Langevin AM16 w/Capitol Records O/P trannies

[wackowill]

Hi. Recently bought some Langevin AM16s off evilBay complete with Capitol Records O/P transformers. Anyone have any idea of what effect this will have on the sound? Over on prodigy forums they recommend sticking a 600 Ohm resister over the outputs to load the standard transformer correctly. Will the Capitol transformer be correctly loaded with the standard impedence required in today's line inputs etc.?

[edited - I since found out that the Capitol transformers are actually the input transformers]

[MJGreene Audio]

To the best of my knowledge the Capitol transformers are just the standard Langevin Trannys with capitol name stamped on them. (Still cool in my book. Wish mine had that!!!) But I will let someone like my new Langevin genius Brian Roth answer the impedence question.

Just a side not. You have some really nice mic pre's sitting there. A bit of an unknown compared to API and Neve. Do yourself a favor and spend the money to have them racked up properly. After years of searching for someone who actually knows what the hell he is doing and that doesn't try and rape me over a console, I found Brian. He answered all the questions I had in a very clear and direct way. I am a person who knows just enough to get me in trouble but also enough to know when I am getting bullshited. You will not regret the money you spend if you do it right.

Good luck and nice pre's,
Michael Greene

[Helsing]

Ive racked quite a few of these but havent found the 600 ohm resistor to be necessary. Let me know if you run into any trouble. Happy to help.

Helsing

[brianroth]

Thanks for the kind words, Michael...I'm blushing.

After running some tests, the outputs of a stock AM-16 do need to be terminated into 600 Ohms, or otherwise they "ring like a bell" when fed with a transient signal, such as a square wave.

Yes, few of us listen to square waves, but they are a useful test signal, and when the unterminated output waveform has a large amount of overshoot and ringing, then a 600 termination (as originally designed) is required to restore the module to performance the designers intended.

OTOH, sometimes an unterminated output can provide a special effect, typically a zingier top end. That's why I added a switch for each channel of Michael's AM-16 channels to "properly" terminate the module, or not. In addition, even if the zing isn't desired, the switchable termination allows the module to properly work with "modern" gear, which has high impedance bridging inputs, or "vintage" gear (including various new reissues) which have a 600 Ohm input impedance. The switch simply drops a 601 Ohm resistor across the output transformer when it needs to interface with a bridging input load.

I first encountered the need for a "TERM" switch decades ago with the Ampex AG-440 and MM-1000 recorders, which had that switch on the rear panel of the audio electronics channels. In that era, both 600 Ohm terminated inputs as well as bridging inputs were all mixed together in a typical studio.

Bri

[brianroth]

Oh...back to the original question re the "2400 ohm" markings on the Capitol transformers. That is indeed an odd-ball to me. I would bench test them with a 1 kHz square wave source and monitor the output with a scope. With no termination, the sqaure wave output waveform will likely show a lot of overshoot and ringing. If so, try terminating the module output with a 2400 Ohm resistor to see if that "tames" the waveform.

Bri

[wackowill]

Great! Thanks for your advice Brian, Michael and Helsing. I'll do some tests and report back.

[wackowill]

Okay. I had a good look at the Langevins today. Guess what! The Capitol "Output transformers" are actually "Input transformers". This is actually pretty cool, because the standard input source impedance required by the Langevins is selectable as only 50 Ohm, 150 Ohm or 600 Ohm. Most modern microphones require a higher impedance to operate at their optimum efficiency (please correct me if I'm wrong). I'm hoping that the higher impedance transformer will allow me to use microphones that aren't compatible with the stock AM-16s.

[brianroth]

DOOH!!!! I'm an idiot.

That end of an AM-16 ****is*** the input transformer.

2400 input Z *should* be a PLUS...if that is indeed correct.

Easy to test.

Connect a low Z oscillator to that node. Note the output level from the preamp.

Insert a 2400 R in series with the oscillator.

Re-measure the output level,

Output level should be 6 dB lower with the 2400 Ohm series R.

Then check everyting with a 1 kHz square wave <g>.

Bri