Please check my work

[withering_drums]

Here's my latest schematic. I ended up using relays because I wanted to have a pad switch that worked on both the DI and the Mic line, without having a giant switch that was super pricey.

I have everything else soldered, but since Im a stagehand and work is crazy slow this time of year, I cant spend any money one this currently.

 

[abbey road d enfer]

Why a balanced attenuator for an unbalanced input?
The DI circuit has too much gain, not very predictable either, as is the operating point.
What are C6, R17, D3 & 4 doing, being unconnected?
I'm not sure the relays will work, being powered via a 6.8k resistor... They draw about 30mA each, and the 6.8k limits current to about 7mA.

 

[withering_drums]

So... I didnt think about it being unbalanced, I could definitely make it way easier with a switch, and a single resistor.

The C6, R17, D3 & 4 are meant to be connected. I meant to label it, but the ground below R17 is connected to the XLR pin 1 like in the Bo hansen. I dont fully understand it, but I guess it isolates it?

I should have put that resistor and led in parallel...

Ok so Im not sure why the DI circuit has too much gain. Its a loss of about 15 dBu and that seems fairly common to me. What am I missing?

 

[abbey road d enfer]

Ok so Im not sure why the DI circuit has too much gain. Its a loss of about 15 dBu and that seems fairly common to me. What am I missing?

Your schemo shows a wrong connection of Q2. Its emitter should be oriented North. So in fact its a Dalington emitter-follower with unity gain.

 

[withering_drums]

Thank you. I feel like before the internet and wonderful people on forums like yourself, I would've had to learn this with many hours/dollars starting fires and making a lot of unpleasant noise. I truly am grateful, and still fully expect said fires. I also appreciate not just handing over answers, Ive learned a lot on this thread.

Soooo. I feel better about where Im at now. Ive triple checked this one for errors, but Im sure Ive done something silly.
I changed the pad on the line level to a -10 dB pad, because it seems like more of a typical level for guitars and Im not worried about messing up the input impedance. I'm a little worried some guitars with active pickups might be an issue though.

I also added the cap to pass some of the hi frequencies. Im not sure if this is necessary, but Im going to try it.

 

[abbey road d enfer]

I'm a little worried some guitars with active pickups might be an issue though.

U2, which is noted Polarity switch, is actually the Pad switch.
R4, C7 and connections to U2 make no sense at all as they are. Check attachment.
C6, R17 and diodes D3 & D4 are still unconnected.
R1 & R2 should be connected directly to pins 2&3 of the XLR, not after the pad.
R13 & R16 make no sense to me; looks like they are a remnant of phantom powering.

 

[withering_drums]

So Im not sure whats up with C6, R17 and diodes D3 & D4. Im assuming that if there was stray voltage of some sort in the ground, it would trap it in the cap? I dont know really.  But Im just copying it from the Bo Hansen DI schematic. The only thing I see different is the ground is connected to the opposite side of R17.  That would make sense, I guess I just assumed it didnt matter because they werent polarized, but that sounds silly now that I type it. Is this whole ground isolating thing necessary though?

I also copied R4, C7 and connections to U2 from the Bo Hansen page. It really didnt make complete sense to me either, and yours make total sense, so Ill go with that. I thought that maybe R8 was my reference to ground for a L pad? I dont know. R4 was supposed to be 2.2M though, forgot to change the label on that.  I also forgot to change the label for the pad.

R13 and R16 I now think were doing the same thing as R1 and R2 and were unnessary, but now that you pointed out that the phantom should be directly on XLR pins, I probably need a new connection to power the DI and can use R14 and R16 again?

 

[withering_drums]

Heres where Im at...

 

[abbey road d enfer]

Heres where Im at...

You don't need R13 & 16.
Make the connection of R7 to pin 9 of the relay

 

[withering_drums]

Ok so the first schematic is without R13&16, which makes sense to me the way I had it layed out, but I forgot to power the di Circuit. The first schematic leaves me with no voltage supply, right?

So wouldnt I have to do something like the second schematic?

 

[withering_drums]

Second schematic

 

[abbey road d enfer]

Second schematic

Ditch R16. Make R13 1k.
You don't need the connection between junct R15/LED2 and pin 2 of the 48V switch, nor the connection between Pins 2 & 4 of U2, nor between pins 7 & 9 of U1. No issues there, but it just clusters the schemo and wiring.

 

[withering_drums]

Changes made. I went ahead and started designing the PCB. I changed the led's to headers, but decided it would be much easier to just solder them to the top of the switches. I left the headers in the schematic, but Ill probably change it back to LED's at some point. I also updated the components to ones I can buy. Not a whole lot different though.

I need to read the grounding thread here (among many many others) I have heard a lot of stuff about star grounds and such but I ended up doing a ground plane simular to the one on the bo hansan design. Im not sure how close I can have Phatom power running to signal traces, but It cant be that big of a deal. Im probably wrong though.