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Old 2nd December 2012, 01:08 PM   #1451
a.wayne is offline a.wayne  United States
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Canonnica ,

Can you post up all your changes with objective/subjective results , currently its scattered all over , a final synapsis on what you have done would help a lot ...

Last edited by a.wayne; 2nd December 2012 at 01:10 PM.
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Old 2nd December 2012, 01:09 PM   #1452
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Default Yep.... tweaked to the bones..... agreed!

I cannot compare using stereo BMW850.... we need same sound entering two channels to compare one channel (tweaked) with the other channel (standard)

regards,

Carlos
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Old 2nd December 2012, 01:40 PM   #1453
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Default I love these VU meters

DX ST com VUs - YouTube

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Carlos
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Old 2nd December 2012, 04:04 PM   #1454
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That's what i'm using since one year. I didn't open it since then. Along with simulation measurements.

Simulations made at full power (1.3VRMS input and 220W RMS at 8R load)
Attached Images
File Type: png Actual_Amp_Schematic.png (59.9 KB, 284 views)
File Type: png Actual_Amp_Fourier.png (35.8 KB, 285 views)
File Type: png Actual_Amp_2nd_harmonic.png (24.0 KB, 273 views)
File Type: png Actual_Amp_3rd_harmonic.png (23.8 KB, 268 views)

Last edited by canonnica; 2nd December 2012 at 04:11 PM.
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Old 2nd December 2012, 04:08 PM   #1455
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Here are the changes I want to implement.
The 56R resistor solely reduces the positive sinus wave ringing present in the sumultaor and confirmed by Bonfis. It does not alter the THD significantly.
The increase in quiescent current greatly reduces THD. The value across the two 0.47R resistors of 54mV is right on with the predicted value of Dr. Self for the lowest distortion level obtainable.

Simulations made at full power (1.3VRMS input and 220W RMS at 8R load)
Attached Images
File Type: png Projected_mods_Schematic.png (86.6 KB, 272 views)
File Type: png Projected_mods_Fourier.png (35.5 KB, 97 views)
File Type: png Projected_mods_2nd_harmonic.png (24.4 KB, 41 views)
File Type: png Projected_mods_3rd_harmonic.png (24.0 KB, 31 views)

Last edited by canonnica; 2nd December 2012 at 04:11 PM.
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Old 2nd December 2012, 05:30 PM   #1456
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As a supplemental reading: http://www.sg-acoustics.ch/analogue_...n_comments.pdf
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Old 4th December 2012, 12:43 PM   #1457
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Here is an interresting thread on odd and even harmonics to sum up the sonics experience provided by them. It's probably referenced elsewhere on this board: Amplifier harmonics and load stability - Page 3

In defining what would be the best driver base stopping resistor and bias current, I realize that these two elements greatly affects the 2nd and 3rd harmonics balance. I'm now trying (in simulator) to determine what's the best theorical combination to erradicate the odd harmonic distortions while keeping some of the 2nd and other even harmonic ones.
When I'm done, I will implement the change and try to compare in the most objective way (which is not easy... )
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Old 5th December 2012, 02:37 AM   #1458
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These days, I'm passing a lot of time in simulation. I try to evaluate the best combination vBias and driver base stop-resistor...

I'm exporting tons of fourier analysis into Excel spreadsheet to graph the results. Here is what I've found tonight...

These graphs represents the scenario where the resistor is of 56R in value and I only vary the vBias. The vBias is expressed in mV measured across both emitter resistors of output transistors.

The plot shows harmonics 2 through 9, their scale in on the left. The scale on the right is for the THD line (dark blue one).

I did these plots at a power of 100W RMS as at full power, the readings are scattered and they don't seem relevant. I will try other powers later on, it's very time consuming.

At 100W RMS, the 1st harmonic (reference output signal) has an amplitude of 40, the left axis shows the amplitude of other harmonics.

As I can see, the bias plays a very important role reducing the odd harmonics, which is logical as they're mainly due to crossover distortions. The even harmonics are not varying significantly, except for the 6th one that is quite high at low bias setting. I can't explain it now. I re-did the test several times with consistent results about that one...

I guess harshness is reduced as bias is increased and a warmer sound is expected... but i'm only into simulation right now.

Enjoy and comment!


I will do these plots for other resistor values and other powers as time permits
Martin
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Old 5th December 2012, 04:23 PM   #1459
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I don't follow.
I see % on the right hand vertical scale.
At the 0.1% level the harmonic for a 40Vpk signal (28.28Vac) should be 1/1000 or about 28mV.
The left scale shows values of voltage of 0.0003V (maybe 0.0002828), this is 0.3mV.
That to me seems to be a discrepancy factor of 100times.
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Old 5th December 2012, 04:54 PM   #1460
a.wayne is offline a.wayne  United States
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Canonnica,

Thanks for posting and I will make the time to go over it all and comment...
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