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70s SVT out to board question, which is right?

DATman

DATman

Jan 18, 2015
40
37
Bozeman, Montana
#1
Folks-
I have gotten a mixed bag of answers to this question, so putting it out to the group...
I recently got (and had restored) an Ampeg SVT-300 serial number makes it 1976-79 (Magnavox) blackline. I expect to mic it, but sometimes also DI out to the board, and want the right cable.
I have heard 3 recommendations:
1. 1/4" instrument cable to board (XLR)
2. 1/4" TRS (like for a PA main/monitor) to XLR
3. 1/4" (TRS I think they said) short to direct box, direct box XLR to XLR
Attached is a photo, and it's important to reference -- the out jack I assume is the one to use is called "pre-amp out" (so for example, the "power output" one that goes to the external).
Maybe if I could find a specs manual, that would be a final answer, but wondering...
 

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#4
Not a lot of info to work from, but your pic was a great help...

If the pre out is a TS 1/4" which I presume it is, that means it is unbalanced audio.
XLR inputs to audio boards are balanced audio.

Unbalanced has a single conductor in the center and is surrounded by a shield conductor.
With unbalanced, audio is traveling over both the center and shield conductors.
The shield conductor also does double duty to try to shield the center from extraneous, noisy signals.

Balanced cables have two internal conductors that are twisted around each other over the length of the cable.
This alone helps reject sone types if external noise.
These two twisted conductors carry the audio signal.
The shield only acts as an additional guard against external noise getting in.
But the shield does not carry any of the audio signal.

The problem comes when trying to use balanced and unbalanced together.
It is not enough to just have the right connector on each end.
And depending on a lot if variables that can occur, it may not even be enough to try to wire as balanced on one end and unbalanced on the other. These wiring schemes are not stuff for the uninitiated in doing audio interfacing.

You can buy adapters that will allow you to plug XLR into 1/4" and the other way around.
They look right, but you still may have not solved the unbal to bal problem.
The symptoms are often lots of hum on the signal or significant loss of signal.

The easiest thing for someone who wants a plug and play solution, is to use a balancing/unbalancing transformer.
You can find these built into an XLR to 1/4" adaptor. Just be sure your adaptor has a transformer and is not just an adaptor alone.

The other possibility is if the mixer has unbalanced line inputs. This way you are going from unbalanced to unbalanced. Technically more correct, but not as good as converting to balanced for the long run to the mixer.
You can convert from 1/4" TS to RCA (phono style) without a problem since they are both unbalanced.
 
#8
Jack said:
Sorry to confuse matters even more, but for an all tube amp like that I'd suggest a speaker level DI (I own and love the countryman) after the power section of the amp.
Click to expand...
Actually a good point in my opinion as well.
If you want to get the tone of the whole amp, you would heed to use a speaker level DI.

Some folks feel that tube amps will color a signal more so than a solid state amp.
That is a discussion for another place and time.

Whatever your tone, or type of amp, where you put the DI, before the amp, in the affects loop, at the output, will affect the tone you send out from the DI.

Note: A DI for use at the amp output may be a specialized unit for that purpose.
You may not be able to use just any DI at any point in the chain.
It all comes down to understanding the audio interface point and applying the right tool.
 
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#9
Jack said:
Sorry to confuse matters even more, but for an all tube amp like that I'd suggest a speaker level DI (I own and love the countryman) after the power section of the amp.
Click to expand...

This.

A lot of the elusive tube tone and vibe so many people who buy tube preamps end up being disappointed over when they aren't quite able to dial it in is because the tube power stage also significantly colors the sound. A tube preamp alone isn't always going to be enough to give that to you.

A lot of that classic "SVT drive" tone comes from pushing its power stage hard. Not saturating its preamp.
 
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#13
it's a tube amp must always be plugged in to the cab.. so DI/CAB box is nice to do. JDX Red box(300watts), and avalon u5(400watt) can do this you plug into the Amp plug the speaker out into the Box the plug the box in to the cab, and the DI in the board. there you go. if I was in your situation that's what I would do. Have fun
 
#14
Chris 'Wighat' Jordan said:
This would be a good time to confirm that the SVT's pre amp out and power amp in jacks are in parallel and neither interrupt the signal between the pre and powe sections like on the orginal V4B. Is this correct @beans-on-toast? If so, then both jacks are a funtionally identical, right?
Click to expand...

In the vintage SVT amps, the pre out and power amp in are simply taps that split the signal out and in much like a Y cord would. There is a shunt on the power amp in jack that breaks the SVT's preamp connection when a plug is inserted. Later revisions such as the CL and VR are slightly different in approach.


1977 SVT power amp patching: J1 is preamp out, J2 is power amp in


svt patch.JPG
 
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#15
Micing the cab with the mic directly in front of a top speaker's voice coil cover is my favorite method, but even when you bring your own very nice mic, stand, and cable, you will find some sound techs will flat out refuse to use it because they're babies. Running a DI line from the speaker out is a very close second, though I've done some preamp DIing with modern SVT's lately and it's really good, too, just not quite as dramatic sounding as going from the power amp. But since you'll need a DI anyway, I'd say just get one that does speaker level, get a couple speaker cables, and go from the main speaker out to the DI to the cab (always have to have a cab plugged in). And don't use the ext speaker jack separately, as this will change the impedance the power amp is expecting from the cab and it won't be getting it.
 
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#16
My most favoured option is to mic the cab. I find that it sounds the best. Next best is to use a DI that can tap the speaker output. This allows the contribution of both the pre and power amp in the signal chain.

But this isn't the only way to have a good sound. You can plug directly into a DI, split the input into the amp, and send a feed via XLR to the mixing desk. The amp serves as a monitor on stage. The sound guy likes this because they receive a constant volume and can process the signal the way that they want. There isn't a contribution from the amp at all, they have a clean slate. From their perspective, this is often the best option. Can this sound good? Absolutely! Especially with digital desks, plugins that emulate amps work very well. Leaving it all to FOH doesn't always work the best.

The problem with this is that if you like your SVT tone, this isn't what is going out to the house. Your sound will be what the FOH person determines it should be. Kind of like going to a barber and letting them do whatever they want with your hair. You should have a say in how you want to present yourself.
 
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#17
I think it depends on how big your venues are.

In most of the places where I play my SVT, I don't mind running a DI pre-SVT for that little bit of bass reinforcement I need. We aren't playing stadiums so people can still hear my amp primarily. I have a few preamps with DIs so I run those last and then send a DI signal to the board.

If you really need that character, I would follow the advice given here of go preamp out to DI to board.

Another option is something like the Broughton P-15. You could use it as a DI pre-SVT and still get a ton of Amore character as it's a copy of the b-15 pre.
 
#18
I think the best option when a mic on the cab is not a option is a speaker level DI. ...I have a countryman and used to use it with my vintage Bassman 100 head that didn't have any kind of DI or Line output.

If you have a really picky sound man, you can always flip a switch on the countryman, and hook it up in front of the amp for a pre-DI signal. If you want a post-DI signal, run it out of the pre-amp out... and if you want to get some of that power tube flavor (which of course you do, because why would you be playing a vintage SVT otherwise), then run the DI speaker level.

Might check out the Radial JDX 48 Reactor DI box too.
 
#19
beans-on-toast said:
No TRS. Use a regular ¼"-to-¼" instrument cable from pre out into DI, then XLR from DI to the mixing board.
Click to expand...

I wonder is the preamp out signal instrument or line level? Is there an issue with plugging a line level signal into any old DI or should it be something with a pad or speaker switch?

The genesis of this question is really more of a tangential query about amps with 1/4" line out taps. On one of my amps I have a line out that's tapped off the OT secondary with a level control, similar to the Mesa 400/+ and some others. I was doing a gig recently where the FOH didn't want to run from an unbalanced line out, and I didn't really think I needed FOH for the size of the room so I hadn't brought either of my DIs, so I ended up going DI before the amp.

I know the obvious answer is that I have the amp, several DIs, and a number of PA or recording options so I might as well do the experiment myself, but I figured I'd ask.
 

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