My DI Design

[a soBer Newt]

So this is a DI that I built from the schematic for the output of a mic pre that I have. I love how it sounds now what if anything am I doing wrong? Should I include DC blocking caps on the front end or larger resistor to ground for a higher input impedance?



Sound Sample

http://soundcloud.com/a-sober-newt/bass-di-evan-1

[Jarno]

Did you use the schematic from the datasheet, thought that these drivers are usually in the feedback loop of the opamp (at least buf634 and LME49600)?

[Gurner]

So this is a DI that I built from the schematic for the output of a mic pre that I have. I love how it sounds now what if anything am I doing wrong? Should I include DC blocking caps on the front end or larger resistor to ground for a higher input impedance?

Whilst the technical purists might differ, from what I can see, what you've done is fine....you're using a bipolar supply, therefore there's gonna little (or almost zero) DC present at the first opamp +ve pin ...i.e. with a guitar plugged in (your pickup will bias the +ve pin to ground once plugged in). Adding a resistor would actually lower the input impedance vs what you have there at the moment (ie no resistor) ....that said without a guitar plugged in, the +ve pin will likely float up in DC a little....so if you intend switching in/out an input signal regularly, you're likely gonna get pops, so then biasing the input to ground with a 1M resistor should help.

[a soBer Newt]

Did you use the schematic from the datasheet, thought that these drivers are usually in the feedback loop of the opamp (at least buf634 and LME49600)?

The buf634 looks to be an unbalanced line driver where as the DRV 134 is a balanced line driver.

So this is a DI that I built from the schematic for the output of a mic pre that I have. I love how it sounds now what if anything am I doing wrong? Should I include DC blocking caps on the front end or larger resistor to ground for a higher input impedance?

Whilst the technical purists might differ, from what I can see, what you've done is fine....you're using a bipolar supply, therefore there's gonna little (or almost zero) DC present at the first opamp +ve pin ...i.e. with a guitar plugged in (your pickup will bias the +ve pin to ground once plugged in). Adding a resistor would actually lower the input impedance vs what you have there at the moment (ie no resistor) ....that said without a guitar plugged in, the +ve pin will likely float up in DC a little....so if you intend switching in/out an input signal regularly, you're likely gonna get pops, so then biasing the input to ground with a 1M resistor should help.

This I know may be a hard question to answer but would the pops come from turning on and off pedals in front of the DI or just inserting the cable?

Would this be a slightly better design at all, I changed resistor values a bit to what I have more readily available.


Screen shot 2011-12-16 at 4.36.21 PM by asobernewt, on Flickr