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Old 8th December 2004, 07:09 PM   #1
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Question Zobel network.....Better bass? Yes or No

I have listened for about 60 hours now and my initial listening impressions to the amp have given me somewhat confusing results.

From the first note the midrange has been outstanding. Open, full, and very detailed. The high end started out very thin. Cymbals and similar instruments were muted and did not carry the tones well at all. At about 20 hours that really started to come around. The notes seemed to open up and sustain much better giving the music a natural and lifelike quality. I am confident that this will continue to keep improving with a little more time. The bass however is a complete mystery to me. What is there is very tight and controlled sounding, but it is lacking any sense of impact or force. This seems to hold true at whatever volume I listen at. My speakers are very capable of delivering good tight bass, but it is not there now.

This leads me to my questions. I have read several posts regarding the use of a zobel network and its advantages or disadvantages. A couple of the posts seem to indicate it has a positive effect on bass output of the gainclone amps.

I am curious to hear what others have found to be the results of this addition.

I would also like to hear from anyone who has installed it and then removed it as to what if any effect it made on the sound of the amp.

I am using a LM3875 kit from Brian with an Avel 250VA 18V+18V transformer driving 4 ohm speakers.

Thanks for your thoughts,
Craig
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Old 8th December 2004, 07:17 PM   #2
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If you want to know, just test to use this filter. It's very easy to attach.

I'm also (really!) convinced that in certain combinations this filter along with the inductor, is pretty unnecessary.... but I'm sure that there are combinations where it's needed.
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Old 8th December 2004, 08:10 PM   #3
Mr Evil is offline Mr Evil  United Kingdom
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Aside from stability issues, a Zobel network shouldn't affect the sound at all. If the corner frequency is too low then it can roll off the high end a bit, resulting a slight softening of the sound, but it really should have no effect on the bass at all. If it does, then it may point towards some slight instability or other anomalous behaviour. If you can check the output with an oscilloscope it may reveal the problem.
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Old 8th December 2004, 08:23 PM   #4
Nuuk is offline Nuuk  United Kingdom
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I put a Zobel on one of my GC's and the bass control was improved. I suspect it will depend on the loudspeaker concerned as much as anything.

Like Peranders says, it couldn't be much easier to try one with only two cheap components per channel and it fitting 'outside' of the main amp circuit!
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Old 8th December 2004, 09:08 PM   #5
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Somebody--I think it was Bob Carver--made a big demonstration out of this. Took the same amp, and put in different Zobel networks. With every change, the sound changed. Depending on whether you use inductors or capacitors..and their relative values...you will change the sound of the circuit. This is known as voicing the amp. It's part of the "art" of amp design, as opposed to the science part.
Still, it's relatively cheap fun, so have at it.
Just remember that different is not always better.

Grey
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Old 8th December 2004, 09:20 PM   #6
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As the Zobel network is in a signal path, both the components type and the values will effect the sonics. Sometimes it may be a change for better, sometimes for worse.
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Old 8th December 2004, 09:37 PM   #7
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Default signal path

Quote:
Originally posted by Peter Daniel
As the Zobel network is in a signal path, both the components type and the values will effect the sonics. Sometimes it may be a change for better, sometimes for worse.
Peter,

I am just wondering, when do you speak about signal path - in my opinion all components in gainclone are in the signal path : input parts define differential voltage on +/- input of the LM, so this is something like "controll signal path", and then after we have current flowing from transformer passing thru diodes (or from PSU caps) and thru LM to the speaker). I do not see any component in this circuit which is not a part of the signal path. Or, am I missing something ?
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Old 8th December 2004, 09:39 PM   #8
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You just confirmed my point, I don't recall mentioning any part that was not in a signal path

I might add that chassis is not in a signal path, yet it still affects the sonics.
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Old 8th December 2004, 10:54 PM   #9
hermanv is offline hermanv  United States
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The purpose of a Zobel network is threefold.

1. The series inductor(s) that makes the low pass filter for the woofer is suposed to work into a constant load such as 8 Ohms. At high frequencies the series inductance of the voice coil causes the voice coil impedance to rise making the low pass filter less effective. By putting a resistor in series with a capacitor across the voice coil the load impedance of the voice coil on the series inductor can be made nearly constant. This results in low pass filter that works as intended/calculated.

2. The Zobel network can help to maintain a more constant load on the amplifier. Less important than #1 but usually a good idea.

3. The Zobel network will help dampen any unplanned ringing in the crossover networks.

All that being said, the effects are small but real and are more likely to affect behavior of tube amps than transistor especially low power tube amps that don't much like reactive loads.

Few cheap speakers have them, many expensive ones do.
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Old 9th December 2004, 01:27 AM   #10
aHobbit is offline aHobbit  Philippines
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Quote:
Originally posted by hermanv
The purpose of a Zobel network is threefold.

1. The series inductor(s) that makes the low pass filter for the woofer is suposed to work into a constant load such as 8 Ohms. At high frequencies the series inductance of the voice coil causes the voice coil impedance to rise making the low pass filter less effective. By putting a resistor in series with a capacitor across the voice coil the load impedance of the voice coil on the series inductor can be made nearly constant. This results in low pass filter that works as intended/calculated.

2. The Zobel network can help to maintain a more constant load on the amplifier. Less important than #1 but usually a good idea.

3. The Zobel network will help dampen any unplanned ringing in the crossover networks.

All that being said, the effects are small but real and are more likely to affect behavior of tube amps than transistor especially low power tube amps that don't much like reactive loads.

Few cheap speakers have them, many expensive ones do.




The zobel is basically for any eventuality (like that of ringing). The problem may not be there at all, and you may not know when or how it is coming. At least, when it comes, something will take charge of it.

The effect of zobel may vary from user to user, due to the fact that we have varying setup/ environment/ circuit layouts etc.
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