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Help to rack v72 telefunken
Old 26th January 2009
  #1
Gear Nut
 
🎧 15 years
Help to rack v72 telefunken

Hello all

Any one know how build v72 rack??

i got all the chasis ready but i need to know how do the elctric conections

like:

leds
phamtom power
on/of switch
pahse
atenuator potentiometer
tnks for advance

ika
Old 19th October 2010
  #2
Here for the gear
 
🎧 10 years
Quote:
Originally Posted by lokillo77 ➑️
Hello all

Any one know how build v72 rack??

i got all the chasis ready but i need to know how do the elctric conections

like:

leds
phamtom power
on/of switch
pahse
atenuator potentiometer
tnks for advance

ika
Hi,
Did you figure out how to rack it? I have Telefunken v72 I have to rack so step by step tutorial will be helpful.
I am not so good at electronics so I will ask someone to do it for me anyway but I'd like to know what kind of parts I have to have first.
So far I have only the module, will buy the pinout but need to know what's next.
Also, was thinking to do a mod for the gain control(do I really need it?) so any help here will be appreciated .

Thanks in advance!
Old 19th October 2010 | Show parent
  #3
Lives for gear
 
🎧 15 years
I would even donate via paypal a couple buck to whoever can put together a decent racking tutorial
Old 19th October 2010 | Show parent
  #4
Here for the gear
 
🎧 10 years
Quote:
Originally Posted by charlesaustin ➑️
I would even donate via paypal a couple buck to whoever can put together a decent racking tutorial
Charlesaustin, have you tried to rack such modules? I mean, at least if someone can tell me the parts I am going to need?
By the way does v72(7vt in my case) have internal PSU?
Old 19th October 2010 | Show parent
  #5
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frans's Avatar
 
10 Reviews written
🎧 15 years
I urge everyone who has one of the old modules to get professional help for racking those. If you got something that good, get the most from it. It's useless to "save" a few bucks in those cases. There are things you don't know about connecting them, their relation to phantom power and much more. Get help!
Old 19th October 2010 | Show parent
  #6
Lives for gear
 
🎧 15 years
I am well aware of the issues in racking things up. I have a tech that has restored various things for me....... It would be very time/$ saving to hand him step by step instructions.
Old 19th October 2010 | Show parent
  #7
Lives for gear
 
🎧 15 years
Quote:
Originally Posted by frans ➑️
There are things you don't know about connecting them,
LOL. Hence the thread. But I suppose it's understandable that the people who have a business racking these things don't want to let that info out.
Old 19th October 2010 | Show parent
  #8
Lives for gear
 
🎧 15 years
well i could point you towards the standard guys in germany racking these. but honestly most of them are nothing but a rip off. so i sent you a pm.
Old 19th October 2010 | Show parent
  #9
Gear Addict
 
13 Reviews written
🎧 15 years
I have one also to rack. Where did you buy the rack to put the V72?
Old 20th October 2010 | Show parent
  #10
Here for the gear
 
🎧 10 years
so the conclusion is that there is not instructions how to rack these. It's some kind of secret )
Actually, do you have to put the module in a rack or you can do it without it.
At least can someone tell me what I have to buy so I can pass it to the nearest tech?
Old 20th October 2010 | Show parent
  #11
Lives for gear
 
DONNX's Avatar
 
🎧 10 years
Go to HEstudiotechnik in Germany. They are the best at racking vintage german modules. Out.
Old 20th October 2010 | Show parent
  #12
member no 666
 
Fletcher's Avatar
 
🎧 15 years
Its not that difficult - the only hard part is finding the connector. The "pin out" is readily available on the internet. They take 220vac to run, which in North America requires a "step up" transformer [readily found at any hardware store for about $15-20 -- 1600w will be more than sufficient].

In terms of the physical "racking" - that requires metal work. If you're not planning on traveling with them get a Mid-Atlantic "universal rack shelf" and while you're at the hardware store pick up some "industrial velcro"... apply the velcro to the shelf and the module and it will sit on the shelf where you left it without a struggle.

Don't try to add "gain control" unless you're an actual expert [which it is apparent, you're not] as that will open up a can of worms you absolutely don't want to know about. V-72 units are fixed gain [34db if I remember correctly] - the mic signal goes in and comes out 34 [IIRC] louder - end of story. They're obviously very useful that way.

The connector was made by Tuchel. It can probably be found through Sonic Circus, Funky Junk or Vintage King [and I'm sure a number of other sources but you might have to dig deeper to find them]. If you get the connector, some wire, some connectors, know how to solder its about a 30-45 minute job to wire these things. If you don't know how to solder then you will want to send these things out to someone who does [or seriously, its a handy skill to have, perhaps worth learning].

All that said - I don't know where you got them or if they have seen proper maintenance in the last 50+ years. There are internal parts that fatigue due to heat that require an actual tech to repair / maintain. I might suggest a visit to Dave Hecht's forum on R/E/P [you can find a link to R/E/P in my signature file]... there are some VERY serious techs who hang there, I'm sure most of them can solve your problems in very short order.

Peace.
Old 21st October 2010 | Show parent
  #13
Here for the gear
 
🎧 10 years
Thanks for the reply Fletcher!
About the connector, will this work 1 x 12 Pin Tuchel Telefunken Siemens TAB V72 V76 - eBay (item 310256533526 end time Oct-29-10 15:30:43 PDT)

Then, what other connectors will I need, like XLR'S etc and what brand are recommended. How about the wires?

How about the power supply, I will use mine in Europe so I am fine with the 220v. Will I need external PSU or v72 has inbuilt one? What's the deal with the phantom power - what is needed there?

About the mods. I am not planning to the them by myself but just want to know about them. So, you say the gain control mod is not needed. There is instructions on the net how this can be done.

Is a low freq cut module a plus?

Sorry for the many questions but just trying to educate myself.
Thanks in advance!
Old 21st October 2010 | Show parent
  #14
Lives for gear
 
el cochino's Avatar
 
🎧 15 years
I have a Neue Heimat rackmount for my v72s and I can only recommend it!

Old 21st October 2010 | Show parent
  #15
member no 666
 
Fletcher's Avatar
 
🎧 15 years
Quote:
Originally Posted by kardinal ➑️
Slow internet where I live so I didn't take the time to open the link... the description sounds right.

Quote:
Then, what other connectors will I need, like XLR'S etc and what brand are recommended. How about the wires?
XLR's TRS TT - wire it to the patchbay... they're yours, how are you going to use them?

Quote:
How about the power supply, I will use mine in Europe so I am fine with the 220v. Will I need external PSU or v72 has inbuilt one? What's the deal with the phantom power - what is needed there?
The units run on 220vac [plug them into the wall] - for phantom take 2x 6.81kΩ resistors, connect one to the "+" pin on the mic input and one to the "-" input on the mic input... tie them together and connect them to +48vdc then take the "0 volt" from your power supply and connect it to the mic ground. You can get a +48vdc power supply pretty easily, but I don't know where in the EU - ask around. All of this adds about 15 minutes to the wiring process.

Quote:
About the mods. I am not planning to the them by myself but just want to know about them. So, you say the gain control mod is not needed. There is instructions on the net how this can be done.

Is a low freq cut module a plus?

Sorry for the many questions but just trying to educate myself.
Thanks in advance!
No problem on the questions - I've never worried about a "low cut" as they add phase distortion I generally don't want -- and if you decide you need it, then pony up and get a very high quality one.

As you're in the EU you should also look into contacting H&# Studiotechnik [which I believe was suggested earlier] - email me [better than PM] if you need their phone number. They make some of the best frames I have EVER seen for these modules and can expertly refurbish them from top to bottom.

Peace.
Old 21st October 2010 | Show parent
  #16
Lives for gear
 
andrew montreal's Avatar
 
🎧 10 years
I have heard of phantom power spikes being an issue with this unit. Here is a thread on the issue:

Telefunken V76 48 volt pantom power supply?
Old 21st October 2010 | Show parent
  #17
Gear Maniac
 
🎧 15 years
How about something like this below?

Tuchel connectors are these days part of Amphenol. I think the part number is T1008 (I don't have the info to hand). I've bought them recently from Amphenol in Europe and they are not expensive. I'm not sure about the connector mentioned above, something about it doesn't look quite like the original item, although I'm sure it will fit OK.
There are some really crappy replica connectors (Chinese?) sold on ebay. They have a clear insulation, not black, and are oversize, so you have to file them down to fit in the shroud around the plug.
Problem with these amps is the dwindling supply of EF804S valves (tubes) which means ever increasing prices for the remaining stocks. Fortunately they don't seem to fail very often.
Attached Thumbnails
Help to rack v72 telefunken-v72housing_02.jpg   Help to rack v72 telefunken-v72housing_01.jpg  
Old 22nd October 2010 | Show parent
  #18
Here for the gear
 
🎧 10 years
thanks for the info Fetcher.I think I'd prefer something like a back panel with all the connectors on it - male/female xlr's etc. So, i'd ask for that whoever will rack it for me. By the way i'd like to use it mainly for vocals as mic pre.
Any recommended brands for +48vdc?

BeeGee, where did you get this racks from?
Old 22nd October 2010 | Show parent
  #19
Gear Maniac
 
🎧 15 years
Quote:
BeeGee, where did you get this racks from?
The racks are custom made for me to my own designs. I got the cage sizes by measuring a REDD17 that I was working on.
Another picture below.

I've made a few, all free standing, some for Mic power supplies (Neumann made power supplies in the "V72" format for U47 & KM sries mics), some for V76 Mic preamps and some for V72's.

In addition to the remarks above, I've added "conventional" phantom power to V76 preamps without problems.
The only problem is, I have taken out the HF roll-off circuit and trimmed the bass response but I've found with the V76 is that the frequency response varies at different gain settings.
Attached Thumbnails
Help to rack v72 telefunken-v72housing_03.jpg  
Old 29th October 2010 | Show parent
  #20
Here for the gear
 
🎧 10 years
Somehow my last reply did not get posted.
It was too long anyway. I will break it down in few parts.
First, I took some pics of the inside of the v72t module I have. I just took the cover off and did not want to go deeper, so if someone can tell me if it will need recapping. Looks like something is unslodered and I am worried about those wires sticking out from the transformer . If you need more pics to tell your opinion I will go unscrew it more get few few more pictures.
Thanks in advance
Old 29th October 2010 | Show parent
  #21
Gear Guru
 
1 Review written
🎧 15 years
Dangerous

The input transformer of a V series steps up the voltage 20-40 times.
Put 48V phantom power on there and you can very easily destroy the transformer. You need a +48 that ramps up and down slowly. Plus you do not make or break connections to phantom mics until the voltage has ramped away. Also the should be run at 220VAC, most step ups are 2:1
With typical US AC of 115-120V, again a problem.
Attenuators should be constant impedance 600 Ohms.
There are a handful of racking companies, not cheap.
I have used hestudiotecknik several times. They rebuild the module as needed, flash or replace the valves and so on. They can tailor the device to your needs, e.g. more gain. Their expertise and honesty is worth the money IMHO. Andy and Marcus are very nice people.
Other companies such as Marquette or Vintage King may be equally good.

DD
Old 29th October 2010 | Show parent
  #22
Here for the gear
 
🎧 10 years
As far as the phantom I already got the 48vdc 0.5A that has to be connected. How do you do that ramp trick? I thought you just connect the 48v with the Xlrs using 2x 6.81kO resistors( I am not an expert at all but that's what I read) I will be using the unit on 220v anyway.
Any comments on the pics?
Old 2nd November 2010 | Show parent
  #23
Here for the gear
 
🎧 10 years
Any comments on the pics. I am afraid something is not right with that wires sticking out of the transformer and those unsoldered spots.
Old 2nd November 2010 | Show parent
  #24
Gear Maniac
 
🎧 15 years
Quote:
Originally Posted by DanDan ➑️
The input transformer of a V series steps up the voltage 20-40 times.
Put 48V phantom power on there and you can very easily destroy the transformer. You need a +48 that ramps up and down slowly. Plus you do not make or break connections to phantom mics until the voltage has ramped away. Also the should be run at 220VAC, most step ups are 2:1
With typical US AC of 115-120V, again a problem.
Attenuators should be constant impedance 600 Ohms.
There are a handful of racking companies, not cheap.
I have used hestudiotecknik several times. They rebuild the module as needed, flash or replace the valves and so on. They can tailor the device to your needs, e.g. more gain. Their expertise and honesty is worth the money IMHO. Andy and Marcus are very nice people.
Other companies such as Marquette or Vintage King may be equally good.

DD
Interesting comment about phantom power.
If the power is applied in the conventional manner, ie. via 2 x 6K8 1% resistors, you are applying an equal and opposite voltage to each end of the primary winding. If the centre tap is actually in the centre, which I hope it is, then zero current should flow, since the two halves completely cancel each other out.
If you put a largeish value electrolytic across the phantom feed it will slow the voltage rise, but when you switch the voltage off, it will just sit there fully charged, since there is no leakage path to bleed the voltage away.
So I'm afraid I cannot see how you can "destroy the transformer" in this way, plus the buffer resistors will limit any current to a maximum of about 7milliamps.
The majority of Mic input transformers step up in a similar way and we never had a sudden rash of failed transformers when manufacturers started using phantom power for microphones.
If you are so wary of switching a phantom supply then why not leave it permanently "on" like Neve used to. Provided you never connect an unbalanced mic. there's no harm in doing that.

I've seen the recommendation to always run V72 etc. on 220V, but I think this is folklore. According to the few V72 & V76 that I've measured, there is a greater variation in HT voltage between examples than is caused by changing the supply from 220 to 240 volts.
All the V72 equipped REDD consoles that EMI used were always operated directly from the UK mains supply, which in the 1960's, was even higher than it is today, with mains voltages often exceeding 250v, and there were no problems with either performance or reliablity. Most people I know with V72/V76 run them directly from the UK nominal 240v ac supply and are not having performance or reliability issues.
Old 2nd November 2010 | Show parent
  #25
Gear Guru
 
1 Review written
🎧 15 years
Doubting Thomas

Well, I am not a repairer or refurbisher of V series modules. However I do own three. I have also read extensively about them. My comments are intended help the OP get the job done safely.
Regarding AC, The largest voltage difference is between the old EU 220 and the UK 240. It is of the order of 10%. Both supplies swing up and down, the 10% remains valid and shortens the life of components and valves.

From Oliver Archut

Quote:
Phantom Powering
One of the biggest concerns with these historic microphone pre-amp input and output transformers, is the phantom powering. Developed in the beginning of the 60s, and initially a sub-standard of powering microphones, this has now moved on to become the industry standard, applying 48V via two resistors to each leg of the modulation (pin 2/3) so there is no potential difference and using the shield as return path/0V.

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!!!! and this is enough for a millisecond energy burst that is powerful enough to burn microscopic holes into the insulation.

It is necessary to keep in mind that in the 1940/50 manufacturers only guaranteed the PVC coated magnet wire for approx. 24V AC, which is why every single layer was insolated with additional material like oilpaper, etc.
Therefore when you dump 48V into a input or output transformer you engage in a slow process of killing your historic transformer. Some og them are already gone due to the cracking of PVC (like the good old M7) over the years.

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 resonace 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.

If you want to use phantom power then it is necessary to use a ramped 48V supply with a time constance of more than 5sec.
This will take care of the problem posed by this energy burst, simply by having a slower time constance than the capacitve property of the transformer can charge.
But still there is a slight chance that something will get burned in the process, as you are dealing with historic/vintage parts, that had a maximum shelf life of aprox. 25 years.
He did post a ramped phantom circuit. You will have to search, it is not popping up easily in my search. It is of course very simple. Similarly the 220V can be achieved by appropriate resistors.

All of the custom racking companies provide the 220 and the ramped phantom. If one were to believe any or all of them, the risk is great. It would appear reckless to take the chance on the phantom issue at least.

DD
Old 2nd November 2010 | Show parent
  #26
Gear Addict
 
1 Review written
🎧 15 years
The easiest way to rack these up is to get the JLM go-between, replace the 10uF with 1000uF and the 470R with 2K2 ohm. That will give you a slow phantom ramp up and a really slow phantom ramp down.

For the output level control you could use a pot or wire up a stepped switch. I went for a balanced bridged-T attenuator with 10 steps (2dB each). If I had to do it again I would do 1dB steps, as the V72 don't sound too great with the input overdriven.

For the input pad I changed the three resistors for a -15dB pad, that works good for my usage.

My units have been running on 230V mains voltage for about 10 years now, without any issues.

hope this helps, Marten
Old 2nd November 2010 | Show parent
  #27
Gear Guru
 
1 Review written
🎧 15 years
Found it

Quote:
For the output level control you could use a pot or wire up a stepped switch. I went for a balanced bridged-T attenuator with 10 steps (2dB each). If I had to do it again I would do 1dB steps, as the V72 don't sound too great with the input overdriven.
I think mart intended to say input level control.

Found Oliver's circuit. I'm sure he won't mind me borrowing it.
Edit, screenshot now.
Help to rack v72 telefunken-picture-2.jpg





Best, DD
Old 2nd November 2010 | Show parent
  #28
Gear Addict
 
1 Review written
🎧 15 years
dandan, I really meant output level control, that is what I did with my units. Setting a course input level with the pad, i.e. -15dB for drums and close miked guitar amps and unpadded for vocals and ambient mics and then fine tuning the level to tape or daw with the stepped output level control.

Though I do agree that for the V72 a continous (pot) input control would be conceptually much better, but far more difficult to implement in regards to cmrr, phantom powering issues, etc.

Oliver's circuit is new to me, would you have a better resolution picture of that? It is hard to see the component values...
Old 2nd November 2010 | Show parent
  #29
Gear Guru
 
1 Review written
🎧 15 years
Sorry

Ah, I see mart, my apologies. My V78's from hestudiotechnik.de use stepped input attenuators. I am sure they would sell you one and tell you how they do it. Andy and Marcus are cool. I believe you can very easily change the gain by using a pot, possibly DC decoupled in the negative feedback line. That's how the 78 gets such high gain. 78dB, although on advice from Andy I had him limit mine to 60dB. I will try a screenshot instead of that thumbnail.
DD
Old 2nd November 2010 | Show parent
  #30
Gear Addict
 
1 Review written
🎧 15 years
ok, that sounds interesting. I had been pondering about the various ways to work these preamps, but right now I really feel no need to go at it again. A lot of times I will use a compressor with variable gain after the V72, that works really good. A guy I know swears by using old fader modules after these preamps, that works really well too, there are some good sounding active ones, that will give you another 15dB of gain if you need it. But with something like an 1176 there is no need for that.

Marcus & Andy do great work, I know, but I feel they should not be asked to give away knowlegde that their business is based upon. Back when I purchased my modules (like when they were still 200,- a piece) I had more time than money and found a way to get them working and learned a lot by doing it...

Changing the gain "inside" the V72 has been discussed a lot as well, it is not as simple as changing the feedback resistance, because other factors have to be taken in account and compensated for. I know Gunther Wagner has found a way to do this, but I've never heard one of his modded preamps. There are other "hazy" mods, like the DI input straight to the first preamp tube, which I failed to get working good, so I've decided to "let it be" and enjoy this kind of limited, but great sounding preamp :-)
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