Old school stereo

[NW-Bound]

In 1975 my Fisher receiver was stolen and moving to Columbus a few months latter, I purchase a discounted quadraphonic, four channel receiver, at a distribution center. I don't think the concept ever took off. Anybody remember a FM station broadcasting in that mode/band? I think the receiver used a internal skewed equalizer per channel to give the four channel depth effect...not certain though.

You are a few years older than me, but I remember in the early 70s, Sansui and other makers had quadraphonic receivers. I forgot about that until now.

From the Web:

• 4-Channel Output: They contain four distinct amplifier sections to power four speakers, placing the listener in the literal center of the soundstage.
• Built-In Decoders: They feature specialized built-in decoders (like SQ or QS) designed to extract four channels of audio from encoded quadraphonic vinyl records or 8-track tapes

Why did they fail?

Quadraphonic sound was essentially an audio marvel before its time. It ultimately failed in the late 1970s because of competing and incompatible record formats, expensive equipment, and a lack of mainstream content

 

[explanade]

Quadrophonic systems were sold at Sears. Maybe there were high-end audio brands at the time which also tried to sell quad systems but quadrophonic was like home theater in a box at the time, along with the 8-track players those mass-market stereos they sold.

 

[YellowSubmarine]

Quadrophonic systems were sold at Sears. Maybe there were high-end audio brands at the time which also tried to sell quad systems but quadrophonic was like home theater in a box at the time, along with the 8-track players those mass-market stereos they sold.

You're right. My Quad system was from JC Penny's -MCS brand. It served it's ST function until I got some bucks for my Marantz and AR components (1979).

 

[NW-Bound]

Speaking of speaker crossovers, I just found out yesterday that I need to recap the ones inside my pair of Mordaunt Short tower speakers. I listened carefully, and the treble was weak and uneven between the speakers.

This crossover has 3 coils, 4 capacitors. So, one driver has a 4th order filter (24 db/octave), and the other has a 3rd order (18 db/octave). But which driver, woofer or tweeter, has which filter? The enquiring mind likes to know. I will trace it out to see.

But more important is the fact that 2 of the capacitors are cheap bipolar electrolytic type. They are the smaller ones soldered standing up. The blue one has its aluminum case bulging out at the top end. Bad, bad capacitors.

Why didn't the manufacturer use the better type like the two bigger caps soldered laying down (black body, yellow end)?

I am looking for replacement capacitors now.

I just repaired the above crossover by replacing the two electrolytic bipolar caps. Here's the weird thing. Instead of the values lowering, these failed caps have their capacitance increased. The black 6.8uF cap measured 8.3uF, while the blue 12uF cap measured 27uF. I have not seen this before!

I surmise that bipolar electrolytic are made by wiring two electrolytic caps back-to-back in series inside the same case. One section must have shorted out, and that could raise the capacitance 2x if the other cap stayed functional.

 

[NW-Bound]

The above capacitors are in the woofer crossover section, and not in the tweeter section. Then, how was the tweeter "weak" that caused me to notice the problem in the 1st place? By the way, larger capacitance values would lower the crossover frequency. This makes the woofer less loud in the midrange, and extends the tweeter coverage down to lower frequencies than it is designed for. This was not what I heard.

I took the tweeter off the enclosure and examined it. Its coil still measures at 4 ohm. But applying a tone signal directly to it shows that it is indeed "weak", meaning not sounding as loud as it should. What the heck?

Could the magnet get demagnetized somehow? Searching the Web for clue, I came to the theory that it is more likely that the ferrofluid in the air gap has dried up to a tar, and this gums up the voice coil. Oh bother.

I need to disassemble the tweeter to examine it further. On the Web, people have disassembled their tweeter, cleaned out the old ferrofluid and applied new fluid. But while some tweeters are built to allow this to be done, I am not sure this tweeter is amenable to such treatment. Taking it off will likely destroy the dome. Perhaps I can get a replacement voice coil to rebuild it. This, I have not done. I guess this is something to do to spend the time indoor in the dog days of summer.

 

[NameTaken2]

Continuing to see this thread in new posts -a derailment to share that it brings back the clear and very happy memory of the day in 1975 that I went to the dimly lit, small and very cool stereo shop run by hippie dudes and spent my hard-earned summer job $ on a Harmon-Kardon receiver, BIC turntable, and Advent Utility speakers.
Hearing is not so great these days -that setup contributed LOL.
Still have the speakers, re-coned many years ago!