B15N Preamp DI layout

[Jatchley]

Howdy yall. i tried to read a schematic and draw a layout from what i read for the first time. i made this preamp. im not sure if it actually works. im still sourcing parts. i did change the 12au7 for a 6sn7. the schematic i found also didnt have a power section so i did my best at thinking what the power supply would be. id love any advice and help with any mistakes. it should be a neat little preamp.

*edit* someone on facebook said the coupling caps (..22) are on the wrong side of the plate load resistors. looking into that. ( turns out to just be on the schematic not the layout)

[PRR]

Welcome.

> looking into that.

https://drtube.com/schematics/ampeg/b12n-jp.gif

[Jatchley]

im also curious to exactly which OT i should get. any suggestions here?

[AmberB]

From the schematic that you posted, it looks like you need an impedance matching transformer, the kind use to convert a low impedance microphone to a high impedance signal.  They work for both inputs and outputs.

[xm52]

https://el34world.com/Forum/index.php?topic=19832.0

[Jatchley]

hey there. the box is built... but im having some hum issues on the XLR out. the 1/4in out works great! so i went with an edcor xsm 15k:600 and i have pretty significant hum and low levels out. the 1/4 in out is much cleaner and higher level. the edcor has a CT for both primary and sec. the primary CT reduced about half of the hum and the secondary CT does nothing when grounded. i have the xlr ground pin to a ground lift switch run straight to the chassis. ive tried lifting all the grounds from the XLR and OT with no difference. i have also tried switching the OT primary and no change. any ideas?

*edit* ALL IS GOOD SOLVED THE PROBLEM! accidentally switched up pins 1/2 on xlr. swapped em and the box is silent.

[tazwolf]

I am going to build this preamp. I wonder if someone can give me some help. I will not be able to get hold of a suitable DI output transformer for a while but I want to use the instrument out until i do, is it possible to use the the pre without the 600R DI out? Do I just leave it unconnected or do I need to put a resistor in its place temporarily and if so what value resistor should I use?

Also if anybody has built this and has any advice in addition to what is already written here then I would be very grateful.

[sluckey]

Just build everything except the transformer. No need for a temporary resistor.