Help designing Input and Vas stage's

[DoomPixie]

Useing the original transformer wired up to the new Power Supplu PCB i get +/- 35V rails!
on my DMM they look good, no fluctiation atall, stable at +35.7 and -35.6 under load they should even out i think
I am going to build the psu into its own enclosure and either make two mono amps in the same style enclosures or two amplified speakers.. they will be connected together useing powercon power connectors or xlr connectors ( havent decided yet, want to use powercon but dont have enough chasis connectors here, have enough here to use XLR..)
Owen

[CBS240]

Hi Owen,

One thought might be to consider using a voltage regulator circuit for the front end.(all but the drivers and outputs) This will improve PSRR and crosstalk especially if you use one PS to run 2 seperate channels, if each channel front end has it's own regulated voltage source from a single power supply. Better quality is........well, better quality.

[DoomPixie]

Good thinking CBS240, i will add links to the PCB's when i make them so i can seperate the power rails.. that way i can still build and test the amps with this single power supply but then i can add another transformer and regulated supply to supply the front end at a later date. Only drawback to this that i can see is intorconecting the amp and power supply enclosures. unless i just make up regulator boards to regulate the V+ and V- that is already in the amps enclosures. I will ahev to think about it, to begin with i just want to get them up and running, i will add the links in though so i can change it at a later date without haveing to remake the pcb's that way i can just remove the links and it's all good no matter which route i use.
Thanks,
Owen

[DoomPixie]

will the transistors for the Vas and CCS need heatsinks?
Can i use BD140 for the input stages CCS aswell or is it only suitable for the Vas CCS?
just checking because i have started trying to lay out the PCB's for them. hard work though.. surley there is a free program somewhere that will convert a schematic into a PCB automatically?
Thanks, Owen

[jaycee]

At 35V with about 7mA through the VAS, no.

You could use BD140 for the input stage current source yes.

EAGLE will do that, and you should be able to fit your PCB into the dimensions allowed in the unregistered version

[DoomPixie]

i did it in the end useing ltspice and expresspcb.. managed to get the ltspice netlist talking with expresspcb. the finished circuit on my first test board is only like 3" by 3" and thats the first prototype.. it will probably end up in the bin..lol..
many thanks, Owen

**goes off to etch the pcb**

[DoomPixie]

Hopefully the rest of the components will arrive tommorow. pcb is etched. have to wait for my drill bits to arrive tommorow though before i can drill the pcb unless i can find a small bit somewhere. will go and look now. if i find one i can drill it and start installign the resistors tonight
Owen

[jaycee]

I had experience of this recently. I managed to get some 0.6mm, 0.8mm and 1mm HSS bits from eBay for quite cheap. They are ok for drilling SRBP based board. You really do need a drill press though.

[DoomPixie]

i have always used my dremel clone , problem is i can only find 0.8 and 1.2mm drill bits at the moment, have some new ones on order that should be arriveing tomorow though.
i have already found a few errors on this pcb, like the transistor pinouts are wrong. but i will work with it as first prototype just too see if this thing works, no doubt i will find more that i want to change on for the final pcb. like the layout and mabey use bigger tracks and space the components out a bit more.. mabey diffrent capacitor footprints. i think i am going to go and download eagle and try and get it to work again, downloaded it a couple of weeks ago but couldnt get it to install properly. sounds like it is just what i need though.
many thanks,
Owen