Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Jatchley on September 11, 2020, 09:32:16 am

Title: B15N Preamp DI layout
Post by: Jatchley on September 11, 2020, 09:32:16 am

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)

Title: Re: B15N Preamp DI layout
Post by: PRR on September 11, 2020, 11:55:26 am

Welcome.

> looking into that.

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

Title: Re: B15N Preamp DI layout
Post by: Jatchley on September 11, 2020, 08:52:51 pm

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

Title: Re: B15N Preamp DI layout
Post by: AmberB on September 11, 2020, 10:41:54 pm

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.

Title: Re: B15N Preamp DI layout
Post by: xm52 on September 15, 2020, 07:10:15 pm

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

Title: Re: B15N Preamp DI layout
Post by: Jatchley on September 25, 2020, 11:51:07 pm

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.

Title: Re: B15N Preamp DI layout
Post by: tazwolf on September 22, 2022, 09:14:43 am

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.

Title: Re: B15N Preamp DI layout
Post by: sluckey on September 22, 2022, 09:27:11 am

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