converting speaker level to line level

Justice C. Bigler

Justice C. Bigler

Senior
Jan 11, 2011
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Tulsa, OK
www.justicebigler.com
A stupid question, that one of my colleagues asked me today, if I had a way to convert an 8ohm speaker level to line level. I simply said "no". I suspect that this has something to do with the back stage program speaker on our loading dock that he disconnected and took down yesterday, but am unsure. So now, I am curious. Is there in fact a way to do this?
 
Re: converting speaker level to line level

Justice C. Bigler said:
A stupid question, that one of my colleagues asked me today, if I had a way to convert an 8ohm speaker level to line level. I simply said "no". I suspect that this has something to do with the back stage program speaker on our loading dock that he disconnected and took down yesterday, but am unsure. So now, I am curious. Is there in fact a way to do this?
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Yes, you definitely can. However, the trick is that there isn't a standard 'speaker level.' You simply need to pad the signal down enough to get back to line level. There are several different units on the market that can do that. Most of them I have seen are designed for 200 watt amps or less. If you're running a bigger amp, all you'll need is an additional resistor to pad the output and you're good to go.
 
Re: converting speaker level to line level

If it's a 70V system you can just use a transformer with a very low wattage tap.

Car audio people deal with this all the time too -but they usually aren't intended for more than 20 watts.

Likewise studio folks have devices to take guitar-amp speaker outputs and provide line outputs for direct recording.
 
Helge Dr. Bentsen said:
BSS AR133 or similar DI with a large pad should do the trick.

And it runs on a 9V battery if you are in a location without phantom power.
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I don't think the BSS unit can. I've had the input side of ours clip from high output stick basses, even while padded. It seems it clips before the pad.

The Whirlwind Director, however, can, though I've never done it.

Jason
 
Re: converting speaker level to line level

I've used it once for that purpose, and I don't recall any problems.

Maximum input level with the pad @-40 is +49dBu, 218V. Should be enough for something like a PLM20000Q or similar.

What I have experienced, is BSS units with broken pads. Try testing yours against a second unit :)
 
Helge Dr. Bentsen said:
I've used it once for that purpose, and I don't recall any problems.

Maximum input level with the pad @-40 is +49dBu, 218V. Should be enough for something like a PLM20000Q or similar.

What I have experienced, is BSS units with broken pads. Try testing yours against a second unit :)
Click to expand...

Hmm. I own eight of them. They all seem to do the same thing every time I would run into a stick bass so I figured it was the output level of that instrument.

It rarely happens when checking them, only as they start to get into playing harder, so I have to run out on stage in the middle of the set and make a swap. I just learned not to use the BSS units for those instruments. Love them for most other things...

Maybe it was an impedance issue or something. Anyways, sorry for the topic swerve. Carry on...

Jason
 
Re: converting speaker level to line level

Craig Hauber said:
If it's a 70V system you can just use a transformer with a very low wattage tap.
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It doesn't even have to be a 70V system for that matter. The transformer doesn't care what is feeding it, as long as certain voltages or power levels aren't exceeded. If it really is a backstage speaker, I can't see that exceeding anything.

As an example, 2W at 8Ω is 4V, which is +14 dBu. But that's not a steady state signal, so if we assume there's 10 dB of headroom, your average level is +4 dBu, or just about exactly what we often consider to be "line level". So IF you were pushing a 2W peak level into that speaker, a 1:1 transformer on the old speaker wire is likely about right to interface with a line input. You don't strictly need the transformer, but it's a good idea in order to isolate the grounds of the two systems, and the output will now be balanced.

If you really do have a 70V system, then a transformer with a 2W tap would be a good one to use. This ends up being a 17.5:1 ratio, if you're keeping score.

That's about the same ratio as a typical direct box (20KΩ to 600Ω), but I suspect a transformer designed for speakers will be less expensive, as well as being rated to handle those kinds of voltages. The other problem with a direct box is that they typically output a "mic" level, and Justice says he's looking for "line" level.

GTD
 
Re: converting speaker level to line level

So, it appears, after I got in this morning and started talking to the guys that took my speaker down, that they thought they could actually just plug a powered speaker into the output taps on the other 70 volt speakers in the area.

I happen to have a bunch of older Pro Co DB-1 direct boxes which have a switch that changes the input between SPKR and INST, as well as what appears to be a line level OUTPUT (in addition to the XLR mic level output). Getting something up to line level from mic level is relatively easy, especially since these guys want to be able to play an iPod or what not through the back stage speaker so they can listen to music while they are doing whatever it is that stage carpenters and electricians do when people aren't watching them too closely. So it appears that I am also hooking up a small mixer for whatever replaces this speaker that they took down.

I'll have to post of picture of this speaker that they took down. But it's gonna be a while. it's buried behind a fork lift and miscellaneous pieces of a Nutcracker set.
 
Re: converting speaker level to line level

Helge Dr. Bentsen said:
I've used it once for that purpose, and I don't recall any problems.

Maximum input level with the pad @-40 is +49dBu, 218V. Should be enough for something like a PLM20000Q or similar.

What I have experienced, is BSS units with broken pads. Try testing yours against a second unit :)
Click to expand...

Helge.

Interestingly, I have also experienced overdriven BSS AR-DIs, from various electric pianos. Are you certain that both of the pad switches truly are pads that are run before all any any electronic circuits? I recall the older Klark boxes having a "pad" and an "attenuation" switch for this very reason (I assume one actually pads the input signal while the other attenuates the OP-AMP inside the DI ciruit).



Anyway, to the OP: There are some really cheap 70v->XLR male step-down boxes out there. I have a couple somewhere.

Also, the RED DI from Behringer specifically says in the manual that it will handle being hooked up to something like 2kW worth of loudspeaker.
 
Re: converting speaker level to line level

Christian Tepfer said:
Yeah, you have to get a DI box with a true pad of around 40dB, essentially we want to pad the amp gain to get to the signal level at the amp's input.
For me it doesn't have to be an active DI box, a good passive's alright.
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According to the spec sheet for the Pro Co DB-1 (original version), it will handle an 8 ohm speaker load up to 600 watts.

But I'm thinking I need to get a couple of those 70 volt to XLR step down boxes just to have anyway. Could be useful in a few different applications. Have a link to said unit?
 
Re: converting speaker level to line level

Justice C. Bigler said:
According to the spec sheet for the Pro Co DB-1 (original version), it will handle an 8 ohm speaker load up to 600 watts.

But I'm thinking I need to get a couple of those 70 volt to XLR step down boxes just to have anyway. Could be useful in a few different applications. Have a link to said unit?
Click to expand...

Different Kristian....

I will see what mine are called tomorrow and post back.
 
Re: converting speaker level to line level

Christian Tepfer said:
Yeah, you have to get a DI box with a true pad of around 40dB, essentially we want to pad the amp gain to get to the signal level at the amp's input.
For me it doesn't have to be an active DI box, a good passive's alright.
Click to expand...

BTW Check out the Countryman Type85 DI. In speaker mode the spec sheet says it can take up to 300V p-p (2800 watts into 4 ohms).
 
Re: converting speaker level to line level

Justice C. Bigler said:
But I'm thinking I need to get a couple of those 70 volt to XLR step down boxes just to have anyway. Could be useful in a few different applications. Have a link to said unit?
Click to expand...

It's just a small 70V speaker transformer in a box. I've made some for a special event (had to get audio from a conference room to an office 10 floors away. Used a 70V amp to drive audio down a 'dry' phone line, and adapted to a powered speaker at the office end.)

JW Davis used to make one of these that included a volume control (just a simple pot on the output side.) Ah, here it is: AO-1A Add-on Amp
 
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