Misc: Spectrosonic Quad Adaptor/Rear Channel Amp

[Quad Linda]

Spectrosonic Quad Adaptor/Rear Channel Amp
Vintage: 1973
Rarity: Very Scarce

Pacific Stereo proprietary (house brand) unit. Does anyone have experience with this?

 

[Retrovert]

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Stereo Mode Selected​

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Phase Shift Mode Selected​

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SQ Mode Selected​

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Discrete Mode Selected​

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Rear View​

 

[Doug G.]

That is a cool looking little unit. It kind of matches my Heathkit -29 stuff.

Doug

 

[jaybird100]

Does anyone know what the phase shift function does?

 

[Jim the Oldbie]

That is a cool looking little unit. It kind of matches my Heathkit -29 stuff.

Hey, I built an AA-29 for my very first stereo, with the walnut case, heh! (Built a second one for my sister.)

Are you still using your Heathkit gear?

-- Jim

 

[Doug G.]

Sorry for the late response, Jim. I just saw this.

I built my first AA-29 in March of 1976 and have bought others since then including two more AA-29s, an AJ-29 tuner, and 2 AR-29 receivers, one of which I gave my son.

My quad system is all based on these units. My original AA-29 is the center used to select sources and modes. The extra auxiliary input really comes in handy for this. The other AA-29s are slaves to drive speakers and the tuner and amp sections of the AR-29 are also used. I have four Advent stacks in the system and each pair is driven by it's own amplifier. SQ, QS, and other matrix or stereo records are played on a BIC 1000 using a Sony SQD-2050 decoder and CD-4 records are played on a BIC 980 (bought from Heathkit at the same time as the AA-29) through either a Panasonic SE 405 demodulator (magnetic cartridges) or a Technics SH-400 (semi conductor/strain gauge cartridges).

I also have a Heathkit AA-2010 quad amplifier I can sub in for two other amps if need be.

Do you still have and are you using your Heathkit?

Doug

 

[surteess]

I presume the Phase Shift inverts 1 or more speaker outputs - to give a more enlarged room atmosphere where sounds will be more echo like.....better than converting a straight 2 channel to drive 4 speakers.

The downside is that sometimes it may sound "hollow".

 

[jaybird100]

I presume the Phase Shift inverts 1 or more speaker outputs - to give a more enlarged room atmosphere where sounds will be more echo like.....better than converting a straight 2 channel to drive 4 speakers.

The downside is that sometimes it may sound "hollow".

Or could the Phase Shift function be RM/QS?

 

[surteess]

In order to place any standard terminology on a piece of gear (eg RM/SQ/QS/UHJ/CD-4 etc) you have 2 issues -

1) you need to pay royalty
2) you need to only use an approved circuit

Phase shifting is such a loose term, that unless you know what phase shifting was applied at the recording stage, and reverse engineer it at the end-user piece of equipment, you will never really replicate it as per original.
This is where using an approved circuit comes into its own, with true seperation occuring by mating.

eg SQ LP with an SQ decoder will give you correct info from each speaker
(SQ LP with QS decoder will give you both potentially wrong phase shift and also wrong amplitude).

 

[audioguy]

Does anyone know what the phase shift function does?

Not sure about this specific unit. But it was common to have a phase shift on many pre-amps. As the audio goes through each component in your system, the phase could be 180 degrees off by the time it gets to your speakers. The phase shift would make up for this. An old audiophile advice back then was to reverse polarity of all speakers in your system. Sometimes it actually sounded better! This was to make up for the lack of a phase shift button. Of course, this was a "try and see if it sounds better" rule as it would depend on all the components in your system.

Actually, Anthony Gallo recently (by recently I mean past decade) gave this advice in one of his papers. Many people are very surprised that they get better audio from changing the positive and negative leads to all of their speakers. It's an audiophile trick that if it works...it hasn't cost you a dime. Try it and see.

 

[Jim the Oldbie]

Sorry for the late response, Jim. I just saw this.

Yikes! Me too, sorry. I've been away from here for awhile.

...My quad system is all based on these units. My original AA-29 is the center used to select sources and modes. The extra auxiliary input really comes in handy for this. The other AA-29s are slaves to drive speakers and the tuner and amp sections of the AR-29 are also used. I have four Advent stacks in the system and each pair is driven by it's own amplifier. SQ, QS, and other matrix or stereo records are played on a BIC 1000 using a Sony SQD-2050 decoder and CD-4 records are played on a BIC 980 (bought from Heathkit at the same time as the AA-29) through either a Panasonic SE 405 demodulator (magnetic cartridges) or a Technics SH-400 (semi conductor/strain gauge cartridges).

Man, that is a trip down memory lane and a great old-school setup you have. I didn't have a quad rig back in the day, but I did eventually fit a set of preamp outputs to my AA-29 so that I could drive my stereo stacked Advents with a Crown DC-300! That was a fun upgrade.

...Do you still have and are you using your Heathkit?

No, I'm afraid mine went to its reward many years ago. I got a lot of use out of it, but eventually it became unreliable due to worn-out switches and RCA jacks etc. I'm really impressed that you've been able to keep using yours all this time - you've obviously taken great care with it.

-- Jim

 

[Doug G.]

Yes, I love this equipment and thankfully, have the knowledge and skills to maintain it all. I have recently had a spate of capacitor failures in some of the Heathkit units. I guess, after 40 years, or so, of use, they can be expected to give up.

I believe the phase shift setting on the unit in question in this thread is probably a type of synthesis circuit for getting quad effects from regular two channel records. That was a pretty big deal back then too so people could be convinced they could have quad even before investing in actual quad records. However, QS was sometimes called the "phase shift" format too.

And, addressing the speaker phase/polarity issue audioguy talked about, it is true that the back speakers may have to be polarity reversed in reference to the front speakers, depending on the room dimensions. In my system, they have to be reversed for the low frequencies to "match up" with the front speakers. Otherwise, bass is reduced and the general sound field is less defined due to cancellation.

Doug