This may depend because you are talking about 2 different CD players. On my CD player, which have both RCA and XLR outputs and which is directly connected to the amp, the XLR output is about 6dB louder than the RCA connection. |
A properly designed balanced output will be at a higher level than an unbalanced output. I'm not sure it's 6 dB though. I seem to recall once I compared the output of my tuner (it has both balanced and unbalanced outputs) using interstation hiss, and measured the balanced output at 3 dB higher. |
Thank You for your perspective on the XLR connections.
The thing that seems tricky is that some CDPs mention the same output level 2.2V (for example) in both RCA and XLR connections while some other CDPs mention exactly twice the output level in XLR compared to RCA. This seem to correspond to the 6db higher output level that you mention here.
From an article on the web, I got this formula:
3dB = doubling the amplitude. If you have a reference signal at 1 volt, 3dB is 2volts, 6dB is 4 volts, and 9dB is 8 volts.
With that in mind, if I choose a CDP with say, 4V output at XLR, will it mean that my amp will ultimately see 8V at the MAX level of the preamp's output? |
In many cases, but not always, there will be a 6 db increase going from unbalanced to balanced, everything else being equal. It depends on the designs of both of the interconnected components. But also, of course, as Jcharvet pointed out different CDPs may have different output levels for the same connector type. So everything else may not be equal. From an article on the web, I got this formula:
3dB = doubling the amplitude. If you have a reference signal at 1 volt, 3dB is 2volts, 6dB is 4 volts, and 9dB is 8 volts. That is not correct. A 3 db increase = doubling of power. A 6 db increase = doubling of amplitude/voltage, which corresponds to a 4x increase in power. (As you may recall, power is proportional to voltage squared, for a given impedance). To be completely precise, this assumes that impedances remain the same as power or voltage is doubled. Regards, -- Al |
If I choose a CDP with say, 4V output at XLR, will it mean that my amp will ultimately see 8V at the MAX level of the preamp's output? Assuming you are referring to an active (not passive) preamp, when its volume control is at max its output voltage will usually be several times or more greater than its input voltage, regardless of whether balanced or unbalanced connections are used. In other words, an active preamp applies significant gain to the signal internally, for both types of connections, when its volume control is at max. Regards, -- Al |
Al,
As always, useful feedback.
I was actually referring to my TVC, which is passive. Yes, active preamps do increase the gain. But since TVCs are just attenuating the voltage, I assumed that the CDP's 4V at XLR, is 4V at each +ve and -ve leg. Hence that would mean 8V at the amp end when the volume on TVC is set to MAX. Is this correct assumption? |
^^ No. It depends on how the output of the CDP is set up.
If balanced but not differential, then you will see double the voltage. But if the output is differential and floating (for example, if an output transformer is used in the CDP), it may be set up so that the voltage from pin 2 to pin 3 of the XLR is the same thing as what is seen across the RCA jack.
So you will want to check with the manufacturer on this one. |
Thanks, Milpai. Adding to Ralph's response just above, I'm not certain that it would be safe to assume that a TVC will necessarily be designed to provide unity gain at its max volume setting, for either kind of input (RCA or XLR). I wouldn't be surprised if at least a few of them are designed to provide a few db or more of voltage stepup at their max volume setting. (As you most likely realize, a transformer can be designed to boost voltage, although it can't boost power).
And to add further uncertainty, I'm not sure that different manufacturers are always consistent with respect to whether amplitudes and gains for balanced interfaces are specified with respect to the voltage on each leg, or to the voltage difference between the two legs (which of course would be twice as much).
Regards,
-- Al |
Ralph,
I am not so tech savvy. Thank You for the heavy dose. I want to learn more. Can you please explain "differential" and "floating"? I understand that pin 2 is +ve while pin 3 is -ve. Based on your explanation I am tempted to try a RCA to XLR adapter on the IC that goes from my existing CDP to the TVC. I believe in this case the voltage that the TVC will remain at 2V instead of 4V which a true XLR designed CDP would provide.
Al,
My TVC is set for unity gain, as I had not opted for the 6db gain. |
Milpai, the adaptor will not cause the circuit to be balanced. It simply allows you to hook things up.
Differential is where the circuit has an output based on the difference between two inputs, inverting and non-inverting.
'Floating' is where the output is independent of ground. Usually though it is referenced to ground in some way, although there is no signal current associated with the ground connection. You have a balanced TVC if I understand correctly; it should be capable of operating this way as all audio transformers can.
'Balanced' is two identical circuits but with opposite phases, inverted and non-inverted. How this **might** be different from differential is that it may not automatically convert a single-ended input to balanced, and it may not always produce one output from the difference of the two inputs.
IOW it is possible to have a balanced and differential circuit, and also one that is merely balanced but not differential. In terms of noise and performance, it is far more likely that the balanced differential circuit will perform better, and even better yet if it is floating. |
Ralph,
Thank You very much for the detailed explanation. Made it so much easier to understand the "real balanced" concept. |
