High Power Class G amplifier

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#4
That's exactly the kind of amp I've been looking for.
Have you made it yet?
Do you think that changing the PMBTA92 for a Bc *** type would have any affect to its operation? (BC556 for example)
and the output pairs to MJ15003/4? or maybe TIP3055/2955 for an easier to manage package.
Other than that I can get everything required to make it.
Well done
 
#5
Hello!

About the sound quality: Spheric, precise, powerful. Perfect for PA use. Problems can arise with cheap drivers that tend to be sharp, because precise+powerful+sharp sound can be unpleasant (the amp itself does not sound sharp). The results with good drivers and bass speakers were excellent (not just my opinion (which is a little biased 🙂.

@Samuel: The amp does have a current limiter/overload protection.

@frost: The transistors were chosen because of their CE-voltage.

With the given rail voltages the PMBTA-transistors can be changed to others with at least 150V CE-Voltage, the inner power transistors can be changes to ones that can withstand 1xouter+1xinner voltage= 170V, the outer can be changes to ones with outer-inner voltage=80V. The power transistors should be able to handle 15A continous current. And a small SOA chech should be done.

The 3055/2955 can not handle these voltages and cannot be used therefore. The BC-types as diff-pair also can not be used because of their CE-Voltage.

Harald
 
#6
fr0st said:
That's exactly the kind of amp I've been looking for.
Have you made it yet?
Do you think that changing the PMBTA92 for a Bc *** type would have any affect to its operation? (BC556 for example)
and the output pairs to MJ15003/4? or maybe TIP3055/2955 for an easier to manage package.
Other than that I can get everything required to make it.
Well done
Click to expand...

BC556 is not useful, due it can handle only 65V. Try to use MPSA92 or 93, which can go up to 200V, of higher.
For output the MJE15003/4 is OK, but I think MJ15024/25, or MJ21193/94 (even MJL 21193/94) is much better.

sajti
 
#7
Is there anybody who can explain, how I can count the voltages for class G amplifiers?
For this amplifier the total psu voltage is +/-125V. But why 45+80? Why not 62,5+62,5? What is ideal for dissipation?

Thanks: sajti
 
#10
Douglas Self has written an article about class-G amps where he presents some curves generated by playing around with the voltage partition. I you like it I can mail it to you.

In general you would have to be able to perform integral calculus to calculate things like that properly. But there are also the possibilities of simulation (like P-SPICE) or you can do an approximation with programs like Excel.

Regards

Charles
 
#11
phase_accurate said:
Douglas Self has written an article about class-G amps where he presents some curves generated by playing around with the voltage partition. I you like it I can mail it to you.

In general you would have to be able to perform integral calculus to calculate things like that properly. But there are also the possibilities of simulation (like P-SPICE) or you can do an approximation with programs like Excel.

Regards

Charles
Click to expand...


Charles,

if possible, please send me the Self article! Due my Hotmail box is limited, please send to: asajtos@pantel.hu
During this time I checked the QSC site. The use 50%-50% in their amplifier...

Thanks:
sajti
 
#14
This is interesting, i was talking to a guy selling german made class G amps in teh weekend at a music expo, i forget the brand name..
He said they had switch mode supplies that would change the rail voltages depending on the power required.. or is that class H?
anyway, does anyone else know of other schematics? This stuff is really intriguing!
 
#15
Optical said:
This is interesting, i was talking to a guy selling german made class G amps in teh weekend at a music expo, i forget the brand name..
He said they had switch mode supplies that would change the rail voltages depending on the power required.. or is that class H?
anyway, does anyone else know of other schematics? This stuff is really intriguing!
Click to expand...
Class G switches between two supply voltages. Class H continuously varies the supply voltage. A switch-mode PSU definitely makes sense for class H to make the most of the efficiency boost.
 
#16
Optical said:
This is interesting, i was talking to a guy selling german made class G amps in teh weekend at a music expo, i forget the brand name..
He said they had switch mode supplies that would change the rail voltages depending on the power required.. or is that class H?
anyway, does anyone else know of other schematics? This stuff is really intriguing!
Click to expand...

As I know Labgruppen make special power amplifiers. They use class D amplifier to get +/-5-10V power supply for the conventional AB class power stages. The PSU also modulated with the output signal, so they can keep the dissipation low...

Class G founded mainly to avoid second breakdown for the output devices. For +/-125V not easy to find any power transistor to use (MJ15024/25, MJ21193/94 are out of question).
Of course class G reduce the dissipation, but I think this is just a feature....

sajti
 
#17
cunningham said:
Have you ever considered using complementary Mosfet transistor to switch the collectors of the outputs to the higher voltage instead of more power BJT's??
Click to expand...


BTW... I am designing a class G using complementary hexfets but driving just two output BJT's. The main reason of course is that I am using hi-current output devices driving 4Ohms and they will not handle any more than 90V...85V to be safe. Found out that a common source is the best way to switch to the higher voltage and also regulate it.
 
#19
About the efficiency: Power dissipation is about 1/2 compared to a normal amp in a "bad" case and 1/3 in a "good" case. Amplitude statistics is an imortant factor for efficiency. Usefull thermal design would be a temperature-controlled fan that will turn on only seldom.

About the power supply: I took a 2x30V 300VA transformer for the lower supply and a 2x80V 1000VA for high voltage supply with normal bridge rectifiers.


Harald
 
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