slow ramp 48v phantom

[Flatpicker]

Good point PRR, and may very well be the reason I selected the HV version in the first place. I researched all this about 2 years ago but can?t remember exactly why I decided to use the higher voltage version 317. Looks like I need to start keeping notes since I can?t remember squat anymore?

 

[Flatpicker]

Here?s the Slow Turn-On circuit.

 

[rafafredd]

should add a diode from out to in for protection.

 

[hitchhiker]

[quote author="cjenrick"]Talked to Kevin from K and K audio at the show. He has a circuit for a ramped phantom that won't limit current draw. uses a transitor in the ref leg of the reg with a rc network. will get the circuit from Tommypiper tomorrow.
cj[/quote]

would love to see this circuit cj

 

[mhartung]

Hey CJ, I would love to see that circuit as well. I have a bunch of Telefunken mic pres that I want to add phontom to.

Thanks

Mike

 

[CJ]

Tommypiper is still looking for it, but it may be the same one posted by the Mr. Harbin.
There was a new preamp at the AES show that had ramp up, ramp down, and a 30 second mute on the output of the whole amplifier.
Very intelligent designer. Said "Unless you like having the foil from your tweeters land on your desk, use a ramp up circuit!"

 

[Flatpicker]

[quote author="cjenrick"]Tommypiper is still looking for it, but it may be the same one posted by the Mr. Hardin[/quote]I just cropped it from the datasheet and turned it into a .jpg file.

Tim Hardin? Didn't he play at Woodstock? :wink:

 

[CJ]

Sorry! Eyes are going quick. It's that guitar, looks like the same one used at Metskers farm!

 

[SonsOfThunder]

I don't want to post this one until I see it work and sort out any value changes. I got it built up this weekend, but have not gotten to test it yet. Monday is always a pain and I had to order up a new AP 2700 and a few thousand in other accessories today :green: but maybe I can get it in this week and then I'll be glad to share.

Cool thing about this circuit is the expandability of the thing.

 

[hitchhiker]

thanks cj and sonsofthunder, we appreciate the help.

:sam:
Lance

 

[SonsOfThunder]

For your DIY pleasure:

http://www.diyfactory.com/projects/softstartphantom/softstartphantom.htm

Any questions? I doubt it, this is so simple!
Many thanks to KEV for hosting this at the DIY Factory.

Enjoy!
Charlie

 

[Svart]

awesome.. my phantom POPs when i turn it on.. i hate it when it does that. this is a very welcome addition. thanks!

 

[rafafredd]

That´s what I need!!!

Is there a board already for this one? I may work on a board, if you are not doing anything yet...

 

[PRR]

> Any questions? I doubt it, this is so simple!

Mebbe I missed it:

What AC voltage?

If it is nominal 48VAC (a standard value, and you need that much to tolerate low-line conditions), then won't the 510Ω resistor burn-up? Ah, the typically half-watt Zeners (assume 24Vz) will burn slightly before the 510Ω resistor.

10mA is the IEC specified maximum per mike.

For one or two mikes (or a dozen typical 2mA mikes), you are trashing more heat in the R-Z network than in the pass element or the load.

What happens when some idiot plugs in a shorted cable?

 

[Flatpicker]

[quote author="SonsOfThunder"]For your DIY pleasure:

http://www.diyfactory.com/projects/softstartphantom/softstartphantom.htm[/quote]Ah, finally an answer to my question of why not use an LM317...

"The coolest difference between this and the LM317 type app circuits I've seen, is that the ramp in this circuit is not dependent on the load!"

Thanks. :thumb:

 

[hitchhiker]

[quote author="PRR"]>
10mA is the IEC specified maximum per mike.

For one or two mikes (or a dozen typical 2mA mikes), you are trashing more heat in the R-Z network than in the pass element or the load.

What happens when some idiot plugs in a shorted cable?[/quote]


how about Eddie's 470r on the voltage output as a fuse?

http://www.tangible-technology.com/power/Phantom_frying.html

or maybe this circuit could be modded into a slow ramp. It sure is easier to buy a 25v transformer for this voltage doubler circuit.

 

[SonsOfThunder]

[quote author="hitchhiker"]how about Eddie's 470r on the voltage output as a fuse?[/quote] How about a fuse for a "fuse"? :green: Seriously, a fuse between the Q1 emitter and Q2/3 collectors would be my recommendation.

It sure is easier to buy a 25v transformer for this voltage doubler circuit.

So eliminate the bridge rectifier and use the V-doubler with an 18V trafo! It's DIY, baby! This is not so much meant to be a "cookbook" circuit, but a starting point. The max input should be about 55V. You want to pull about 5mA thru the zeners. So figure the resistor value by: (Vin-48)/5mA.

Not so much difference in this regulator circuit and the one that Ed uses. That circuit is going to send a lot of power out as heat as compared to that delivered to the load as he has ~70V at the input of the reg. With an 18V trafo and V-doubler, you'll get about 51V at the input of the reg. Some of the "12V" wallwart trafos will hit 18V with no load...that'll probably work fine for a couple of mics.

For one or two mikes (or a dozen typical 2mA mikes), you are trashing more heat in the R-Z network than in the pass element or the load.

Compromises everywhere, eh? As i said in the description this is a part of another bigger PS project not yet finalized...But I thought since I needed it in other projects that others would as well. On the prototype, I loaded it to 10mA with a 4.8k Ohm resistor and nothing on the PCB got very warm even.

Rafa, if you make PCBs, please make them double-sided...Then I'll buy some from you!

HTH!
Charlie

 

[SSLtech]

Glancing at it quickly, it looks like C3 is slowly charged to the full unregulated voltage through R3. This is fed to the base of the Q2/Q3 darlington, the mutual collector of which is fed from the (lower) regulated 48V. (or 49V... whatever...)

I usually keep NPN base voltages down below the collector voltage... I know that R3 is limiting any potentially damaging current, but that's the only bit I might look at doing a little differently if it were mine... I think you'd be relying on the 1.0V-1.2V drop through the two series emitters of the darlington to stop the base voltage from rising, if the incoming power were to shut off (which presumably is the reason for D6 and D5 being there) then the stored charge in C3 might be able to do some damage through the B-C junction of Q2....

Keith

 

[PRR]

> The max input should be about 55V.

And the minimum input about 51V, right?

55V/51V= 8% variation.... you are asking for the power company and transformer regulation to be better than the mike really needs?

> he has ~70V at the input of the reg.

That's normal in commercial design. You can't expect to know the local utility voltage to 8% precision. 30%-40% over regulated voltage is common in robust (don't crap-out when the light-show starts) regulators.

> How about a fuse for a "fuse"?

10mA fuses are rare. And as I read the specs, the current must be limited, not just fused. Fuses take time to blow.

I over-stated something. A shorted mike cable is no big deal. It can only draw 48V/3.4K= 14mA, no fire or silicon-smoke likely. My worry, especially in DIY, is a short on the raw 48V supply before the 6K8 resistors. Stuff happens.

> the stored charge in C3 might be able to do some damage through the B-C junction of Q2....

Probably not, not with 10uFd. And holding Base to Collector is not all that odd or dangerous.

 

[SonsOfThunder]

[quote author="PRR"]> The max input should be about 55V.

And the minimum input about 51V, right?

55V/51V= 8% variation...[/quote] Uhh...I meant to say "for the given value of R1". If you want to hit the design maximums of 300mW for a TO-92 package, you can go up to 30V drop across Q1 which allows for 78V at the input, you'll just need a new value for R1, but i was trying to make this easy, not a lesson in how to calculate resistor values for zener shunt regulation...that can be found elsewhere on the net...or in a book.

Oh, and if you do the 78V...watch out! Q1 will be hot to the touch! Or you can just use a TIP31 or 41 as I said before.

A shorted mike cable is no big deal. My worry, especially in DIY, is a short on the raw 48V supply before the 6K8 resistors. Stuff happens.

If it were some super high dollar transistor, I might be worried about that but MPSA06 grow on trees, nearly. :green: And they are not so easily blown up. Its an 80V part...