CHOKE Loaded MOSFET, easy to build

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#41
Ferret, or ferrite dimensions are important to avoid core saturation

That produces some strange audio as a consequence.

I do not know how to calculate the size..but with this current may be a little bit big.... will be the biggest component into the amplifier case..and maybe the second heavier considering the power transformer beeing the bigger and heavier one into this amplifier.

regards,

Carlos
 
#42
Re: Thank you by the schematic Patrick

destroyer X said:
here is the schematic Patrick sent to me by request..because Lineup have not posted.
Click to expand...

Thanks, Carlos.
I love your posts for the latest times.
More audio and less off-topic south-american philosophy.

Yes, that is the original Tyimo schematic.
I just left out one small parallell cap at output.
Because in my own opinion, those are just wasting your money :att'n:
Not that they ruin anything.
But sure I know they do nothing good,
but to trigger some 'subjective impression' that can give your mind a good kick = 'hear some better sound'
😎

Thanks again for posted audio info & schematic.
Those you have plenty of, Carlos.
As most people already knows so well 😉
And we want more of your audio amplifier wisdom, man ....


your
swedish lineup
 
#43
Hi guys,

This topic is very dear to me.

I'm choke loading a differential power buffer with the 80mH primaries of a very large EI transformer. I believe it's rated at 1800 V/A.

The 1800 V/A transformer primaries flows 20 amps which it sends to the center tap of a bifilar wound 1000 V/A transformer which splits and feeds the source pins of the diff pair (x2). IRFP044N.

Idle AC voltage before the power choke is 0.006 volts, and after the choke is between 0.000 and 0.001 volts. So, it acts as a filter too. DC measures around 2.75 volts between the 1800 V/A transformer and the bifilar choke.

I can't say whether the core is saturating, but the amp sounds better with the choke than with power resistors. High notes are crisp and smooth. I hear nothing weird... only good.

The 1800V/A transformer get slightly warm to the touch, the bifilar transformer get very warm: 70C.
 
#45
Re: Uncovered schematic please lineup, the one you have posted is covered

destroyer X said:
Do you think it can operate with 750 miliamperes?
...say, adjusting the circuit to this current. in my imagination those field effects works better with that current....
with 1.5 amperes and higher they start to muffle the trebles as i could see in my home.
Click to expand...

As 750mV / 0R54 = 1.5 A
this is the idle class a current
14 Volt x 1.5 Ampere = 21 Watt for the IRFP240
This is not much for one of those. Does not get very warm.

I did not adjust and test for some higher currents.
I Just let the pot stay at default 50% giving that current.

Later adjusting pot to 2.5 Ampere lowered the distortion less than half (-6dB) at 1 Watt.
I see from posts here 'the original' had this much current for similar circuits.

It is a fact that these HEXFET, when operating in Nelson Pass Class A
likes heavier currents than BJTs (like MJ3281 for example) 😎
This will lower the higher distortion (at same current) that these HEXFET have.

So, if anyone builds this nice little OneTA - one transistor power Transistor Amploifier)
I recommend to try some good high currents.
🙂

We can have this plan for Class A CURRENT Level:
- Not so high the FET gets too warm .... say avoid >= 100 C junction temp.
- High enough to smooth out the transistion distortions and reduce capacitance errors.

Remember, we are talking compatively low Voltage DRAIN-SOURCE
in this case.

Normally we can see 30 VDS at 1 Ampere class A = 30 Watt
for this amp 30 Watt means a bit above 2.0 A idle current.
 
#46
Carpenter!

I'm choke loading a differential power buffer with the 80mH primaries of a very large EI transformer.
Click to expand...
A Zeus style amp?

can't say whether the core is saturating, but the amp sounds better with the choke than with power resistors. High notes are crisp and smooth. I hear nothing weird... only good.
Click to expand...
Yes, it sounds better than with resistor and even better than with anykind of CCS.🙂


Tyimo
 
#47
Lineup!
Later adjusting pot to 2.5 Ampere lowered the distortion less than half (-6dB) at 1 Watt.
Click to expand...
I use my second version with ca. 24Vdc 3A optimized for 6Ohm speaker.
Sounds also good...🙂

I just left out one small parallell cap at output.
Because in my own opinion, those are just wasting your money
Click to expand...
Yes, you have true, but you could try one time to put a foil cap and make the amp in "biwire" style. Tha bass is come from the Elko and the tweeter get the signal from the foil cap. A kind of "built in XO" 😉

Tyimo
 
#48
Tyimo said:
Carpenter!


A Zeus style amp?


Yes, it sounds better than with resistor and even better than with anykind of CCS.🙂


Tyimo
Click to expand...


Hi Tyimo,

It's more of a ZV7-T with the bifilar choke on the source pins rather than the drain. You can see this amp on my website:

www.inlowsound.com

Looks at the DIY Class A amplifier page.
With the 1800 watt primaries as the CCS feeding the bifilar, the bifilar becomes the feedback (source degeneration)--I think. Without the CCS and the bifilar center tap connected directly to ground, the amps still works, but it's not nearly as smooth.
 
#49
The schematic doesn't show the final stage. It's a simple differential pair connected as a follower.

I also use small inductors in the first two gain stages as the CCS. It works beautifully. The idle AC voltage ripple is reduced to ZERO after the CCS. and the amp sounds much more lush...
 
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