Zobel network.....Better bass? Yes or No

[DF96]

This thread seems to be confusing two quite different uses of a 'Zobel network'.

One is across a driver so that the crossover network sees a closer approximation to a resistance.

The other is across the amp output (usually in conjunction with an inductor) to maintain ultrasonic stability in the feedback loop.

Which are we talking about?

 

[AndrewT]

Posts 1 to 8 inclusive, are only considering Amplifier Output Zobel.

Post9 is the first to introduce the Speaker Zobel.
That is a different subject.

Post19 is discussing the speaker Zobel.
This is an amplifier Thread, not for speaker tuning.

 

[Mark Whitney]

And ten years to late.

 

[kpsthakur]

Trying to increase Bass and reduce offset

Hi!!!
If you need more bass and better control of sound then add 10 000uf to your
power supply.
And increse input and feedback cap.
Example 10uf input,100 uf feedback.

I tried your suggestion rolloff expected at 2.3 Hz for 680Ohm/100uF Ri/Ci setup...gain designed in my Gainclone is close to 32.


There is a huge improvement...question back to you is in this case how far can I increase Ci value...can't this go higher...e.g. 1000uF... with the same setup I may reach 0.2 Hz, technically not lose any audible bandwidth....I am doing something very wrong here

Next query will be around DC offset...what happens if I use a 4700uF cap at output...it certainly should take care of my DC offset, but what will it destroy in audio bandwidth

 

[starkeyg]

Hello,

There is a point of diminishing returns. Especially as over 98% of music does not go down below 30 hertz.

As far as the cap blocking DC on the output - there is a reason that is not done by pretty much anyone since the 1970's. Caps large enough to be used here are pretty much electrolytic's, and far less than ideal caps. Far better to use a DC servo to eliminate any DC offset or use a design that minimizes the offset.

 

[kpsthakur]

Hello,

There is a point of diminishing returns. Especially as over 98% of music does not go down below 30 hertz.

As far as the cap blocking DC on the output - there is a reason that is not done by pretty much anyone since the 1970's. Caps large enough to be used here are pretty much electrolytic's, and far less than ideal caps. Far better to use a DC servo to eliminate any DC offset or use a design that minimizes the offset.

Thanks Starkey


I understand, however I am looking for quickfix as I am learning while I am burning...don't want to mess with my speakers...I took this input from test circuit from LM3875 datasheet...


DC servo...something I have not yet jumped in...but heard this term few times in other forums...will try and understand more about it.


Cheers

 

[nigelwright7557]

I don't think a zobel makes any difference to the sound at all.
The amp output impedance is so low it drowns out any effect the zobel might have.
The zobel just cancels out some of the speaker inductance and gives the amp a more constant load.

 

[AndrewT]

the Amplifier Output Zobel is typically 10ohms+100nF
That has an F-3dB of ~160kHz
At 160khz the Zobel has a reactive impedance of 10hms and a real impedance of 10ohms giving a total impedance of ~14ohms.
The amplifiers sees the Output Zobel as a 14ohms load @ 160kHz.
At 20kHz the combined impedance has risen to ~80ohms.
This would be in parallel to the speaker load.
It should be completely inaudible.

 

[indianajo]

I own an amp that came without a zobel on speaker terminals, a dynaco ST120. I added it myself, diy. The bass wasn't audibly different before or after the "TIP mod", always quite satisfactory, but the RF interferance before addition certainly was. I had to do other mods also to get rid of an AM radio station.