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BIC Venturi Formula 6 and 6-1a

Stuart Pedaso said:
I've compiled crossover information for most, if not all variations of Formula 2, 4 and 6 models prior to Spec II. Since the OP's intention is to have a public information based thread, I'll post schematics here for quick reference should anyone be on the hunt.

Early crossovers are fairly simple -- free running woofers and first order filters (discounting RLC filter). Note differences in component values between Formula 2 and Formula 4. Later versions are identical for both models.

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The early Formula 6 crossover is the only one I've found with a slight variation of the RCL filter, which is identical among all other model iterations. This version has BIC 020 phenolic ring tweeters rather than the later 030 piezoelectrics.

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Next version of Formulas 2 and 4 are more robust with 2nd order filters, and share identical component values. Only woofer size differs.

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Later Formula 6 shows similar changes to crossover filters and now sports piezoelectric tweeters.

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Latest Formulas 2 and 4 add fuse protection for each driver.

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It's possible, probable even, that Formula 6 also had a fused version. Haven't seen an example though, so it's speculation until one turns up.
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Stuart ,first I and other early BIC owners are in your debt for your excellent crossover schematics that you have shared with the AK community. I don't know how you can classify the early BIC's crossovers as "fairly simple". Just take a look at your own schematic of the Piezio version of the Formula 6's. Obviously the woofer is not free running going through both a choke and the Brightness Control with it's own cap which can be ran on auto or through the control pot. I have yet to figure out what is going on if the auto is switched on. But in retrospect a lot of this voodoo is simple for speaker techs and math geniuses. Again thanks for your sharing your schematics.
Also if anyone has a source for a true 5" midrange ( 5.125") frame size will not work. Please inform me.
 
smoothtune said:
I don't know how you can classify the early BIC's crossovers as "fairly simple". Just take a look at your own schematic of the Piezio version of the Formula 6's. Obviously the woofer is not free running going through both a choke and the Brightness Control with it's own cap which can be ran on auto or through the control pot.
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My "fairly simple" comment was meant for comparison of the phenolic ring tweeter version against the later, more complex piezo tweeter version. After the Brightness Control circuit, the base crossover circuit is spartan: no filter on the woofer, only a 1st order high-pass on the 5" (no band-pass), only a 1st order high-pass on the horn (no band-pass) and a 1st order high-pass on the tweeters. Three capacitors -- that's all. As a 4-way crossover, it doesn't get much simpler than that.

Much different in your later piezo version Formula 6. Though the Brightness Control is about the same, after which the woofer still runs free, there's now a band-pass filter on the 5" and a 2nd order filter on the tweeters with resistor providing an "impedance," allowing the filter to work.
smoothtune said:
I have yet to figure out what is going on if the auto is switched on.
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Switching to "Auto" just replaces the manually adjustable resistor (potentiometer) with a thermally activated adjustable resistor (thermistor).

In Manual mode, you can adjust the filter's effect any time you want, at any playback loudness level, by turning the nob adjusting the resistance leg of the filter.

In Auto mode, the potentiometer is switched out of the circuit and replaced with a thermistor. It will adjust resistance just like the pot, but only as its temperature changes. It becomes warmer at louder listening levels as more current passes through it. And cooler at lower listening levels.
 
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jboerger3 said:
Your schematic is easier to read than the diagram found inside the speaker.
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The wiring diagrams are handy for maintenance purposes by showing how components are physically laid out and where all the connections are. Including them was a thoughtful touch by the manufacturer. But as you point out they aren't very good for viewing flow of the circuitry. That frustration led me to draw the schematics after becoming intrigued with these speakers.
jboerger3 said:
Has anyone had any luck finding a good 5" replacement driver?
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smoothtune said:
Also if anyone has a source for a true 5" midrange ( 5.125") frame size will not work. Please inform me.
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The closest 5 inch I've found is Dayton RS125P-8. Manufacturer claims it's outside diameter is 125.5mm.

Dayton_5in_woofer.png
125.5mm = 4.94". That's only 0.06" shy of 5" -- about 1/16". Centered in an exact 5" diameter inset would leave a 1/32" reveal around its circumference. That's less than 1mm -- a very close fit.

Has a nice response curve across the lower midrange needed in a Formula 6.
Dayton_5in_FR.png

Though one might want to study its specs carefully to confirm it would make a suitable replacement. Seems a bit pricy to try on a gamble.
 
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Stuart
Thank you again for your excellent description of the operation of the Brightness Control and for your tip on the Dayton 5" midrange. I think it would work out fine for a mid replacement in the formula sixes.
 
smoothtune said:
I have a pair of the Formula 6 with the two square 3 1/4" lend Piezos below the horns. I believe these were the first version of the Formula 6. The OP's photos show one crossover diagram labeled "MODEL FORMULA 6-1A" which shows three CHOKES which are contained in my units. Sadly I had to have my cabinets redone after spending too many years of their lives powering the music in a college drinking establishment. The only replacement so far were one woofer that the outside ring had became too flimsy. I think it is time for new caps and resistors as that speaker's woofer still moves with any movement of the receiver's volume control. Also have new Piezos for them.well, may as well replace the other woofer and mids while I'm in there. The diagram for my units show the negative side of the tweeters to the resistor and a 250muh CHOKE and the positive side to a.5MF/100VNP capacitor and a.5 Mh CHOKE. I don't understand what all this means but I can operate a soildering iron. Hope I don't need any wicking wire! I have enjoyed my BIC's through the years when I wanted to rock out but I don't know that they will play hapy with a Fischer 800C I have comming. I also want to thank the OP for starting this thread.It motivated me to register on the forum.
I contacted the BIC company and they were nice enough to reply but they did not have a clue. I think some one else just bought the BIC name.
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smoothtune said:
My speakers are 6-1a. They have a 12" woofer, a 5" mid-range, two biconex horns, and two Motorola piezo electric tweeters in each cabinet. The speakers shown attached to your post are not 6-1a's
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Thanks. So is what is in my picture first generation?
 
JerStC said:
Thanks. What's the general consensus on how they stack up to their earlier gens?
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i've seen it said here that the original sounds the best, but I have'nt heard the spec II myself. My buddy had the original and I remember it had a chest kicking bass.
 
The major problem i see with the Spec II's are the unobtanium coaxial woofer/ lower midranges. As far as i know, these are the only woofer/ mids coaxials on the planet?!.
 
Walle said:
Good luck with those hefty BIC's! I still own my BIC Formula 5's (Avnet Corporation Westbury, New York) that I purchased new in 1975-76. They have the T-slot Biconex horn (mids & highs) coupled with 10" woofer. Their cabinetry is top notch with walnut veneer over MDF, well braced inside and weigh around 35-40 lbs each. The highs were cutting out on occasion so I pulled the control unit at the top to take a look. This contains the crossovers plus other circuitry that enabled a clipping indicator, reset buttons and unique L-Pad type controls (Pop/Rock). I considered replacing the caps (5 per unit) but decided against it as you never know what else is bad, or about to go bad when something is over 45 years old. There were some transistors, etc. on that board as well. In retrospect, a gimmicky feature but it sounded good when I was 20. I disconnected and left the "control units" in place for aesthetics and installed Kasun (China/Amazon) 3-way crossovers with two L-Pads from Simply Speakers and am very pleased with the results. Other than the occasional stridency that horn drivers exhibit they sound pretty awesome, especially with jazz which is my thing. Hope this helps.
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Hi, so I'm revisiting this as they've sounded awful regardless of the music source since I installed the Chinese crossovers. The high frequencies hurt my ears with the l-pads on the midrange and tweeter turned all the way down. AI says that it's due to some sort of impedance mismatch and that the oem board with the original crossovers contains circuitry to enable a balanced sound between the drivers. I know they're older speakers, but they are all I have so I'm considering recapping the board and putting things back to original. Any comments would be appreciated. I think that I have all the capacitor values to work with.
 
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