Realistic Optimus 2 tweeter replacement/upgrade

[Jason299]

I recently picked up a set of four realistic Optimus 2s from the original owner. He included a QTA-790 quad receiver (with working remote!) that he bought as a package in ~1974. Speakers are in very good physical condition including the woofers which appear to have fabric surrounds. However, all of the tweeters appear to be blown. This is a two-way speaker with an 8 inch woofer and 2 1/2 inch tweeter. I suspect all for capacitors also need replacement, they have a 10 uF capacitor which provides a crossover at 2000 Hz which I feel may have ultimately killed the small cone tweeters.

I can pick up cheap 2.5” cones for a few bucks, but will need to change the cap to crossover at ~3500. Other option is to upgrade to phenolic ring units and crossover at ~2500. For the latter I will need to widen the mounting hole by about 3/8”.

Any thought on these or other options? Will I need to modify anything other than the caps? Also, is there any concern that the 8” woofer will underperform with the higher crossover frequency?

Thanks.

 

[Lavane]

Search eBay for "Realistic Parts". That tweeter was probably used in one or more other models. They do pop up pretty regularly. If the seller doesn't list or show the part number printed on the magnet, ask them to take a look. The 8ohm Goldwood paper cone tweeter Partsexpress would probably work good until you find a replacement. You would probably have e to drill new mounting holes though. You can replace that cap with a 10uf polypropylene film cap. I have a pair of Optimus 2B's. I replaced the 7uf cap with a polypropylene film cap.

 

[Jason299]

Thanks. I haven’t had any luck on eBay with this unit. I’ve seen the gold wood unit and may use it, but I need to modify the caps if I do so.

if anyone has experience with reducing the cap uF (increase crossover frequency) let me know. For example, do I need to modify anything else?

 

[Stuart Pedaso]

0705Ad have a history of getting blown and can be rare to find. In 1975 the new Optimus-2B tweeter was upgraded with an aluminium voice coil for better power handling. That tweeter, 0725Ac, can be used as direct replacement in Optimus-2. It has the same form factor and same wide frequency range. It is also used as the tweeter in Optimus-5B and Nova-8B.

There are at least a couple currently listed on ebay. Search Optimus-5B as well as Nova-8B and Optimus-2B to increase odds of a hit. But be careful on ebay. Someone has a 16Ω 0705Ae incorrectly listed as an Optimus-5B tweeter. This family of tweeters look very similar and are sometimes confused.

 

[Jimbo40]

Phenolic rings are also very good, very cheap.

 

[Jason299]

Thank you for the additional info on the 0725 and Phenolic. The Phenolic would require widening of the cutout otherwise I’d probably already have them. I will take a look at the 0725. I saw a post from an Optimus 2b owner stating that he had a 7uF cap. I have 10uF which may have contributed but it’s fatigue on the drivers (~2k crossover). I’ll see if I can find specs on the 0725 and may try to find a slightly lower uF cap to up the cross to 2.5.

 

[dr*audio]

I replaced one of the tweeters in each of my Optimus 1's with a Philips 8 Ohm dome tweeter. I didn't change the crossover frequency, and I left the other tweeter in place to fill the hole. They sounded great like this. I did it on my dad's Optimus 1's as well. Both pairs now reside with friends and are still in use with the Philips tweeters. So they have lasted since 1975 or so. The dome tweeter is an excellent upgrade.

 

[Stuart Pedaso]

I saw a post from an Optimus 2b owner stating that he had a 7uF cap. I have 10uF which may have contributed but it’s fatigue on the drivers (~2k crossover). I’ll see if I can find specs on the 0725 and may try to find a slightly lower uF cap to up the cross to 2.5.

They might have moved crossover frequency up in the 2B if its new woofer rolls off at a higher frequency (model no. 2013Bb -- with claimed frequency range of 40Hz to 3.5kHz). I doubt there would be a problem crossing 0725Ac at a lower frequency by using the 10µF cap. It's a very wide range "tweeter."

 

[Jason299]

Thanks again for the feedback on the Optimus 1’s and the cap size. My concern is that with a relatively “low” tweeter crossover of 2k, will typical dome tweeters work well? Most have a range of 2-20k…this seems like I’d be on the edge for smooth transition from woofer to tweeter. if I put in an 8.2 uF cap, it would push the crossover up to ~2500.

 

[Jason299]

They might have moved crossover frequency up in the 2B if its new woofer rolls off at a higher frequency (model no. 2013Bb -- with claimed frequency range of 40Hz to 3.5kHz). I doubt there would be a problem crossing 0725Ac at a lower frequency by using the 10µF cap. It's a very wide range "tweeter."

View attachment 2496145

Thanks. I’ve had no real luck with the 0725. I did message a seller who claims to have more RS stock not listed. Would you happen to know the specs on the 2003Bd woofer in the Optimus 2? This would help me make a call on the crossover.

 

[wallacefl]

If the Optimus 1 really is crossed at 2000 with a single capacitor then an EPI 100 , OLA or Parts Express phenolic tweeter may work … a far number of modern tweeters with FS< 750 hz would probably work even better with the correct capacitor and attenuation.

 

[dr*audio]

Thanks again for the feedback on the Optimus 1’s and the cap size. My concern is that with a relatively “low” tweeter crossover of 2k, will typical dome tweeters work well? Most have a range of 2-20k…this seems like I’d be on the edge for smooth transition from woofer to tweeter. if I put in an 8.2 uF cap, it would push the crossover up to ~2500.

Like I said, I used dome tweeters and they sounded great and have lasted for over 40 years so far.

 

[Lavane]

Thank you for the additional info on the 0725 and Phenolic. The Phenolic would require widening of the cutout otherwise I’d probably already have them. I will take a look at the 0725. I saw a post from an Optimus 2b owner stating that he had a 7uF cap. I have 10uF which may have contributed but it’s fatigue on the drivers (~2k crossover). I’ll see if I can find specs on the 0725 and may try to find a slightly lower uF cap to up the cross to 2.5.

Different drivers were used in the 2B's than what was used in the 2's. So the crossover cap is different because of this.

 

[dr*audio]

This is the tweeter I used. Unfortunately I don't recall the model number. Maybe someone will recognize it. https://www.pinterest.pt/pin/612771093025966829/

 

[Lavane]

I replaced one of the tweeters in each of my Optimus 1's with a Philips 8 Ohm dome tweeter. I didn't change the crossover frequency, and I left the other tweeter in place to fill the hole. They sounded great like this. I did it on my dad's Optimus 1's as well. Both pairs now reside with friends and are still in use with the Philips tweeters. So they have lasted since 1975 or so. The dome tweeter is an excellent upgrade.

I don't doughty at all that the dome tweeter sounded good. I'm a fan off dome tweeters. PE sells some nice sounding silk domes.

 

[Jason299]

If the Optimus 1 really is crossed at 2000 with a single capacitor then an EPI 100 , OLA or Parts Express phenolic tweeter may work … a far number of modern tweeters with FS< 750 hz would probably work even better with the correct capacitor and attenuation.

Thanks for the heads up on the EPIs. Looks like that model used the same 10uF cap. New tweeter “replacements” for that model are a bit pricey but lots of listings on eBay.

 

[Jason299]

Just bought a circa 1985 pair of “working” EPIs for $40. Sounded like a legit seller. Also picked up 2 new Dayton 10uF caps so I’ll let everyone know how it goes.

If all goes well I’ll match the second pair with the same setup.

 

[Jason299]

This is the tweeter I used. Unfortunately I don't recall the model number. Maybe someone will recognize it. https://www.pinterest.pt/pin/612771093025966829/

Thanks. I picked up two of the EPIs for one set, but I’ll also try to locate the specs on these as they may be a good option for the other pair I have.

 

[Jason299]

All-

Closing the loop on this thread, I sourced two EPI dome tweeters from a set of EPI 100s. That model was spec’d to cross at 2000Hz, the same as the Optimus 2’s. Since I couldn’t fully comprehend the odd crossover layout, I ended up replacing the inductors with new 0.6mH Jantzen Air Cores and used a standard (1st order 2-way) design. I also ended up leaving the caps in place since the original Elna’s both tested well within range at 10.4uF.

I forgot to take a photo of the new setup prior to installing, but speakers look and sound fantastic running off my c.1978 Realistic STA-84. I also decided to leave the integrated Hi-filter switch in place and it works as designed.

Thanks for the feedback and suggestions.