Flatpicker
Well-known member
[quote author="sismofyt"]I don't remember just how HV the LM317HV is.. isn't it just 57V?...[/quote]Yes, max out is 57V. The max in/out diff is 60V. The emitter follower and big cap trick would be cool to try.
slow rise phantom power schem
- Thread starter rafafredd
- Start date
Help Support GroupDIY Audio Forum:
Flatpicker
Well-known member
[quote author="Greg"]The FMR Audio RNP that I have has the ramping phantom power. Don't have any schematics though. I didn't know why it did that, but this sheds some light on why they did it.[/quote]FMR RNP wouldn't have the same problem as it doesn't use a transformer. FMR probably did it so the user wouldn't hear a loud "thump" when the pp was turned on. I'm not 100% on this, but I think the FMR uses a PIC/DAC to control the +48V.
[quote author="sismofyt"]I have more than 30 old Telefunken/TAB/Siemens modules and a bunch of other gear with old, and perhaps fragile, trannies. Never had a problem.
I've seen that quote from Ollie, and he knows a LOT more than me, but in practice I've not encountered any problems. Same thing with phantompower and ribbonmics.[/quote]
ok, even the federal broadcast stations here in germany used to feed phantom via 2x 6k81 and no ramping, blocking caps or anything, with their v72/v76 setups. also, e.g. the neumann external phantom psu's doesn't have blocking cap's in the audio lines going to the pre... makes you think that it actually is not a problem, since those guys should have known...?!
but then again, as far as i understood ollie, it's supposed to be a slowly advancing process, probably unnoticeable in an early stage? so maybe no-one ever got aware of the problem, because by the time any xfromer deterioration would have become noticeable, the v7x valve setups were replaced by new consoles?
also, many of the old modules people use as micpre's nowadays never have seen phantom on their input primaries, since they originally were used in a different part of the audio chain (e.g. v72 as a line/booster/separation amp...), so it might take some time to really do harm to the trannie if you're the first owner to ever apply phantom.
of course it may also be due to different materials or techniques changing over the years, which were employed for making the same transformer in a single module, some resulting units being more sensitive than others? faults might even be due to other things, like general deterioration of material...? so the actual reason of bad xformer performance might be harder to track down? just a SWAG though, i'm not an expert =o)
[quote author="cjenrick"]I am wondering about ramp down. That would be tougher, because you have to catch the spike at the x-former primary, on the other side of the 6.8 k resistors, if you are using any. [/quote]
dumb question: if you use that 100 ohms in series to 100uf which ssltech suggested, it should automatically slug the discharging when you put the on/off switch to the "off" position, no? provided the "off" is connected to ground, the cap should discharge via the resistor, providing the same time constant as for turn-on.
of course this doesn't save you from spikes if accidentally (un-)plugging the mic cable with phantom on :?
I've seen that quote from Ollie, and he knows a LOT more than me, but in practice I've not encountered any problems. Same thing with phantompower and ribbonmics.[/quote]
ok, even the federal broadcast stations here in germany used to feed phantom via 2x 6k81 and no ramping, blocking caps or anything, with their v72/v76 setups. also, e.g. the neumann external phantom psu's doesn't have blocking cap's in the audio lines going to the pre... makes you think that it actually is not a problem, since those guys should have known...?!
but then again, as far as i understood ollie, it's supposed to be a slowly advancing process, probably unnoticeable in an early stage? so maybe no-one ever got aware of the problem, because by the time any xfromer deterioration would have become noticeable, the v7x valve setups were replaced by new consoles?
also, many of the old modules people use as micpre's nowadays never have seen phantom on their input primaries, since they originally were used in a different part of the audio chain (e.g. v72 as a line/booster/separation amp...), so it might take some time to really do harm to the trannie if you're the first owner to ever apply phantom.
of course it may also be due to different materials or techniques changing over the years, which were employed for making the same transformer in a single module, some resulting units being more sensitive than others? faults might even be due to other things, like general deterioration of material...? so the actual reason of bad xformer performance might be harder to track down? just a SWAG though, i'm not an expert =o)
[quote author="cjenrick"]I am wondering about ramp down. That would be tougher, because you have to catch the spike at the x-former primary, on the other side of the 6.8 k resistors, if you are using any. [/quote]
dumb question: if you use that 100 ohms in series to 100uf which ssltech suggested, it should automatically slug the discharging when you put the on/off switch to the "off" position, no? provided the "off" is connected to ground, the cap should discharge via the resistor, providing the same time constant as for turn-on.
of course this doesn't save you from spikes if accidentally (un-)plugging the mic cable with phantom on :?
sismofyt
Well-known member
I really do not worry about it. I can sleep safely at night..
Winston OBoogie
Well-known member
...
sismofyt
Well-known member
Well, maybe when I'm 64 all my luvly TFK modules are screwed because I didn't listen to that ol' man way back in 2004 :?
I don't doubt there's some truth in the matter. I just never had a problem...
I don't doubt there's some truth in the matter. I just never had a problem...
sismofyt
Well-known member
Winston, do trannies age? I can see the insulting materials could go bad, but I've looked at all my many TFK/Siemens trannies and they all look like they we're made yesterday.. :?:
SSLtech
Well-known member
Well, in reality, the 'slow ramping' is actually just a filter, which will move the 'pop' down and to the bottom of the audio band, as well as making it less intrusive in level.
I have a couple of pres on the bench right now.... transformer and transformerless... I think I'll try it out. On the transformerless preamp, I did put a bit of ripple on the phantom feed and I do actually notice it's pretty bad a high gains using a transformerless microphone... i think that the CMRR of this setup might be quite poor... Anyhow, it perhaps ties in with what sismofyt is saying...
Other than that, in large professional consoles the 48V supply is miles away, and there's almost always lots of filtering after long lines. Since a 100Ω/100µF combo will do nothing but good in terms of filtering as well as cause a slow ramp up/down, I see no reason at all not to do it.
And Tim, you're right of course. -switching to 0V will make the cap ramp down.... duh! -I shoulda thoughta that!
I'll try it this evening.
keith
I have a couple of pres on the bench right now.... transformer and transformerless... I think I'll try it out. On the transformerless preamp, I did put a bit of ripple on the phantom feed and I do actually notice it's pretty bad a high gains using a transformerless microphone... i think that the CMRR of this setup might be quite poor... Anyhow, it perhaps ties in with what sismofyt is saying...
Other than that, in large professional consoles the 48V supply is miles away, and there's almost always lots of filtering after long lines. Since a 100Ω/100µF combo will do nothing but good in terms of filtering as well as cause a slow ramp up/down, I see no reason at all not to do it.
And Tim, you're right of course. -switching to 0V will make the cap ramp down.... duh! -I shoulda thoughta that!
I'll try it this evening.
keith
Winston OBoogie
Well-known member
...
sismofyt
Well-known member
Thanx man! I went over an ol' Soundcraft Series II last year... some of the 6k8s were WAY off, I even found a 5k6 with a 6k8. The trannies, small Sowters, all seemed fine..
DynaMurphy
Member
This is an excerpt of the 1969 Beyer Dynamic catalogue.
"BEYER-DYNAMIC'S AF input transformers are made by a patented winding method similar to ring core transformers. They are famous for their small dimensions and high transmission quality. The world's largest and best known electronics manufacturers use there components in professional amplifiers, studio mixers and other equipment wherever highest demands are made in respect to frequency response, lowest distortion and insensitivity to stray magnetic and electric fields.
These transformers can however only be used in circuits where AC voltages are low and no DC loads are applied."
So how can we avoid a DC load when we need phantom power?
Murphy
"BEYER-DYNAMIC'S AF input transformers are made by a patented winding method similar to ring core transformers. They are famous for their small dimensions and high transmission quality. The world's largest and best known electronics manufacturers use there components in professional amplifiers, studio mixers and other equipment wherever highest demands are made in respect to frequency response, lowest distortion and insensitivity to stray magnetic and electric fields.
These transformers can however only be used in circuits where AC voltages are low and no DC loads are applied."
So how can we avoid a DC load when we need phantom power?
Murphy
Winston OBoogie
Well-known member
...
as for dc blocking caps - see quote from ollie on page 1... :wink:
just a guess: being from 1969, i suppose these are trannies intended for solid state designs, i.e. with a low step-up ratio? thus a 48v-spike shouldn't pose that much of a problem... but probably the denial of dc loading is rather aiming at the avoidance of core magnetization and resulting low-freq distortion.
just a guess: being from 1969, i suppose these are trannies intended for solid state designs, i.e. with a low step-up ratio? thus a 48v-spike shouldn't pose that much of a problem... but probably the denial of dc loading is rather aiming at the avoidance of core magnetization and resulting low-freq distortion.
[quote author="Winston O'Boogie"] As a matter of fact, I just racked up a V72 that recently sold on eBay and I used all original iron but new circuitry and mods etc. (I'll post a picture of the insides if anyone is interested)[/quote]
yes please! can you give details about the mods?
to be exact, there were different versions of these modules - v72, v72a, b, c, and s. functionality differed somewhat, and not all companies made all versions of the modules. the companies were tab, telefunken, siemens and maihak, and i'm pretty sure each company had their own plant.
so no low freq distortion due to magnetization? cool.
yes please! can you give details about the mods?
to be exact, there were different versions of these modules - v72, v72a, b, c, and s. functionality differed somewhat, and not all companies made all versions of the modules. the companies were tab, telefunken, siemens and maihak, and i'm pretty sure each company had their own plant.
so no low freq distortion due to magnetization? cool.
Winston OBoogie
Well-known member
...
Winston OBoogie
Well-known member
...
winston,
very interesting v72 business :razz: couldn't find your auction, but sometimes the "completed items" search doesn't work somehow... so if you do get some time to post those pic's... :wink:
so you've owned quite a lot of v72's - so you collected those british modules, like germans do here with the german modules, amassing them in their garage?
I've seen a schematic of the v72s, but can't remember the differences to the german v72. only differences in the feedback loop? different biasing? or different transformers, even?
never heard of v72c, what's that about?
if there's a v72f... the "f" could mean "remote-controllable", f being the first letter of german "fernbedienbar"? wouldn't make sense, though, since there's nothing much to be remote-controlled! :?
have you owned a v72t? i always wondered what that germanium sounds like!
as for the mods:
- i suppose you simply bridged the 1uf cap between the i/p primaries for lower bass rolloff?
- can you post or pm a schematic of the emi attenuator? i mean, in comparison, the w77 combined feedback/attenuator switch has coarse steps really.
- better supplies? do you mean active stabilization?
- about the pcb's and everything, do you have to change capacitor values for that, as to make up for changes in wire / pcb track / etc. capacitances? i'm not that much of an expert when it comes to tweaking valve circuits, but i suppose that might be an issue due to the high Z of valves?
regarding phantom:
sure, if you turn phantom off before un/plugging anything, a big time constant or otherwise ramped supply should be fine. the real problem seems to be accidental un/plugging with phantom on - dunno if there's any cure for it? zeners were my first thought, too, but the argument of not de-floating the signal made me think otherwise... hum :roll:
very interesting v72 business :razz: couldn't find your auction, but sometimes the "completed items" search doesn't work somehow... so if you do get some time to post those pic's... :wink:
so you've owned quite a lot of v72's - so you collected those british modules, like germans do here with the german modules, amassing them in their garage?
I've seen a schematic of the v72s, but can't remember the differences to the german v72. only differences in the feedback loop? different biasing? or different transformers, even?
never heard of v72c, what's that about?
if there's a v72f... the "f" could mean "remote-controllable", f being the first letter of german "fernbedienbar"? wouldn't make sense, though, since there's nothing much to be remote-controlled! :?
have you owned a v72t? i always wondered what that germanium sounds like!
as for the mods:
- i suppose you simply bridged the 1uf cap between the i/p primaries for lower bass rolloff?
- can you post or pm a schematic of the emi attenuator? i mean, in comparison, the w77 combined feedback/attenuator switch has coarse steps really.
- better supplies? do you mean active stabilization?
- about the pcb's and everything, do you have to change capacitor values for that, as to make up for changes in wire / pcb track / etc. capacitances? i'm not that much of an expert when it comes to tweaking valve circuits, but i suppose that might be an issue due to the high Z of valves?
regarding phantom:
sure, if you turn phantom off before un/plugging anything, a big time constant or otherwise ramped supply should be fine. the real problem seems to be accidental un/plugging with phantom on - dunno if there's any cure for it? zeners were my first thought, too, but the argument of not de-floating the signal made me think otherwise... hum :roll:
Winston OBoogie
Well-known member
...
Similar threads
- Sticky
