Mikelm,
I often use only 1 output resistor...for measuring Iq only.
Adds a miniscule amount of second harmonic, but that doesn't bother me.
I often use only 1 output resistor...for measuring Iq only.
Adds a miniscule amount of second harmonic, but that doesn't bother me.
I found this datasheet from Mouser:
http://www.fair-rite.com/catalog_pdfs/2661000101.pdf
I would prefer to get a ferrite bead sampler kit and test different beads to see what worked best.
However I think some suggestion from the professionals is needed here because choosing beads isn't like choosing resistors. There are two variables, resistance and inductance.
- keantoken
http://www.fair-rite.com/catalog_pdfs/2661000101.pdf
I would prefer to get a ferrite bead sampler kit and test different beads to see what worked best.
However I think some suggestion from the professionals is needed here because choosing beads isn't like choosing resistors. There are two variables, resistance and inductance.
- keantoken
I thought that the bead was placed at the gate leg on the mosfet and thus was it only inductive..
I found this PDF..that gives good explanation on the use of gate ferrites
http://www.microsemi.com/micnotes/APT0402.pdf
I found this PDF..that gives good explanation on the use of gate ferrites
http://www.microsemi.com/micnotes/APT0402.pdf
Dejavu, MiiB:
http://www.diyaudio.com/forums/soli...as-lateral-output-perfect-26.html#post2616970
In fact I seem to remember the same dejavu happened in another thread? Odd...
Ferrites are lossy inductors. The cores are lossy so at high frequencies they act like resistors. Maybe you could call it a critically-damped inductor. Because the impedance does not rise above that necessary for the application, it is more efficient than simply using a resistor. Furthermore, sometimes DC characteristics are improved, especially in the case of a BJT where a base stopper would impede base current and decrease transconductance.
- keantoken
http://www.diyaudio.com/forums/soli...as-lateral-output-perfect-26.html#post2616970
In fact I seem to remember the same dejavu happened in another thread? Odd...
Ferrites are lossy inductors. The cores are lossy so at high frequencies they act like resistors. Maybe you could call it a critically-damped inductor. Because the impedance does not rise above that necessary for the application, it is more efficient than simply using a resistor. Furthermore, sometimes DC characteristics are improved, especially in the case of a BJT where a base stopper would impede base current and decrease transconductance.
- keantoken
I didn't realize what KenPeter was trying to say, so I did not follow that link....sir...!!
The beads could also prove quite handy in Power supplies where the can help removing RF artifacts from diode switching... though it may also require some small film/ceramic caps to short residuals to GND. I have always likeed the sound of Tube rectifiers, I believe it's because they don't make switching noise...With the beads we can target RF-switching residuals to a much higher degree without compromising DC resistance...
The beads could also prove quite handy in Power supplies where the can help removing RF artifacts from diode switching... though it may also require some small film/ceramic caps to short residuals to GND. I have always likeed the sound of Tube rectifiers, I believe it's because they don't make switching noise...With the beads we can target RF-switching residuals to a much higher degree without compromising DC resistance...
Here I found a guy saying
that for audio (not for hi speed switching) we can forget about ferrite beads:
that for audio (not for hi speed switching) we can forget about ferrite beads:
I found a definite difference in sound moving from 100R to 10R gate stoppers for my MOSFET class A amp. The sound was clearer. I think using beads would be a good idea for sonics, although many get away without them. I think using beads might simplify the process of choosing gate resistors. It may also simplify PCB layout. I think in a practical sense, the idea of using beads at the gate is well-founded. Especially for BJT output stages.
- keantoken
- keantoken
Can't advise on ferrites for audio, have never used them.
However, the gate resistor has profound influence on sound quality. Too low makes the sound very bright, as oscillation begins to affect the audio waveform, too high slows the amp, making it bassy and dark. None of this seems to affect the measured frequency response in the audio band, which is peculiar, but there it is....
Hugh
However, the gate resistor has profound influence on sound quality. Too low makes the sound very bright, as oscillation begins to affect the audio waveform, too high slows the amp, making it bassy and dark. None of this seems to affect the measured frequency response in the audio band, which is peculiar, but there it is....
Hugh
Hi there,
I'm quite interested in some further practical investigation on this ferrite bead subject as well.
Maybe it could and would be worth starting up a new tread with this as specific?
Ferrite beads for BJT base and Fet gates???🙂
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If anyone can do some tests on an amp where the output stage was confirmed unstable, that would be a good thread-starter.
I think the best idea is to get a bead sampler kit, and listening to the amp, move from the largest bead to the smallest, while watching for oscillation. One should also do a frequency sweep to look for peaking at RF, which can disrupt the stability of a feedback loop.
- keantoken
I think the best idea is to get a bead sampler kit, and listening to the amp, move from the largest bead to the smallest, while watching for oscillation. One should also do a frequency sweep to look for peaking at RF, which can disrupt the stability of a feedback loop.
- keantoken
I seem to remember that Charles Hansen of Ayre said that ferrites in PSU lines was a bad idea - they start off sounding good and end up sounding bad - I think because they don't like DC current - perhaps someone else can recall.
Its desireable to have zero DC current in a core regardless if it is a transformer, an inductor or a ferrite bead.
But that is not the case in real life. But you have to make sure that the peak current does not exceed saturation current.
2. You also have to look on the inductance curve versus DC current in inductors. The inductance is related to the current as well. Some state that saturation current is at 80% inductance.
3. Ferrite bead has a series inductance as well. If not taken care about the design the circuit will have a peak at a certain frequence instead of damping.
4. in CFP it is used by onkyo to remove oscillation by inserting into the base of the output BJT's.
But that is not the case in real life. But you have to make sure that the peak current does not exceed saturation current.
2. You also have to look on the inductance curve versus DC current in inductors. The inductance is related to the current as well. Some state that saturation current is at 80% inductance.
3. Ferrite bead has a series inductance as well. If not taken care about the design the circuit will have a peak at a certain frequence instead of damping.
4. in CFP it is used by onkyo to remove oscillation by inserting into the base of the output BJT's.
Mike... It might well be so....for sure saturated transformer cores in tube amplifiers ruin the sound...so maybe a strong DC-field in the beads may do the same...by ruing their ability to increase impedance at high frequencies...have NO practical experiences though...
For PSU usage..one could think about some kind of common mode arrangement that way the DC will balance itself out, and as the switching noise will be out of phase..the damping will still retain intact....
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