lm3875 at 94V

[tonitonitoni]

hi i dont have enough parts at stash,run out of good transformers and hi curent regulators ,and in sort of hurry to finish amp.at +-45v dc is it better to drop 10v with 2sc1943, 2sc5200 or put them in output(dont care i need pair more i have stash) ,sort of using 3875 as first stage but on 94v still ? i know neither solution is good but i need to have spare amp in few days from now,so cant wait for parts to arrive.

i think is lot better to put in output but want to make sure i didnt miss something.

 

[tonitonitoni]

ok this should work, i will try this afternoon to make then post if it is working and why not,but i will use 3875

 

[AndrewT]

Absolute maximum ratings are 94V rail to rail when no signal is present and 84V rail to rail when a signal is present.

Your measured 94Vdc may not be worst case.
How high could that go when mains is at it's highest?

I suggest that you build a non feedback voltage regulator using a Zener and emitter follower (Pass has examples) to bring your supply down to +-40Vdc, or lower.

A capacitance multiplier could also drop significant voltage to enable your chipamp to survive.

 

[tomchr]

Absolute maximum ratings are 94V rail to rail when no signal is present and 84V rail to rail when a signal is present.

I suggest that you build a non feedback voltage regulator using a Zener and emitter follower (Pass has examples) to bring your supply down to +-40Vdc, or lower.

+1

Here's a good intro to zener regulators: Voltage Regulators, Different types, Working principle, Design

Tom

 

[tonitonitoni]

hi, now in another doubt, option 1 or option 2

 

[AndrewT]

Left works. Right does not work.

 

[tonitonitoni]

sry , my mistake i was in hurry and just made mirror of top image.

will this work

 

[AndrewT]

Now both work.

Did you look at Pass?

 

[tonitonitoni]

it burned resistor on negative side, and for few seconds there was 1.5v on output. i cant find Pass labs version of this.

 

[tonitonitoni]

well managed to put 84 volts on -ve somehow, and burned both 3875 ,still not sure how. found stk module which works on 90+ volts.

 

[Nisbeth]

TDA7293?

/U.

 

[tonitonitoni]

have only 1 7293 so cant make stereo, found stk module , on sony powerboard from some component, cant make it work either its only oscilating... dont have enough time to order new parts

 

[tonitonitoni]

its working now with stk 403-130 on unregulated 86v for mid/high, lm3886 on unregulated 80v for bass. thank you for help

 

[Speedskater]

If you have a stash of random transformers, use one as a buck/booster transformer to lower the line voltage.

Bucking Xfmrs

 

[tonitonitoni]

hm, interesting solution. but does bucking transformer has to be same primary wire diameter as transformer i am connecting it to? i sort of need to order some parts now so i will probably order 20 or so lt1083 and that is sort of easy solution to me as i have bigger heatsink stash than good transformers stash.

 

[Speedskater]

Not the primary, but the secondary needs to handle as much current as the main transformer's primary.