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Old 25th March 2004, 11:58 AM   #1
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Default Zobal question

whats the best value of components to use for a zobal on a 3886 amp? I have tried everything to get rid of the high frequency clipping bass notes cause, from adding more caps to the ps to changing gain of the amp. The distortion is still there. I am almost thinking it may have something to do with the zobal. Right now I have it connected like in the datasheet, 1k resistor on pin 3. but i used a 10uf electrolytic for the capacitor, not a 22uf non-polarized cap. Could this be the cause of the distortion?

Power is no problem, the trafo is from my old z680s so its capable of powering 500W of amps. It puts out dual 23VAC

thanks, mike
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Old 25th March 2004, 12:18 PM   #2
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I think you need to look at the data sheet again. The Zobel network is typically 2.7ohms in series with 0.1uF parallel with the speaker.

When you talk about 1kOhm and 22uF, I'm assuming you're actually refering to the feedback network. 10uF there will limit you bass response, as it puts the -3dB point at 15 Hz.

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Old 25th March 2004, 12:20 PM   #3
macboy is offline macboy  Canada
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Quote:
I have tried everything to get rid of the high frequency clipping bass notes cause
Have you tried turning down the volume? It seems as though you are clipping the amp, plain and simple.
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Old 25th March 2004, 12:39 PM   #4
flubug is offline flubug  United States
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This discussion raises another (dumb?) question I've been pondering: Why do some schematics use an inductor and others a capacitor in the output filter? Are there any advantages of one over the other besides the fact that capacitors are easier to come by? Also, is there a source somewhere for calculating the cut-off of the combinations similar to that for a passive speaker x-over?
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Old 26th March 2004, 01:03 AM   #5
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Quote:
Originally posted by macboy

Have you tried turning down the volume? It seems as though you are clipping the amp, plain and simple.

thats the thing, i have 8ohm 92db speakers, and they are not loud at all. I mean, yeah, they are loud, but no where near what about 50W should be able to do into 8ohm 92db.

Will adding a zobal help anything? I will also change the 10uf to something else. Maybe 50uf to make sure i get as much bass as possible.
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Old 27th March 2004, 11:32 AM   #6
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hello?

anybody?
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Old 27th March 2004, 02:03 PM   #7
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It's hard to say whether a Zobel will help in your situation. Why don't you try it?

Does the chip get warm when it distorts?

Rune
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Old 27th March 2004, 02:23 PM   #8
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Quote:
Originally posted by soundNERD
Will adding a zobal help anything? I will also change the 10uf to something else. Maybe 50uf to make sure i get as much bass as possible.
You have totally missed to point of this filter. The is frequency compensation (> 100 kHz, more like MHz) and the capacitor should be max 100 nF and with good HF properties. Please take a close look at the datasheet of the IC and also the AN-1192 because there you have facts about it.

http://www.national.com/appinfo/audi...gn_Guide13.xls
http://www.national.com/appinfo/audi...sign_Guide.pdf
Good!
http://www.national.com/an/AN/AN-1192.pdf
http://www.national.com/pf/LM/LM3886.html

Seriously, I think you ought to have 200 Watts or more. 50-70 Watts for your speaker will not make it to a party animal.

23 VAC is not max. You can have 28 VAC. This will maybe give you a couple of dB's more.
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Old 27th March 2004, 07:02 PM   #9
maylar is offline maylar  United States
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Quote:
Originally posted by flubug
This discussion raises another (dumb?) question I've been pondering: Why do some schematics use an inductor and others a capacitor in the output filter? Are there any advantages of one over the other besides the fact that capacitors are easier to come by?
Different animals. The inductors are used for amplifier stability. Capacitors are used to isolate the load from DC voltages in amps that do not have split power supplies.
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Old 28th March 2004, 11:49 AM   #10
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Originally posted by runebivrin
It's hard to say whether a Zobel will help in your situation. Why don't you try it?

Does the chip get warm when it distorts?

Rune
Yes, I will try it, i wasn't sure if it was one of those things that is a guarentee that it will help (like more caps on the ps for more bass).

about the chip getting warm, yes it does. It gets warm like normal when the amp is running normally, but when it distorts it gets hot.
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