Possible Phasing Issue with SDA 2.3TL’s

jevchance

Hey everyone. I recently moved my 2.3 TL’s up from the basement. I also swapped amplifiers so that I can bi-amp. For some reason while bi-amping I’m getting extra hot out of phase sound. If I run a phase test, the in-phase audio sounds normal, but the out of phase is extremely hot. If I had to guess I would say the out of phase audio is a good 6 DB louder. This makes music sound kind of weird. If I disconnect my crossover cable, it sounds normal. The speakers sounded normal when they were down in the basement on a single amp so I’m not sure if it was the move or the switch to bi-amping that has caused this. Does anyone have any thoughts on what it might be? I do know the crossovers on these units have been rebuilt.

jevchance

Also, I did double check to make sure everything is hooked up properly. I confirmed that proper phasing is going to all eight binding posts.

F1nut

You cannot use non-common ground, mono blocks or dual mono amps with SDA speakers unless you use the AI-1 or Dreadnought isolation transformer.

Toolfan66

F1nut wrote: »

You cannot use non-common ground, mono blocks or dual mono amps with SDA speakers unless you use the AI-1 or Dreadnought isolation transformer.

jevchance

Thanks, that is almost certainly the problem. Thanks for the info. I read about the transformer but thought my amp surely must be common ground. Upon digging deeper, sure enough the Adcom 7400 is not common ground. I’ll swap out amps for now and look into the dreadnought. Thanks again! Hopefully I didn’t damage anything.

msg

Interesting, good info and thanks for posting your experience with this here. I always wondered what would happen with something like this, how it might present.

Curious, how did you determine that your amp is not common ground? I've seen some discussion on it here and there, but just wondering what you did to figure it out. In the manual? Physical testing?

pitdogg2

I thought it was well documented here that the 5xx series was and the 5xxx/7xxx was not common ground.

jevchance

Yeah I couldn't find any information in the documentation. I did some Googling and saw references to the Adcom amplifiers with 4 digit model numbers being non-common ground.

invalid

This amp may be like the 5800 the main ground for each channel is connected to chassis ground through a 100 ohm resistor, which makes it non common.

msg

Is the "main ground for each channel" at the binding post, or somewhere else in the circuit?

Same chassis ground?

bcwsrt

Stop being so serious, Scott. It's not like you and it's freaking me out.

Schurkey

F1nut wrote: »

You cannot use non-common ground, mono blocks or dual mono amps with SDA speakers unless you use the AI-1 or Dreadnought isolation transformer.

I guess that depends on the actual amplifier topology of the "mono blocks", or your definition of "dual mono".

My favored amplifier brand has several models advertised as "dual mono"; there's separate power transformers, separate power supply caps, separate circuit boards for the two channels connected to the red-speaker-terminal side of the circuits. (Photos of older models, but showing generally the same physical layout as the amps I have now.)




The black speaker terminals are connected to chassis ground via 10-ohm resistors; easily bypassed with a couple of banana speaker-cable ends, and eight inches of stranded copper wire connecting the negative speaker terminals. In short, the ground side is not separated except by a couple of resistors. This is exactly the same as the 4-digit Adcom amplifiers except for the value of the two resistors--10 ohm vs. 100 ohm, I guess. I consider them "partial non-common ground" amplifiers. Cram in a jumper wire, and enjoy.

The Adcom GFA-565 monoblocks of thirty-ish years ago are similarly compatible if you're sharp enough to jam a jumper wire between the negative terminals of the two amplifier chassis.

No doubt there are other examples of "dual mono" or "monobloc" amplifiers that are entirely compatible with SDA speakers provided a jumper wire is installed that connects the negative terminals, thus bypassing the resistors. I know guys like the isolation transformer, but that's not an option with older SDA speakers such as 1Bs, 2As, etc. For those older-generation speakers, the jumper wire is "the" solution.

The real problem is with bridged/balanced/differential amplifiers where both the + and the - speaker output terminals are powered, with the negative output terminal set up for reversed polarity, and neither terminal connected to chassis ground. Or the older Carver amps where one channel is in reverse polarity to make life easier on the power supply, then wired backwards at the output (speaker-wire) terminals to bring the polarity "correct" again.

audioluvr

Why does this conversation sound familiar?

xschop

Schurkey wrote: »

F1nut wrote: »

You cannot use non-common ground, mono blocks or dual mono amps with SDA speakers unless you use the AI-1 or Dreadnought isolation transformer.

I guess that depends on the actual amplifier topology of the "mono blocks", or your definition of "dual mono".

My favored amplifier brand has several models advertised as "dual mono"; there's separate power transformers, separate power supply caps, separate circuit boards for the two channels connected to the red-speaker-terminal side of the circuits. (Photos of older models, but showing generally the same physical layout as the amps I have now.)




The black speaker terminals are connected to chassis ground via 10-ohm resistors; easily bypassed with a couple of banana speaker-cable ends, and eight inches of stranded copper wire connecting the negative speaker terminals. In short, the ground side is not separated except by a couple of resistors. This is exactly the same as the 4-digit Adcom amplifiers except for the value of the two resistors--10 ohm vs. 100 ohm, I guess. I consider them "partial non-common ground" amplifiers. Cram in a jumper wire, and enjoy.

The Adcom GFA-565 monoblocks of thirty-ish years ago are similarly compatible if you're sharp enough to jam a jumper wire between the negative terminals of the two amplifier chassis.

No doubt there are other examples of "dual mono" or "monobloc" amplifiers that are entirely compatible with SDA speakers provided a jumper wire is installed that connects the negative terminals, thus bypassing the resistors. I know guys like the isolation transformer, but that's not an option with older SDA speakers such as 1Bs, 2As, etc. For those older-generation speakers, the jumper wire is "the" solution.

The real problem is with bridged/balanced/differential amplifiers where both the + and the - speaker output terminals are powered, with the negative output terminal set up for reversed polarity, and neither terminal connected to chassis ground. Or the older Carver amps where one channel is in reverse polarity to make life easier on the power supply, then wired backwards at the output (speaker-wire) terminals to bring the polarity "correct" again.

Knowledge over rhetoric is a rare bird in these woods. Great insight. TY.