Revisiting some "old" ideas from 1970's - IPS, OPS

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still4given

still4given

Member
Joined 2004
I'm in the middle of building a preamp and amp for my son so my bench is buried. I will try to find time to hook up my Symasui and see what it is doing. It seems that the servo wouldn't have to do anything if the initial offset is only 2.5mv. I wonder if there is a cap that is pulling the servo off while it charges.
 
vzaichenko

vzaichenko

R.I.P.
Joined 2010
Ampi said:
Hi Valery,

thanks for the info.
Sorry, I lost the overview in so many post and was not able to find my first post ;).
Makes it sens to build the NS-OPS only with 1 or 2 output pairs to get the idle current down?
Click to expand...

Hi Ampi,

Well - it all depends on particular requirements.
What sort of maximum power per amplifier channel do you have in mind?
What is the speaker minimal impedance (I'm mostly interested in LF section)?
 
A

Ampi

Member
Joined 2011
Hi Valery,
I'am thinking about a "normal" Setup.
tweeter: AirMotionTransformer
mid: wavecor wf120bd or wf152bd
bass: 2*TIW200XS
So minimum impedance sould be 4 Ohms.

In my opinion especially the tweeter or the mid don't need so much power.
So the task would be to design a smaller pcb with one or two pairs transistors in the outputstage.
 
vzaichenko

vzaichenko

R.I.P.
Joined 2010
Ampi said:
Hi Valery,
I'am thinking about a "normal" Setup.
tweeter: AirMotionTransformer
mid: wavecor wf120bd or wf152bd
bass: 2*TIW200XS
So minimum impedance sould be 4 Ohms.

In my opinion especially the tweeter or the mid don't need so much power.
So the task would be to design a smaller pcb with one or two pairs transistors in the outputstage.
Click to expand...

Yes, in this case 2 pairs will be enough. I recommend MT-200 devices - good current provision capability.

Why are you trying to minimise the idle current? 70mA per output pair is pretty low already. It runs cool enough, you can't really save on PSU as you have to keep it capable driving the rated power... so - what's the point?
 
T

thimios

Member
Joined 2009
Servo experiments.

Today i have try to modify the servo controller as this schematic.
What i found?
Using TL072 servo started from 3v and ended up (after 12'')at 24mv!
Using LF412 servo started from 3v and ended up (after12'')at 2.5mv!
I will try the Valery mofification soon.
 

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A

AndrewT

R.I.P.
Joined 2004
the 411 is better for servo duty than the 072
It's what was recommended 20years ago and probably long before that.

But why does the amp try to start with only 2.5mVoffset and move to 3Voffset to come back slowly to 24 or 2.5mVoffset?

That's what you have to find out.
Something is going wrong during start up.
 
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A

AndrewT

R.I.P.
Joined 2004
jwilhelm said:
Could this be from C12 slowly charging on power up?
Click to expand...

thimios said:
I will try to remove this and see what happen then;)
Click to expand...
C12 is connected to Power Ground on one side and via 470k+Speaker to Power Ground on the other side.
If the speaker is open circuit there is an alternative path to Power ground via R24 - R25 - R3
During power OFF C12 should be completely discharged.
At Power ON it should not acquire a charge. Where would that charge come from?
 
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vzaichenko

vzaichenko

R.I.P.
Joined 2010
So, it looks to me like it's the servo itself moves the output to 3V and then, as C12, C13 charge-up, corrects itself :rolleyes:

Time to arrange some standalone servo test. It will require 2 opamps - one foe integrator and the other one - for phase inverter. Connect the phase inverter to the servo output, the servo input resistor - to the output of the phase inverter.
The whole thing is expected to start with the offset close to zero and stay there (probably even closer to zero after some time).
 
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