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Old 7th December 2012, 12:48 PM   #1481
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Default Ma lo que passa?... what happened?

Or... what is going on?

heheheheheh.

Carlos
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Old 7th December 2012, 12:51 PM   #1482
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Default But i really would like you to make your own Juan

To make alike the Dx Super A...that resulted beautifull...just use the shape Alex mm made... resulted good... despite i do not like long boards this way....long strip boards...but it is looking good.

Use condensers the way Alex did, and was made this way to fill the empty spaces, the clearances there.... all surrounding is standard...power transistors are the same in zillion of designs..but your style to the Dx Super A applied to this amplifier will be good.... say...to the center core of the layout...the audio amplifier itself but the output..then will be great.

And beeing your the design, from the scratch, you may be rid of these comments.

I am having people asking for this design in Brazilian foruns...you may have some orders if you make it.

regards,

Carlos
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Old 7th December 2012, 01:12 PM   #1483
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I think you are correct, is better from scratch it take longer but at the end will be a complete different design I will try to make it more like the Dx Super A style we all see how is going to end maybe smaller or a bit larger we really don't know because according to your format specifications it take more time, alignments, parts no so close each other, letter fonts all the same, space between transistors the same, is not easy but with lot of patience I can do it why not I don't have noting to lose anyway lol jejejejejejej

Regards
Juan
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Old 7th December 2012, 03:06 PM   #1484
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Quote:
Originally Posted by bonfis View Post
Just discovered that the thread has come alive again. The modifications contemplated by Cannonica were implemented in my Mk III when I observed instability after attempting to increase the quiescent bias. I found that an 56R base stopper completely eliminated the instability and allowed the bias to be increased to 57mv. per pair. This in turn substantially reduced measured THD. A further reduction was achieved by increasing the feedback ratio (and reducing closed loop gain). My amp has a gain of approximately 25 which is adequate for a system using a preamp but on the low side for those driving the amp with mp3 players. I'm also interested in reducing Cdom further (currently at 180pf) to improve slew rate. Look forward to hearing about the results of Cannonica's experiments.
I was also wondering about the zobel network comprised of the 47nF cap and 15R resistor... Some bias induced oscillations can be dampened by this, but the values used doesn't seem to be optimal (no pun intended to the designer) . The optimal values is more around 100nF and 10R. the higher cap will pass-on lower frequencies oscillations while the 10R resistor will dampen it more. In "standard" designs "default" values always seem to be 100nF and 4.7R-10R for the resistor (never higher than 10R as per Dr. Self) ...

I may start modifying those two components first to see if it gets rid of the high-biased oscillations observed by me (and bonfis).

Martin.
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Old 7th December 2012, 03:31 PM   #1485
BMW850 is offline BMW850  Netherlands
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It is a pity that there is spoken about "different amps and boards", "I think" it belongs in a other topic.
So this topic Dx Blame MKIII-Hx - Builder's thread becomes a mess.
Carlos opened this topic, so he is the boss and decides what to do ...

Martin and Bonfis you both do a great job, to get this amplifier to a higher level.

Regards,
Rudy
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Old 7th December 2012, 04:27 PM   #1486
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Default Other kind of layout BMW....another type of layout

Not really another amplifier... this same amplifier with a different pcboard with other "decoration" you know?

Also i am not the boss my dear.... if i was the boss i would say:

- "Do not mess with my amplifier"

And i did different, i said:

- "Try by yourself to make it even better"...and i also cooperate with all of you trying to.

I would love if i ever have a boss this way man!

regards,

Carlos

Last edited by destroyer X; 7th December 2012 at 04:32 PM.
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Old 7th December 2012, 07:30 PM   #1487
bonfis is offline bonfis  United States
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Originally Posted by canonnica View Post
I was also wondering about the zobel network comprised of the 47nF cap and 15R resistor... Some bias induced oscillations can be dampened by this, but the values used doesn't seem to be optimal (no pun intended to the designer) . The optimal values is more around 100nF and 10R. the higher cap will pass-on lower frequencies oscillations while the 10R resistor will dampen it more. In "standard" designs "default" values always seem to be 100nF and 4.7R-10R for the resistor (never higher than 10R as per Dr. Self) ...

I may start modifying those two components first to see if it gets rid of the high-biased oscillations observed by me (and bonfis).

Martin.
Hey Martin-
I think the zobel might very well be adjusted to damp the parasitics. Mine has the standard values but it did not prevent the oscillation from being present at the output. My suggestion would be to try and eliminate them at the source. The stopper resistor change accomplished this nicely with minimal fuss. Before the change high freq oscillations (a few Mhz) were visible on my scope riding the peaks of a 1 Khz sine wave that was driving the amp. Once the stoppers were increased these disappeared at all power levels and all bias settings. If you don't have a scope this is a leap of faith kind of change. However if you notice that bias voltage changes suddenly as you try to adjust it upward there's a good chance you've got the oscillation too. After making the stopper change bias can be increased smoothly with no sudden jumps up to and beyond 56 mv across 2 emitter resistors. That should be all the evidence you need to feel confident that you tamed the beast.
Good Luck
Steve
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Old 8th December 2012, 02:37 AM   #1488
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Thanks bonfis for the advice. Also in simulator, tampering with the zobel doesn't change anything about the + side ringing.
I have the necessary components, need some time now to execute. As you mentionned, my only indicator is a sudden jump in bias voltage when adjusting.

As a bonus, here are the distortion figures for 3 values for base-stoppers and for vBias from 2mV to 66mV. As demonstrated, changing the stopper values does not much on the harmonics behavior, but increased bias can reduce odd harmonics significantly but more importantly: below even order ones...

Again vBias is measured between the TWO emitter resistors. The Magnitude scale on left refers to the harmonics while the right scale is exclusively for THD. Left and right scales are NOT related, I just wanted the THD to be present on the same graph.

Regards,
Mart.
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Old 8th December 2012, 09:26 AM   #1489
Vostro is offline Vostro  South Africa
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Quote:
Originally Posted by bonfis View Post
I found that an 56R base stopper completely eliminated the instability and allowed the bias to be increased to 57mv. per pair. This in turn substantially reduced measured THD.
Something I'm not understanding,
You say that with a low base stopper (whose function is to 'stop' oscillation) the output shows ringing on a real ciruit.
But when increasing the base stopper value to >= 56R it completley eliminates the instability,
I agree this is true, base stoppers doing there job.

But then I'm confuced that you say that "This in turn substantially reduced measured THD"

Did you really measure the THD or just simulate for it.

I can't believe that a output full of ringing has less THD than an output with no ringing.

Personally a Bias of 30mA +/- 5mA per output device is enough for me

Regards
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Old 8th December 2012, 12:27 PM   #1490
AndrewT is offline AndrewT  Scotland
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Originally Posted by BMW850 View Post
..........................Carlos opened this topic, so he is the boss and decides what to do ..................
Yes, any Member can open a topic. No, that does not make the Thread opener the "boss".
The Thread opens the door to all Members that want to make a comment or observation.

Every Member has the right to contribute to ANY Thread.
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