Stereo Reamp, DI Box, Passthrough

[facon]

Hey guys, so I need a rack mount box with two guitar reamps (line to unbalanced guitar), a DI box (line to mic level) and I'm including a few passthroughs that will make things convenient to have at the front of the rack unit.

For the reamp design I'm using: http://www.jensen-transformers.com/as/as092.pdf

For the DI Box I'm using: http://www.jensen-transformers.com/as/as007.pdf

Can somebody take a look at this layout and verify that I've done things correctly? This is the first time I've worked on a project like this from a schematic. Also, any pointers on grounding or potential noise issues with having these all in one unit? Thanks!



*And for anybody interested. The reason for this is for my band's live show. We will be using a digital recorder to send prerecorded tracks out individually. Stereo guitar tracks through the reamps to two amplifiers. Synth through the di box to the FOH. 3.5 mm for the click track for drums.

[facon]

BTW, I'm not completely sure if the schematics are calling for electrolytics or film. The schematic for the reamp seems to indicate electrolytic, but at .01 uf, that's pretty small right? Can I get away with film for that?

[tubegeek]

My first gut reaction: snip off the 3.5 mm plug from your clicker, replace it with a 1/4" TRS plug, replace the female jack in the passthrough section of the diagram to match.
You NEVER want to depend on a 3.5 mm interconnection with your live-performance reputation on the line!

.01 film is fine, preferable in fact.

'Splain me - is the synth played live or is it triggered by MIDI coming from the pre-recorded stuff or what? Which way is the DI box going? 1/4" unbal from the synth  to XLR bal feeding FOH? I would send the synth at line level to FOH rather than transform it down, assuming it can operate at a low enough impedance. Maybe an isolation (1:1) transformer if you want to be loop-proof.

[facon]

Okay, the idea was to use it for a headphone out. I guess it would be prudent to just have a couple 1/4th inch to 3.5 mm adapters handy? The Neutrik XLRs are all the multijacks, so I'm just going to replace the 3.5mm with another Neutrik. Thanks for your input!

The synth is on the digital recorder as a mono audio track. The distances on some of the stages from the digital recorder to the board are so long that I'd prefer to bring it to mic level than rely on carrying the signal line level. We play some 2000+ venues. The audio would be coming from the recorder into the 1/4 mono switchcraft and would be coming out of the Neutrik XLR at the top.

[tubegeek]

Okay, the idea was to use it for a headphone out. I guess it would be prudent to just have a couple 1/4th inch to 3.5 mm adapters handy? Thanks for your input!

So your expected situation is a stereo pair via XLR from the recorder to a 3.5mm headphone stereo pair? I assume you are adapting a 1/4" TRS headphone out on the recorder to this special stereo-XLR cable and you're doing that so you can use standard mic cables for all those runs? Then get a pair of headphones with 1/4" TRS plugs (or re-terminate your favorites) and adapt back from special-stereo-XLR to 1/4" TRS. Or terminate the headphones with special-stereo-XLR I suppose. I'm all for having a tested and pre-determined setup for consistency's sake so I don't want to discourage you from packing exactly what you want for your show. And if you're worried about the headphones being "special," pack a few spares. Headphones are cheap. But you can expect to be able to find 1/4" TRS headphones commonly available, ar at least headphones with a screw-on, somewhat reliable 3.5mm to 1/4" adapter as part of the package. What I'm trying to say is, don't rely on a 3.5mm female jack anywhere in your rig if you can plan a better choice.

The synth is on the digital recorder as a mono audio track. The distances on some of the stages from the recorder to the board are so long that I'd prefer to bring it to mic level than rely on carrying the signal line level. The audio would be coming from the recorder into the 1/4 mono switchcraft and would be coming out of the Neutrik XLR at the top.

Me, I might use a center tapped transformer to balance the synth cable on its long run, but I wouldn't cut the level down to mic level for no real reason. I suppose you might POSSIBLY cause crosstalk by having a line level signal in the snake to FOH, but I REALLY REALLY doubt it - each twisted pair is shielded from its neighbors inside the snake.

FOH will be able to accept a line level signal at the mix position in all but the most completely bass-ackward cases. Murphy's Law states you will run into such a case, now that I've brought it up....

[facon]

Okay, the idea was to use it for a headphone out. I guess it would be prudent to just have a couple 1/4th inch to 3.5 mm adapters handy? Thanks for your input!

So your expected situation is a stereo pair via XLR from the recorder to a 3.5mm headphone stereo pair? I assume you are adapting a 1/4" TRS headphone out on the recorder to this special stereo-XLR cable and you're doing that so you can use standard mic cables for all those runs? Then get a pair of headphones with 1/4" TRS plugs (or re-terminate your favorites) and adapt back from special-stereo-XLR to 1/4" TRS. Or terminate the headphones with special-stereo-XLR I suppose. I'm all for having a tested and pre-determined setup for consistency's sake so I don't want to discourage you from packing exactly what you want for your show. And if you're worried about the headphones being "special," pack a few spares. Headphones are cheap. But you can expect to be able to find 1/4" TRS headphones commonly available, ar at least headphones with a screw-on, somewhat reliable 3.5mm to 1/4" adapter as part of the package. What I'm trying to say is, don't rely on a 3.5mm female jack anywhere in your rig if you can plan a better choice.

No this makes sense. I really didn't think about the reliability of 3.5mm jacks. I'm glad you said something. And to think about it, we do have studio headphones with 1/4 inch jacks. It's just that normally the small monitor style ear buds that are convenient for live come with 3.5mm standard, so I'll probably have the adapters around just in case.

The synth is on the digital recorder as a mono audio track. The distances on some of the stages from the recorder to the board are so long that I'd prefer to bring it to mic level than rely on carrying the signal line level. The audio would be coming from the recorder into the 1/4 mono switchcraft and would be coming out of the Neutrik XLR at the top.

Me, I might use a center tapped transformer to balance the synth cable on its long run, but I wouldn't cut the level down to mic level for no real reason. I suppose you might POSSIBLY cause crosstalk by having a line level signal in the snake to FOH, but I REALLY REALLY doubt it - each twisted pair is shielded from its neighbors inside the snake.

FOH will be able to accept a line level signal at the mix position in all but the most completely bass-ackward cases. Murphy's Law states you will run into such a case, now that I've brought it up....

Hmm, I guess I'm confused as to why so many people use a DI box then. I've read loads and loads of articles stating that line level instruments on stage benefit from using a DI. When we used to use live keyboards, almost every venue we played said they preferred to use a DI box for it. Regardless, I'd really like to have a DI available just in case.

Here's a quick article that popped up first when I googled "why use DI box": http://www.soundonsound.com/sos/aug11/articles/qanda-0811-5.htm

Btw, I hope I'm not coming off as snippy in the slightest bit. I'm legitimately very interested in learning what I can.

[ashcat_lt]

The assertions in your link are all true.

I find it difficult to believe that the added noise from the higher impedance is worse than the effect of running a lower level signal and amplifying more at the mixer, but I've never tested it.  Yes you want those long runs to be balanced.  Yes ground isolation can be useful.  But you could use a 1:1 transformer to get all of that AND keep the signal level higher to maximze S/N ratio.  Most places you play don't have 1:1 DIs lying around, but if you're building your own.

I don't believe that treble loss is much of an issue at line level imledances either, until your cables get to be absurdly long.

Then there's the thing of interfacing with the mixer.  Most places which have a stage snake will not have any TRS runs set up to hit mixer channels.  If they exist at all their usually used as "returns" to the stage, or far more often just not plugged into anything.  And the XLR runs hit microphone preamps which "expect" a low microphone level signal.  Thing about that is that they also have trim pots and often pad switches which work perfectly fine. 

My bands come pre-mixed.  We send pseudo-balanced line level signals via XLR tbrough the stage snake where it exists straight to a pair of mic inputs.  I've never had a problem.  When somebody other than me is running the mixer they are usually impressed by how easy and low maintenance we are.  Ground loop hum can be a problem in places which do not have the FOH and the stage power sharing a circuit.  That's unconsciobly dangerous anyway, though, and in those situations I insist on running our power from wherever the mixer is plugged in.

[facon]

The assertions in your link are all true.

I find it difficult to believe that the added noise from the higher impedance is worse than the effect of running a lower level signal and amplifying more at the mixer, but I've never tested it.  Yes you want those long runs to be balanced.  Yes ground isolation can be useful.  But you could use a 1:1 transformer to get all of that AND keep the signal level higher to maximze S/N ratio.  Most places you play don't have 1:1 DIs lying around, but if you're building your own.

I don't believe that treble loss is much of an issue at line level imledances either, until your cables get to be absurdly long.

Then there's the thing of interfacing with the mixer.  Most places which have a stage snake will not have any TRS runs set up to hit mixer channels.  If they exist at all their usually used as "returns" to the stage, or far more often just not plugged into anything.  And the XLR runs hit microphone preamps which "expect" a low microphone level signal.  Thing about that is that they also have trim pots and often pad switches which work perfectly fine. 

My bands come pre-mixed.  We send pseudo-balanced line level signals via XLR tbrough the stage snake where it exists straight to a pair of mic inputs.  I've never had a problem.  When somebody other than me is running the mixer they are usually impressed by how easy and low maintenance we are.  Ground loop hum can be a problem in places which do not have the FOH and the stage power sharing a circuit.  That's unconsciobly dangerous anyway, though, and in those situations I insist on running our power from wherever the mixer is plugged in.

Thanks for the info. After reading both suggestions, I'm considering adding a switch at the input (line level) of the direct box that will allow me to choose between the mic level DI and a 1:1 line level ISO. This should cover all the ground I might possibly need correct? Am I taking the information correctly? Budget isn't as much of a concern as making sure we're covered for all situations. I could also easily just add a bypass to both that simply sends the signal straight through without any change.

[ashcat_lt]

And that would work fine in most situations anyway.  When I said the my lines are psuedo-balanced I meant just that.  The output from my line mixer is unbalanced TS straight off of an opamp gain stage.  I run the tip of the jack to one of the inner conductor of the XLR, sleeve to the other.  The shield is connected to the third pin on the XLR, but not connected at the TS end.  Gives most of the benefit of a balanced run with none of the drawbacks of a transformer.

[tubegeek]

Thanks for the info. After reading both suggestions, I'm considering adding a switch at the input (line level) of the direct box that will allow me to choose between the mic level DI and a 1:1 line level ISO. This should cover all the ground I might possibly need correct? Am I taking the information correctly? Budget isn't as much of a concern as making sure we're covered for all situations. I could also easily just add a bypass to both that simply sends the signal straight through without any change.

Certainly nothing wrong with a belt-and-suspenders approach.

I think the typical situation where a keyboard DI is used, is when you want to split it to go into the mix AND to a local amp near the player. But in any case there IS more than one way to skin a cat.

[facon]

Thanks for the info. After reading both suggestions, I'm considering adding a switch at the input (line level) of the direct box that will allow me to choose between the mic level DI and a 1:1 line level ISO. This should cover all the ground I might possibly need correct? Am I taking the information correctly? Budget isn't as much of a concern as making sure we're covered for all situations. I could also easily just add a bypass to both that simply sends the signal straight through without any change.

Certainly nothing wrong with a belt-and-suspenders approach.

I think the typical situation where a keyboard DI is used, is when you want to split it to go into the mix AND to a local amp near the player. But in any case there IS more than one way to skin a cat.

Great. Thanks for all of your input!