phantom etc for TAB V modules; gobetween kit good? which 48v psu?

[pongi]

phantompower, pad,  etc for tab v76 v72 modules; gobetween kit good? which 48v psu?
jlm says its ramped, true? and how long is the ramping time?
then i'd need a 48v psu for phantom, are there cheap, built ones available?

thanks a lot or every hint!

best

 

[Mike Cleaver]

Lots of cheap and good power supplies on Evilbay.
Wide variety of voltages and amperages.
A quarter amp supply at 48v is more than adequate.
Phantom is a very simple implementation, just a couple of matched resistors and the power supply.

 

[mjrippe]

Ramping is good, especially for V76/72, because these have input transformers that can be damaged by sudden DC pulses.  Even better is to use some high quality non-polar caps between the +48 and the input transformer.  A search for "V72 phantom power" should give you more info here or on gearslutz.

 

[pongi]

thanks!!

1-so anybody can tell if the go between kits from jlm audio needs 48v ac or dc? (sorry for the stupid question)

2-and whats the lowest current it should have ? (for one microphone)

3-anybody know if that go-between kit is really ramped and good enough for a v76 module?
(jlm don't respond to this by email i sent)

thanks!

 

[Harpo]

1-so anybody can tell if the go between kits from jlm audio needs 48v ac or dc? (sorry for the stupid question)

DC

2-and whats the lowest current it should have ? (for one microphone)

Wrong question. You want to know the max.current it could draw.
10mA per microphone (worst case 14mA with a shorted mic cable, leaving nothing for your mic) + (48V- 2V)/6k8=7mA if you fit the status LED to show up when phantom is engaged.
IE 10mA without status LED or 17mA with LED fitted.

3-anybody know if that go-between kit is really ramped and good enough for a v76 module?

Not ramped. The 470R/10uF is only a filter.

Dunno your mics, but some later mics come with an internal switching supply to generate a higher than 48V capsule voltage and these might behave funny with a ramped +48V source.

 

[pongi]

thanks harpi

so a 50mA psu is good for two mics as well.

do you or anybody else knows how to implement a ramping circuit to the go between kit?
it seems that the v modules need that. because of the 1:30 input transformer and spikes who can
burn the transfomer wiring and damage it.

thanks

 

[Harpo]

thanks harpi

so a 50mA psu is good for two mics as well.

do you or anybody else knows how to implement a ramping circuit to the go between kit?
it seems that the v modules need that. because of the 1:30 input transformer and spikes who can
burn the transfomer wiring and damage it.

This will not be a circuit to the go_between kit but within the go_between or whatever, or it would only ramp when you initially power the unit on. The ramping will have to be done between the channels phantom switch and the 6k8 phantom resistors, FI at the 470R at the go_between. IE on/off switched +48V to collector of a NPN, capable of Vceo >48V, emitter to this 470R, maybe 15k between collector/base, maybe 22-47uF between base/shield, diode between emitter/base, anode side to emitter. A maybe 100k between collector/shield will drain the charged cap at the r/c in reasonable time to start ramping again.
I fail to see how a ramped phantom could prevent damaging your transformer if some ******* pulls out a phantom powered mic or disconects the xlr cable. Phantom voltage is common mode, so there won't be a turn on spike across the transformers primary winding. Just make sure the 6k8 phantom resistors are matched and have sufficient power rating in case of a shorted mic cable, else you catch the feared spike because they won't fail simultaneously.

 

[mjrippe]

Again, the best option for V7x modules is to isolate the DC with quality capacitors.

 

[pongi]

ok thanks guys

i found this thread:
http://www.groupdiy.com/the-lab/v72-phantompower-question/

and according to all suggestions, my plan is to:

1:buy the go between kit, and replace the 10uF with a 1000uF in the kit
  according to:"jlm replied that when using a 1000 uF cap instead of the 10uF cap, The phantom will be slow ramp"

2:do the following to block dc:"If you run the P48 feed to the input XLR your could put 2 100uF/63V caps between the XLR and V72 Input to block DC."


3:could this psu be good for the phantom supply?
https://www.distrelec.ch/schaltnetzteil-5-3-w-1-ausgang/mean-well/ps-05-48/366236

good plan?

thanks pongi

 

[ruffrecords]

it seems that the v modules need that. because of the 1:30 input transformer and spikes who can
burn the transfomer wiring and damage it.

thanks

That's a new one on me. Where did you find out about this?

Cheers

Ian

 

[pongi]

h&e studiotechnik:

"-Both channels are coming up with switchable +48 Volts ramped Phantom, including indicator lights.
(ramped +48V doesn`t harm classic input transformers with high ratio like V72, V76, V77 (1:40!!!!!!!!)"

mercenary audio:

"Theoretically this shouldn't pose a problem for a none center taped transformer, but in practice there is always the capacitive property; primary to core or the Faraday shield, then also the primary windings to secondary windings etc. These will become charged if 48V DC is applied and the transformer (standard tube input x-former and tube mic outputs have ratios from 1 to 10 and even higher) acts like a ignition coil creating approx. 1 to 2KV!! on the transformers secondary. Mic pres with no damping resistor like the V76 (input transformer has 1 to 30 ratio) can even create up to 3KV!!!! this is enough for a millisecond energy burst that is powerful enough to burn microscopic holes into the insulation."

and mercenary audio about dc-blocking caps that do NOT WORK!!?!:

"DC blocking capacitors do not help at all because the time required to charge the capacitive property is still too much, and sometimes even make it worse due to resonance spikes and every time the microphone gets disconnected while the phantom power is on, the entire energy of those caps is dumped charging the windings of the transformer and pre-magnetizes the core."

link:
http://www.mercenary.com/youbrmeintrd.html


and the solution from them is:

"If you want to use phantom power then it is necessary to use a ramped 48V supply with a time constant of more than 5sec. This will take care of the problem posed by this energy burst, simply by having a slower time constant than the capacitive property of the transformer can charge. There is still a slight chance that something will get burned in the process, as you are dealing with historic/vintage parts, which had a maximum shelf life of approximately 25 years."


SO IT SEEMS ALL HAVE DIFFERENT SOLUTIONS AND NO CONSCENSUS??

what to do??

thanks

 

[mjrippe]

Interesting point about the blocking caps not working.  I would think that if you used blocking caps AND ramped phantom you would be about as safe as one can get.

I have personally replaced a V72S input transformer where the secondary had gone bad just as described.  It is an expensive repair!