Hafler DH 500 common ground?

[jmitchell59]

Good evening! I have a Hafler DH 500 that I'm selling on anther site. An interested buyer has asked if his Polk speakers, which require a common ground, will work with this amp. Does anyone know the answer to this? Why would speakers need a common ground?

 

[dshoaf]

You can answer your potential buyer with, "Confirmed, all Hafler amps, including the DH-500 are common ground."

As for why speakers _need_ a common ground amp, I'm still scratching my head. Since most consumer amplifiers made in the past 50 years are common ground, I'm not clear why a speaker manufacturer would produce a speaker with any unique features requiring specific amps. That would limit their potential buyers. Why would this be interesting?

Personally, I think these sorts of questions are likely based on dubious knowledge.

Cheers,

David

 

[eickmewg]

The Polk SDA (stereo dimension array) speakers require a common ground to operate properly with the interconnect cable. I know that I have asked this very question a time or two when considering a new amp for my SRS SDA 2.3 speakers and came to learn what David said, that stereo amplifiers now virtually all share a common ground between channels. Certainly not the case with monoblocks and a special A1 transformer interconnect system is needed.

 

[whoaru99]

Personally, I think these sorts of questions are likely based on dubious knowledge.

Cheers,

David

It is not dubious knowledge. It is a caution in the speaker manuals, directly from Polk, for some of their speakers like the SDS/SRS models.

In addition to the typical speaker-to-amp connections, there is a jumper cable that runs between the two speakers. It's this interconnection between the speakers that necessitates common ground amplifier.

In the case of biamping, the HF amp doesn't need to be common ground but the LF amp still must be common ground.

There is a workaround if you modify the jumper cable by putting an isolation transformer into the cable.

 

[dshoaf]

Thanks for the background, Whoaru99. That helped. As I said, why a speaker company would create features that require unique amps just limits the ability to sell them, I would think.

I'm sure Polk had good reasons to build their systems like that but jeez......

To our OP, the potential buyer will be looking for a while, I suspect. Its a great amp so someone should find you soon. Have you considered stepping up to Subscriber status and posting in Barter Town here at AK? We're a pretty good lot of guys and qualified to be interested in audio gear!

Cheers,

David

 

[eickmewg]

All I can say is that the Polk SDA system is quite complicated, involving a reverse phase signal between speakers to the SDA drivers via the interconnect that works to keep the left channel signal from affecting the right ear and vice versa. The spacing of the regular and SDA drivers introduces the appropriate time delay relative to the average head and ear spacing. The system really does work to expand the stereo stage. And I am expecting in 95% plus of all modern stereo amps, there are no special requirements. Many years ago Stereo Review had the full SDA system expose that was pretty mind blowing. The SRS SDA speakers, in addition to the special SDA arrays, had big passive radiators for excellent low bass response, and despite their large size and multiple drivers, were quite efficient at around 92 dB.

 

[jmitchell59]

Huh! Who knew?

 

[highwaychile]

I'm a recent convert to the SDA's. I picked up a pair of SDA 2A's for so cheap I couldn't pass them up. After getting an interconnect and placing them as best I could according to recommendations, I'm very impressed with the depth these things produce.

 

[Schurkey]

1. Many amplifiers CLAIMING to be "common ground" turn out to have resistors in the ground path that makes the amplifier unsuitable for use with Polk SDA speakers. The resistors can be bypassed with a jumper wire between the left negative binding post and the right negative binding post. Some, but not all Adcom, Parasound, and my Aragon 8008BB are built like this, and various others are sure to be similar, I just haven't looked at the schematics. MEASURE the resistance from left negative to right negative with an ohmmeter. Less than one ohm is suitable. More than one ohm is questionable. Twenty ohms (a ten-ohm resistor on each channel's ground circuit) made my SDA 1Bs unlistenable. Of course, "bridged" or "balanced" amplifiers CANNOT be common-ground, along with certain Carver amplifiers that have one channel inverted.

2. Not all SDA speakers are compatible with the isolation transformer. The first three generations of SDAs CANNOT use the transformer, the last (newest) two generations can accept the isolation transformer. Most but not all of the fourth and fifth-generation speakers use an interconnect with a pin and blade terminals, the previous generations were (usually) blade/blade terminals.

3. While the third, fourth, and fifth generation of SDAs do not need common-ground amplifiers for treble when bi-amping, the first two generations will (and you'll have to modify the earlier speakers to biamp.)

4. The Polk SDA speakers tended to be 4- or 6-ohm loads, so the 92 db sensitivity is misleading. They're more like 92 db with 2.83 volts, which on a four-ohm speaker is two watts of input power. Knock off 3db for 1-watt specs.

5. There's aftermarket and Polk support for some of the SDA drivers and other parts, and the Club Polk folks are advocating for various crossover and driver-mounting upgrades. In sum, the speakers can easily be hot-rodded to sound better than new. I know this because I bought my 1Bs back in the mid-80s as the original owner. Replacement caps, an inductor or two...mine sound better now than they did with the original parts.

 

[whoaru99]

Common ground amps are not particularly unique. In fact, I'd go out on a limb and say common ground amps, at least relative to typical home stereo and pro audio, are way more common that not.

This is not unlike most stereo disaster concerns.

Is it possible to have this problem? Yup.

Is it probable to have this problem? Nope.