AB100 Class AB Power Amplifier

[Freecrowder]

So NP or anyone, i'm trying to understand just how far I can go with biasing my amp. I'm running 42 vdc rails with large heatsinks for a 200W amp into 4 ohms. I have the original 4 pair of outputs and .68 ohm emitter resistors. I have each transistor running at 30mA. Is this a problem? Can I go higher? The heatsinks are just barely warm after 15-30 min. can I just base it on heatsink temp as far as biasing higher?

 

[Zen Mod]

if heatsinking allows (Pa's magic number of 55C maxx!) then look at max dissipation per device , which you're in mood to allow

 

[Nelson Pass]

Take a look at how well the bias is matched between devices and how
stable it is with temperature. You might be able to reduce those Emitter resistors
and/or increase the bias.

 

[Freecrowder]

Ok will do guys thanks.

 

[Freecrowder]

So after an hour of biasing at 30mA per transistor in a room at 30c my heatsinks are 31c. I will move up and keep monitoring temps.

 

[Freecrowder]

Ok so biased at 63mA per and heatsink temp stable at 93 deg F. Room is at 83 deg.F
Seems like there is plenty of headroom.

 

[Nelson Pass]

Heat sink temperature is a good indicator. 55 deg C. is pretty much the
standard. Also you want to keep an eye on how equally the parallel
devices are sharing the current.

 

[Freecrowder]

Ok follow that. How tight of a current match is needed between transistors.

 

[Freecrowder]

So I have just noticed a potential problem in my build. One channel I have used 220 ohm base resistors and the other channel I have used 180ish resistors. Will this cause any problems in operation. Should I change the 180's out.

 

[vvs07]

So I have just noticed a potential problem in my build. One channel I have used 220 ohm base resistors and the other channel I have used 180ish resistors. Will this cause any problems in operation. Should I change the 180's out.

This should not be a problem. I would leave it as is.

 

[osscar]

these resistors are meant to prevent potential oscillation.it seems to me that 100 or 200 is not that important - if no oscillation. I like it if everything is the same on both channels but value are not critical 180 or 200 or 220.

 

[Freecrowder]

Would there be any issues with the gain between channels. would they still be the same?

 

[RickRay]

Anyone have circuit boards for this amp? I know there have been a couple group buys.

 

[Mark Johnson]

Nelson Pass posted his full and complete Gerber CAD files (the "blueprints" for a PCB) here in the thread. You could send them off to a PCB fab in China and have 10 copies made for $35 including shipping back to Kansas. Use one, sell or give away the rest.

 

[RickRay]

I was thinking of doing that IF no one else had a couple spare.

 

[Mark Johnson]

I can loan you $20 if $35 is too steep.

 

[RickRay]

Thanks Mark, please send me the $20. PM me for my address.

 

[Freecrowder]

I have a couple of boards here in Oklahoma. I went to PCB fab in China. Mine are 1.6mm thick but more than $35. Mine cost 70 with shipping. I would only sell 2 at $10 each to cover shipping. Let me know

 

[Mark Johnson]

It is possible to pay $70 to have ten AB100 boards fabbed and shipped to you. As shown in the quote below, from a website I highly recommend (pcbshopper dot com), it is also possible to pay $29 for 10 boards.

Click on the image and then click on the white "X" at bottom left, to see it full size.

_

 

[Dennis Hui]

Hi Mark,

Thanks for the info about pcbshopper; it's great to get one-stop comparisons.
I'll definitely check before ordering pcbs next time.

Cheers,
Dennis