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Help to rack v72 telefunken
Old 2nd November 2010 | Show parent
  #31
Gear Guru
 
1 Review written
🎧 15 years
Lucky

Good points mart. I too use an1176 LN after. The level match is pretty good, this version of the Urei gets into trouble after 21dBu. A 5534 chip input.
I have an amazing unit, which needs XLRs and I am slow to cut the metal work, but must get on with it. On my to-do list. It is an old lab unit. A balanced 600 ohm attenuator. Three switches 0-90dB
x10 x1 x 0.1 dB steps. Made in England by Standard Telephone and Cables.
Slutty eh?

By the way do you load your ins and outs with 600R? Does it sound different?

Best, DD
Old 2nd November 2010 | Show parent
  #32
Gear Addict
 
1 Review written
🎧 15 years
yes, the metal work is mostly pita, having good tools helps though. I have a 1176 with an input attenuator (rev A), that works pretty good. Nice score on the attenuator, that should work out nice!

Regarding the 600R termination: I leave it unterminated, even when feeding high impedance inputs, I actually even forget sometimes that it is switchable on my units. It is not worlds apart with or without. Here a blurry old pic of my units, they are in a proper rack now heh

Old 2nd November 2010 | Show parent
  #33
Here for the gear
 
🎧 10 years
About the input gain mod, will the following one work on all v72 units(including v72t I have), does anyone have better solution, and if this one is fine can I just give the instructions to regular tech so he can do the job for me?

"1/ Remove RK1 (1.25K).
2/ Remove small jumper on opposite side of board that connects end
of feedback loop to RK1 tie lug. (jumper is approx 3/4" long & is
at right-angles to & between the .05 & .025 caps.
3/ Solder one end of a 100 ohm 1/2 watt resistor to the ground end
of where the 1.25 RK was located. (use something of good quality
that is non-inductive)
4/ Remove the 2K - 7.5K resistor (usually 5K) from the F.B. loop.
5/ Solder the two small value F.B. caps across just the 80K FBr.
(or better still, replace with high quality 90pF polystryrene)
6/ Solder a (small as you can find) 2uF/250v+ electrolytic where
the 2K - 7.5K R was located. Orient the +tve end towards 80K R
7/ Strip a piece of twin conductor/shielded cable. Attach tails to
screens ala Neve & cover w/ shrink tubing.
7/ Solder one end of cable to V-72 as follows:
a) tail lead = other end of 100 ohm resistor, cover w/ shrink-tube
b) +tve lead = -tve end of 2uF/250V.
c) -tve lead = RK1 tie lug.
8/ Get yourself a 1K pot. (anti-log is best for correct taper but
since these are next to impossible to buy in small quantities
a linear will work fine with a slightly less than optimum taper)
9/ Solder other end of cable to pot as follows:
a) tail lead = top of pot
b) +tve lead = wiper of pot
c) -tve lead = bottom of pot.
(note: orientation of top & bottom are opposite from normal volume-pot type
wiring. If you get it wrong, gain adjustment will
happen in reverse).
10/ Plug in & Stand Back."

This mod is supposed to take you from approx 33dB to +/-50dB and there is to be slight noise as you turn the pot. Is there anyway the noise to be avoided?
If I want to use stepped attenuator instead of the pot will be there any modifications on the above instructions?
Old 2nd November 2010 | Show parent
  #34
Gear Guru
 
1 Review written
🎧 15 years
DC

The slight noise would be DC on the pot. I believe you can eliminate that by installing a capacitor at the wiper. Don't know the value. I expect a high value is needed with no leakage. e.g. a big Polycarb.
DD
Old 3rd November 2010 | Show parent
  #35
Here for the gear
 
🎧 10 years
DanDan, do you think the transformer of the unit I have is screwed judging by the pics I posted few replies back? If so, is it easy to find one and what kind will I need?
Thanks
Old 3rd November 2010 | Show parent
  #36
Gear Guru
 
1 Review written
🎧 15 years
No

Kardinal, I couldn't tell from those pics or probably any pics. The insulation could be punctured anywhere. The transformers are of course hard to find, expensive etc. etc. There are other parts which will need changing, maybe the valves. All in all, I would send it to studiotecknik. If they refurb it, you will have one of the best sounding pres, probably for a long long time.
DD
Old 3rd November 2010 | Show parent
  #37
Here for the gear
 
🎧 10 years
I understand. I guess the best is to check with tech.
By the way, I got the T version so no valves there I think.
Thanks to everyone for the answers and the tips!
Old 3rd November 2010 | Show parent
  #38
Gear Addict
 
1 Review written
🎧 15 years
you will have a hard time finding replacement transformers for the V72, don't know if the transistor version has a different model. I had my input transformers rewound by Vintage City, they did a great job!
Old 3rd November 2010 | Show parent
  #39
Here for the gear
 
🎧 10 years
hopefully, the transformer is fine , I just don't like all the wires sticking out but will know for sure next week when I check with a tech.
Old 3rd November 2010 | Show parent
  #40
Gear Guru
 
1 Review written
🎧 15 years
Confusion

The OP was V72, most of our comments were regarding that.
Kardinal's unit is a t, no similarity whatsoever, apart from the case. So none of our comments are true!
The input traffo is very low ratio so no phantom problem.
There is an internal PSU which is regulated so there is no AC voltage issue either.
DOH.

http://audio.kubarth.com/rundfunk/ge...D9%40%60%60%0A

DD
Old 12th April 2011 | Show parent
  #41
Lives for gear
 
🎧 10 years
Quote:
Originally Posted by mart ➑️
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

Does anybody else used JLM go-between (10uF with 1000uF and the 470R with 2K2 ohm)?
Old 13th April 2011 | Show parent
  #42
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frans's Avatar
 
10 Reviews written
🎧 15 years
To sum up a few of the earlier points:
No, it's not a "secret" the techs hesitate to put out to "save their business". I'm not one of those techs either, so I'm in no way advocating their "business".

The reason there are no hard and fast rules for these V series modules is simply there are lots of them and versions and versions and they differ. The right thing for one of those could damage another version. It's true some of them have input transformers that get killed by phantom power over time. Some don't.
Here is where the techs come in: they can identify your module and do what needs to be done. Racking them up after all the possible problems and needs are pinned down and catered for is a piece of cake.

You decide.
Old 21st July 2013
  #43
Gear Addict
 
gpiccolini's Avatar
 
4 Reviews written
🎧 10 years
sorry to revive this old (but interesting) thread.
I was informed that I can run phantom on my V76 if I turn on the phantom psu (external) before connecting it to the preamp or before turning on the preamp. Is that correct?. I don't have many 48v mics, mostly 12V here, but I do have some and I'd like to know before using them.
regards
G
Old 21st July 2013 | Show parent
  #44
Gear Guru
 
1 Review written
🎧 15 years
40

Afaik the input traffo on the V76 has a 40:1 ratio. So if you apply phantom power there is a possibility of 48x40 volt spikes, or higher.
The only safe way to use phantom with the V series is to ramp it up slowly electronically.
DD
Old 21st July 2013 | Show parent
  #45
Lives for gear
 
andre tchmil's Avatar
 
🎧 15 years
http://www.sonicmessiah.com
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