Nelson Pass and Michael Rothacher Presenting at Burning Amp!

[Soundhappy]

 

[Soundhappy]

 

[woody]

In the MoFo that 50mh inductor has a dcr of .7 ohms so the 1.7A across it should be
about 1.2 V . Could we simply do away with the output cap after all that would only
bias a 6 ohm driver at about 200 ma ?

 

[Ben Mah]

It doesn't sound like a good idea to me. Without the capacitor blocking DC, R5 and more importantly the speaker DCR become parallel resistance to the inductor DCR. The resultant decrease in resistance changes Vgs of the Mosfet and therefore changes the operating point of the amplifier.

 

[PRR]

changes Vgs of the Mosfet and therefore changes the operating point of the amplifier.

Less than 0.2V, for the example given. Anyway don't most folks measure and tweak bias? There is a lot more than 0.2V variability among MOSFETs.

The 0.2A in the voice coil can bother many small "full range" speakers by shifting them off the center of the magnet field. Long-throw woofers have huge tolerance (especially working at few-Watt power like these amps) but even a JBL D-130 has to be within a mm(?) of design centering or the response and THD go sour. FE-103 may be more fussy.

The power (heat) won't cook any useful "hi-fi" speaker, so you can go ahead and try it.

A secondary issue is that a bad joint in the choke (do you really think oven-coils are made perfect?) can drop large current in the voice coil. The -130 will survive, the -103 may not....

 

[woody]

I was mentioning this in regard to Nelson mentions using some amplifier DC offset voltage to source several hundred ma
of current through the speaker voice coil to reduce speaker distortion . This happens around 38 min. into this vidio,

 

[Zen Mod]

do that in controlled way, not with amp

 

[woody]

But didn't Nelson mention just using some amplifier DC offset voltage to do this?

 

[Zen Mod]

dunno Bro

he is ( as you maybe are) FAB

ZM is Chicken

 

[Ben Mah]

Woody, Some amplifiers have bipolar power supplies and no output coupling cap so DC offset at the amplifier output can be adjusted.

 

[nicoch58]

But didn't Nelson mention just using some amplifier DC offset voltage to do this?

I remember that he use a separate psu not the offset maybe

 

[Michael Rothacher]

Our first pair of UltraLite's are up and glowing! Nice work, Monk.

https://www.diyaudio.com/community/threads/ultralite-baf21.378593/page-3#post-6924951

 

[peppennino]