| soundNERD |
I am planning (key word: planning) to build a 6-channel amp based on either the 3886 or the 3875.
Should I put a zobel network on all of the amps? none? or just the rear channels since the cables are much longer?
thanks! |
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| gengcard |
| You should put a zobel network on all of the amps :cool: |
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| muhy3 |
I do not believe you should implement zobel's directly on the output stage of the amplfiier, because you may not know how the crossover/speaker that you will be using behaves. Once you have designed and built the amplifier you could try with and without a zobel network to see if sound is improved, generally you shouldn't hear any improvement if the amplifier is good as it will cope with some discrepancy in impedance but in the event that you do notice a difference the zobel network will most definately be good.
Also the zobel comes after the crossover from what i've read, but I may be wrong. http://www.trueaudio.com/st_zobel.htm |
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| rx7speed |
just figured I would ask a stupid quick question since the post is already here
what is a zobel network? |
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| psychosteve |
its a capasitor in series with a resistor, these are wired accross the output of an amplifier to help with certain loadings from speakers and cables, it can help if you have long cable runs.
its common to find them in PA systems where cables and speakers get moved and or leads are coiled up when in use.
whether you need one or not is down to your own hearing, it is worth trying it coz the parts are dirt cheap, and if it dont work, take it out.
hope this helps, steve.. .. |
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| psychosteve |
you used to be able to buy ready made cables for PA work with a zobel wired into the jack plug!!! so i wonder if using two zobel networks has any effect????? one each end?
HMMMMMMM, strange, this may need some experimenting... steve.. .. |
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| Mr Evil |
There is no way to say for sure if they will be necessary. A Zobel network should have no effect on sound quality; they are there only to provide a low impedance termination for RF.
If all the amps are in one box, then my experience is that if one amp needs a Zobel then they should all have one, since stray RF from one amp can be picked up an amplified by another.
My advice would be to leave space for them on the PCB but not put them in initially. Use an oscilloscope to look for RF on the output and add them if there is any. Do this with the speakers and cables you are planning to use, in the location you are planning to use them. If you find you don't need Zobel networks, but at a later date start noticing slight fuzziness in the treble, check for RF again as it often manifests itself as slight distortion at audio frequencies. |
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| skyraider |
| I implemented my zobel externally at the output post when there is a need. Usually I dont have it 'built-in'. |
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| richie00boy |
There is a lot of misunderstandings circulating regarding zobels. Please see my post for the all the answers :)
Zobels aren't there for protection against RF, but this can be a byproduct. |
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| Mr Evil |
| Compensating for an inductive load and terminating RF are manifestations of the same thing, Inductive loads aren't a problem if there is never any RF on the output, and conversely any RF that appears on the output won't be a problem if the load is not inductive (although there may be cases where you need a Zobel to prevent instability with no load connected which has nothing to do with inductance of the load, due to high output impedance of an amp at RF). |
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| Jocko Homo |
You guys are confusing zobels used to compensate for driver inductance, placed a the driver terminals, with zobels on amps placed at the amp output. Adding to that confusion........RC networks placed on cable ends to make an HF load.
That is all I am going to say.......I going to sit back an watch you guys continue to go around in circles.................
Jocko |
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| skyraider |
| quote: | You guys are confusing zobels used to compensate for driver inductance, placed a the driver terminals, with zobels on amps placed at the amp output. Adding to that confusion........RC networks placed on cable ends to make an HF load.
That is all I am going to say.......I going to sit back an watch you guys continue to go around in circles.................
Jocko |
Thats a big help!! thanks!!
Zobel is only needed when you have problematic loads. Im not really sure the TRUE idea behind it, I just use it if it sounds better. In my amp, the wires from the chip to the output post is very short. When I want to add zobel, I just tie it to the output post. That eliminates the extra work with switches, drilling holes, etc.. |
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| psychosteve |
| the only way to be sure, is to listen, since in theory C/R circuits should have little affect on the rest of the circuit, try them, in what ever position you want, and if you dont like them, take them out. thats what i usualy do anyway. see you later, steve.. .. |
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| richie00boy |
| The only way to be sure is to hook an oscilloscope up to the output of your amp and drive it with your intended speaker connected. |
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| psychosteve |
personaly, and this is a personal view, i dont listen to music with my eyes on an oscilloscope, so as long as the amp dont smoke, i dont care what the scope says.
OH MY GOD, i sound like and Audiophile.............
....AHHHHH, some one shoot me now.. lol, only joking, see you soon, steve.. .. |
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| richie00boy |
| I know what you are saying and I agree with you, but instability at HF may not always be audible but can cause unwanted effects like heating and RF pollution. It's just good engineering practice :) |
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| soundNERD |
One quick question,
Is the resistor and capacitor from pin 8 (neg input) on the 3875, different than the one from output to ground? (anotherwords, does the side of the feedback resistor matter?)
Basically, do I need that one also? |
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| richie00boy |
| Yes, they are totally different. If you look at the one on the inverting input (-) you will see it is connected to the output via a resistor. These three components make up the feedback network and are what set the gain. It's basically a potential divider so the inverting input sees a fraction of the output voltage. It does not serve any zobel function! |
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