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Very simple and very stable power AMP
Very simple and very stable power AMP
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Old 1st December 2017, 07:53 AM   #51
Guitar.mod is offline Guitar.mod  Lithuania
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Quote:
Originally Posted by nauta View Post
Hi
In a split-rail amp for say a 20W amp, the whole VA rating of the PT is available on an instantaneous basis from either half of the secondary. For each half of the wave, only one rail is loaded so only half the PT is loaded and the PT can be 20VA for the 20W amp.
Quote:
Originally Posted by nauta View Post
guitar mod: You have ignored an important detail to make the scenarios equal - which they are not, as I've explained above.
Dear Nauta, in both cases PT average outcoming power raitings will be the same. I am not ingnoring Your details. Please take a closer look.
For instantaneous output power split rail could look less power hungry because each half is loaded alternately. For example if it is needed 1.58A of current to 8 Ohms load, the corresponding voltage would be 12.64 V . The losses in Vds and others not overlooked here for simplicity, just concentrating only to Power Supply power demands.
So, 12.64V multiplying by 1.58A = 20W. 20W to the load and 20W from power supply.

In single rail supply the voltage would be twice as big (12.64*2 = 25.28V) but current remains the same. So power demand from power supply from the first look is: 25.28V*1.58A = 40 W. Twice as big. But stop here. What happens in the negative cycle of the signal? It looks like no power demand is needed from power supply, because negative voltage rail is not -12.64V, but zero or GND. Power supply "rests" here. No current is flowing from Power supply, because upper half transistor is closed.

So instantaneous power demand looks better in split supply version, but average power demand and whole effectiveness are the same.

Last edited by Guitar.mod; 1st December 2017 at 08:08 AM.
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Old 1st December 2017, 12:37 PM   #52
mindutis is offline mindutis  Sweden
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It is easy to get lost with schematics and tests here. So the bootstrap is C15 capacitor for schematic nr2? right? And it simulated much better compared to schematic nr1.
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Last edited by mindutis; 1st December 2017 at 12:38 PM. Reason: none
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Old 1st December 2017, 01:01 PM   #53
Guitar.mod is offline Guitar.mod  Lithuania
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Hi mindutis,

No, C15 is compensation capacitor - for stability and for lower VAS impedance at High Frequencies because of the local negative feedback in schematic no2.
I ended with 18pF. Originaly it was 47pF.

Yes schematic No 2 is better, but not "bullet-proof stable" as the first one - without any compensation.
Further more for better stability it is good idea to have Zobel networks at the output of the amplifier (both versions) and also I recommend to use Zobel network just at the speaker cabinet terminals. (not shown in schematics as it should be obvious)
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Old 1st December 2017, 01:35 PM   #54
voltwide is offline voltwide  Ireland
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Quote:
Originally Posted by cumbb View Post
Some years ago ...

My suggestion:

Very important to get a clean, real sound is, not to use complementary devices - as complementary MosFets. Just one complementary stage and you have got "din", noise. Never a clean, clear tone.
Built up without a board. The result will be a MUCH cleaner, finer tone and better dynamic (quiet-loud/ piano-forte;-).
Just try it;-)

LG
Omitting the PCB will produce more messie sound imho
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Old 1st December 2017, 05:41 PM   #55
nauta is offline nauta  Canada
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Hi

I don't see any purpose for R28.

The input base is biased by the divider, which then sets the output to the midpoint voltage. Gain is set by R17.27 and C9.

The nr2 topology is the same as Nelson et al did in the early 1960s as the next step to improve the Lin amp, by adding an input stage to separate the functions of error correction from bulk gain. Still stable and wide-bandwidth since the input and VAS are configured as what modern builders call a current-mode amplifier.
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Old 4th December 2017, 09:04 AM   #56
Guitar.mod is offline Guitar.mod  Lithuania
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Quote:
Originally Posted by cumbb View Post
Some years ago ...

My suggestion:

Very important to get a clean, real sound is, not to use complementary devices - as complementary MosFets. Just one complementary stage and you have got "din", noise. Never a clean, clear tone.
Thank You for suggestion, could You provide the schematic You are enjoying?
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Old 4th December 2017, 11:07 AM   #57
Ultima Thule is offline Ultima Thule  Europe
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Quote:
Originally Posted by cumbb View Post
Just one complementary stage and you have got "din", noise. Never a clean, clear tone.
What does "din" mean?
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