[b5pt9]

I want to fabricate some Y-splitter cables with a female XLR input connector and 2 male XLR outputs on short cable leads.  This would allow me to keep my existing long XLR cables from preamp to amp (close to speakers) and split the signal at the amp(s) to experiment with passive bi and triamping.

I was told (by someone knowledgable that a Y-splitter would cause a 3dB drop in signal level on output compared to input.  They also said a tri-splitter (ie 3 outputs) would cause a 4.5dB drop?

Is this correct?   I've got some electrical background and I'm thinking it's not right.  If it is true I'd appreciate an explanation.

[werd]

I want to fabricate some Y-splitter cables with a female XLR input connector and 2 male XLR outputs on short cable leads.  This would allow me to keep my existing long XLR cables from preamp to amp (close to speakers) and split the signal at the amp(s) to experiment with passive bi and triamping.

I was told (by someone knowledgable that a Y-splitter would cause a 3dB drop in signal level on output compared to input.  They also said a tri-splitter (ie 3 outputs) would cause a 4.5dB drop?

Is this correct?   I've got some electrical background and I'm thinking it's not right.  If it is true I'd appreciate an explanation.

Ask him what kinda db it is? There would have to be a resistor in inline somewhere for a drop in gain other wise its just a share in current. I cant see it either.

[art]

There are such things as resistive splitters that do this, and for a purpose. But a splitter that is nothing more than a "Y" will not.

Unless you really load down both ends, which is usually not the case in audio.

The 3 dB loss would be the result of a "double termination". But since it probably isn't terminated to begin with.........

O/T: At the present time, I am designing a PCB that does have a resistive splitter. I need a custom one to do some speciallised measurements on our network analyser. Using the one that comes with the analyser won't work for this one specific application. We need to modify the termination impedance, so the stock 50 ohm one will not work. We will be using a much different impedance on one of the legs.

Does that obtuse example give you some hints on how a resistive splitter works? As opposed to just a "Y" connection.

Pat

[werd]

You should be mindful too when using y splitters in this application as current will take the easiet path. I am sure there will be times when most of your current draw will head straight for the low end amps or speaks. This will nerf your high freq output.

[Mad Mr H]

Exactly what ART said  .

(although I am not building the PCB he mentions!!!)


Werd - In usual hi fi distance of cables this should never be an issue......


I have to say it would be a great addition if 2ch or more amps had a "link ch input" switch, Many commerial amps I use have this already it means you run one cable to the 2 or more ch amp and internally it sends the same signal to all channels.......They are a great little switch or bi or tri amp systems.......etc.

[b5pt9]

OK thanks for the comments.  That's exactly what I was thinking about needing to build a voltage divider network out of resistors to cause this 3dB drop. 

Werd I think I know what you're getting at with your last statement.  This is why the amps are going close together and the y-splitter will be right before the amps with leads as short as possible.

[SF]

I think your friend is correct. The Y splits the signal in a parallel fashion; this means your voltage stays the same in the Y limbs, but your current is reduced by 1/2. Power (W)=V*I. Here V stays the same but I is 1/2, so your power (W) is 1/2. Given that doubling power = 3dB gain, halving power should result in 3dB loss in power (dBpower=2log[P2/P1]).
I think this is correct, but I am many years away from my electronic class.

[b5pt9]

SF that's what I was thinking at first too and I agree the current is affected by the reduction in load impedance with 2 amps in parallel.  But the amps use the input voltage as a reference for producing an output, not the input current.

Ideally the amp has a high input impedance to minimize current flow, and the preamp has a low output impedance to reduce any voltage drop on the signal resulting from current flowing through output impedance.

Good stuff folks I bet a lot of people arent' perfectly clear on this .

[art]

I am not is place to make a drawing, so I will try to explain it in a verbal manner.

Imagine that the "Y" has 2 parts: the lower bar, and the upper "v".

The bar would be the preamp output impedance. Somewhere from 10 to 100 ohms, usually.

The "v" has two parts, each one the input impedance of the amps Which would be 10k-100k, roughly.

Unless you are in the pro audio world, or telephone system, where the bar and "v" would each have 600 ohm values, there is no 3 dB drop when you double terminate.

In the case of 600 ohms, when going from a single 600 ohm load to a 300 ohm load (2 600s in parallel), you pick up an additional 3 dB of loss.

Help any?

Pat

[werd]

SF that's what I was thinking at first too and I agree the current is affected by the reduction in load impedance with 2 amps in parallel.  But the amps use the input voltage as a reference for producing an output, not the input current.

Ideally the amp has a high input impedance to minimize current flow, and the preamp has a low output impedance to reduce any voltage drop on the signal resulting from current flowing through output impedance.

Good stuff folks I bet a lot of people arent' perfectly clear on this .

Yes just like SF said this is a blast from the past for me and my electronic class. I still dont think it will matter if its line level like b5pt9 said above. I think the current split is only goin to make a diff between the amps and speaks for a dbw loss. It shouldnt matter and there should be no audible loss of power on line level with the splitters. I was commenting on using splitters for biamping vertically,occassionally he might lose enough current to the higher freq amp to make a diff from current draw to the amps driving low freq. This is probably one of the reason why a good active crossover network is used.

I wonder who designs the 10B over at Bryston. Drop him an email and ask him, it would be interesting to hear what he has to say.

[Mad Mr H]

Again, Art is correct...........

Can I also just mention that I have done this 100+ times..........

I frequently wire up large rack systems, at times there may be 6 or 8 amp channels wired to a single output.

There is no loss.


Try it for youself............

[SF]

Thank you guys. I think it is a bit more clear to me. The gain stages in the pre-amp and the amp are gains in voltage, and are independent of current, which are minimal in high impedance connections (such as preamp-amp ICs). So in splits or 8-way parallel systems, where voltage is not affected, the impact on the current is a non-issue in terms of voltage gain. I think I get it.
Thank you.