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In Reply to: RE: Electro-Voice Regal lll posted by Paul Eizik on January 17, 2017 at 09:23:24
Paul,
Thanks for the schematic! Just curious, what did you use for the low and high crossover frequencies?
I was hoping I could keep the speakers original in design but update it with new caps. That's not turning out to be the case. I checked with Bob Crites. He says he has NOS 16 ohm T35 diaphragms but wants $100 each installed. Through my research I have come to believe the MR-10 horns were 16 ohms in the Regal III. That would make the 5.7uF mid cap a little closer to what is expected. Since I'm not willing to drop $200-$400 on new 16 ohm diaphragms and since mine measure 8 ohms and new 8 ohm ones are readily available it makes sense to change the crossover & L-Pads to work with what I have.
What is the reason for the 16 ohm and why did 8 ohm become common? The following are the parts I'm considering. The L-Pads have me a little confused. There are different wattages & mono vs stereo.
https://www.parts-express.com/dayton-audio-dmpc-56-56uf-250v-polypropylene-capacitor--027-425#!
https://www.parts-express.com/dayton-audio-dmpc-20-20uf-250v-polypropylene-capacitor--027-436
https://www.parts-express.com/jantzen-audio-037mh-18-awg-air-core-inductor-crossover-coil--255-222
https://www.parts-express.com/jantzen-audio-065mh-18-awg-air-core-inductor-crossover-coil--255-236
https://www.parts-express.com/speaker-l-pad-attenuator-15w-mono-1-shaft-8-ohm--260-250
Craig
Follow Ups:
Craig
The schematic I posted uses 1000 Hz for the low end and 3500 Hz for the high end like the original crossover did, and it's also a 1st order crossover. The parts you link to for C1,C2,L1 and L2 should be fine. I'm not sure how a "stereo L-pad" applies here, as you want a separate mono L-pad on each mid horn and horn tweeter. Dave wanted me to remind you that the L-pads for my schematic should all be 8 Ohm units, and it looks like you are aware of that. You pay more for higher Watt L-pads so budget according to the amp you are using.
16 Ohm speaker drivers were more common in the vacuum tube amp days as tube amps had an efficiency advantage with higher resistance drivers, while transistor amps had an efficiency advantage with lower resistance drivers. The Regal seems to come from that time in the late 60's when the transition from tubes to transistors came about in the market.
Does the schematic make sense? Note that when a wire crosses over another wire, they are not connected to each other at that point unless there is a dot at the cross road. I used the schematic format from one of the calculators we discussed here for the sketch, and I corrected an error where they omitted a dot where the mid minus connects to the amp minus. It's a trivial point but it may have confused someone not used to reading schematics.
Hope all this helps
Paul
I haven't taken the time to try and decipher the schematic. I'm guessing it is the same way the speaker is currently wired.Mystery Solved?
I was looking around the Great Plains Audio website and discovered this:NOTE 2 - When the original 24 ohm impedance is not required, use the diaphragm manufactured for the Altec Lansing 299-8A, Altec original part #25884 (8 ohms), or the diaphragm manufactured for the Altec Lansing 299-16A diaphragm, Altec original part #25885.
I had no idea speakers went above 16 ohms. When I first found the KBapps calculater I played around with it trying to get the cap values to come out to the numbers I had on the caps. If you make the tweeter = 16 ohms, mid horn = 26 ohms and woofer = 4 ohms you get a C2 value of 5.667265. It also shows L2 = 0.63662, so I might be able to reuse one of the original coils if I could verify the value.
Edits: 01/20/17
Another newbie question. The woofer surround has separated from the cone in two places. How do I re-attach the surround to the cone? I got some cloth surround sealant from Vintage-AR but now I'm not sure if this is what I should be using. It seams this sealant is used to keep air from flowing through the cloth surround. Does it also attach the surround to the cone? If it does attach the surround to the cone do I apply it between the cone and the surround?
Craig
Try a bit of the surround sealant and see how it works. In the past I've made my own speaker dope for this when the surround on one of our Pioneer CS88 in the HT started to separate. I used some DAP silicone rubber in a tube, and I thinned it with xylene as is said on the label, and it worked fine. Silicone rubber comes in different colors (looks like your project would need clear) and can be thinned with various things. I used the DAP because of the xylene which seemed a milder solvent than acetone, and I didn't want to melt the rubber surrounds on the Pioneers, but this is likely not that much of a concern on the accordion surrounds on the EV woofers.
I love the smell of rosin core solder in the morning! It smells like music!
Paul
Paul,
Crossover parts are on order. The smell of rosin core solder in the morning will be soon. Any recommendations on solder? Any reason to replace the wires in the speaker? What do you think of the possibility of the mid horn being 24-26 ohm originally; makes the calculator work.
Craig
Craig
Solder has tended to go lead-free in recent times. Radio Shack has (or at least they used to) Lead- Free Silver Bearing Solder 96/4 # 64-025 but ti's difficult to work with as the solder joints tend to look "cold" (read: not nice and shiny). So it can make an impatient expert into an amateur. I have a lifetime supply of good old Kester "44" Sn 60 which always gives good results, but I dunno if you can still buy it.
Wire: Monster XP is good, reasonably priced and easily available.
A check with your DMM of the original L-pads may reveal more of the mystery, though you should disconnect them first. A reading between the center lug and one of the other ones should reveal either a very low reading or the maximum value of the L-pad as you turn the knob to the end points. Also look for a resistor added to the L-pad which may affect the circuit impedance. To re-iterate: you stated that the T35B's are marked as 16 Ohms units, but measurements show them to currently be 8 Ohm units. If the L-pads don't match the driver they will actually change the crossover frequency as the knob is turned up or down, and it's difficult to imagine EV designing it this way.
Paul
PaulI measured both L-Pads. The low readings are 0.2 and 0.7 ohms. The high readings are 104.2 and 103.8 ohms. Both are disconnected.
Craig
Edits: 01/26/17
Measured my new L-Pads 0.1 to 7.5 ohms
Craig
This starts to explain some of the mystery of why the parts values n the original crossover didn't seem to make sense, and the nominally 100 Ohm L-pads seem to account for the missing Ohms to match the parts. As to why they did it that way I can only speculate. In the page of the 70's EV catalog I posted here they were expecting that DIY'ers would use a "building block" approach which would mean starting with a "full range" woofer in a suitable box which would be made. Later you would add a tweeter for some highs. After you had that awhile you would add a midrange horn for "presence". The mid horn and tweeter were presented as add on tone controls.
As you'll be nearing a time when you can compare the new crossover to the old one, it might be time to move this up page to a new thread, as we're stretching the limit of how far we can go to the right down here. Hopefully the speakers sound better!
Paul
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