New ClassD project Starting from 0

[DjLeco]

Originally posted by Ouroboros
The inductance and capacitance in the output filter are a function of the expected load capacitance. Values which are optimal for an 8R load, will not be optimal for a 4R load (and vice versa).

A standard passive filter design program will help you determine the C and L values if you (for example) want a second-order L-C filter, going between a source impedance of 0.1R and a load impedance of 8R, with a -3dB frequency of 35kHz.

Ok, then how they put on same amplifier 2-4-8 ohms on output?

Classically Itech series amplifier of Crown wich says safe loads of 1-2-4-8 ohms on each channel...

How they do that?

[Pafi]

They designed it to 1 ohm, then apply feedback after the filter.

But since you build a sub amp, pre-filter feedback, you don't have to design the filter this way. Trust me! ~20 uH is a good value, but there is no equation to calculate it!

Against ringing, you can use an RC damper in parallel with output. Rl+C3. C3=2 uF is enough, there will be more residual, but it doesn't matter at all! (But you have to use polipropilene foil capacitor!)

Ouroboros!

This is a sub amp, operating at 125 kHz! Why would you set fc=35 kHz?

[DjLeco]

Originally posted by Pafi
They designed it to 1 ohm, then apply feedback after the filter.

But since you build a sub amp, pre-filter feedback, you don't have to design the filter this way. Trust me! ~20 uH is a good value, but there is no equation to calculate it!

Against ringing, you can use an RC damper in parallel with output. Rl+C3. C3=2 uF is enough, there will be more residual, but it doesn't matter at all! (But you have to use polipropilene foil capacitor!)

Ok, got it, do you tell me to put some resistor seried with C3, I will try it (against speaker missing ringing).

And, if I want to modify feedback to be Post Filter,what will be the difference?

Presumimg I want to transform that amp in a fullaudio amp?

Carrier will be by ex 250 Khz, for full audio, I think it's enough...

I observed on Crown K2, is post filter feedback, and they used triangle carrier on pin 3(+) input, instead mine wich is on pin 4(-) input...

[stinius]

Hi DjLeco

I’m sure that you have read this before, but it’s just meant for those that haven’t read it.

link:

Cheers

[dudaindc]

Good one Stinius - thanks!

[DjLeco]

Excelent link,thank's Stinius!

[Pafi]

Ok, got it, do you tell me to put some resistor seried with C3, I will try it (against speaker missing ringing).

No, you need an other capacitor, with the same value, in series with a resistor which has the same resistance as the load, and then you have to connect this parallel with the output.

Series connection as in the linked page can also work, but that is more expensive, and bigger (because you need twice as much capacitance for the same result).

And, if I want to modify feedback to be Post Filter,what will be the difference?

You ought have to make some tiny, but very important modifications, but I'm afraid I don't have time to share the know-how.

[DjLeco]

Originally posted by Pafi


No, you need an other capacitor, with the same value, in series with a resistor which has the same resistance as the load, and then you have to connect this parallel with the output.

Series connection as in the linked page can also work, but that is more expensive, and bigger (because you need twice as much capacitance for the same result).



You ought have to make some tiny, but very important modifications, but I'm afraid I don't have time to share the know-how.

Ok Pafi, thank's anyway!

[DjLeco]

So, I received from the producer, exact parameters of mine Dark Blue Cores :

G1W 88S540 :







What's your opinion?

Is or isn't , suitable for classD Output filter?

Can anyone tell , for 20uH, at how mant amperes it will saturate?

Also I can buy some of these cores:

Cores in material grades:

N (60ui),

Z (125ui),

S (140ui),

NH (60ui),

ZH (125ui)

SH (140ui).

So, wich will be the best for classD inductors?

[sawreyrw]

Core saturation is a function of amp turns. Inductance is a function of Al. So for a desired inductance and peak current, find a core with a suitable Al and NI (amp turns) rating. Cores with lower Al have higher saturation NI capability.