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MoFo inductor options for use above 1kHz only
MoFo inductor options for use above 1kHz only
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Old 21st November 2017, 03:31 PM   #31
Michael Rothacher is offline Michael Rothacher  United States
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MoFo inductor options for use above 1kHz only
And, if you really want to bark at the moon you can power your compression driver amp with a battery.
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Old 22nd November 2017, 09:19 PM   #32
xrk971 is offline xrk971  United States
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MoFo inductor options for use above 1kHz only
So a 4mH air core will get me to -1dB at 20Hz? That’s not bad at all. In fact, darn good for most speakers that I have.

Click the image to open in full size.

Jantzen Audio 4.0mH 15 AWG Air Core Inductor Crossover Coil

Sound of air core should be better right?
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Old 22nd November 2017, 09:34 PM   #33
Circlomanen is offline Circlomanen  Sweden
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Click the image to open in full size.

Here is my air cored bifilar chokes I use in my split load phase splitter amplifier.

Split load phasesplitter amplifier with bifilar choke load

It is a variation of the MoFo. It has 2 times the gain and a second harmonic cancellation effect to lower THD. If one wants to get all fancy you could call it a feed forward error correction quite similar to Nelson Pass super-symmetry. If you want to drive a high frequency unit then you would probably only need two 30 meter cables to each choke.
With two times 100 meter I get a nice response down to 10 Hz from this amp.

Cheers,
Johannes
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Old 23rd November 2017, 06:28 AM   #34
PRR is online now PRR  United States
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Quote:
Originally Posted by CharlieLaub View Post
@PRR: what about the suitability of a powdered core type inductor like .....
Do it if you like it.

I think iron (or ferrite) is the most problematic material in audio. It just won't be linear, and not even simple non-linear. It does make a major difference to the amount of copper. Also the side-spray. So it can be good, maybe better.

But "nothing" sounds good to me, and air is about 99.999% as good as nothing.
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Old 23rd November 2017, 06:32 AM   #35
PRR is online now PRR  United States
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Originally Posted by woody View Post
...a 1mh coil using # 16 wire on a 1" form .5" long would only use .46 lb of wire and have a resistance of 24ohm. ....
1mH is awful reactive for 1KHz and 8r load. You want the inductive reactance significantly higher than the load impedance. More like 3 to 7mH.

24 Ohms of DC resistance is far too high for 8 Ohm loading. We may as well use incandescent bulbs (while we can still get some) (didn't someone else try that? ) Or is it 0.24, typoed?
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Old 23rd November 2017, 06:35 AM   #36
PRR is online now PRR  United States
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Originally Posted by xrk971 View Post
So a 4mH air core will get me to -1dB at 20Hz?....
SMALL signal. The MOSFET has a very-very low small-signal output impedance, maybe a quarter-Ohm. This is indeed 0.004H at 10Hz.

But in a *power* amp, the choke impedance must be greater than the *load* impedance at the lowest frequency where we want big power. For 1KHz 8r this means more than 1.3mH, so really 3 to 7mH. Yet with DCR much less than load impedance, certainly under 2 Ohms.
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Old 24th November 2017, 01:38 PM   #37
Michael Rothacher is offline Michael Rothacher  United States
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MoFo inductor options for use above 1kHz only
Quote:
Originally Posted by xrk971 View Post
So a 4mH air core will get me to -1dB at 20Hz? That’s not bad at all. In fact, darn good for most speakers that I have.
Well, don't be fooled by the FR measurement alone. This example isn't a full range amp, for all the astute reasons which PRR provides, and the distortion goes quite high below 600 Hz, which is where the posted graphs start. The OP was asking about 1 kHz and up, and I think it wise to get well below whatever XO frequency is intended.
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Old 10th October 2018, 01:58 PM   #38
JRKO is offline JRKO
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Hey CharlieLaub

How did you get on running your compression driver from the modified MoFo?
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Old 10th October 2018, 04:08 PM   #39
sontero is offline sontero  Italy
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Originally Posted by Michael Rothacher View Post
And, if you really want to bark at the moon you can power your compression driver amp with a battery.
I would like to bark ..... but how long is the charge .... and how many volts that battery delivers?
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Old 12th October 2018, 07:48 PM   #40
woody is offline woody
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Back to post 32 by XRK971 that low frequency cutoff just doesn't
seem right. Was that an actual measurement and what was the load
impedance ?
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