Bi-amping With "Y" Splitter: Any Impedance Problem?

[Ron Resnick]

Did andromeda pass on his motel high to you?

Huh? I'm reporting nearly verbatim what David Freud said to me in person.

 

[DaveC]

Mr years ago at an AC/DC concert. Women to the left of me, women to the right. Coz I am…

View attachment 135121

No earplugs?! That explains it!

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I do the same (drive 2 amps) with my tube pre, but it uses a cathode follower output and has about 250 ohm output impedance and ~7 mA current capability. I can't imagine any SS pres having an issue driving a 67 KOhm load, even tube pres without a proper output stage would work.

 

[Ron Resnick]

Unless the two preamp outputs are separately buffered, the outputs are in simple parallel.

If the outputs are in simple parallel, then it doesn't matter whether you parallel the amps on the preamp side of the interconnect or you parallel the amps on the amplifier side of the interconnect, correct? Preamp outputs in simple, unbuffered parallel are just an internal "Y."

In both cases the preamp output stage is seeing the same lower impedance caused by the amps being in parallel.

If the foregoing is correct then why would these two connection configurations result in any difference in sound?

I guess because it's still the case that two runs of interconnects connected to the preamp output stage still result in a slightly different RCL load than one run of interconnect?

 

[DonH50]

Unless the two preamp outputs are separately buffered, the outputs are in simple parallel.

If the outputs are in simple parallel, then it doesn't matter whether you parallel the amps on the preamp side of the interconnect or you parallel the amps on the amplifier side of the interconnect, correct? Preamp outputs in simple, unbuffered parallel are just an internal "Y."

In both cases the preamp output stage is seeing the same lower impedance caused by the amps being in parallel.

If the foregoing is correct then why would these two connection configurations result in any difference in sound?

I guess because it's still the case that two runs of interconnects connected to the preamp output stage still result in a slightly different RCL load than one run of interconnect?

Are you saying there is a difference in sound? For starters, turn off the amps and mute the preamp, swap cables at either end, and see if the issue follows the cable or sticks with the amp.

If the preamp outputs are just parallel connections then the load seen by the preamp is basically the same no matter how you connect the amps. Assuming identical cables, then any differences could be from cable routing, i.e. one cable having more noise coupled into it.

If the amps are near each other, I would personally prefer to use one long high-quality cable from the preamp to the amps to minimize added capacitance and the chances of noise coupling into two different cables (plus it's cheaper to have one long cable), then split just before the amps and use short cables to the amps themselves. Your last statement is true; two 50' cables will double the capacitance of a single 50' cable. In practice, I would expect negligible (inaudible) differences from just, that but it is a difference.

As mentioned previously, gain and phase matching of the amps may (should) be (probably is much) more critical than the cable. In the past I had to tweak my crossover design to allow the best integration when I had a SS bass and tube mid/treble amp (plus learned ARC inverted phase on the 4-ohm vs. 8-ohm taps of my amplifier, fairly obvious by the deep "hole" at the crossover point when I got it wrong the first time).

HTH - Don