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Old 2nd March 2013, 09:59 PM   #11
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Thanks again Steve.
I'll try a few things and see how I go. I'll definately lose the tank capacitor on the woofer first. (The brochure suggests the 18s and 38s tweeters are ferro-fluid cooled, and I can't see evidence that any has leaked.)
Cheers
Peter
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Old 3rd March 2013, 09:35 AM   #12
system7 is offline system7  United Kingdom
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Ferrofluid oil tends to dry out and turn solid (the ferrite particles) more than anything. That makes sense if you think about it, because it's working at high temperature at parties which shorten its life.

We can only hope for the best.

You don't really have many options with the AR-38S. I think harsh bass cone-breakup is always going to be the problem. But I do want to hear how it goes.

My college friends often had the lively AR-6, whereas I was more into the dull smoothness that was bextrene plastic cones or B&O electrically filtered paper cones. Nothing is perfect.
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Well, there it is! Best regards from Steve in Portsmouth, UK.
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Old 1st April 2013, 09:21 PM   #13
system7 is offline system7  United Kingdom
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I spent some more time on the AR-38S, Graveyboat. It was tougher than I expected.

Unless you add Inductance to the circuit, which will make it bassier, you really can't do much with it.

The 6uF 3kHz Tank does a good job of rolling off the bass and aligning phase IMO. But it was deeper than necessary, and in fact only the non-polar capacitor resistance stops it being a huge pit. I found adding a 3.3R resistor made it smoother. But for all that, the mod might damage phase alignment. I don't know if AR's circuit is brilliant or stupid! Without the tank, you get quite a peak at 4kHz anyway.

There is also the possibility of doing a second order tweeter without dropping the impedance much at the top end. Say 5 ohms goes to 4...worth a go, I'd think. The tweeter ought to sound smoother. Hope that helps.
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Well, there it is! Best regards from Steve in Portsmouth, UK.
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Old 2nd April 2013, 04:30 AM   #14
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Hi Steve. Thank you for the effort you have put in. I thought about a 2nd order for the tweeter, but decided to do this: I removed the tank cap completely (ignoring the phase shift). I then included a 1.5ohm 10watt resistor in series with the tweeter, increasing impedance, and changed the cap to 4.7uF. The caps are nice polypropylene ones made in the UK, which sound quite smooth. I also lightly doped the tweeters with some polyurethane. The crossover point shifts slightly and the tweeter is down about 2db. Resistor is inductive, but I can only hear to 12K, so not much difference there. The bass then sounded a little bloated, but this was remediated by de-coupling the speaker on stands, away from the wall. The stands just sit on the carpet, hence the decoupling. I actually think the best move was buying good quality MKP caps. The last replacement ones were stated to be polyprop, but the sound was so harsh I expect they were polyester, and poorly designed at that. So, overall I now have a quirky sound I can live with, but it was always going to be a compromise, wasn't it?
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Old 25th June 2013, 09:35 PM   #15
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Hi guys. I just bought a set of AR38s 1981 speakers that have a little damage on the outside and the 10" woofers need refoaming. I have started the refoaming process but I was thinking if I should take this a step further and try to improve their sdesign in any way....
I have been looking online for a picture or drawings of how they are constructed and how they look on the inside so that I can know more before I make up my mind what to do, but I have not found much of any use. I am a noob in speaker refurbishing but I have a lot of professional experience in making and refurbishing furniture. So Im good with my hands and have to tools but am not very knowledgeable about the science of making speakers.
Can you give me some advice or maybe some links that would help ?
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