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Is this consider a push pull amplifier?
Is this consider a push pull amplifier?
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Old 2nd February 2010, 01:13 AM   #1
motbuddy is offline motbuddy  Singapore
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Default Is this consider a push pull amplifier?

Hi,

I just bought a power Amp DIY circuit recently. Just want to start to learn everything about power amp. Does the part that i quoted with a box consider a push pull amplifier?
ABCD0012.jpg

thank you.
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Old 2nd February 2010, 02:44 AM   #2
stratus46 is online now stratus46  United States
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Quote:
Originally Posted by motbuddy View Post
Hi,

I just bought a power Amp DIY circuit recently. Just want to start to learn everything about power amp. Does the part that i quoted with a box consider a push pull amplifier?
Attachment 156387

thank you.
Push-pull back in the tube days (still for some) was a center tapped transformer with 2 power tubes driven 180 degrees out of phase. When 1 tube 'pushed', the othe 'pulled'. What it implies is separate devices (tubes or transistors) for the positive and negative peaks. The section you circled is the driver section for the output devices. Q1 and Q3 form a Sziklai pair which is configured to have some voltage gain since the opamp "IC" can't deliver the full voltage swing by itself. Q2 and Q4 perform the same function for the negative part of the signal. Overall gain of the amp is R4/R10 + 1. Adequate but not impressive as power amps go.

G
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Old 2nd February 2010, 02:45 AM   #3
bear is offline bear
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That part provides current and voltage gain and drive for the outputs, and creates the required bias for the output transistors.

The output transistors are doing the "push pull" part, but there is also a "push-pull" output circuit inside the opamp.

If you want to learn everything about power amps, read some text books and everything in this forum - then you will be either expert or very crazy person?

_-_-bear

PS. no need to buy "circuits" schematics - there are so many here and online.
Kits are also here and online.
Take a look in the "Pass Labs" section for some nice amps and sources of PCBs and parts... have fun!
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http://www.bearlabs.com -- Btw, I don't actually know anything, FYI -- every once in a while I say something that makes sense... ]
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Old 2nd February 2010, 03:36 AM   #4
motbuddy is offline motbuddy  Singapore
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Quote:
Originally Posted by bear View Post
The output transistors are doing the "push pull" part, but there is also a "push-pull" output circuit inside the opamp.
thanks for all the replies. So do u mean that Q1 and Q2 work as a push-pull?
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Old 2nd February 2010, 08:42 AM   #5
motbuddy is offline motbuddy  Singapore
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hi,
can i say that the Op-Amp works in a way of negative feedback?

thank you.
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Old 2nd February 2010, 08:47 AM   #6
jan.didden is offline jan.didden  Europe
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Quote:
Originally Posted by motbuddy View Post
hi,
can i say that the Op-Amp works in a way of negative feedback?

thank you.
The opamp itself works open loop, but the whole ampolifier has neg feedback via R4 and C7: a part of the output is fed back to the neg input.

BTW a good check for push-pull is to look at the two output devices. If the signal goes up, does the current through one output device increase and through the other device decrease? Yes? Then it's push-pull.

jd
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Old 2nd February 2010, 01:32 PM   #7
wahab is offline wahab  Algeria
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this is a genuine push pull amp with an output compound pair
with voltage gain...and also vbe variation gain !! that will
lead to great themal instability...
the power devices have no base to emitter resistors that
would allow to get rid of eventual stored charges as these
device can be driven into saturation in this kind of topology,
thus allowing for stored charges to occur...
anyway, a doubtful design...
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Old 5th February 2010, 06:36 AM   #8
motbuddy is offline motbuddy  Singapore
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Originally Posted by janneman View Post
BTW a good check for push-pull is to look at the two output devices.
jd
hi thanks for the replies. BTW which two output devices do u mean?

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Old 5th February 2010, 07:16 AM   #9
jan.didden is offline jan.didden  Europe
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Quote:
Originally Posted by motbuddy View Post
hi thanks for the replies. BTW which two output devices do u mean?

thank you.
Errr... The two devices that drive the output?

jd
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Old 6th February 2010, 10:00 PM   #10
stratus46 is online now stratus46  United States
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Quote:
Originally Posted by motbuddy View Post
hi thanks for the replies. BTW which two output devices do u mean?

thank you.
Q1 and Q2 are the final output devices and arfe the physically largest of the group.

G
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