PaX amplifier: invitation to discussion

[Elektor Editor]

Please use this forum topic to tell us what you think of the paX error correction amplifier published in the April and May 2008 issues! The author, Jan Didden, is ready to discuss issues and exchange opinions here.

Jan

[janneman01]

Well, one thing I am interested in is to hear from someone who has been using those Sanken darlingtons before. Any experiences with thermal stability (or not )? In my amp, theres no traditional Vbe multiplier, so no bias transistor on the heatsink for thermal feedback. That's totally unnecessary with those inbuild-diodes, and for me is a real advantage of these devices.

Jan Didden'

[shahriar]

Dear Sir

I will be difinetly build this nice amplifier. Because I am tired of those classical designs.

But some Few points:

1- I Love Building active cross over systems, So I don't need High power amplifiers. 28VDC of power supply is enough for me.
Maybe I could Redesign it for lower power but I would not be completely sure of results. so If it is possible for U, Put a lower power version too. i.e. just with a pair of output Transistors.
No matter if U didn't put any PCB. just a schematic is enough

2- Please put a factor measurement table of your built prototype.
i.e. Slew rate, damping factor, intermodulation distortion, signal/noise ratio and ...

3- All Famous brands Digital sources have Differential outputs But elektor never put an Amp design with XLR inputs. So if it is possible add a differential input or if U don't do that, guide us how to add a diff. stage.

ThanX in advance
Shahriar.Farmanesh

[janneman01]

Hello Shahriar,

Niced that you want to built my amp! I'm sure you will be happy with the sound.
I am also using active xovers, at the moment a heavily modified Behringer DCX2496, see my website for details if you are interested.

You can lower the power supply voltage for lower power, but maybe 28V is a bit too low, I will check and let you know. I can give you the changed component values for a lower supply.
I will also see if I can dig up any measurements I have. I must say after designing amps for 25 years I know what to measure and what to listen for, and that numbers don't tell the whole story, so I don't tend to measure all of the things you mentioned.

Do you really need a balanced input stage? I can give you an example, but if you don't absolutely need it it is better to avoid an extra stage.

Jan Didden

[shahriar]

Thank you very much

- Can I see Lower power design (at least components to change) in Next elektor Magazine, or to look for it in your website?

- I would greatly appreciate it to see the balanced input stage you recommand!

BTW, Have you seen this kind of Ballance input implemented by accuphase. I put it just to see, not anything else!

http://www.4shared.com/file/48473266/61e625dd/p-3000_ea.html

ThanX
Shahriar

[janneman01]

Hello Shariar,

I must apolgize for the silence, but I have been travelling away from home.
I will post the necessary changes for a lower power version either tomorrow or Monday. I had a quick look already and maybe a supply voltage of 28V is a bit too small; it would make some resistor values too small, but I'll see. Maybe 30VDC would be a good compromise? That would give you between 40 and 50W of output power.

Best regards,

Jan Didden

[janneman01]

OK, I checked the changes necessary to run the paX amp at +/-30VDC for 40-50W output power.

There are several resistor value changes and two zener value changes. I added a page to my website with the details, here:

http://www.linearaudio.nl/pax-5.htm

Let me know if you can work with that, and how it goes.

Best,

Jan Didden

[shahriar]

Dear Jan

Thank You very much.
With lower power, Using two pairs of output Transistors is critical or can we use just One pair?

If yes, write about what other components should be omitted!
I can Guess, but Your opinion is superior!

absolutely, Using two pairs can tweak Amp Parameters, but
imagin when it is to drive just a Tweeter or midrange in an active cross over system!

ThanX
Shahriar

[janneman01]

Shahriar,

I have added the info to run with a single output pair to my website.

Let me know if you need more info.

Best regards,

Jan Didden

[shahriar]

Thank you very very much.

Dear Jan

when designing feedback amplifier PCBs, we should pay great attention to the feedback tracks. Which tracks are most important and should be kept them as short as possible in your design?

I ask this because I will be probably design my own PCB for the lower power design as soon as I get free time!

BTW how is the noise immunity of Error correction topology in comparison with feedback amps?

Thanx again
Shahriar