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Easy-MOS is a simplistic, efficient and evolutive all-MOS amplifier for beginners
Easy-MOS is a simplistic, efficient and evolutive all-MOS amplifier for beginners
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Old 22nd April 2019, 02:26 AM   #11
indra1 is offline indra1  Indonesia
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Quote:
Originally Posted by Elvee View Post
... it would be possible to operate with lower, or even no source resistors at all.
MOSfets, even vertical ones have some in-built compliance, ...
I think the IRF530/RFP15P05 are good, but not advisable for the larger verticals. I had thermal runaway with parts of higher Gm such as the IRF 540/9540, 640/9640 and the IRFP 240/9240 at fix bias without source resistors nor thermal feedback, from very low quiscent like 30mA onwards.

Off course your opinions are correct regarding the risk, but I feel that 0.5 ohm is a bit excessive, the H3 has riisen above -60dB at 1W.

Last edited by indra1; 22nd April 2019 at 02:49 AM.
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Old 22nd April 2019, 09:03 AM   #12
Elvee is offline Elvee  Belgium
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To illustrate what I said about the source resistors, here are a few sim examples, @1W & 100mA fixed bias.
First the circuit with its 0.5Ω source resistors:

Easy-MOS is a simplistic, efficient and evolutive all-MOS amplifier for beginners-ezmosb2-png

The THD is 0.25% with a moderate dominance of H2 H4 (in the same conditions, the measured value on the real circuit is 0.085%).

Now, same conditions but 0.1Ω resistors:

Easy-MOS is a simplistic, efficient and evolutive all-MOS amplifier for beginners-ezmosb3-png

The THD has had a huge increase, to 0.63%, and now H2 and H4 are heavily dominant.


If the 0.2Ω is placed in the NMOS, with the other defaulted to 1mΩ, the THD level and the even character is even more apparent:

Easy-MOS is a simplistic, efficient and evolutive all-MOS amplifier for beginners-ezmosb4-png

With the opposite situation, the THD has been reduced, almost to the original value, but still with a strong even character:

Easy-MOS is a simplistic, efficient and evolutive all-MOS amplifier for beginners-ezmosb5-png

All this shows that it is perfectly possible to tweak/manipulate the harmonic profile without thermal risks or a penalty in the global THD
Attached Images
File Type: png EZmosB2.png (63.5 KB, 1142 views)
File Type: png EZmosB3.png (68.9 KB, 1113 views)
File Type: png EZmosB5.png (72.6 KB, 1048 views)
File Type: png EZmosB4.png (76.4 KB, 1073 views)
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Old 23rd April 2019, 05:16 AM   #13
indra1 is offline indra1  Indonesia
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Of course Elvee, your circuit is very versatile with a great choice for the semis. My point is that it can satisfy a plurality of needs with very simple changes, even the ones like mine.

Last edited by indra1; 23rd April 2019 at 05:19 AM.
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Old 29th April 2019, 10:51 AM   #14
danielwritesbac is offline danielwritesbac  United States
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Quote:
Originally Posted by Elvee View Post
...With the opposite situation, the THD has been reduced, almost to the original value, but still with a strong even character...
What happens if R3, R4 both at 0.5 and a diode parallel with R4?
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Old 29th April 2019, 04:49 PM   #15
Elvee is offline Elvee  Belgium
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It slightly reduces the overall THD level, without greatly affecting the harmonic profile:

Easy-MOS is a simplistic, efficient and evolutive all-MOS amplifier for beginners-ezmosb6-png

In // with R3, it changes even less, but these are sim results and in reality they will heavily depend on the actual MOSfets (remember that the measured THD level is ~1/3rd of that predicted by the sim)
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File Type: png EZmosB6.png (67.7 KB, 998 views)
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Old 29th April 2019, 10:17 PM   #16
danielwritesbac is offline danielwritesbac  United States
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Quote:
Originally Posted by Elvee View Post
It slightly reduces the overall THD level, without greatly affecting the harmonic profile...
I must have read something backwards. Looks like 0.38 is higher than 0.25, from earlier? But, it is like your 3rd example with the 1m vs 0.2 resistors, except different than all of the examples in what happens to the bass beat if the popular double-woofer speakers were connected. MiniStatements

A different option is the one diode across both of the resistors. I'm not sure if that's safe? But, what happens is that the 0.5 resistors change to 0.25 dynamically, per the bass beat. Maybe a diode per each is better with asymmetric music signal?

Some of this might allow values approaching 1R, if that would be helpful with the THD? Although if the resistor value were too high then the diode switching might be noise. I have no idea.
Just something to consider.
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Old 30th April 2019, 07:49 AM   #17
Elvee is offline Elvee  Belgium
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I had forgotten that the examples above were based on 1W/8ohm.

With such a low current, even schottky's would not be able to begin conducting and change the behavior

With the diode, I increased the power to ~12W, near the maximum, which explains the THD increase to 0.46%.

By increasing the resistors to much more than 0.5, it would be possible to lower the action threshold, but with an effect so brutal and severe, it would resemble an instrument amp + effect box
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Old 3rd May 2019, 02:00 PM   #18
danielwritesbac is offline danielwritesbac  United States
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If I use a $9, 24v 96W (36W clean) SMPS, then the diode idea isn't needed because it doesn't switch on (thus also measuring that the 0.5 resistors are perfect).

That's probably 8W to 8R size; but, the laptop style power supply is convenient.

I'd wonder about a ~2db soft clipper, with engagement set to when the amp has started clipping (just a clip-duration reduction scheme). Seems another useful tube amp like feature. I wonder what the options are for that?

UK studies fets first at uni, so in a few months when the rains and studies start, there could be some more of these amplifiers made. If 24v power, EZmos is right sized for office, dorm, kitchen and bedroom.
Quote:
Originally Posted by Elvee View Post
...remember that the measured THD level is ~1/3rd of that predicted by the sim...
That's a good feature! The singleton-input inverting amp matches well with modern headphone sources (laptop, chromecast-audio, bluetooth, digi-tuner, phone) and they've got digital volume control already.

Good application matching! Just a few fets makes a power amp for most common source in most common room size and using SMPS laptop pack. The aspects match up to a good combination of doable and useful.
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Old 3rd May 2019, 03:38 PM   #19
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by danielwritesbac View Post

I'd wonder about a ~2db soft clipper, with engagement set to when the amp has started clipping (just a clip-duration reduction scheme). Seems another useful tube amp like feature. I wonder what the options are for that?
I do not like very much "artificial" soft clippers, because they inevitably reduce the max undistorted output power.
When the behavior is natural, as for tube amps, this is certainly a bonus, but otherwise I don't think so.

A fast and relatively transparent anti-clipping agc/compressor Peavey-style is certainly preferable, but it would make the circuit much more complicated if implemented with discretes.

I will think about it anyway.
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Old 5th May 2019, 08:40 AM   #20
danielwritesbac is offline danielwritesbac  United States
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Quote:
Originally Posted by Elvee View Post
I do not like very much "artificial" soft clippers, because they inevitably reduce the max undistorted output power....
That early engagement problem is avoided by: hard/brink engagement with soft/minimal effectiveness (1 or 2 db at most). In other words 'soften' the opposite parameter. Good function is preventing a clip from being louder than max undistorted output. Other possible functions are (fast recovery) decrease duration of clip (nip off the corners to decrease flat top span/duration), or clip anything other than the outputs (any smaller discharge).

Both large and small amplifiers need means that doesn't involve increased power voltage.
Quote:
Originally Posted by Elvee View Post
...A fast and relatively transparent anti-clipping agc/compressor Peavey-style is certainly preferable, but it would make the circuit much more complicated if implemented with discretes....
Found one. Last schematic on the Tracerphone thread. I had it set slightly too strong. I used it with a little tuner and speaker, so I it was set to resist those loud CAR commercials and caffeinated DJ's. Not very much speaker amp, but I bet the huge imaging would make it highly addictive as a line or headphone amp.

Last edited by danielwritesbac; 5th May 2019 at 09:03 AM.
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