donnysparks

Langevin AM16 on my bench!!!
« Reply #20 on: April 14, 2005, 10:49:42 PM »
you guys have inspired me to finally rack the am16 that's been staring at me all this time.  also, its time to stop spying and start posting...

Quote from: "scott_humphrey"
Quote from: "JLM Audio"
Remember the AM16 output must be loaded by 600ohms to keep the frequency response flat. If you do not load the output you will have a 1 to 3dB rise by 20kHz which rises to about 6 to 8dB at around 40khz. Doesn't sound much but in listening term it is the difference between warm or harsh.


Joe

www.jlmaudio.com


I'm confused here.  wouldn't just about any piece of gear being fed by the am16 output provide at least a 600 ohm load?  if you don't mind, what's an example of a situation meeting your criteria and one not?

also, the JLM Go Between and JLM DI Kit look very interesting.  would those work with the AM16?




and Rob,
"Just a small point but if you have these mic amps set for +24dBm operation the harmonic generation is greater by 0.25% than if you have them set for +18dBm."

is that desireable harmonic generation as in even harmonics?



and Scott,
as Sleeper asked, what ARE those big caps off of the connector doing?




I am in constant awe of what you people are able to cook up!

thanks in advance for any help.

--donnysparks
--donnysparks


alk509

Langevin AM16 on my bench!!!
« Reply #21 on: April 14, 2005, 11:23:55 PM »
Welcome Donny!

Quote from: "donnysparks"
I'm confused here. wouldn't just about any piece of gear being fed by the am16 output provide at least a 600 ohm load?


Yes. But when the load is much greater than 600 Ohm, there's a bump in the high frequency that some people don't like. The (lower) 600 Ohm load kinda keeps it under control.

BTW, don't some people permanently strap a  ~600 Ohm resistor across the output of these things when they rack them? And whatever happened to CJ's DIY AM16?

Peace,
Al.

Lest laziness get the best of you!

Langevin AM16 on my bench!!!
« Reply #22 on: April 14, 2005, 11:30:53 PM »
Quote
and Scott,
as Sleeper asked, what ARE those big caps off of the connector doing?


Smoothing for the phantom power.

Quote
BTW, don't some people permanently strap a ~600 Ohm resistor across the output of these things when they rack them?


I put a 600 ohm resistor at the output that I can switch in and out. It really does change the sound quite a bit. I like the option, though, of being able to to add the extra sizzle if the source being recorded needs it.

donnysparks

Langevin AM16 on my bench!!!
« Reply #23 on: April 14, 2005, 11:48:01 PM »
Quote from: "alk509"
Welcome Donny!
Yes. But when the load is much greater than 600 Ohm, there's a bump in the high frequency that some people don't like. The (lower) 600 Ohm load kinda keeps it under control.

Peace,
Al.


Thanks Al and Scott.  I see.  I had read Joe's post as "less than a 600ohm load would cause that undesireable shift".  so putting a 600 ohm resister across the output (meaning from the + to the - output lead on the am16 connector?) would reduce the load on the output because the resister is basically in parallel with the downstream piece of gear?

now i have to go dig up the manual to my console and tape machine and see what the input impedances are...

donnysparks
--donnysparks

PRR

Langevin AM16 on my bench!!!
« Reply #24 on: April 15, 2005, 01:42:45 AM »
> and see what the input impedances are...

In 1928, when tubes were expensive and gain was hard to get, most boxes used input transformers to step-up the voltage and provide "free gain". And for maximum flexibility in patching, including patching through long (telephone) lines, everything was 500 ohms, later 600 ohms except ABC used 150 ohms.

Today with $0.10 chips (actually since the 1940s), we are not hurting for gain and "most" gear has "high impedance" inputs. Line inputs are usually 10K to 50K. We still tend to have outputs able to drive 2K down to 600 ohms, so we can simply Y-connect many 10K inputs to one output.

Yet there are still a few old-time 600 ohm inputs. Passive EQ are often true 600. Fairchild 660 is true 150/600. A modern studio won't have old junk like this hanging around, but guys who play with AM17s might.

Langevin was one of the last of the old-style audio systems. Gear like the AM16/17 may have 150/600 ohm inputs, and was intended to have a full load, often a 600 ohm attenuator. It will "work" with a 10K load, and the midband gain is about the same, but Joe says (he's surely right) that small errors in the transformer, tuned to work perfect with a 600 ohm load, will ring-out the top of the audio band when the load is much greater than 600 ohms.

On these amps, 500 or 1,000 ohms is "loaded". 10K is "barely loaded" and will be "ringy" as Joe says. As Scott says, sometimes the "sizzle" from "mis-loading" is musically useful. In a complex busy studio, sanity suggests putting a 650 ohm resistor on the output permanently, and only using it with hi-Z inputs. You can always get a top-end ring with an EQ. Situations where a producer "must have" the AM17 unloaded-ring, or must interface a true 600 input, can be handled as special cases with a little extra money for the electronics technician.

NewYorkDave

Langevin AM16 on my bench!!!
« Reply #25 on: April 15, 2005, 11:36:02 AM »
Minor correction: it was CBS who used 150 ohms for all their infrastructure. However, other networks sometimes used (and may still use) 150 ohms for studio-transmitter links. I did some work for a station in the Bronx circa 1999 and although most of their infrastructure (studio and transmitter) was new, their STL was a good old-fashioned 150-ohm line with good old-fashioned repeat coils--I think they were WE 111C--at either end.

Rob Flinn

Langevin AM16 on my bench!!!
« Reply #26 on: April 15, 2005, 03:27:04 PM »
Donny Sparks

With regards to my post:
Quote
and Rob,
"Just a small point but if you have these mic amps set for +24dBm operation the harmonic generation is greater by 0.25% than if you have them set for +18dBm."

is that desireable harmonic generation as in even harmonics?


Probably the best thing to do is try it both & see if you notice a difference.  Then you have the option of hardwiring one way or being able to select the harmonic generation with a switch.
regards Rob

donnysparks

Langevin AM16 on my bench!!!
« Reply #27 on: April 15, 2005, 10:53:23 PM »
OK, Thanks for the help.  I think I may have just learned something!

Actually, I went ahead and wired up my AM16 to in/out connectors and PSU.  
Real world example of the whole loading thing maybe:  plugged a 57 in and got good sounds.  then i tried an ev 635a (150 Ohms) and the AM16 freaked out.  it was 99% noise and 1% signal.

Funny, I recently came into an Orban 111b spring reverb and wondered why there were resisters wired to the output terminals.  i took them off.  i've always thought that it was a bit (a lot) noisy.  Maybe i'll try with the resisters.

--donnysparks
--donnysparks

alk509

Langevin AM16 on my bench!!!
« Reply #28 on: April 15, 2005, 11:05:47 PM »
Quote from: "donnysparks"
plugged a 57 in and got good sounds.  then i tried an ev 635a (150 Ohms) and the AM16 freaked out.


I don't think that's normal... The 57 has higher output impedance than the EV (assuming you're right and it is in fact 150 Ohm). If it had anything to do with loading, the 57 would have a harder time driving the AM16 than the EV, not the other way around.

Does the 635A work OK with other pres?

Peace,
Al.

Lest laziness get the best of you!

donnysparks

Langevin AM16 on my bench!!!
« Reply #29 on: April 15, 2005, 11:34:12 PM »
Quote from: "alk509"
Quote from: "donnysparks"
plugged a 57 in and got good sounds.  then i tried an ev 635a (150 Ohms) and the AM16 freaked out.


I don't think that's normal... The 57 has higher output impedance than the EV (assuming you're right and it is in fact 150 Ohm). If it had anything to do with loading, the 57 would have a harder time driving the AM16 than the EV, not the other way around.

Does the 635A work OK with other pres?

Peace,
Al.


yeah, you're right.  that doesn't make sense does it? i had it backwards.  the 635 works great with other pre's.  i'll have to open it up.  could it be that the ev is wired hi-Z?  my grounding scheme is probably wrong, too.  i had the in/out grounds, am16 ground (pin j) and the AC plug grounds twisted together.  that was my best guess.  i was feelin' good for a second there...

--donnysparks
--donnysparks


wackowill

Pin out
« Reply #30 on: September 14, 2005, 10:49:04 PM »
Hi there.

Try as I might, I can't find a pin out for the power and ground connections to an AM16.

Can anyone help me out?

Thanks in advance.  Will :O)

CJ

Langevin AM16 on my bench!!!
« Reply #31 on: September 15, 2005, 12:56:05 PM »
Are you using the stock connector on the end of the module?
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

wackowill

Langevin AM16 on my bench!!!
« Reply #32 on: September 15, 2005, 08:12:49 PM »
Quote
Are you using the stock connector on the end of the module?


In two out of four cases, yes.  In the other two - no.

I have four modules in total.  The two with the connectors are stock Langevin AM16s.  The remaining two have Capitol Records output transformers installed - which appear to be a modified model TF-425-C trannie and have "2400 Ohms" written on the outside.  A different impedence?

CJ

Langevin AM16 on my bench!!!
« Reply #33 on: September 15, 2005, 08:47:39 PM »
http://vacuumbrain.com/The_Lab/TA/Langevin/langevinam16.pdf

just for the heck of it, this is the 17, connector looks the same, transformer output colors have been changed to protect the innocent:



If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

donnysparks

Langevin AM16 on my bench!!!
« Reply #34 on: September 15, 2005, 10:17:30 PM »
Quote from: "CJ"
http://vacuumbrain.com/The_Lab/TA/Langevin/langevinam16.pdf

just for the heck of it, this is the 17, connector looks the same, transformer output colors have been changed to protect the innocent:


I got's em both.  for power its the same pins in the AM16 and AM17.
--donnysparks

wackowill

Langevin AM16 on my bench!!!
« Reply #35 on: September 18, 2005, 10:02:13 AM »
Thanks gents!  A great help indeed.  Here's a picture of the langevin AM16s with the "Capitol Records" transformer installed.

Here's a picture:  http://gearslutz.com/board/attachment.php3?attachmentid=10178&stc=1

CJ

Langevin AM16 on my bench!!!
« Reply #36 on: September 19, 2005, 01:31:19 PM »
Cool! Looks like you got the retro cans on the Capitol transistors.
Measure the DCR if you can on the output secondaries. Stock is about 110 ohms with sec's in series. Those cans were obviously wound by Electrodyne or whoever was doing the Langevin coils back then. I wonder if they are really custom units or just shipped with the sec's in series, which is listed as 600 ohms in the manual. If they did double the turns (equals 4 times imp/ind) then you have some custom transformers.

You would then get about double the dcr or more, since they would have to use smaller wire to squeeze on the extra turns, so I expect around 220 ohms dcr if custom transformers.
cj
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

EmRR

Langevin AM16 on my bench!!!
« Reply #37 on: October 22, 2006, 03:39:42 PM »
Quote from: "Rob Flinn"
Donny Sparks

With regards to my post:
Quote
and Rob,
"Just a small point but if you have these mic amps set for +24dBm operation the harmonic generation is greater by 0.25% than if you have them set for +18dBm."

is that desireable harmonic generation as in even harmonics?


Probably the best thing to do is try it both & see if you notice a difference.  Then you have the option of hardwiring one way or being able to select the harmonic generation with a switch.


I'd think the distortion would be primarily 3rd harmonic, being a balanced circuit.  

I think this power/distortion issue needs to be looked at another way.  WITH 6 DB MORE LEVEL GOING THROUGH THE UNIT, you get another 1/4% distortion.  This is true of most any gear at some point approaching the maximum headroom.  I bet it's at least the same (if not lower) distortion when set for high power with identical levels (say, +16 dBm) passing.  Is it the transformers approaching saturation at the higher power level?  Is it the transistors?  Is it both?  Anyone really know?

Another thing; this is a fixed gain preamp.  When you go high power for more output capability, the maximum input point also moves.  So, there is a magic point in the headroom shift where the lower power setting will crap out and have more distortion than the higher power setting.  If the specs are to be trusted, then -27dBm is maximum input for the low power setting, and -21dBm is max for the high power setting, so -24dBm would be a problem for the lower power setting and yield more distortion than the higher power setting.  If you extend that thought to 20 db input pads, you still end up in a zone where the output of many modern condensers could cause problems with the low setting.  Hell, with the high settting too.  At any rate, I'm not convinced there's a great reason to run at the lower power setting, at least not with any type of loud input signals and hot mics.  If you're always putting a 77DX into it then it could be another story.

There may be some noise issues with the power shift that I can't address from experience yet.  I believe Soundguy had some commentary about greater noise in the AM-17 with the higher power strapping, but that is actually a shift from 1W (high line level) to 8W power amp level, with power transistors as outputs.  They may behave differently.

Put in a power shift switch if you really want to nerd out......
Best,

Doug Williams
Electromagnetic Radiation Recorders

"I think this can be better. Some kind of control that's intuitive, not complicated like a single knob" - Crusty

"Back when everything sounde


 

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