TIPS ON RACKING Langevin AM 5116 B mic pres?

[emrr]

I have a pair here with trays that I need to get going sometime.

The schematic I've seen floating around gives some variable resistor values in the feedback path for slight gain change. You could put that on a stepped switch, and add a standard 20 dB input pad.

Power One makes a 250-285 VDC linear PSU, available from Mouser for about $45.

The mating connectors will be almost impossible to find.

A re-cap will kind of suck too, given the way the can cap is mounted on the (tiny) circuit board.

[walth]

good to know

[Antonio_4346]

A long time has passed since this thread was active, but perhaps it'll pop up on somebody's radar.

I just purchased a set of Langevin 5000 series modules: two 5116B Preamps, a 5117 Line amp Module, a 401-B Input Transformer, and the 5208 Power supply.

I've tracked down schematics for the 5116B and the 5208, which have been extremely helpful, but there are still some loose ends to get tied up before I run AC into this bad boy and try to test it out.

I'm hoping somebody out there might be able to help me out.

Below is a general picture of the unit. Notice the modules from left to right are the 5208, 5117, 5116, 401 and 5116.



Now the rear:



First off, the Input routing on this sucker is a little bit confusing. There's only one XLR input, which is wired into the first 5116 preamp. Makes sense. Then, the outputs of that preamp are fed into the 410 input transformer. Then, they continue through into the second 5116 preamp. From there, they finally exit out of the unit through the jacks on the front of the unit.

Why would it be routed this way? Why would there need to be one stage of amplification, followed by transformer, then by another stage or pre-amplification before exiting the unit? Can I simple re-route the inputs and outputs of these units to make them independent from the 401 transformer module, therefore providing two separate channels of mic preamps?

I can't find the schematics for the 401 or 6117 anywhere, so its difficult to tell whether or not certain characteristics are indeed accurate upon visual inspection (at least for me, somebody with minimal electronics experience). For instance, there's a multi-pin jack on the top of the 401; it very closely resembles a tube socket, though I'm not sure which tube accommodates it, or even if it requires one. The person I bought the unit from seemed to think that was a way of integrating it with the rest of the PA/Comm system of the Naval vessel he seemed to think this thing originated from (aka a multi-pin output).

This socket is pictured below:



There are also two sets of pins on the 5116 schematics that are labeled "HTR". I'm unaware of what this is short for, though I do know through my research that the pins labeled "MTR" on the schematic refer to the optional Meter that could have been purchased and installed with these units. These pins, labeled HTR, then route to a very peculiar looking unit, pictured below. I have no idea as to what this is doing. It does seem fairly obvious that each lead set is a send and return to this device, however.





I suppose my last question is whether or not the 5117 can be converted into a microphone preamp with little to no modifications. And, if so, could it be a dual channel preamp or is this unit designed to be a mono program amplifier?

Lastly (for now, anyway), I'm still confused as to where I should try and wire in some sort of output potentiometer, so as to regulate the level I send to the tape machine or A/D converters in the studio. Not to mention the fact I could really use some advice for where to insert the input pad, phase switch, and the phantom power supply!

Here are a few other more detailed photographs, for your reference.






Any and all help/assistance is greatly appreciated. I've already combed the internet for references and other tools, but the resources are wearing very thin at this juncture.

[mjrippe]

Wow, that's a nice setup you scored! I can address a few of your questions, others will probably know more.

Yes, you can separate the two 5116 modules and use them as individual preamps. I can't imagine why they ran them in series and how that wouldn't overload the second stage.

The 401 unit is probably missing a plug-in transformer that fits the socket. You don't need it as the preamps have in and output transformers already.

The HTR wiring is for the tube HeaTeRs, or filaments.

The 5117 is a mono power amp for monitoring. It *can* be wired as a preamp with a lot of gain and a really hot output. Not the best use for it.

[cathode]

Originally Posted by Antonio_4346

I just purchased a set of Langevin 5000 series modules: two 5116B Preamps,
a 5117 Line amp Module, a 401-B Input Transformer, and the 5208 Power supply.

I've tracked down schematics for the 5116B and the 5208, which have been extremely helpful, but there are still some loose ends to get tied up before I run AC into this bad boy and try to test it out.

I can't find the schematics for the 401 or 6117 anywhere,

I suppose my last question is whether or not the 5117 can be converted into a microphone preamp with little to no modifications. And, if so, could it be a dual channel preamp or is this unit designed to be a mono program amplifier?

Lastly (for now, anyway), I'm still confused as to where I should try and wire in some sort of output potentiometer, so as to regulate the level I send to the tape machine or A/D converters in the studio. Not to mention the fact I could really use some advice for where to insert the input pad, phase switch, and the phantom power supply!

The preamps in the photos are 5116's, not the "b" versions. The schematic for the 5116 is on the web though rife with errors.
The 5117 can indeed be converted into a high gain, high headroom mic preamp. Requires very few modifications. JJP was the one of the first modern knob turners to employ them 30 years ago.
An output control such as a bridged or straight T can be installed on the output. ClassicAPI has them. Be aware that a relatively low headroom preamp such as the 5116 was not designed to feed a recording device directly, at least not in the +4 dBm=0VU world. If driving a A2D or tape machine with input gain (yes, breaking cal), not an issue.

[emrr]

A 5116 will feed a recorder directly with no problems. The problem with 5116 or 5117 is the input headroom is low compared to modern gear, and you'll find yourself using a 20 dB input pad in most situations. The 401B may be a multi-use utility tray, having no function unless something plugged into it. What's the guts on it look like?

[cathode]

Originally Posted by emrr

A 5116 will feed a recorder directly with no problems. The problem with 5116 or 5117 is the input headroom is low compared to modern gea

The 5116 clips at about +18dBm, do the math. An API 312 clips at about +29 dBm.
What exactly is input headroom? Output stages clip first.
Virtually preamps need an external switchable pad.

[emrr]

It's pretty simple, it's a fixed gain preamp with loop negative feedback, so they are one in the same. I don't need to do the math to know they work into modern recorders; I use this sort of preamp this way all the time. Most people are using +18 systems these days, so if you're clipping one, you're clipping both. I can't say I know anyone using any record input at +29 dBm, that's the territory of mixer output headroom.

It doesn't apply in the 5116 case, but a lot of preamps from this era have input transformers that clip pretty close to the level which equals max out minus gain.

Look at the power strapping on the Altec 9470/9475 or Langevin AM-16 for another analogy. The gain stays the same, the max output moves up or down, and therefore the max input moves with it.

The 401B is not an octal transformer in my experience, and wouldn't be much good as a passive component on a tray. I would assume the 401B here is the tray itself.