I see HBP types faster...
> what does Leff & Reff means??
A real choke has L (inductance) and R (resistance).
The "fake choke" has effective values of L and R.
It is interesting that it says "47H 60 Ohms" but the formula for Reff, R3 [1+(R1/R2)] seems to give 20 Ohms.
> How could I calculate the attenuation provided by the gyrator?
Pretend it is a real choke and use the standard method for choke-capacitor filtering.
> Would it make sense to cascade 2 or more gyrator stages in order to have more (better) filtering?
Any time you ask if you need more than one somewhat complicated circuit, you should re-examine the real problem. Not stack-up solutions which may not be great solutions for your specific problem.
HOW much filtering do you need?
How much allowance for varying supply and load?
> to build a bass preamp
A preamp??
Preamp stages often suck 2mA each. Even a 10-stage preamplifier is only 20mA. A 250mA "solution" may be solving a different problem.
Common-sense. A zillion tube preamps were built without fake-choke filters. Half of them have no audible buzz from B+ ripple. Simple excess DC voltage and simple R-C filtering is usually ample for even complicated preamps.
The choke approach is "non-optimum" for several reasons. A choke's low DC resistance means delivered voltage hardly sags as load current varies. However typical preamp stage current does NOT vary. The low resistance promises low waste heat, but how much heat can you get from 20mA? (100V resistor drop at 20mA is 2 Watts, which is tiny next to the 10 Watt heater power of a 10-stage preamp.) The choke AC impedance should be "high" compared to load impedance, but a preamp's B+ load is a high resistance (300V @ 20mA is 15K) so we need a very-very high inductance choke to get any improvement.
Since electrolytic caps became cheaper than iron, THE way to power low-level stages is a C-R-C-R-C-R-C filter, with 1K-5K for each R and a bulk-pack (price break) of 40uFd caps for the C. Taking 2K for R, this gives 6K total resistance. At 20mA this is a 120V drop. If you start from 420V of raw B+ you get near 300V at the end, which ought to be ample for preamps.
Most preamps have low-low-level, low-level, and medium-level stages. The pickup input stages need the cleanest B+. The output stage can usually tolerate a bit more ripple on its B+. We also need to prevent signal "sneaking back" through the B+ from higher level to lower level stages. So we tap each stage or two from a different point on the C-R-C-R-C-R-C filter. This means the last R may only carry 2mA-4mA, so it can be a larger resistor for the same B+ drop. Maybe 10K-22K, which gives this one filter stage 10X the filtering of a 1K-2K+40uFd filter.
There's other rules of thumb. However IMHO the "best" way (if you want to build instead of think hard) is to steal a plan from a commercial product of similar purpose. Then, because you do not have to watch every penny like a profit-making factory, double the cap size. A 4-stage filter with 2X the caps is _16X_ the filtering (2*2*2*2). Since caps are often cheaper each when you buy 10, you can parallel 2 caps at each node, get great filtering, and have 2 spare caps for repair or other projects.
Topic: Cap voltage question (Read 3278 times)