DIY DI and ReAmp Boxes?

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carboncomp

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Feb 22, 2022
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Hi, first I hope this is the right section to ask in. If not, sorry mods!

I'm on a super tight budget trying to set up a home studio set up mainly for guitar and am a total noob with recording/production. Right now I just have a 2 input audio interface, but would really like to use my guitar pedals in my DAW, and reamp some of my amps, I'm really only going to be using guitar so believe I can get away with just passive DI and Reamp boxes, right?

Are there any good open source builds people would recommend, would rather etch my own PCBs and use my stash of components than grab some DIY kit.

Any help, advice or criticism is welcome, as I say this is all new to me, so if I have asked or said anything silly, then I'm sorry!
 
The Bo Hansen DI box is great, it's not passive but it runs on phantom power, so no need to worry about external PSU. It's very easy to build and sounds great. It's a much better choice for guitar than a passive DI box.

Transformer choices are a bit limited for passive DI, whereas the Bo Hansen DI uses a regular mic input transformer wired in reverse. It also doesn't use any exotic JFETs or anything like that, just a complementary pair of transistors. BC550C and BC560C will work. I built mine on tag board using random parts I had on hand.

The top pic on this page (the original DI box from 1975) is nicely laid out using tag strips and P2P wiring, that approach is ideal if you want to avoid buying PCBs.

http://www.hansenaudio.se/techpage.htm
There are various reamp circuits floating around on here too, but I haven't got any direct experience with any of them.

This thread is worth checking out, if you haven't already seen it.

https://groupdiy.com/threads/di-reamp-theory-questions.69875/
 
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The Bo Hansen DI box is great, it's not passive but it runs on phantom power, so no need to worry about external PSU. It's very easy to build and sounds great. It's a much better choice for guitar than a passive DI box.

Thank you so much for the reply and links, can I ask what are the cons of a passive over the pros of a powered DI box?
 
Thank you so much for the reply and links, can I ask what are the cons of a passive over the pros of a powered DI box?
The obvious answer is that it's not powered.

Phantom power is standard on large format mixing desks which long ago every studio used daily. But these days the big analog desks aren't used as much. I don't have statistics of course but your average recording environment probably does NOT have phantom power available that would be useful for a DI. The small format mixers are quite common but usually they only allow switching phantom power on all channels together which can easily add noise to a mix. Phantom power noise on USB audio interfaces can be even worse because they have to use DC converters which are difficult to implement properly without polluting the noise floor with whistling noises.

IMO the ideal modern DI would be a dual 9V single op-amp impedance balanced output in a smallish steel box. Unfortunately because that's so trivial, nobody seems to make such a thing.

Currently I have one DI which is cheapo off-the-shelf unit that I hacked with 1) dual 9V battery bipolar supply and 2) a switch to make it impedance balanced out so that it can drive unbalanced loads. The op-amp is a dual and there's an LED but it lasts for literally months on two batteries as long as I don't forget to switch it off.

Another possibility depending on your circumstances is to just get some little booster pedal and make a TS to TRS or XLR cable or whatever cable you need. I have an Ernie Ball MVP active volume foot pedal which seems to be as simple as it needs to be very quiet. And having an active volume foot pedal can be useful for a variety of reasons (great for a keyboard rig if that happens to be what you need the DI for).
 
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The small format mixers are quite common but usually they only allow switching phantom power on all channels together which can easily add noise to a mix. Phantom power noise on USB audio interfaces can be even worse because they have to use DC converters which are difficult to implement properly without polluting the noise floor with whistling noises.
I have a USB powered 'Universal Audio Volt 2' Audio Interface that has two inputs that have independent instrument/line in/phantom power on each, for context.
IMO the ideal modern DI would be a dual 9V single op-amp impedance balanced output in a smallish steel box. Unfortunately because that's so trivial, nobody seems to make such a thing.
Interesting is that 2 9v in parallel or series? (ah, battery bipolar supply, so +9v and -9v) I like the idea of a 9v unit as would really like to have pedalboard-friendly DI and Reamp box as my pedalboard spends most of its time under the computer desk with an isolated power supply ready to go in 9-18V......could maybe do +9V into a MAX1044 DC to DC switching regulators to give me the bipolar supply??

Are there any simple textbook circuits out there I could use for the opamp part?
Currently I have one DI which is cheapo off-the-shelf unit that I hacked with 1) dual 9V battery bipolar supply and 2) a switch to make it impedance balanced out so that it can drive unbalanced loads. The op-amp is a dual and there's an LED but it lasts for literally months on two batteries as long as I don't forget to switch it off.

Would love to see that if you ever find yourself making a schematic.
 
I have a USB powered 'Universal Audio Volt 2' Audio Interface that has two inputs that have independent instrument/line in/phantom power on each, for context.
I would test the noise. Connect a mic (you can use a dynamic mic like an SM57 even when phantom is on), wrap it in a towel and stuff that under some couch cushions, turn on the USB interface, turn on phantom, crank the gain to the max, put on some headphones and listen carefully. Do you here pure white noise hiss only or is there any whistling? I would not be shocked if there were some whistling. The USB interfaces run on 5V (from USB) so they need to use a pretty agressive DC converter to make 48V. This is not a trival bit of circuitry. If not implemented perfectly, you can frequently get whistling noises in the noise floor.
I like the idea of a 9v unit as would really like to have pedalboard-friendly DI
Using a pedalboard supply can also easily introduce noise. Pedals are designed exclusively for single ended I/O because they have to assume you're connecting something that needs to be grounded like a guitar which would otherwise be floating electically which will cause all sorts of hum to be picked up. A guitar needs a low impedance 0V path. So they cannot use an impedance balanced output which is the go-to solution for eliminating group loop noise.

So you would probably get noticably better noise performance from a battery powered device. A single 9V battery would work just fine but if you want to generate pro-level signals, such as because you're driving some existing pro-level gear, using dual 9V bipolar supply with an extra 6dB is worth the extra battery.

There are now high performance op-amps with quiescent current of less than 1 mA. So one low quiescent current amp driving a typical load of 10K would last probably a couple of years.

Would love to see that if you ever find yourself making a schematic.
https://groupdiy.com/threads/livewire-adi-active-direct-box.69884/
 
I would test the noise. Connect a mic (you can use a dynamic mic like an SM57 even when phantom is on), wrap it in a towel and stuff that under some couch cushions, turn on the USB interface, turn on phantom, crank the gain to the max, put on some headphones and listen carefully. Do you here pure white noise hiss only or is there any whistling? I would not be shocked if there were some whistling. The USB interfaces run on 5V (from USB) so they need to use a pretty agressive DC converter to make 48V. This is not a trival bit of circuitry. If not implemented perfectly, you can frequently get whistling noises in the noise floor.
Thank you will give that a try!

And thank you so much for the link.

Slight tangent here but you seem to know what you're talking about. As my main usage is going to recording guitar tracks via a cheap USB interface and plan to use the DI box mainly so I can get a clean DI signal into my DAW while playing with my amp and then post-production on the clean DI track and would love to use my pedal in my DAW (I have too many guitar pedals), so thinking about reamping more as a way to play with the pedal setting, could I (or rather should I?) be better off making a couple of passive DI boxes set up in a signal chain like DI track from:

DAW -> Output of audio interface -> Reamp box -> Pedal chain -> DI box-> audio interface -> DAW?

As if I use a passive DI can I just flip it 180 and use it as a reamp box? The internet seems not to agree on if this can/should be done. So I would really like to hear your thought on the topic, keeping in mind this is going to be used just for a $200 audio interface budget home "studio" AKA my computer desk in my front room.
 
The big problem you're going to have with all of that is ground loop noise with the PC. It is very common to find that trying to connect the USB audio interface to a bunch of guitar pedals and amps and such causes ground loop currents that equate to hum in the signal.

However, this should be 100% fixed by just making the right cables. If you have a vaguely new USB audio interface, you just need to make a cable that takes a low impedance output from some pedal that's known to have a good low impedance out, and adapts that to the balanced XLR input (or balanced TRS if the interface has one). See this page:

https://www.ranecommercial.com/kb_article.php?article=2107
You want connection diagram 13 (or 14).

Note: The guitar needs a really solid earth connection. This should be provided either by the guitar amp.

For capture, you need a pedal like the livewire thing I have that has a "through" connection or equivalent pedal that splits the unmodified signal to the amp and then outputs to said cable to your USB interface.

Note: The livewire ADI direct box (LWADI) would work stock EXCEPT for the fact that the input impedance is only ~175K. So you could use it with a clean buffer in front. Or you can change the two resistors as described in my mods and get the impedance higer. But even then, it will be in parallel with your amp which is probably 1M so the impedance seen by the guitar would only be around 400K which is probably ok but some real pedants might take exception to it. So you might just use a clean buffer in front of the LWADI.

For re-amp, you can make another cable but this depends on whether or not the USB audio interface has a balanced output or not. If it does, then use connection diagram 5 probably and just plug right into the amp or pedal board or clean buffer. If it's not balanced, you probably want connection diagram 3 but in this case you are connecting grounds so you might get hum. This is another place where the simple impedance balanced single op amp device I originally mentioned would be good.

Re-amping will definitely require a bit of experimentation. I would just get your cables right as described above and verify that you can capture and re-amp without hum from ground connections. Leave out the pedal board. Play with the levels. If you re-amp into the LWADI you can simultaneously record loopback and verify that the levels are correct. You can also invert and mix the capture track with the re-amp capture and verify that they sum to zero and that they are therefore identical in signal and level.

This is all just thinking out loud though. If I were doing this, I'm sure I would find little issues that need to be tweaked to get a re-amping rig correct.

Note that a lot of comments on the Internet about reamping and devices that are advertised as being good for reamping are total BS. If you invert and mix as described previously and the two signals are verified to be identical, then your good.
 
I have a USB powered 'Universal Audio Volt 2' Audio Interface that has two inputs that have independent instrument/line in/phantom power on each, for context.
Are the instrument inputs on your interface not suitable? They're basically a DI input, so should be fine for the signal coming out of your pedals, assuming that ground loops don't get in your way. Depending on the pedals in question, you might be able to get away with a 10k:10k transformer for isolating the stompbox outputs from the inputs on your interface, that should eliminate any ground loops, should they appear.

If that works, you just need to figure out the reamp side of the equation.

Thinking about it, it sounds like you want something identical to the Radial EXTC-SA. It's a handy little box which is specifically designed for interfacing guitar pedals with pro audio gear.

https://www.radialeng.com/product/extc-sa
I've got an EXTC-SA stashed away somewhere (from before I got into DIY), I'll try to dig it out tomorrow and take some pics of it's guts. If it's as simple as the other Radial gear I've looked inside, tracing the circuit could be a viable option.
 
Are the instrument inputs on your interface not suitable? They're basically a DI input, so should be fine for the signal coming out of your pedals, assuming that ground loops don't get in your way.
Oh yes, they are fine for just recording I DI track, I was looking into DIY DI options mainly for the pass-through option, so I can hear my amp while I'm playing and then go back and tinker with the DI track and emulate or expand on the IRL amp, or reamp.

I think I will build one of the highly recommend around here Bo Hansén 1975 DI boxes, so that should cover my pass through to amp option, and maybe give me a slightly different sound over the audio interface instrument input.
Depending on the pedals in question, you might be able to get away with a 10k:10k transformer for isolating the stompbox outputs from the inputs on your interface, that should eliminate any ground loops, should they appear.
Yes, here is where it gets a little tricky as I have a lot of vintage pedals where I feel I'm going to run in with some issues as seems things like impedance and phase where are afterthoughts in the 60's
Thinking about it, it sounds like you want something identical to the Radial EXTC-SA. It's a handy little box which is specifically designed for interfacing guitar pedals with pro audio gear.
YES! that looks like exactly the kind of thing I'm after!
I've got an EXTC-SA stashed away somewhere (from before I got into DIY), I'll try to dig it out tomorrow and take some pics of it's guts. If it's as simple as the other Radial gear I've looked inside, tracing the circuit could be a viable option.
Thank you so much, that would be really appreciated even a stripped-down version without 2 loops and stereo would cover 90% of what I need (but do like the idea of having two pedal chains or two amps, just $300 is a little rich for my blood)
 
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