What's your choice for negative feedback capacitor in amplifiers?
Polar,Bi-polar,low esr,high esr.etc
I see designers put everything in that position.
Polar,Bi-polar,low esr,high esr.etc
I see designers put everything in that position.
I use nichicon KA audio grade 2 in series there with one 100n wima paralleled to that, just because i feel its best, however not sure if that counts or its wasting...
On an SS amplifier, the NFB is usually DC coupled and the capacitor with resistor in series, sets the AC gain and lower roll off frequency.
In valve amplifiers, the Williamson for example, has a NFB resistor with a capacitor of a small value to reduce the very high, unwanted frequencies.
To that end, please explain what you mean.
How critical is ESR in this specific application? In the Bedini 25.25 a 47uF 63 V cap is used, and I have used both polarised and bipolar caps here with no audible difference. I needed to replace them every 4 to 5 years because they went soft due to the high heat generated by the Bedini (quite small heatsinks for a 25 Watt Class-A.)
ESR is not critical as a resistor is in series with it on an SS amplifier.
If you choose 125℃ capacitors, no need to replace them as often.
If you choose 125℃ capacitors, no need to replace them as often.
Hi JonSnell,
That is exactly what I have done with my new PCBs. I have Kemet PEG124MB 47uF 63 V caps, rated at 125℃. These caps have an ESR of 1.8 Ohms. I'm just waiting to get new the new toroidals for the rebuild. And the new heatsinks have 80% more radiating area than the originals.
Kevin
That is exactly what I have done with my new PCBs. I have Kemet PEG124MB 47uF 63 V caps, rated at 125℃. These caps have an ESR of 1.8 Ohms. I'm just waiting to get new the new toroidals for the rebuild. And the new heatsinks have 80% more radiating area than the originals.
Kevin
Bipolar electrolytic capacitors distort a bit less than polarized electrolytic capacitors and some bipolar types are fairly cheap, although not quite as cheap as the polarized ones. Then again, as long as the signal currents are not too large and you don't drive them more than 1.5 V in reverse, the distortion of a polarized aluminium electrolytic capacitor is already quite small.
So, are you willing to pay a negligible amount of extra money for a negligible performance increase? For hobby projects, I usually answer that question with yes and either use Panasonic SU series bipolar capacitors, or design some kind of DC bias loop such that the electrolytic capacitor is not needed anymore. For projects where lifetime and simplicity are more important than performance, I just use the longest life polarized electrolytic I can find.
So, are you willing to pay a negligible amount of extra money for a negligible performance increase? For hobby projects, I usually answer that question with yes and either use Panasonic SU series bipolar capacitors, or design some kind of DC bias loop such that the electrolytic capacitor is not needed anymore. For projects where lifetime and simplicity are more important than performance, I just use the longest life polarized electrolytic I can find.
John Snell Electronic is exactly right it isn't as simple as speaking about "the feedback capacitor ".
In designing a power amp there is normally a DC -path back but what is Basi meaning ?
From his post it probably means the capacitor _resistor gain setting as he talks of polar/bipolar .
When designing an amplifier from scratch layout and components are a big problem so the amplifier has to be "tuned " .
Every design I tried out had to have the correct value --COMPENSATION capacitor , this very small value feedback capacitor is crucial to the design ,some like D.Self use a standard 100pf value ,others have several capacitors in different parts of the circuit ,it depends on design philosophy of the audio engineer .
As I follow JLH basic designs with various circuit changes I only need a much smaller value than 100pf .
This can easily be seen in an oscilloscope display by fitting a very small value variable capacitor and tuning the new circuit and watching the output .
I realize people get confused by the blanket term "feedback " but really should be talking about compensation (stabilization ) if referring to stability of the amp under load conditions .
There is more to this in a practical sense but that is the basics.
In designing a power amp there is normally a DC -path back but what is Basi meaning ?
From his post it probably means the capacitor _resistor gain setting as he talks of polar/bipolar .
When designing an amplifier from scratch layout and components are a big problem so the amplifier has to be "tuned " .
Every design I tried out had to have the correct value --COMPENSATION capacitor , this very small value feedback capacitor is crucial to the design ,some like D.Self use a standard 100pf value ,others have several capacitors in different parts of the circuit ,it depends on design philosophy of the audio engineer .
As I follow JLH basic designs with various circuit changes I only need a much smaller value than 100pf .
This can easily be seen in an oscilloscope display by fitting a very small value variable capacitor and tuning the new circuit and watching the output .
I realize people get confused by the blanket term "feedback " but really should be talking about compensation (stabilization ) if referring to stability of the amp under load conditions .
There is more to this in a practical sense but that is the basics.
The larger value cap the less its imperfections matter as its seeing less and less signal voltage - however the ESR itself is then the limiting factor - how linear is the ESR? Hopefully its mainly aluminium foil and thus as good as any metal film/foil/wire.
And larger cap value tends to mean lower ESR anyway, so set the roll off well below 5Hz for good distortion performance. Keeping it
small requires a low voltage part, which then needs protection from overvoltage (if the outputs fail large voltages fall across it,
so back-to-back LEDs can be used as clamps across the cap.
And larger cap value tends to mean lower ESR anyway, so set the roll off well below 5Hz for good distortion performance. Keeping it
small requires a low voltage part, which then needs protection from overvoltage (if the outputs fail large voltages fall across it,
so back-to-back LEDs can be used as clamps across the cap.
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