The Hafler Airplane

[John Svensson]

I just picked up the 2005 remasters of the Jefferson Airplane LPs, (finally replacements for my well worn 30 year old vinyl) and run through DPLII the rear channels are quite alive on albums like After Bathing At Baxter's and Crown of Creation. A bit of the "triangular effect" that Quadzilla has referred to, (I have my own non-technical, subjective theory behind that, but I've found 1967-69 era stuff just seems to "QS" better than recordings made after that.....) but some of the percussive effects seem to almost be exclusive to the rear speakers. Anyways, has anyone experimented recently (like since 1971....) with wiring the passive Hafler circuit between their speakers and what LPs did you A/B with it for comparison? What was the overall effect in terms of discrete back channel signals? I recall a recent discussion of Hafler wiring in regard to the early EV units on here and some links, but I don't think anyone actually mentioned specific examples that they have tried. Before I start splitting speaker wires for a hoot I thought I would elicit some of your experiences. Might not be worth the 15 minutes of effort required??? John S.

 

[Wagonmaster_91]

I used to use the Hafler system when I used a Dynaco amp that had it built into it. It was all I could afford at the time since it really only requires an extra speaker or two. You can either use one rear speaker in the middle (connecting the positive right channel lead to one terminal and the positive left channel lead to the other) or two speakers with their negative terminals tied to each other (but not to the amp) and the positive leads going to the the respective right and left rear speakers. You must use an amp that has a common ground for this to work.

Dynaco/Hafler insert a 10 ohm resistor between the amp's negative speaker terminals and the wire connecting the two rear speakers negative leads together to allow a little bit of common signal to bleed to the rear speakers. I prefer not to use the resistor. This is similar to the blend resisters in Sansui's Variomatrix decoders and like most people I prefer they not be in the circuit allowing the rear speakers to be more discrete. If you aren't getting enough sound in the rears (with bass frequencies usually being common to both channels the rears might sound a bit thin), use the resistor.

This is a cheap and easy way to get fake quad in a car stereo set up, btw.

The vast majority of low cost passive quad synthesizers from the quad era use this method. Whenever you see a 'quad adapter' where you hook up an amp's speaker terminals as the input to the adapter, you can bet it is the Hafler method it uses to create the rear speaker signals.

Since it works by subtracting the common frequencies, any recording that has a wide stereo mix or instruments that only appear in one channel will have the most noticeable effect. It is fun to play with if you have never tried it.

One note about the Jefferson Airplane re-masters from 2005 - If they are the Sundazed "Baxters", "Pillow" and "Takes Off", they shouldn't reproduce any signal in the rear channels. Those are mono remasters. Using this wiring set up no mono information should appear in the rear speakers.

 

[Key]

I've messed with it in the analog and digital domain. I made a digital quadapter with a few slight mods/updates that I think sounds great. I don't really like the straight hafler trick though. I use numbers that are closer to the quadaptor where you feed the inverted opposite channel at about 3/9th of the original volume and the dominant channel at about 7/9th of the original volume to the rear channels in stereo. I haven't a/bed or checked but I think the sansui recievers with the quarter turn, half turn function are variations on the quadaptor.

Oh I tried Spinning Wheel of course with the my quadapter - sounds fantastic. I tried Surf's Up and the other two Beach Boys tracks that are encoded. I really liked Cool Cool Water and a couple of tracks from surf's up. But Surf's Up did give off some wonky effects at times. Seems like I could tell what they were going for but just a blurry image in the rear when they try to send vocals and stuff back there.

Oh and did you know that they actually reissued the quadaptor? I've never actually seen it for sale but I've seen reviews of a new QD-1 and QD-2 quadaptor.

http://www.enjoythemusic.com/Magazine/equipment/899/decoder.htm
http://www.audioreview.com/cat/amplification/preamplifiers/dynaco/PRD_117424_1591crx.aspx

 

[Wagonmaster_91]

"I haven't a/bed or checked but I think the sansui recievers with the quarter turn, half turn function are variations on the quadaptor."

The quarter and half turn functions on the Sansui's are not decoder settings. They are speaker assignment settings. It is a way to actually turn the entire 4 speaker soundstage. So, a quarter turn to the right makes your right rear speaker now the right front channel, the right front speaker now the left front channel, the left rear speaker now the right rear channel and the front left speaker now the left rear channel. A quarter turn to the left has the opposite effect.

A half turn completely reverses the soundstage so that the rear speakers are now the fronts and vice versa. (Right rear speaker becomes front left channel, left rear speaker becomes right front channel and so on.)

All four speakers need to be identical for this to have any real use.

 

[Key]

ah okay that's pretty lame I thought it was refering to something different.