Power supply design w/ tl783 problem

[Mailliw]

Hello,

I am adapting the G7 power supply (see here) to produce +32V and +70V for my Neumann M147 microphone (previous discussion). The 180V after the rectifier is split to 90V using two 5kOhm, 5Watt resistors. The 90V feeds two TL783 regulators to give 70V and 32V.

When I connect the TL783s, their outputs are low, ~28V. The voltage at the second filter cap drops from 90V to ~30V.

Schematic:

BIG

Any help would be appreciated.

Thanks,
William

 

[guavatone]

I wouldn't do it like that!

At least get a different 2nd transformer. I think you are asking for danger by dividing AC like that. :twisted:

I would splurge for transformer with 3 windings, especially with an M147.

 

[Kamel]

the divider can only work when no current is taken, in that case the 2 tl783 drawn current, so the 30 v seems normal, if you don't want to buy an other transformer, you have to know the total current needed, calculate the drop resistor by ohm'law to get the right voltage 90v at the tl783 input, do a thirst stage régulation to get your 70 v and in serie behind the first stage put the second regulation stage to get the 32 v, remember that all current pass through the first stage regulation, you will need a heater for that
and of course never forget once,

Hi voltage is DEATHLY DANGEROUS!!

 

[Samuel Groner]

Or replace the voltage divider with a simple zener regulator:

www.tpub.com/content/neets/14179/css/14179_210.htm

Samuel

 

[Mailliw]

Thanks for the replies.

I suddenly realized the second transformer has dual primaries, so I put it in series (was in parallel) and I get 98V after the rectifier.

Is it best to run the regulators as parallel branches off the 98V or cascade them (32V reg off 70V regulated)?

And for some reason, when I was testing on a bread board, the regulator output cap (10uF/250V) got really hot and almost burst.

Anyway, I am on the right track now, thanks guys!!!!

 

[Kamel]

take each secondary to do each regulation, don't put them in série,use them floating, as it you will reference the ground by the minus pole of the regulated output, use drop resistors, and better, like neumann does by the past use successive RC filter to lower the input voltage of each regulator, if not they will heat too much, the heat of your cap is maybe due to underrated voltage cap?

and remember Hi voltage is DEATHLY DANGEROUS!!

 

[Mailliw]

I finished a week or so ago, it works perfectly and the mic sound great!

Thanks everyone!

 

[RedNoise]

noob question : Do you think it sounds "better"??(rather than N149A)
thx.
spec.

 

[Mailliw]

[quote author="RedNoise"] noob question : Do you think it sounds "better"??(rather than N149A)
thx.
spec.[/quote]

Unfortunately, I've never tried it with the original power supply. I imagine it probably sounds the exact same.

And, I just found out that the N149A contains some extra mic signal circuitry that balances the output (and maybe more?), see this thread.

I am not too worried though :thumb:

 

[RedNoise]

thx mailiw... :grin: