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Old 3rd May 2014, 08:10 AM   #21
juma is offline juma  Germany
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No, it doesn't make a difference. R14 is there to set the bases at 12V (half PS voltage) and to determine resistive value of Zin. R18's 220R doesn't change anything in that regard. R18 is there just to slightly isolate the bases and to provide some serial resistance in the input circuit should the input LP filter cap be needed.
Of course, since you intend to use TO3 devices (k135/j50) it would be nice to rearrange the output LatFETs connections in appropriate manner - Source and Drain of the upper LatFET can trade their places so there will be no need for a jumper and the Drain trace can be thicker and shorter. The same goes for lower LatFET's Gate and Source pins.

Last edited by juma; 3rd May 2014 at 08:16 AM.
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Old 3rd May 2014, 11:10 PM   #22
mos57 is offline mos57  Italy
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Quote:
Originally Posted by juma View Post
I'm afraid that not understanding that one disqualifies you as a critic, but here it is:
R12/R13 create a voltage divider which central point is held stiff at 12V (half PS voltage) with C4 which filters the residual ripple from the rail and that is the voltage set through R14 to the bases of Q1/Q2 and through the feedback network to the drains of LatFETs. R14 predominantly determines the Zin of the amp (since the base currents of Q1/Q2 are very low) and D1 takes care of C4's discharge.

Build a quick prototype and be amazed how nice it works...
Before posting any further comments, I want to begin by clarifying two aspects:
  1. I'm not a critic nor a professor.
  2. I never thought to put myself in competition with anyone.
What I wrote is what I thought when I saw your circuit.

So to see if there was some truth in those of my insights, I had to simulate your circuit and then break it down into its basic skeleton to pull out any imbalances that at first glance do not seem to be there.

Here I attach the simulations of the original circuit completed with transient analysis, frequency response and distortion.
Attached Images
File Type: png FIG_1_Yuma_Mosfet_1.png (20.5 KB, 651 views)
File Type: png FIG_2_Yuma_Mosfet_1_Transient.png (18.7 KB, 539 views)
File Type: png FIG_3_Yuma_Mosfet_1_AC.png (20.1 KB, 519 views)
File Type: png FIG_4_Yuma_Mosfet_1_Distortion.png (28.8 KB, 511 views)
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Old 3rd May 2014, 11:26 PM   #23
fab is offline fab  Canada
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Hi mos57
You seem to have Microcap simulator. How do you configure it to measure harmonics like that?
Thanks
Fab
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Old 3rd May 2014, 11:30 PM   #24
mos57 is offline mos57  Italy
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In the pictures below I removed the two resistors in the feedback loop to eliminate the effects of masking due to the reaction. I also rearranged the value of the two emitter resistors to bring the bias current of the output stage to their original values​​. Obviously also the value of the signal generator has been adjusted to have the same output level as the previous case.

The result is very clear to me:

The circuit does not work in a symmetrical manner. The upper mosfet behaves as a follower and does not amplify in voltage for which the positive half-waves do not reach the amplitudes of the negative half-waves where they are amplified in voltage by the lower mosfet.
Attached Images
File Type: png FIG_5_Yuma_Mosfet_1_noFB.png (20.5 KB, 522 views)
File Type: png FIG_6_Yuma_Mosfet_1_noFB_Transient.png (18.3 KB, 152 views)
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Old 3rd May 2014, 11:35 PM   #25
mos57 is offline mos57  Italy
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Quote:
Originally Posted by fab View Post
Hi mos57
You seem to have Microcap simulator. How do you configure it to measure harmonics like that?
Thanks
Fab
Hi Fab, send me a PM, so i may answer your question in detail
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Old 3rd May 2014, 11:39 PM   #26
fab is offline fab  Canada
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Quote:
Originally Posted by mos57 View Post
Hi Fab, send me a PM, so i may answer your question in detail
Ok, I will !
Thanks
Fab
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Old 3rd May 2014, 11:49 PM   #27
mos57 is offline mos57  Italy
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In this post I entered the circuit of Yuma modified only where strictly necessary to work with a dual power supply and below you can see the results of measurements that are substantially identical to that of the original circuit (post 22).

What do you earn?
A considerable simplification: in particular with elimination of large reactive elements or as a minimum reducing them. Another aspect is the elimination of the bias circuit of the input transistors of avoiding noise and ripple originating in power stage goes to dirty the input signal.
Attached Images
File Type: png FIG_7_Yuma_Mosfet_Bal.png (19.8 KB, 196 views)
File Type: png FIG_8_Yuma_Mosfet_Bal_Transient.png (19.6 KB, 160 views)
File Type: png FIG_9_Yuma_Mosfet_Bal_AC.png (20.1 KB, 72 views)
File Type: png FIG_10_Yuma_Mosfet_Bal_Distortion.png (28.7 KB, 75 views)
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Old 4th May 2014, 12:07 AM   #28
mos57 is offline mos57  Italy
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And now the real test!
the circuit with dual power supply, but without feedback loop.

The examination shows that the output voltage of this circuit is really balanced and confirms what I have written and intuition in previous posts.

This circuit is more suitable to work natively with dual power supply than with single power supply.

Tomorrow I will present an optimized version.

Good night!
Attached Images
File Type: png FIG_11_Yuma_Mosfet_Bal_noFB.png (18.5 KB, 160 views)
File Type: png FIG_12_Yuma_Mosfet_Bal_noFB_Transient.png (19.0 KB, 145 views)
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Old 4th May 2014, 12:38 AM   #29
Bigun is offline Bigun  Canada
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with such simple topologies you can have poor PSRR, is there a way to improve it ?
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"The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed." Robert M Pirsig.
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Old 4th May 2014, 09:48 AM   #30
juma is offline juma  Germany
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Quote:
Originally Posted by mos57 View Post
And now the real test! ...
... Said the Dorothy and went to Oz...

I made this amp for real and sims can be made to show anything you want so I use them only for simple calculations to save the time spent with calculator.
But if you want sims here you go: DC values, frequency/phase plot, transient analysis, Fourier analysis. I used highly unmatched LatFETs (see Vgs difference) to provoke high H2 and it's still 80dB below the signal...
Attached Images
File Type: gif sim1.gif (10.3 KB, 280 views)
File Type: gif sim2.gif (58.5 KB, 275 views)
File Type: gif sim3.gif (59.0 KB, 146 views)
File Type: gif sim4.gif (56.4 KB, 126 views)
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