R/E/P > Oliver Archut

V672 Racking


Hi Oliver and all,

I have two telefunken v672/2 modules which I want to rack.
I have few question regarding the connection of the modules.

In one place, I was told that the input goes to pins 1&2. others said that the input goes to 7&8 and the input impedance goes between pins 1&3 and 2&4.

Im planning to make a switch of two impedances. one position will be suitable for ribbons, the other for condensers and dynamic mics.

what impedances should I use?

What potentiometer value would you use for the gain control? I was told that a resistor in series with the put is vital, is that so, if so, what resistor value?

I hope this isn't a rude thing to ask for this information, since this is your work.(no sarcasm!)


the impedance switching may be referring to the TWO output transformers which you MAY want to wire together to lower the impedance of the output..

I don't know WHY you would want to do such a thing.

the input impedance is not changeable..

the connections of the output transformers can be used for driving two separate inputs, or doing some MS tricks with phase.

so connections are input, output unbalanced, output balanced transformer 1, output balance transformer 2

you will also need to connect an external gain control via resistors.. which change the amount of neg feedback therefore gain in the amp
PSU is 24v

The v672 has zero ohm input impedance, that's why you have to create an impedance for it.


Oliver Archut:
Hello Eliya,

original the input resistor was located on the unit so the differences with the pins, 1/2 goes right to the x-former the other pins have the input(setting) resistors....

What impedance to use??? That is specified in the original spec sheet of the V672 that you can download on almost any DIY site. But, please be careful, the spec sheet that is out there is only for the discrete V672 original made by Telefunken, so any later Telefunken/ANT or similar boxes won't work as good or at all, min. can be 20 Ohm (two 10 ohm resistors in line) max. can be 6.8K or higher with a proper change in inductance. The max. feedback resistor is specified with 300k ohm.

Please understand that I do not publish what I am doing to change them, there is a bit more than just racking them up. in order to get the proper impedance vs. the make up gain several key components must be change. Most of the time the input x-former of the by now 40 year plus discrete units are shoot so the unit is pretty much not useable.


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