Yet Another Altec 2-Way

je2a3

Senior Member
Sounds is pretty darn good so far. I finally got around to flipping the cabinets (placed them on some floor dollies), and that definitely helped to further blend the the horn with the 412c. I also picked up a pair of RCF H3709 horns for cheap, and I hate to say it, but I do prefer their sound over the 811s. I'm probably heading down a rabbit hole that will eventually lead to 32s.

One thing I've been doing is flipping back and forth between the crossover I built and a simple 1.5uf cap to the 806a. Both approaches seem to have their own merits sound-wise, but I think I prefer the crossover a bit more in this particular configuration. One thing I'm considering is building a second pair of crossovers using better quality parts--mainly using PIO caps instead of the inexpensive polys that are currently in there. I've got a lot of experience building amps and such with classic PIO caps like Vitamin Qs and old Russian stock, but I've never used motor run caps before. Are there certain brands that are preferred for one reason or another (reliability, etc.) or are they all basically the same when used in a crossover? Looking at various sites that sell such caps, and prices seem to be all over the place--you can get a 10uf motor run cap for $7 or $40, but I have no idea if the more expensive ones are better or not for audio applications.

There's my N1600 clone which I used when I rolled off my 414As. These are loaded with Sprague PIOs and Russian MBGO wax/paper in a metal can (smallest and rusty can).

Here's another one I made with Sangamo PIO + motor start run caps. Honestly the difference between the US PIOs and MBGOs isn't as great as the MBGO vs. plastic caps. I use motor start run or MBGO caps when I can't find a reasonably priced US PIO equivalent.
 
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Yes, Earl. My 806s have the original 20275 diaphragms. I can definitely hear the roll off of the 806, but it does enough good stuff before the roll off for my ears to be happy with most types of music I listen to. I have a few different super tweeters around here that I used to sometimes mate with a pair of Altec 755Cs in Silbatone clones...I might need to dig those out and give them a try here. My ears do tell me that the 811 allows a bit more HF extension than the RCF, which I'd guess has something to do with the 32-ish horn profile you speak of. Honestly, I didn't really notice the 811s being objectionable in any huge way until I swapped in the RCFs. Perhaps my ears just prefer a more mellow sounding horn. Could also be that I'm doing all of this in a NYC apartment, and the RCF might just be better in the smaller space. Thanks for the pics!

@je2a3 - I've never used the Russian MBGO caps, so I'll have to add them to my list. I've got a bunch of those large Sangamo PIOs around here, but not in all of the values I would need. Thanks for the additional pics as well!
 
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@je2a3

Are you ( really ) using Motor Start or ( the more typical ) Motor Run capacitors ??

( There's a notable difference in construction and capabilities between the two types ).

Google; Motor Run vs Motor Start capacitors

@mdye

Personally, I wouldn't over spend on any motor run caps ( since/because I typically only use them up to about 50-60% of the total needed capacitance anywhere in the circuit ).
- Used like that I find they are all the same >> giving that deep midrange solidity that helps anchor/mesh a horn driver onto a baffle mounted woofer.
- FWIW, I use surplus Mallory motor-run capacitors.

Looking at the currently very affordable prices for the MBGO caps, one really can't go very wrong just filling up a shoe-box with various useful sizes for future projects.

I like to make up the other 40-50% of needed capacitance using various industrial grade film caps ( typically MPP types ).
- It's this upper half where I go searching for sparkle and clarity ( elusive qualities to say the least ).

From time to time, I do roll various film caps in and out of my horns HiPass ( just for laughs actually ) .

:)
 
@je2a3

I would ( visually ) identify your circled cap as Motor-Run.

Temco Capacitor FAQs

I ( visually ) identify any round black phenolic type as Motor Start ( as mentioned in my link ).

Apart from that, I use catalogues and part numbers to make a proper identification.

Within conversation, I always advise for Motor-Run since they are speced for Continuous Duty.

:)
 

je2a3

Senior Member
@je2a3

I would ( visually ) identify your circled cap as Motor-Run.

Temco Capacitor FAQs

I ( visually ) identify any round black phenolic type as Motor Start ( as mentioned in my link ).

Apart from that, I use catalogues and part numbers to make a proper identification.

Within conversation, I always advise for Motor-Run since they are speced for Continuous Duty.

:)
I used the wrong term, I meant motor run. I've seen the black phenolic "motor start" but never used them for XO. 😊

Thanks for correction @EarlK 👍I love learning something new!
 
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