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destroyer X 6th April 2010 11:22 AM

Symetrical schematics are alike plague in Brazil, do you like them?
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Brazilian epidemic, contagion, plague, pestilence!

This the national standard, to me seems a plague, all
copies of the Leach amps ... some of them, the copies, includes
the same part number, same board layout, same resistances and capacitance
and sometimes same capacitor values..they use more modern transistors
disguise, but actually copied and neither took the
work to make a good copy .... epidemic seems to me .... as
contagion spread throughout the national territory,
all factories dozens of professional models... all them with the same ..
circuit .... I do not like the sound .... seems to me, synthetic , alike the
comparison of natural orange juice with Tang synthetic powder.
But there are those who prefer tang.
I have assemble..the ones i can remember, 5 amps in this same style,
then gave up permanently .... you had some
very good experience with this type of amplifier?
those symetrical ones, double differential ... made comparison with others?
Have you appreciated this one...this topologie, this style?

They are multiplying..alike viruses....3 new factories each month...there are already
hundreds in operation, all them using the same circuit...something you could see
in Marshall Leach pages.

Now a days, the almigthy Selenium (second most important speaker factories in to Bravox) bougth two factories, and now they are also
producing the same kind of circuit.

I have simulated...fourier is fine..harmonic distribution not so nice.... THD very high...
even using other transistors and voltage regulation in the rails, series rail resistances
and tweaking values..i could not have decent a days..amplifiers are
distorting less than 0.009%

Do you disagree?.... tell us why...have tested....had experienced moments of satisfaction with
these kind of amplifiers?



destroyer X 6th April 2010 11:40 AM

I remmeber i have assembled, using huge transformer, a Cygnus model
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I had almost 200 watts rms..undistorted ... and pumping two selenium speakers, they were under my bed...bed had holes and feet..distant from the floor...look alike this one you see in the picture..but that bed had drawer and parts were inside..transistors, capacitors and all stuff.

The bass punch was nice...i used to be layed down feeling vibration..another amplifier was pumping treble and midranges.... passive filters in the input...independent volume controls.

Two big Selenium drivers, 15 inches each one of them...200 watts each series, each one of them 4 ohms.... inside their own tuned enclosures, having ports and tuned to 30 hertz.

One day i decide to try a small amplifier... from Elektor...boostrapp one... that one Elektor published that you could use several supply voltages, and they have provided a chart for you to substitute resistances.

I have connected the 30 watts amplifier, the these speakers..and believe it or not....more punch, more deep bass..things started to shake.

I have tried to increase low frequency response increasing feedback condenser (gain) and input condenser in the symetrical one..but no good result.

This is the reason why i dislike...stucked!... clogged!..obstructed..jailed..confined!..sound does not go out from the speaker..remains there..strange thing.

Speakers, to mids and highs where on a shelve... separated amplifier and volume controls near the can see the way that bed ways (that other bed i had)... holes to remove upper plate, space below and holes to exaust air (tuning the whole thing)..inside strong 3 inches extructure made of plywood and two main divisions..a non vibrating thing...very strong bed that other one was..this one i am using is not so strong..reason why have no speakers inside.



Eva 6th April 2010 11:53 AM

When you clip a low power amplifier, subsonics are added to the output signal. This produces the shaking effect and more cone excursion and bursts of air from the ports in vented speakers.

Car audio folks love that ;)

destroyer X 6th April 2010 12:16 PM

They are multiplying, someone may say, because they are good
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I can agree this is a good signal...the population aproval, but, they have not the chance to compare, as the same style of sonics are playing everywhere, football stadiuns, parties, ball, carnival, celebrations, electricall trio (mobile power units assembled inside big trucks..... plays loud.... treble is fine...also voices...i dislike the bass only.

Those Brazilian amplifiers, use to put out 40, 50, 60 volts and even more than that, and some of them can face 3 ohms or less output impedance... they are used in groups, say... ten, twelve or more amplifiers distributing sound to several speakers.

I think they are appreciated because loud.... some others tried digital amplifiers and some Class H, but population have not accepted.



destroyer X 6th April 2010 12:38 PM

We love music..we have hundreds of these trucks, so, speaker, amplifiers
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and music are important for us.

We have a say here, first in portuguese because translation is difficult:

- "Atraz do Trio Elétrico só não vai quem já morreu!"

Behind (following, walking with) the Electrical Trio, the one does not go, is because already died (living beings cannot resist).

Visit Brazil, a lovely country, happy and friendly people..violence New York too!



destroyer X 6th April 2010 12:40 PM

And these you like them?
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My people likes...i am exception i think..... and i want to contact other "exceptions" produce the "rarities, the exotic ear group..bad taste tribe!"

You know...for me...all this is fun...i do not mind...i like blonds, but there are exceptions.



Eva 6th April 2010 01:19 PM

The question is: Would blonds like you? :D

These class B and AB amplifiers are becoming popular because they can be mass produced at low cost and without having a clue about electronics.

Class H and class D are lower cost but there are fewer people capable of getting these circuits right and dealing with mass production problems (like sourcing magnetics, dealing with component tolerances without trimmers, mixed thru-hole and SMD in power PCBs, EMI, etc).

It's not a matter of customer acceptance, people tend to buy the most cost effective product.

a.wayne 6th April 2010 03:03 PM

My head hurts .... :Pawprint:

Where are the girls , Brazilian sound system and no girls , dats illegal carlos , you know that , Lula looking for you now .....:p

wg_ski 6th April 2010 03:49 PM

You can make a very good or very poor Leach amp out of substantially the same components. If you "don't have a clue about electronics" it can be on the poor side.

Carlos - your simulation is flawed. First, the VAS -and therfore the front end -is seriously and intentionally out of balance. Tsk, tsk tsk. Eva's going to put you to bed without any supper. Second, the MJE1503x suck as VAS transistors unless they're buffered (miller capacitance is too large and nonlinear). Heck, use the models for the BD139 if that's all you have. Third, with only one output pair you're suffering from beta droop at high power - even with an 8 ohm load. Put in the rest of them (just use the area scaling factor if your simulator limits the # of transitors). The good professor solved this problem by using a triple. Fix some of this and you'll get better than 0.797%.

mlloyd1 6th April 2010 04:44 PM

in addition to wg_ski's comments, there looks to be a pretty significant error in the schematic. the top mje15031 after the diff amp looks to have it's collector and emitter connections reversed. i would guess this stands out in the sims at least for dc operating point?


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