At the risk of showing my complete ignorance, I have prepared a vero layout for the Langevin AM-16 preamp.  I’ve been interested in building a few of these and thought it would be a good opportunity to learn how to read schematics and do layouts.  I’d really appreciate any advice you can give to both forward my learning and help prepare an efficient layout for this pre.  I have attached a preliminary layout image and the schematic used can be found at

I like the idea of veroboard since it doesn’t require etching or waiting on an ordered pcb.  Please offer any input you can on errors or possible ways to be more efficient.  I tried to lay this out in a way that all traces and cuts could be seen.  I believe I could make it about 5 columns smaller by placing some components diagonally, however being that it is going in a 1u enclosure, this layout is plenty small to fit depth-wise.

I really don’t have a solid understanding of wiring the transformers, pots, and switches.  In this layout, I use the JLM Go Between with variable pad on the input to handle phantom power, phase, and pad.  I'm also considering adding the JLM FetDi as well  Do you think the DI is a good plan or better to use an external DI? 

For visual purposes, I placed a column of cuts to separate the in and out of the transformers.  I used the 600ohm impedance wiring for the XLR in jack.  If you think it should be switchable impedance, please let me know how to do this.  I couldn’t figure out how to do it with an SP3T switch.  Also does anything need to be done with the transformer wires that are not shown to be connected on the schematic? 

On the output I’ve used an SPST for switching between high and low power mode and the CAPI or Hairball 600 ohm variable attenuator  I really don’t understand the transformer wiring.  I see on the schematic to tie the green and blue wires for the center tap, but I don’t know where the center tap should go from there.  I’m also assuming I can save column space by twisting the transformer wires that are connected to each other and soldering them both to a single hole. 

I gather that the downward triangles are to ground, but I don’t understand which ground they’re going to.  I believe one is to the chassis, and I’m guessing that one is the downward triangle consisting of lines rather than an outline of the triangle.   I really don't know though so please clear this up for me.

I’d also really appreciate any advice you can give on powering the pre.  I’d like to fit 4 of these in a single chassis with a separate power supply.  So which power supply kit would be needed to power 4 of these AM-16’s between the JLM Power Plant 2 or Power Station  If there are other kits you would recommend, I’m all ears.  I’d like to design one from scratch, but for a learning project I figure it would be good to go with a kit.  I learned a lot from building the AML EZ-P1A kits.  Fantastic, well organized, and well documented instructions for those newer to diy. 

Thanks for taking a look!
« Last Edit: November 02, 2016, 01:23:15 PM by swimtoview »


Nice that you are doing it in Veroboard, although you might have difficulty in having help around here for that design since most circuits are pcb based.
But anyway do your own thing, thats brave.

1) First thing, were are you located?
that will help in guiding you in sourcing parts and PSU

2) what transformers for the AM16 are you planning to use?

Do you think the DI is a good plan or better to use an external DI? 

I like to have a DI input in all my Mic Pres, it's practical, convenient, makes me faster in busy sessions

On the output I’ve used an SPST for switching between high and low power mode and the CAPI or Hairball 600 ohm variable attenuator

If you are in Europe you can get cheaper  T-PADs from Avdo, search around here.
Also you can use an 1K Pot at the output, will work fine

5) As for the PSU, don't buy one,  use veroboard also. You need a 2 rail PSU,  24v for to supply the Am16 circuit and 48V for phantom power, use LM317 regulators. it's easy enough to do.
 The AM16 will have a consumption between 55mA to 110mA.  so the Maximum of 4 units is 440mA. Do an 1 Amp PSU and you're overly protected. 
Use a Toroidal Power transformer with 2x22v secondary (2x20v will work also, 2x24 will work also) rated at 25VA
Check the JLM GO between schematic, skip the negative rail and copy the other 2 rails to a verboard. Then you have your PSU.
LM317 are variable regulators so you then use the trimmer to adjust to  24v and 48V (phantom power)