Langevin AM16 w/Capitol Records O/P trannies

wackowill · 18th September 2005

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 · 18th September 2005

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 · 19th September 2005

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 · 20th September 2005

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 · 20th September 2005

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 · 20th September 2005

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

wackowill · 21st September 2005

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 · 22nd September 2005

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

18th September 2005	#1
wackowill Gear nut Joined: Jul 2005 Posts: 114 Thread Starter	Langevin AM16 w/Capitol Records I/P trannies 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] Attached Thumbnails __________________ The Audio Trinity - Neumann, Neve, _ _ _ _ _ _

20th September 2005	#4
brianroth Lives for gear Joined: May 2005 Location: Oklahoma City Posts: 1,818	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 __________________ Brian Roth Technical Services Oklahoma City, OK www.BrianRoth.com

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread starter	Forum	Replies	Last Post
Mercury AM16 (Langevin AM16 reissue) Anyone try it?	C/G	So much gear, so little time!	33	9th August 2010 10:23 AM
Trannies for a dbx 118	jarbar	Geekslutz forum	3	7th April 2006 03:52 PM
can anyone describe the sound of langevin AM16 preamps?	joninc	High end	1	29th September 2005 05:03 AM
Racking Langevin Am16	StudioFvictor	So much gear, so little time!	7	16th April 2004 04:34 AM

18th September 2005	#2
MJGreene Audio Lives for gear Joined: Mar 2004 Location: The Land Behind The Zion Curtain Posts: 1,119	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

19th September 2005	#3
Helsing Gear maniac Joined: Nov 2003 Location: San Diego Posts: 261	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

21st September 2005	#7
wackowill Gear nut Joined: Jul 2005 Posts: 114 Thread Starter	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.

22nd September 2005	#8
brianroth Lives for gear Joined: May 2005 Location: Oklahoma City Posts: 1,818	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