To zobel or not to zobel,that is the question !
Can any one give a reasonable explanation (or link to) why to zobel or not at the output of an Amp ?
Secondly,
In the emitters of the output stage there are low ohmic resistors (0.1 to 0.33 ohm).
Some say it s not necessary, others put them in !
What do you use ?
And i mean, how to get such low values (put some in parallel )
or ............... ?
grtz
Simon
Can any one give a reasonable explanation (or link to) why to zobel or not at the output of an Amp ?
Secondly,
In the emitters of the output stage there are low ohmic resistors (0.1 to 0.33 ohm).
Some say it s not necessary, others put them in !
What do you use ?
And i mean, how to get such low values (put some in parallel )
or ............... ?
grtz
Simon
You need to use emitter (source) resistors if you are paraelling output devices. No pair of transistors is super matched, you allways see some difference in Vbe (Vgs) and transconductance of transistors. Because of this you have to use emitter resistors to "symetrize" current flow trough devices.
Zobel network is used to eliminate parasitic hf noise inducted on cables.
Zobel network is used to eliminate parasitic hf noise inducted on cables.
Commentable Thoughts
TO MY DEAR FRIEND BLU_LINE
SIR,
Zobel network enhances high- frequency Stability of amplifiers.
Zobel network prevents the amplifier from breaking up into high-frequency oscillations.
It acts as a shunt at the output of amplifier which inturns dampens the high impedance of very high frequency components[IF PRESENT] at output.
Secondly, The Emitter resistors,
Since the VBE characteristics of Transistors vary to some extent which hampers the equal current sharing between them when paralleling them .There fore to ensure proper current sharing one must implement emitter resistors and they also restrict the thermal runaway phenomena to some extent and thus contribute to stability and ensure stable biasing.
Therefore according to my opinion u must use Zobel network and must implement emitter resistors .
REGARDS
ampman
A friend in deed is afriend in need!
TO MY DEAR FRIEND BLU_LINE
SIR,
Zobel network enhances high- frequency Stability of amplifiers.
Zobel network prevents the amplifier from breaking up into high-frequency oscillations.
It acts as a shunt at the output of amplifier which inturns dampens the high impedance of very high frequency components[IF PRESENT] at output.
Secondly, The Emitter resistors,
Since the VBE characteristics of Transistors vary to some extent which hampers the equal current sharing between them when paralleling them .There fore to ensure proper current sharing one must implement emitter resistors and they also restrict the thermal runaway phenomena to some extent and thus contribute to stability and ensure stable biasing.
Therefore according to my opinion u must use Zobel network and must implement emitter resistors .
REGARDS
ampman
A friend in deed is afriend in need!
If you have one pair of output devices you need emitter resistor to achieve temp stability and if you have more than one pair they will also create current sharing.
If you have mosfets you don't have to use these resistors if you have only one pair. In some cases you can also skip them if you more two pairs or more. This is valid for Hitachis lateral mosfets but for normal vertical ones I think source resistors are a must.
Zobel network, resistor + cap at the output is a frequency comensation for the output stage, even though it not seems so. If you don't have this res+cap the output stage will have a pole at a not so good freqeuncy, way too low (= oscillation).
If you have mosfets you don't have to use these resistors if you have only one pair. In some cases you can also skip them if you more two pairs or more. This is valid for Hitachis lateral mosfets but for normal vertical ones I think source resistors are a must.
Zobel network, resistor + cap at the output is a frequency comensation for the output stage, even though it not seems so. If you don't have this res+cap the output stage will have a pole at a not so good freqeuncy, way too low (= oscillation).
(for the money) 
Per,
Heatsink is irrelevant, it's the peak current overload. Of course, you can hugely overrate them, say for 50 amps, but most people wouldn't think about it. Take a 100W RMS amp in 8 Ohms, that's, what, 4 amps RMS tops, so a Caddock with 8 amps current rating seems OK. But with some speakers and sound material etc you can easily get peaks of 20 amps or more. Thats too much for those Caddocks.
Just relating some stuff I found in the datasheets AFTER I blew my R's. These were the TO220 Caddocks, IIRC.
Jan Didden
Heatsink is irrelevant, it's the peak current overload. Of course, you can hugely overrate them, say for 50 amps, but most people wouldn't think about it. Take a 100W RMS amp in 8 Ohms, that's, what, 4 amps RMS tops, so a Caddock with 8 amps current rating seems OK. But with some speakers and sound material etc you can easily get peaks of 20 amps or more. Thats too much for those Caddocks.
Just relating some stuff I found in the datasheets AFTER I blew my R's. These were the TO220 Caddocks, IIRC.
Jan Didden
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