sca n72

hey i tried posted this over at the sca forum, but there doesn't seem to be much traffic over there so i was hoping someone here could help me.

i finished building 2 sca n72 revision 2.2 or 2.5 not sure witch one.  the first time i powered up my r40 resister was to hot so i rewired the input transformer and that problem went away.  so i got out my dmm to calibrate the unit and the most volts i can get to q6 is between 9 and 10, it's supose to be around 21.5 i think

any ideas on what the problem could be, the one i could think of is i skimped out and got a voltage regulator lt1075 or 1085 can't remember witch one from radio shack, the bom uses LT1085CT#PBF-ND.  could that be causing that problem?

i did hook it upto my interface and tried to get signal through it just to check, when i flipped the phase switch it would spike the input for just a sec but that's the only thing that happened.

only other thing is i have jumper heads on j2, pins 1 and 2 of j3 and 4-( the ones by the xlr connectors)


also one more question, when wiring up the carnhill input transformer do the leads you make just have to be soldered to the pins on do they have to touch the base of the pins as well?

Maybe you could link to the schematic or something, as then it would be that much easier to reference exactly what you're talking about.

http://www.seventhcircleaudio.com/N72/N72R31/docs/n72_sch.pdf

bump

Is the entire 24V rail down to 9 volts or just the collector of Q6?

When you see lower voltages than you would expect. Turn of the unit and check for dc resistances (to gnd for instance)

Why rewire the tranny when R40 went too hot? Did you followed the building pdf step by step and wired as written? And have you been checking all resistors with DMM one by one before soldering etc???
I think i had R40 getting too hot also, are you talking of the 2watt or 1/2 watt carbon resistor? If yes then IIRC you have to turn the trimmer the one next to R40 fully CCW, but please refer the building document, and check everything back carefully, like transistors in the right way an the right one, electrolytic capacitors soldered in the right way, as well as the tantalum, if not then you need to change them, and transistors also, wrong way means ruined in most cases...
And if still stucked the designer of the SCA's will help you ASAP, just mail him directly.
Just my 0.00002 cents.
Good luck  

i had a problem on a 72 model and the help from SCA was non existent.

i had to trace the circuit and found that one one of the pcb "thru holes" was open!!!!

i had to stick a small piece of wire thru pcb to complete the circuit, its working ok now, but thats the last time i deal with SCA...

No problem for support on my side, i bought them 2 years ago IIRC, and if the SCA Forum was not efficient i remember sending a mail to the designer directly and he responded so...., but hey maybe your problem was known and not assumed, my PCB version was the latest tough, everything went fine from A to Z, i did one mistake that's all....

i found out that i wiring the output transformer wrong, i wiring it like the 2.5 directions stated and apparently 2.2 was different so i'm going to try that.


when r40 was too hot the other thing i did was reflowed a couple places i thought could go either way on how good the connection was.  also on this circuit there is a conn 3 that isn't on any of the other ones , does anyone know what to do with that, do i need to put a jumper on it?

Ok i just Pm'd you the mail of the designer Tim Ryan, try your questions there, you'll see, i'm sure he will get back to you, well hope so, if not then repost over here.