Can someone explain +4 / -10

Unless something else is screwed up, you can just go w/ the -10 and hope you don't blow out speakers or something. ;-)

But maybe something is wrong w/ the vm (I'm assuming it is +4).  +4 into -10 should mean the vm is needing to run very quiet, so the input gain and output is turned way down.  Maybe a problem w/ the tube if running at normal levels brings up distortion?

@

-10 is actually -10 dbv not dbu. There is a different reference level involved. The dbV setting relates to 1V as the ref level where as dbU uses the 0.775 v as the ref level. -10 dB V is actually -7.8 dBu just to add to the confusion. +4 dBu always relates to the dBu ref level.

But for most purposes what people are saying here is still correct in that -10 is a more sensitive input but a lower output and +4 means higher signal going in and louder signal coming out.

It does not matter which you use as long as the signal that goes into your soundcard matches the input setting you have chosen and the level coming out of your soundcard also matches well to the equipment it is connect to. BTW some sound devices allow you to select a different setting for input and output levels. This is handy as it allows you to better match your input and output levels to the various devices that are feeding it and what the sound card is driving.

Hi Dave. Well I downloaded the manual for this unit and it looks pretty good actually. It says the nominal output is supposed to be +10 dBu and a maximum output of +20 dBu. Now these seem like pretty decent output levels so one could expect to be able to get a decent level going into your soundcard even with the +4dBu input setting which is what I would definitely use in this case. I also see that even the high Z unbalanced outs are sporting exactly the same levels as well.

I see there is no separate output level control so I assume you get this output level by setting the input gain accordingly. Usually when there are balances output connectors on anything the levels there are +4dBu. I assume you are leaving the Hi and Lo controls set flat.

So what happens when you set your soundcard to +4dBu (input) and just keep increasing the input gain until the desired level is reached going into the Delta. The input pad should also be OFF. Is it BTW? If the PAD is on then your output level is going to drop 20dB hence the nominal output goes from +10dBu down to -10dbu which could explain things. Under normal conditions the Peavey should easily drive  +4dBu level nicely into the Delta without any distortion as +4dBu is already 6dB down on the nominal output level (+10dBu) so it should be easy to get there.

If your PAD is OFF as it may well be it might be good to have the Peavey checked out. Sounds like it is working but for some reason your output levels are way low hence the reason you have to go down to -10 on the Delta input in order to get anything going in properly. You should be blasting the Delta even on the +4dBu input setting easily.

from: http://www.harmoniccycle....sic-26-+4dBu-10dBV.htm

"Introduction

  This is an explanation of how to compare analog sound levels associated with +4dBu professional audio gear and -10dBV consumer or home entertainment audio equipment.

  Professional analog audio electronics gear is often interconnected with cables. The input and output connections are often times described as designed for nominal +4dBu signal levels.

  Consumer and Home Entertainment analog audio equipment is also often interconnected with cables. The input and output connections are usually described as designed for nominal -10dBV signal levels.

Nominal signal level

  The term nominal level describes the audio signal level which any particluar piece of electronics is designed to work with. The analog sound signal is AC voltage. The signal level can be measured on decibel meters that are calibrated to AC voltage levels. Decibel meters are used in an attempt to mimic the nature of sound as its energy level must increase or decrease exponetially for it to be percieved as doubling or halving in listening level.

  When connecting professional and entertainment grade gear it is helpful to know how the nominal signal levels compare.

  The AC voltage difference, in decibels, between +4dBu and -10dBV nominal signal levels is 11.79dB.

  At first glance it may seem there is 14dB difference between +4dBu and -10dBV nominal signal levels but this is not the case. The 11.79dB difference between nominal +4dBu and -10dBV signal levels is evident when the different unit scale values are both referenced to AC voltage.

Unit scale values

  The unit names "dBu", "dBv", "dBV", and "dBm" all have case sensitive spellings and have specific defintions regarding audio signal levels.
Professional analog gear is measured with dBu and dBv and dBm unit scales.

  For example;
0dBu = 0.775 volts AC with an untermninated load.
0dBv = 0.775 volts AC into a 600ohm load.
0dBm = 1milliwatt at 0.775 volts AC into a 600ohm load.

  Consumer and Home Entertainment analog gear is measured on a dBV unit scale. The opper case "V" indicates a different unit scale than the professional lower case "v" scale..

  For example;
0dBV = 1 volt AC regardless of impedance load.

  dBu, dBv, and dBm are considered somewhat interchangeable but, as mentioned above, The use of the units dBv and dBm suggests that the voltage is measured across a 600ohm load. There is very little 600 ohm gear made today, for a variety of reasons, most gear has a higher input impedance. The use of dBm and dBv has been deprecated and replaced by the dBu unit which is measured regardless of impedance.

Compare the volts

  When +4dBu or -10dBV values are reconciled to the other's scale and the actual difference in voltage is compared you can see that there is a 11.79dB difference in voltage levels.


  for example;

-10dBV = 0.316 volts AC

0.316 volts AC = -7.79dBu

-10dBV = -7.79dBu

+4dBu - (-7.79dBu) = 11.79dB difference

in other words, a -10dBv signal is 11.79dB lower than +4dBu



  or for example;

+4dBu = 1.23 volts AC

1.23 volts AC = 1.79dBV

+4dBu = 1.79dBV

1.79dBV - (-10dBV) = 11.79dB difference

in other words, a +4dBu signal is 11.79dB greater than -10dBV

Why -10dBv?

  The history of -10dBV is simply that old hi-fi gear was made to have lower output than professional gear as a cost saving measure.

  When a pro item has a -10dBV input option the intention is to use the gain in the pro item rather than forcing the user to over drive their -10dBV gear into a input that expects a +4dBu signals. The idea is that you use the semi pro gear in it's sweet spot and the pro gear has enough gain to handle the rest.

  An obvious question is to ask whether the *pro* gear is optimized for +4dBu or -10dBV. If the former, it will have adequate head room above and beyond +4dBu. Perhaps +26dBu max or 22dB headroom. If the *pro* gear is optimized for -10dBV then the +4dBu input may simply be padded to bring down the pro grade levels to the semi pro region. This would be done for cost cutting reasons and the headroom above +4dBu will generally be well below 22dB in those devices.

  The only reason to use a -10dBV input is if your gear only works at -10dBV standard levels. In all cases connecting a -10dBv output to the input of +4dBU gear will increase the noise floor... if you do so and need to gain up to +4dBu nominal levels it is often cleaner to do it in the pro side of the connection.

  If you connect a +4dBu output to a -10dBv input then you are sending a hot signal over the line and this will minimize the noise floor but it will also be hot and may overload the input. If you pad it down you may reduce the noise floor a bit but the -10dBV input will have to rebuild the gain if it goes further to another +4dBu device and the noise will likely return at the next stage.

Stuff that is good to know about +4dBu and -10dBV

  If you plug a +4dBu output into a -10dBV input the signal is coming in 11.79dB hotter than the gear was designed for... turn something down.

  If you plug a -10dBV output into a +4dBu input the signal is coming in 11.79dB quieter than the gear was designed for... turn something up."

Well that is interesting. I get the feeling there is something going on there. It makes you wonder if the unit introduces harmonics (or nice distortion) exactly when in the gain structure and at what output level does that take place. 

I get the feeling that if the Peavey was delivering a nice hefty +4dBu then you should be getting a nice healthy level going into your DAW. Not right down so low as you have indicated. It might be worthy of getting tested. I would put a test tone going in (at mic level) raise the gain slowly and measure the output voltage across pins 2 and 3 of the balanced output. And connect a CRO across the output as well to see the integrity of the waveform. I would expect the output to easily get to +4dBu while the output is still a perfect sinewave (perhaps, depends when harmonics are meant to set in) 

The fact the jacks are bypassing the output transformers sounds feasible for sure. The Peavey has an unbalanced output but the jack inputs on the Delta are balanced TRS INs. How have you wired those. Are you shorting sleeve and ring on the Delta inputs using mono leads. Try connecting the Peavey to the Delta using a balanced female cannon to balanced TRS lead just to rule out any problems that might be occurring using just the jack leads.

A thought: could there be some signal loss due to an impedance mismatch between the 1/4" output of the preamp and the Delta's 1/4" input channel? The transformer output, which the designer intended as the primary output, is going to have a lower output impedance than a 1/4" TS. 

I'd try an experiment, bringing a test tone into the preamp and recording it simultaneously from both the 1/4" and XLR connections. That would tell you right away if there are significant level differences between them, and if you used a white noise test signal you could also compare their spectral content and see if there really is a downside to going through the transformer.

The manual does not say what the output impedance is but the XLR output is quoted into a 2K load which means the output impedance is lower than that. The unbalanced outs are specified into a 10 K load so looks like unbalanced output impedance is higher than the XLR. But I would be surprised if an impedance mismatch would cause this much voltage drop. It has to be pretty bad before that much level is reduced.

There would not be anything wrong with the transformer outputs either. They would simply contain the sound of the output transformer which would well be nice and should be included in your options for sounds from this pre amp. A transformer sound from the XLR and a cleaner more transparent sound from the unbalanced outs. If it was in a rack I would wire both outs to the patch bay. I would tend to start using the balanced XLR outs from any gear first. It could be argued it is what the manufacturer intended you use to represent the total sound from the unit. 

Balanced XLR (male and female) leads to balanced TRS leads are handy to have around to be able to patch things when and if they come into your studio. In your case the first hookup I would have tried would be the balanced signals connected from the preamp to the Delta. When they put balanced TRS connectors on things I always try to connect from a balanced output. You get an extra 6dB of gain just by using the balanced outputs. 

Hey gang,
there has been a lot of good info in this thread, but there appears to be some misunderstanding. It will take far more than a short post to explain all the issues involved, so I will sit down and try to write a clear, understandable explanation about interfacing audio devices.
In the meantime, to address the specific issues here:
dB is a power ratio! That's it, that's all it is, that's all it can ever be. (We'll ignore, for the moment, the fact that is the logarithm of the ratio of two powers.)
When the world switched from 'matched impedance, maximum power' transfer to voltage transfer engineers figured out a way to use a power ration to describe a level ratio. Because of the relationship between level and power you can use the dB to describe voltage ratios.
When the dB is used to describe a signal level it must always be with respect to a standard reference level.
There are two generally accepted reference voltage levels:
0 dBu (the 'u' means unreferenced, save the math for later) uses 0.7746Vrms (saving where that came from for later too)as the reference. A positive dBu means that the level is greater than 0.7746V. A negative dBu means it is less.
+4 dBu is the nominal operating level for 'professional' audio inputs and outputs.
+8 dBu is the nominal operating level for broadcasters.
0 dBV (the 'V' stands for volts, and like everything else surrounding this standard it makes sense... oh well!) uses 1.0Vrms as the reference level. Positive and negative dBV numbers represent levels above or below 1V.
Because the two standards use different references we can not simply add or subtract them. The difference between +4 dBu and -10 dBV is about 11 dB - note that in this case we are talking about a difference in levels expressed as a power ratio.
As if that wasn't enough, input stages, output stages, and the connection between them can be balanced or single-ended (aka unbalanced). Balance refers to impedance only - it has nothing at all to do with levels.
A balanced output presents an equal impedance from each signal conductor to ground. AND, ground is not used as a reference.
A balanced input looks at the impedance from each signal pin to ground, and uses that to cancel out any signal that is common to both conductors, while retaining the difference between the two pins. Again there is no requirement for a ground reference.
A balanced cable has two signal conductors. It can also have a ground conductor (which has problems) or a shield that connects to ground at one or both ends.
Most balanced cables twist the signal conductors to make them more immune to magnetic interference. The shield has little impact on magnetic fields. The shield, on the other hand, protects from RF fields, something twisting the pairs does little to prevent.
A single-ended source has only one signal conductor, and uses ground as a reference.
A single-ended input responds to the difference between the signal conductor and ground.
A single ended cable is usually made up of a single signal conductor and a shield, but it can be two signal conductors.
You can drive a balanced input from a single-ended source easily. The noise immunity is dependent on the design of the input stage, a simple op-amp input stage will suffer from the impedance imbalance, an instrumentation amplifier, a transformer, or the InGenius chip can tolerate huge imbalances.
A quick word about symmetry. A signal is called symmetrical if the level on each conductor is equal in amplitude, but opposite in polarity (not phase!) This provides a bit more headroom, and some improvement in S/N ratio, but it is not the feature that makes a balanced interface work.
The best way to connect a single-ended source to a balanced input is

- connect the pin on the RCA connector (or tip of the TS connector) to pin 2 of the XLR (or the tip of the TRS connector) through the first signal conductor.

- connect the second signal conductor from the sleeve of the RCA or TS connector to the ring of the TRS connector or pin 3 of the XLR.

- connect the shield to the sleeve of the RCA or TS connector and the sleeve of the TRS or pin 1 of the XLR (or even better, to the chassis at the receive end!)
This will work almost as well as a balanced to balanced connection if the input stage is properly designed. It's really pretty remarkable how well it works.
It is usually safe to send a -10 dBV signal to a +4 dBu input, you will lose a little bit of S/N ratio, but the preamplifier should be able to provide sufficient makeup gain. And you'll have TONS of headroom<G>!
It is a bad idea to send a +4 dBu signal to an input designed for -10 dBV. You'll need an pad or attenuator in front of the input, and you'll lose both headroom and S/N ratio.
Phew - I still haven't addressed impedance!

Impedance means the opposition to current flow. It can be resistive, which means it applies to energy at any frequency equally. It can be reactive, which means that it is dependent on frequency. It can also be the result of the relationship between wavelength and conductor length.

What matters for now is that in order for an interface to be good at transferring voltage the input impedance needs to be much higher than the source impedance. The rule of thumb range most often quoted is 10:1. And that certainly works<G>!

Typical source impedances for audio devices are usually very low, a couple of ohms is not uncommon. In order to prevent damage to the output stage most manufacturers add a build-out resistor, anywhere from 10 ohms to as high as 50 ohms.

Typical input impedances range from 100K ohms on up. The actual input impedance for a typical op-amp is in the Meg ohms, but additional circuitry is added to protect the inputs, reduce RFI, etc, and so it is made lower.
That's a lot of detail, I know, but it's the shortest thing I could write without resorting to pictures and equations.
I hope it helps, but if you have questions just ask!

Musicroom

I went thru something like this a while back. Although you are enjoying a lot more technical help here I did have "several" people lend me a lot of good advice.

Here is the thread...(is is quite long!)
http://forum.cakewalk.com/tm.aspx?high=&m=2477795&mpage=2#2518211

I was having an issue with my monitor management device the "Atty 2 d" holding back my sound delivered to my monitors......

so I went and dug out everyone of my manuals for "Everything" and followed the Train...
was it +4 or was it -10
 
Also all my cables are "Balanced" cables and this is a factor as well.

Everything was built with the +4 reference
Except my Atty which I bought a Mackie Big Knob to replace it

so I went thru my signal chain and set everything in the +4 configuration, inserted the Mackie and what a difference....huge difference.....very happy right now......

I then grabbed my SPL meter and set my levels, got out ARC and took measurements and it was set....

But my advice would be to do the same....get your manuals and go thru your signal chain and set your levels....

Best I can do cause all the other technical data already provided will take me days to read and re read and figure out....

Clifford

Dave I don't think you are going to have issues making the balanced connection. You might just get enough extra gain that way so you can back off the input gain again in order to get a good level going into your DAW. (and hopefully get a cleaner sound) The distortion you are hearing might just be your preamp going into distortion mode that is all. I would hope not as you should have the option of a totally clean signal at +4dB if you want it. When you hear this distortion does backing off the input gain control clean it up? And if it does is this signal just low at the moment going into your DAW. What reference level and how high a level are also you trying to achieve in your DAW.  Remember rms levels that average -20dB are very acceptable. You need to test and measure rms levels when calibrating any system. (K system sorts all that out!)

This is where I believe recording everything you do through something like this is not necessarily a good idea. And where clean transparent transformerless solid state preamps come into their own. Get a fantastic clean version of what it is you are recording no matter what and use plug-ins later to add the warmth and sound of analog later. The more I work with great sounding analog plug-ins the more I believe they can do it. I love them! More control over the sound now than ever before. 

Bill brings up the question of how to connect an unbalanced signal output to a balanced input. There is another version (not sure if Bill meant this version) where a 2 wire connection with just a hot wire wire and shielded cable can be used to connect to a balanced input. This is where the tip or hot signal of the unbalanced output feeds either the tip of the TRS or pin 2 of the XLR in. The shield of the unbalanced output simply connects to pin 3 only of the XLR or the ring of the TRS. The sleeve of the TRS or pin 1 of the XLR is simply left un connected. This still works because the shield of the cable is still grounded from the unbalanced end and protects the inner hot wire from hum and other noise. It also avoids any possible ground loop hums etc. or noise. Dave you won't get this cable as a commercial product, you have to wire this one up for yourself. Only do this if you feel there is some noise or possible earth hum between the two. 

Your Peavey may just not be well either. How old is it? How much have you used it? Replacing all the valves might just be the ticket and after a decent service it springs back into a louder sounding device with a much cleaner sound.