X150 amplifier compatibility

[Heiney9]

I have a question about the compatibility of the Pass Labs X150 with a certain type of speaker. I own Polk Audio SDA 1C’s which have a cable running between the speakers. The short and skinny is a low level signal from one channel is sent to a pair of drivers in the opposite channel. The objective is the cancellation of inneraural crosstalk. It works quite well. In the owner’s manual (and myself being a member of the Polk Audio forum) there is caution against using the SDA’s with a non-common ground amplifier.

My questions are 3:

1) Is the X150 considered a common ground amplifier?
2) If it’s not; can the negative speaker terminals be tied together to make it common ground (assuming heavy duty wire and connectors).
3) If neither of #2 is possible can the amplifier operate in a non-common ground configuration w/o damage based on how the speakers are connected to each other.

I’ve included a copy of the x-over schematics to help further understand how the SDA’s are wired together. I don’t think any damage can be done to the speakers but I’m more concerned of how the amplifier will react and if it can result in long term damage.

It’s been discussed many times on the Polk Audio forum and for some people and their associated equipment there are no issues and for other and their equipment there are issues. So there is no cut and dried general answer. So I’m looking for an answer for this particular amp. Hopefully Nelson will chime in an give me a decisive opinion.

[Heiney9]

For some resaon the schematics didn't attach to the original post.

[Heiney9]

another

[Heiney9]

Full schematic

[Nelson Pass]

The X series have common ground, but neither output is at
ground - the outputs are balanced. This means that if you
bleed a small amount of current between the channel outputs
it will be OK, but I doubt that it will work as Polk intended.

Under no circumstances should the outputs of the amp be
directly connected together.

I suggest that you check with Polk. You have two channels
that know what ground is, but no output terminal is directly
connected to ground.

[Heiney9]

Thanks for the reply. I've been told by knowledgeable members on the Polk forum this:

I've only seen early and late SRS 2 schematics. On the early blade/blade speaker, the wide blade, called Pin A (# 1), is connected to the positive side and the narrow blade, called Pin B, (# 2) is connected to the negative side of the dimensional tweeter/drivers. Each terminal on the blade/blade SDA interconnect cable carries a signal.

On the late pin/blade SRS 2, the pin is connected to the negative side of the dimensional drivers, and the blade is connected to the negative speaker terminal. Just the pin carries a signal in the standard pin/blade SDA interconnect. The blade terminal is not connected.

SDA 1C's use the same IC cable as SRS 2's. My 1C's are pin/blade.

It's also my understanding that because of senario (2) above (pin/blade) that using the X150 or similar topology amplifier will not allow the dimesional drivers to output any sound. Is that what you mean by "but I doubt that it will work as Polk intended"

Am I understanding this correctly? Also I will consult Ken Swauger over at Polk about this issue furthur.

Thanks again, I appreciate the quick direct response.

Brock

P.s. There is a workaround which includes building an isolation transformer into the IC cable. Polk offered one at the time of production for my model as an option but they are no longer avail new. That may be my best choice if I want to use this amp.

[Nelson Pass]

Probably right - a 1:1 8 ohm audio transformer would
likely do the job, something about 50 VA or so.

[Heiney9]

I know I'm being somewhat of a pain but I really need to know this info.

Considering purchasing an Alpeh 30. Same question, is it a common ground amplifier that is compatible with Polk SDA's. I don't want to guess, but I assume it's the same as the "X" series in that it uses a floating ground and they are not common.

Could someone confirm this?

I do appreciate the responses and all answers are noted so I don't have to ask again.

H9

[GRollins]

In the Alephs, ground is ground. Only the X and XA series are bridged, meaning that the output ground is floating.
Note that the Alephs are not current product, but that doesn't keep them from being rather nifty amplifiers.

Grey