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Vintage threads from the first ten years

Line Out

3/7/2000 2:25 AM
BILL R	Line Out What are the basic requirements for a line out/in? In other words, what ac voltage is considered the "standard". if there is one? Are there any impedence standards? Thanks, Bill R.

3/7/2000 3:13 AM
Gil Ayan	Rather than giving you different values here, I suggest you look at a copy of Pittman's book and look in the Mesa Boogie section. All of the Marks had a line out in them and you can see how they changed a little bit from amp to amp (they called it the slave out). Now, the above will be a resistive netowrk, with a pot, tapped off the speaker jack. HOWEVER, you mention a LINE IN as well. Are you thinking of having a signal interrupt arrangement (FX loop)? If so, you can make a signal interrupt, passive loop very simply: if your amp has a master volume, instead of feeding the PI input cap directly, go from the wiper of the pot to the SEND jack, and from the RETURN jack to the PI. Of course, the jack needs to be the switching type such that when nothing is plugged in to the RETURN jack, the SEND jack shorts the signal to it, and gets a path to the PI. Of course, the signal interrupt loop kind of sucks because it has a very large output impedance (if your master volume pot is 1M, depending upon where you set it, the OI will be as high as 1Meg). But, if you send the signal to a very high impedance devide, you will not lose too much of the signal. Otherwise, expect a loss of power AND tone as well. What I suggest you do is maybe build yourself an active FX loop inside the amp, of perhaps you could put the unit in a 1-space rack chassis. Essentially, the interface is a cathode follower and a return gain stage, so all you need is one tube in there. Of course, the alternative is to build a solid state FX loop. Gil

3/7/2000 3:13 AM

Gil Ayan

Rather than giving you different values here, I suggest you look at a copy of Pittman's book and look in the Mesa Boogie section. All of the Marks had a line out in them and you can see how they changed a little bit from amp to amp (they called it the slave out).

Now, the above will be a resistive netowrk, with a pot, tapped off the speaker jack.

HOWEVER, you mention a LINE IN as well. Are you thinking of having a signal interrupt arrangement (FX loop)? If so, you can make a signal interrupt, passive loop very simply: if your amp has a master volume, instead of feeding the PI input cap directly, go from the wiper of the pot to the SEND jack, and from the RETURN jack to the PI. Of course, the jack needs to be the switching type such that when nothing is plugged in to the RETURN jack, the SEND jack shorts the signal to it, and gets a path to the PI.

Of course, the signal interrupt loop kind of sucks because it has a very large output impedance (if your master volume pot is 1M, depending upon where you set it, the OI will be as high as 1Meg). But, if you send the signal to a very high impedance devide, you will not lose too much of the signal. Otherwise, expect a loss of power AND tone as well.

What I suggest you do is maybe build yourself an active FX loop inside the amp, of perhaps you could put the unit in a 1-space rack chassis. Essentially, the interface is a cathode follower and a return gain stage, so all you need is one tube in there. Of course, the alternative is to build a solid state FX loop.

Gil

3/7/2000 4:24 AM
BILL R	Gil: thanks for the reply, but I wasn't thinking in terms of just guitar amps. Most audio equipment these days has line in or line out jacks. What level of signal can be expected to come out of a line out jack (I realize it is a range, maybe what I need to know is the maximum), and what level is expected by a line-in jack?

3/7/2000 5:46 AM
Gil Ayan	There are two definitions, by the book, of what line level is/should be: 1. 0 dBv = 1 VRMS 2. 0 dBu = .775 VRMS Why is the second number so funky? From the old radio days, they defined "line level" as the voltage that would dissipate 1mW of power into a "standard" 600 ohm impedance. Do the math and you will find that .775 V is that voltage. Gil

3/7/2000 7:07 AM
Steve A.	Gil: I don't have the voltages handy but line levels may also be specified as -20dBv, -10dBv, and +4dBv. I believe that -10dBv corresponds to consumer gear while +4dBv is more common with balanced lines going into a studio. -20dBv would correspond to guitar levels. I noticed that Boss uses dBm and Digitech uses dBv, but they both define them as being 0.775VRMS (...which I always thought was half the square root of two plus tax and tip). Steve Ahola

3/7/2000 7:07 AM

Steve A.

Gil:

I don't have the voltages handy but line levels may also be specified as -20dBv, -10dBv, and +4dBv. I believe that -10dBv corresponds to consumer gear while +4dBv is more common with balanced lines going into a studio. -20dBv would correspond to guitar levels.

I noticed that Boss uses dBm and Digitech uses dBv, but they both define them as being 0.775VRMS (...which I always thought was half the square root of two plus tax and tip).

Steve Ahola

3/7/2000 7:25 AM
Carl Z	Here's a bit of info courtesy of the fine folks at Rane Pro Audio..... 0 dBu A voltage reference point equal to 0.775 Vrms. [This reference originally was labelled dBv (lower-case) but was too often confused with dBV (upper-case), so it was changed to dBu (for unterminated).] +4 dBu Standard pro audio voltage reference level equal to 1.23 Vrms. 0 dBV A voltage reference point equal to 1.0 Vrms. -10 dBV Standard voltage reference level for consumer and some pro audio use (e.g. TASCAM), equal to 0.316 Vrms. (Tip: RCA connectors are a good indicator of units operating at -10 dBV levels.) 0 dBm A power reference point equal to 1 milliwatt. To convert into an equivalent voltage level, the impedance must be specified. For example, 0 dBm into 600 ohms gives an equivalent voltage level of 0.775 V, or 0 dBu (see above); however, 0 dBm into 50 ohms, for instance, yields an equivalent voltage of 0.224 V -- something quite different. Since modern audio engineering is concerned with voltage levels, as opposed to power levels of yore, the convention of using a reference level of 0 dBm is obsolete. The reference levels of 0 dBu, or -10 dBV are the preferred units. 0 dBr An arbitrary reference level ("r" = "re") that must be specified. For example, a signal-to-noise graph may be calibrated in dBr, where 0 dBr is specified to be equal to 1.23 Vrms (+4 dBu); commonly stated as "dB re +4," that is, "0 dBr is defined to be equal to +4 dBu." 0 dBFS A reference level equal to "Full Scale." Used in specifying A/D and D/A audio data converters. Full scale refers to the maximum voltage level possible before "digital clipping," or digital overload of the data converter. The Full Scale value is fixed by the internal data converter design, and varies from model to model. ---------------------------------------------------- Now....if you're not completely confused at this point you should be! The whole line out thing is a mess with very little standardization from mfg's Here's another problem. The output should NOT be ground referenced. So any arrangement such as the one Mesa uses is useless for sending to a board. To a power amp...sure, but not a board! Hope I've done my part to confuse everybody completely! I seem to be doing a lot of that lately! HA HA Regards; Carl Z Summit Amps

3/7/2000 7:25 AM

Carl Z

Here's a bit of info courtesy of the fine folks at Rane Pro Audio.....

0 dBu A voltage reference point equal to 0.775 Vrms. [This reference originally was labelled dBv (lower-case) but was too often confused with dBV (upper-case), so it was changed to dBu (for unterminated).]

+4 dBu Standard pro audio voltage reference level equal to 1.23 Vrms.

0 dBV A voltage reference point equal to 1.0 Vrms.

-10 dBV Standard voltage reference level for consumer and some pro audio use (e.g. TASCAM), equal to 0.316 Vrms. (Tip: RCA connectors are a good indicator of units operating at -10 dBV levels.)

0 dBm A power reference point equal to 1 milliwatt. To convert into an equivalent voltage level, the impedance must be specified. For example, 0 dBm into 600 ohms gives an equivalent voltage level of 0.775 V, or 0 dBu (see above); however, 0 dBm into 50 ohms, for instance, yields an equivalent voltage of 0.224 V -- something quite different. Since modern audio engineering is concerned with voltage levels, as opposed to power levels of yore, the convention of using a reference level of 0 dBm is obsolete. The reference levels of 0 dBu, or -10 dBV are the preferred units.

0 dBr An arbitrary reference level ("r" = "re") that must be specified. For example, a signal-to-noise graph may be calibrated in dBr, where 0 dBr is specified to be equal to 1.23 Vrms (+4 dBu); commonly stated as "dB re +4," that is, "0 dBr is defined to be equal to +4 dBu."

0 dBFS A reference level equal to "Full Scale." Used in specifying A/D and D/A audio data converters. Full scale refers to the maximum voltage level possible before "digital clipping," or digital overload of the data converter. The Full Scale value is fixed by the internal data converter design, and varies from model to model.

----------------------------------------------------

Now....if you're not completely confused at this point you should be! The whole line out thing is a mess with very little standardization from mfg's Here's another problem. The output should NOT be ground referenced. So any arrangement such as the one Mesa uses is useless for sending to a board. To a power amp...sure, but not a board!

Hope I've done my part to confuse everybody completely! I seem to be doing a lot of that lately! HA HA

Regards;
Carl Z
Summit Amps

3/7/2000 9:06 AM
Llamma	O.K... I have a question, What is the easiest way to convert the Output of My 100watt Tube Amp to Line Level, to go to a mixing console to use at church, (We have a specialised Foldback system using Headsets so I don't want to use the Speaker and Mic it, I would also Like to put a DI into this circuit if Possible so A Design to go straight from the Speaker out to this Unit and then to a Mixing Console is Ideal. Regards Blair

3/7/2000 9:06 AM

Llamma

O.K... I have a question,

What is the easiest way to convert the Output of My 100watt Tube Amp to Line Level, to go to a mixing console to use at church, (We have a specialised Foldback system using Headsets so I don't want to use the Speaker and Mic it, I would also Like to put a DI into this circuit if Possible so A Design to go straight from the Speaker out to this Unit and then to a Mixing Console is Ideal.

Regards

Blair

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