F5 power amplifier

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fredlock

Member
Joined 2008
I built the F5 amp and it really sound good.

I have a question though, I was able to balance the voltage on R11 and and R12 to .6v and made the dc offset to 0 when it was already warmed up. After monitoring the dc offset for while, I was wondering it fluctuates from -1.0 mv to 2mv, is this normal? or it suppose to be steady at zero all the time? This is a monoblock and I'm using 18V dual 300VA Piltron transformer with CRC PSU. Please advise.
 
Zen Mod

Zen Mod

Official Court Jester
Joined 2003
zenmod.in.rs/
Paid Member
fredlock said:
I built the F5 amp and it really sound good.

I have a question though, I was able to balance the voltage on R11 and and R12 to .6v and made the dc offset to 0 when it was already warmed up. After monitoring the dc offset for while, I was wondering it fluctuates from -1.0 mv to 2mv, is this normal? or it suppose to be steady at zero all the time? This is a monoblock and I'm using 18V dual 300VA Piltron transformer with CRC PSU. Please advise.
Click to expand...


did you ever measured any other amp than that ?

that's completely normal .......
 
juma

juma

Member
Joined 2005
gaborbela said:
Hi Jacco
I understand your point , but already a lot of people built these amp someone could help me with the layout (at least I thought)
Any way thanks an if no one will share his lay out I will wait until Mr.Pass will post the desing on his site .
Regards
Click to expand...


Before you get all bittered about others not sharing, why don't you just browse/read this thread from beginning - you'll find 3 good layouts at least.
 
P

pencoat

Member
Joined 2005
HBarske said:

Perhaps this is an unbelieveable dumb question, but I dare: Why should someone do that (except for protection purposes)?
Click to expand...

Well, that is the only reason. I've got Lowther drivers for years, and now have compression drivers and really fears DC current thrue them.
And I'm also not sure a protection circuit will act promptly enough to avoid any damage on the coil.
Obviously, if it's not transparent enough to my ears, I will have to live dangerously (for my wallet...), it's always a question of compromise, is'nt it?

Anyway, I will try it soon and report,

Arnaud
 
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audiorob

Member
Joined 2006
how is the feedback part of this circuit working?

Can someone please explain how the feedback part of the F5 circuit works to reduce distortion? One issue that is confusing me is that the signal we are using for feedback appears to be in phase with the signal at the point we are inserting the feedback. So if this is not negative feedback, how does positive feedback work?

Also, isn't this using global feedback? I realize this is an over simplification, but isn't global negative feedback supposed to be bad? Does this mean that generally, global positive feedback is ok? I'm confused!

The next issue that confuses me is that we are inserting the feedback at the source pins of the first stage (as opposed to the gates). Why there? And if this will provide more drive current than a LTP, do we need to be concerned about the Ids and power rating of Q1 and Q2? And I thougth the MOSFETs we're driving do not require much current to drive the gates. If so, why is the drive current of this first stage important?

Would it have been too conventional to take a part of the first stage's output and feed it back to the input of the first stage, and take a part of the output of the second stage and feed it back to the input of the second stage? As they both invert the signal, I would have thought this to be more "natural".

I guess I'm saying that I don't understand the, "how's and why's" for the feedback mechanism we are using. Could someone help me understand? Please feel free to disagree or correct anything I've said. I'm still learning, so I've probably made a lot of misstatements or wrong assumptions...

thanks,
Robert
 
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