6AL5 for Slow Start Phantom

I thought this might work for a slow start phantom for saving input transformers, ribbons, and all that stuff.

Just wanted to run it by this place so I don't rip the chassis up for nuthin.

Heater warm up and cool off would provide ramp up and down.

Too much noise?
Using dc on heater off course.
What say?

Your input/output are reversed. Input should go to plate, output to cathode.

I think leaving the 6AL5 in a cold-cathode state (heater switched off), with the plate energized, would be detrimental to its longevity.

Why not just use an R-C filter with an appropriate time constant? That's how it's usually done. To avoid excessive voltage drop, you'd use a small-ish R and a large C. To turn off phantom and bleed off the charge, you could disconnect from the supply and connect to another resistor to ground, also chosen for an appropriate time constant.

Doh on the polarity.
Fixed the drawing.
thx.
figured a tube in the phantom circuit will provide warmth to the signal. :razz:

Doh again. Why not use the 6AL5 instead of the solid state bridge?
No switching noise to the mic and built in warm up time!
I'm yanking out those nasty 1N4001's tonight.

Rock Over London.
Rock On Chicago.
RCA. We bring noiseless rectification to your home.

they are a dandy detector out to many megahertz, so make sure some of those things you drew with the plates together say picofarad on them. =)

slow start phantom for saving input transformers, ribbons, and all that stuff

Click to expand...

I never understood that: Phantom-Power is supposed to put no voltage on the both signal lines - only in relation to GND there is voltage-flow. Right or Wrong? If right, it shouldn't make any difference if the 0 Volts come at once or slowly. Or did I miss an important point?

I don't mean this as provocation but I'm really interested since this is often mentioned for te V72 and I wonder if slow-start really makes sense for phantom..

Chris

You can use a simple 300 ohm resistor and a 330uf cap will give a short ramp up, very simple and works well, better than that you can use a cicuit like Bryston uses on their Pre, a 5 second delay, using a relay and a TC circuit.

Just a thought....

[quote author="Mike Keith"]You can use a simple 300 ohm resistor and a 330uf cap will give a short ramp up, very simple and works well, better than that you can use a cicuit like Bryston uses on their Pre, a 5 second delay, using a relay and a TC circuit. It mutes the output for 4 seconds.
Just a thought....[/quote]

[quote author="chriss"]

slow start phantom for saving input transformers, ribbons, and all that stuff

Click to expand...

I never understood that: Phantom-Power is supposed to put no voltage on the both signal lines - only in relation to GND there is voltage-flow. Right or Wrong? If right, it shouldn't make any difference if the 0 Volts come at once or slowly. Or did I miss an important point?

I don't mean this as provocation but I'm really interested since this is often mentioned for te V72 and I wonder if slow-start really makes sense for phantom..

Chris[/quote]
The 48v hits the amp in a condenser mic for example and creates a pop, same thing when you power up a console, the speakers pop..

When the voltage is "comming up" fastly, from 0v to 48v, the transformer and/or the caps blocking phantom sees it as AC, and not DC... just the first wave.

When the voltage is "comming up" fastly, from 0v to 48v, the transformer and/or the caps blocking phantom sees it as AC, and not DC... just the first wave

Click to expand...

That's what I mean: There shouldn't be ANY voltage be 'coming up' for the transformer - neither AC nor DC! If so, you'd have an DC-offset probably caused by not-so-well-matched 6,8k Resistors. And if so, the DC will stay - if coming up fast or slow.

The 48v hits the amp in a condenser mic for example and creates a pop, same thing when you power up a console, the speakers pop..

Click to expand...

That's true. I can understand this better.

Chris

Yeah. I think you are right. If it comes up together at the same time, even if it´s very fast, I think it should cancle, just like DC...

I´ve contacted oliver and asked him for a link where he describes the problem and the need for ramp phantom, specially with vintage, very high turns ratio transformers, like in the telefunken V series...

ok, i stuck a 12AL5 in there, tied the plates and cathodes together, not much to it:




little bugger...





which makes shields a pain, but...found one.....



ramps up like jello....5 seconds per square, so 10 seconds before any action, then nice slow ramp up and down, about 35 seconds til full power, just enough time to run and unplug the ribbon you left plugged in the nite before. Chewed up a little voltage I was tring to get rid of with resistors, so a non switching noise ramped phantom, just for drilling out a socket hole, I am a happy camper. Gotta love these new scopes, easy to trace stuff like this.



Plus, it's like , tube analog, dude! How many freaks own a tube phantom supply?


:thumb:

Let us know how it sounds... :green:

It sounds killer, and I haven't even tried it yet.
The basis behind all of my posts! :grin:

Nice job, CJ! Original thought, too, I think.

If someone is looking for a solid-state something like this, don't forget the slow-ramp ckt that i posted a while back...

Hosted by the DIY Factory here

Enjoy!
Charlie

I tried it out last night and it works fine. No new noises or anything. Can't say it sounds less like solid state diodes as far as any switching garbage. But sometimes diodes, if they get nuked over a long peroid of time with line spikes, can start to develop stuff from being partially injured, so it's nice not having to worry about that. Aslo, some solid state brands can be worse than others. So no screening requied or special diodes to buy like Freds or something. Those darn Freds are expensive, and a pain with ship/recieve.

You know what, I looked at the delay curve on my old solidstate supply and it was not all that bad. The filter caps take a while to charge, especially with any ssries R in there, so you already have quite a time constant built into a pi network. The only way I see to get a good spike would to be to switch the phantom off and on.

So if you do not have a ramping phantom, I would not sweat it.