RMI-FC100, a single stage audio power amplifier

[DRZ1]

Originally posted by roender


Hi DRZ1,

I don't know what is this "milling prototype machine" and what type of files can be use to make boards.
I can send to you all CAD files if you want to make some changes but I must warn you that you will need a valid EAGLE license because the PCB dimensions is over maximum permissible free version size.

Mihai

It's a milling machine specialised for milling PCB board. It's used for testing PCB design before production. Works with gerber files. I use Protel soft.

http://www.mitspcb.com/


Denis

[aparatusonitus]

Originally posted by lumanauw


You can try this correction system by putting C from output node (before L) to emitor of Q14. Initial approximation value could be 30pf (C8//C9), but it must be adjusted in the real amp.

(in aparatusonitus' amp, put another 47p//165k from output to emitor of Q11a)

Hi lumanauw,

A and B nodes are input and output nodes of current mirror, so in my sch C3//R34 have to be connected to collector of Q11A, not emiter, see sch below.

[roender]

Originally posted by lumanauw
Hi, Roender, aparatusonitus,

... looking at your schematics, it is quite easy to experiment with it.
If you look at this attachment, the correction system is possible because there is a "virtual" inverting input of the output stage, that is point A.
The correction works optimal if impedance of "32a" (that is element 56+54) is the same (calculate the gain first) to the impedance of "36a" (that is element 62+60).
In your schematic, element "32a" is C8//C9.
(In aparatusonitus' is C12//R38)

You can try this correction system by putting C from output node (before L) to emitor of Q14. Initial approximation value could be 30pf (C8//C9), but it must be adjusted in the real amp.

David,

The distortion cancelation method, a la Wurcer's ad797, is applicable only if you have the same impedance, as high as possible, into the input and the output of the current mirror. In my design there is no floating current mirror and the input has low impedance compared with the output.
I am not sure if it is possible to implement AD797 topology in a discrete power amplifier.

Mihai

[aparatusonitus]

Originally posted by roender
I am not sure if it is possible to implement AD797 topology in a discrete power amplifier.Mihai

Hi Mihai,

Before I went this road in design, I have ask the man himself, Scott Wurcer, whether is it possible to design AD797 style discrete preamp/opamp…guess you know the answer.

[roender]

Originally posted by aparatusonitus


Hi Mihai,

Before I went this road in design, I have ask the man himself, Scott Wurcer, whether is it possible to design AD797 style discrete preamp/opamp…guess you know the answer.

It is pointless ... because for a discrete preamplifier you can use an class A output stage, well ... it is highly recommendable to do that!
The cancelation method described in US patent 5166637 is applicable only if you want to avoid high power dissipation in output stage.

[forr]

Hi Aparatusonitus,

I think you use Baxandall's constant current sources.
No high frequencies problem with them ?
What's the purpose of the CCS around Q5 and Q6 ?

[aparatusonitus]

Originally posted by roender

The cancelation method described in US patent 5166637 is applicable only if you want to avoid high power dissipation in output stage.

I have tried to sim my sch with and without cancellation network, and IIRC got something like 25dB less H2 with cancellation network (not that I’m a THD freak). Try to look at it as a first experiment if I ever decide to build a power amp upon it.

Originally posted by forr


I think you use Baxandall's constant current sources.
No high frequencies problem with them ?

I have not notice any HF problems in sim (mind you I’m not an EE and will never be, I have just keep notes from the gurus here ), but as usual I have to build the real thing first to see wether it oscilates or not.

Originally posted by forr

What's the purpose of the CCS around Q5 and Q6 ?

Wrong copy/paste move, just neglect all schebang around them.

[lumanauw]

Hi, aparatusonitus

Sorry I don't look at your schematic further, you've already implemented the patent

In the schematic in post #132, what is the function of Q12? What does it do in your SIM?

[roender]

David,

Q12 make current mirror point C to swing with output voltage level. In this way, the input of CM, point A, has the same impedance as the output, point B.

Guys, please open a new thread dedicated for this ad797 topology.

Thank you
Mihai

[lumanauw]

OK, lets continue with Roender amp.