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Dartzeel amp schematic - build this?
Dartzeel amp schematic - build this?
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Old 19th September 2020, 06:19 PM   #1641
selfy is offline selfy  Bulgaria
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I already tried to remove the diodes in simulation. That is why I asked if someone tried the effect in the real world
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Old 19th September 2020, 07:27 PM   #1642
analog_sa is offline analog_sa  Europe
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Dartzeel amp schematic - build this?
Quote:
Originally Posted by marigno View Post
So we expect some distortion from them.
It doesn't seem to be quite so simple. Especially with such low resistors values.

Selfy, please double check your sims, as mine shows the opposite: much lower distortion with the diodes in place.

My faith in the sim is limited as my physical amps generally seem to distort less than what the sim predicts.

Now i have little choice but to actually measure the distortion without the diodes
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File Type: jpg With diodes.JPG (62.7 KB, 144 views)
File Type: jpg Without diodes.JPG (57.1 KB, 143 views)
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Old 19th September 2020, 08:01 PM   #1643
marigno is offline marigno  Italy
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It could be that there is some limitation coming from the CCS together with the diode/absence of diode. Without diode the output impedance seems to be higher so higher is the distortion.
To drill a bit you should try, if possible, to lower the R and try again down to 0Ohm.
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Old 19th September 2020, 08:25 PM   #1644
bogdan_borko is offline bogdan_borko  Serbia
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In this case you have output bjts switching when in class b and diodes switching when base pulls enough current trough base resistors, so in theory it makes things worse as I understand, but maybe I'm missing something... So value of the base resistors is critical for intended operation, and I'd like to know how is that determined?
I use Micro Cap for simulation and when I find time I'll give a look what is "the catch" if there is any..
Btw are values of resistors same as in the original circuit?
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Old 19th September 2020, 08:32 PM   #1645
analog_sa is offline analog_sa  Europe
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Dartzeel amp schematic - build this?
Quote:
Originally Posted by bogdan_borko View Post
Btw are values of resistors same as in the original circuit?
Indeed they are.
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Old 19th September 2020, 09:41 PM   #1646
marigno is offline marigno  Italy
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My WHA-217 does not switch on output pairs but does on their driving diode.
But let's forget about heavy mods like mine, too many variables and understanding each other would be difficult. Let's also forget about accessories like midpoint keepers and so on. We will find a solution for everything at the right time.
If you like, let's go to the core and keep it simple.
Have the original schema as a base, I reposted here, that is the mother of all variants.
Since you (plural YOU) have the knowledge of simming, there are a lot of "core" aspects you could investigate on this original. One of them is about the heavy (for the signal) L-pad R7/R5 (R8/R6). But we are now dealing with the way to drive the final stage across the diode. So let's point our focus on this first goal: presence/absence of the diode and varying the resistor value.
Would you?
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Last edited by marigno; 19th September 2020 at 10:07 PM.
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Old 19th September 2020, 11:43 PM   #1647
analog_sa is offline analog_sa  Europe
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Dartzeel amp schematic - build this?
There is no easy way to automate this in LTspice, so each instance has to be run separately and cannot be displayed graphically.

The base resistor value and the bias current are shown on top. 20W/4ohms


1ohm, 724mA

no diodes 0.09637%

diodes 0.09637%


10ohm, 387mA

no diodes 0.2534%

diodes 0.26338%


20ohm, 268mA

no diodes 0.3891%

diodes 0.3451%


27ohm, 224mA

no diodes 0.474%

diodes 0.3%


30ohm, 210mA

no diodes 0.5092%

diodes 0.3798%


It looks quite fascinating. 27ohm seems to be a sweet spot where the diodes become really helpful.

Selfy is also right: at lower resistor values/higher currents the diodes appear detrimental to distortion.

Could this be a distortion compensation mechanism where use is made of the diode non linearity?

In a real amp the optimal value is perhaps different and may be worth the effort to adjust.
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Old 20th September 2020, 03:03 AM   #1648
marigno is offline marigno  Italy
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20W/4Ohm___I=2240mA___TR hfe avg=90

IF ABSENCE OF DIODE

Idle mA___R mA___R Ohm____R mV
____724___32.9_______1____32.9 too far from diode threshold, diode remains off;
____387___29.2______10___291.9 far from diode threshold, diode remains off;
____268___27.9______20___557.3 close to diode threshold, diode would start switching sometimes;
____224___27.4______27___739.2 close to diode threshold, diode would switch;
____210___27.2______30___816.7 over diode threshold, diode would switch hardly.

At different output power/impedance everything changes.
I have to think about the meaning of all this.

It was hard to align the text!
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Old 20th September 2020, 03:14 AM   #1649
marigno is offline marigno  Italy
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Quote:
Originally Posted by analog_sa View Post
And here is Damir's circuit as a possible replacement for the diamond.
Would you like to simulate Damir's ciruit with Q10's collector moved to B- and Q12's collector moved to B+?
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Old 20th September 2020, 05:28 AM   #1650
bogdan_borko is offline bogdan_borko  Serbia
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Quote:
Originally Posted by marigno View Post
Would you like to simulate Damir's ciruit with Q10's collector moved to B- and Q12's collector moved to B+?
Collectors moved to rails gives little slower circuit (inpit bkts are not bootstraped). With collectors on emitters, like in schematic you could use lower power, higher ft bjts...
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