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PRR

PRR

Member
Joined 2003
Paid Member
When discussing inductance, remember:

The output of the Source Follower is VERY low impedance. Most of the foibles of iron-core inductors vanish when driven low-Z.

Inductance will drop with frequency, but inductive Reactance rises with frequency! Iron-core coils retain enough inductance to be high impedance over the audio range. When they stop rising, we call it Capacitive reactance. I'd expect the proposed lump to be say 2,000pFd stray capacitance. At 8 Ohms, MHz!

What lack of infinite impedance in the choke does is limit Power Bandwidth, not frequency response. 50mH starts to steal a lot of energy from 8 Ohms at and below 27 Hz. You seriously don't expect <30Hz response from a 12 Watt amplifier. No domestic loudspeaker makes enough 30Hz to hear with 10 Watts, and no headphone needs anywhere near all 12 Watts.
 
Soundhappy

Soundhappy

Member
Joined 2012
Michael Rothacher said:
Wow, that was fast! Well done. Enjoy:)
Click to expand...

2.5 A bias x 1.12 Ohm R of L1 = 2.8 DCV across L1
Every parameters match perfectly the criteria from article about Big MoFo.
Feel Gooood
 

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C

Circlomanen

Member
Joined 2004
This is a great design to test the IRFP7430.
I am sure most of you will be quite surprised by the change of character and subjective increase in muscle and vitality.

I have tested many different mosfet source followers with many different mosfets, and the IRFP7430 is by far the best sounding mosfet in this kind of simple design IMHO.
Keep the supply voltage below 20 volts, since you don't want to exceed the 40 volt rating of the IRFP7430.

Cheers,
Johannes
 
xrk971

xrk971

Founder of XSA-Labs
Joined 2012
etsy.com/shop/XRKAudio
Paid Member
PRR said:
When discussing inductance, remember:

The output of the Source Follower is VERY low impedance. Most of the foibles of iron-core inductors vanish when driven low-Z.

Inductance will drop with frequency, but inductive Reactance rises with frequency! Iron-core coils retain enough inductance to be high impedance over the audio range. When they stop rising, we call it Capacitive reactance. I'd expect the proposed lump to be say 2,000pFd stray capacitance. At 8 Ohms, MHz!

What lack of infinite impedance in the choke does is limit Power Bandwidth, not frequency response. 50mH starts to steal a lot of energy from 8 Ohms at and below 27 Hz. You seriously don't expect <30Hz response from a 12 Watt amplifier. No domestic loudspeaker makes enough 30Hz to hear with 10 Watts, and no headphone needs anywhere near all 12 Watts.
Click to expand...

Thanks for the explanation. I think I have enough to go on that I will order these Hammonds to try out.
 
M

Michael Rothacher

Pass DIY Apprentice
Joined 2001
passdiy.tv
Paid Member
You'll lose some output capability due the the extra voltage you'll be dropping across the higher DCR and a little bit of damping factor. You can adjust by using a higher supply. I'd use a 24V switcher and run the bias a little closer to the full 2A. You'll probably get a distortion performance boost from the extra Henries and higher bias. I say go for it. :)
 
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