snubber helps the low freq. and hurts the high freq.

From what I hear the snubber does great things across the board...but I have not built a snubber yet. The amp that I am designing uses a snubber across the board
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Old 2nd July 2005, 11:02 AM   #6
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Quote:

I think he thinks the snubber helps the low freq. and hurts the high freq.
Correct, that's the impression I get. Most fans talk about it improving the bass, and don't mention the highs. Others say it does not improve the sound overall.

I will build and test both, to see if I can tell any difference.

The question was also technical, as my electronics knowledge is not very good, but I want to learn.

As I'm not short of trafos I can protoype with a trafo per amp, but i'd like to keep the final product small(ish)
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Old 19th November 2005, 10:04 PM   #7
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Default never did get an answer!

I'm finally building.

My box design is now a generously proportioned split level design, So I could use 2 trafos. However at 300VA I think one is plenty.

I have a total of 2xLM3886, 2xLM3875, and 2x snubber. I will be driving a FR125S from 160Hz-20kHz, and a 10" woofer from 30HZ-160Hz, both are 8ohm.

My current plan is LM3875 driving the FR125S and the LM3886 snubberised driving the woofer.

However I could reverse this, or I could run both amps from one snubber.

What would you do?
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Old 20th November 2005, 03:45 AM   #8
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I think actually what the point of the snubber is, is to allow you to use large capacitance (to improve the bass) WITHOUT it making the mids/highs become mushy.... I haven't tried so can't comment from experience. The whole reason the snubber (in the context of gainclones) came about if I'm not mistaken, was because the (mids/highs apparently sound best with a low capacitance PSU, but this low capacitance is bad for bass (and continuous power capability) enter the snubber (if that is really the correct name for it) which allows the use of large capacitance which improves bass, and overall power output capabilities, and apparently also fixes the problem of the mids/highs being adversly affected by the large capacitance.

So I think Jimbo's approach is fine, as the low capacitance PSU doesn't(?) need a snubber for nice mids/highs..... The old story if it aint broken why fix it

One thing to be aware of though jimbo. You will have much higher continuous power capability from your bass amp compared to the mid/high amp, which probably isn't a bad thing.

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Old 20th November 2005, 11:10 AM   #9
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are you guys referring to the 100nF caps that should be put on each of the rectifiers at the input (as in after the tranny??)..i thought this was more to get rid of diode snap associated with slow devices...what are you guys talking about may i ask?...and how do you work out the values for the snubber?
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Old 20th November 2005, 11:32 AM   #10
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Hi DemonsWing, you have just touched on why I said "If that's really the correct name for it"... yes my understanding of snubbers was for reducing the ringing of the rectifier diodes. This is (I think) different. have a look at Carlosfm's PSU thread ---> The (high-cap.) unregulated PSU for chipamps

and I think Peranders has a modified version as well.

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