I picked up some more speakers to restore this week.
Interdyn P33 which is a nice unit, when I got there the mid ranges weren’t working and the woofers had been replaced. I nearly walked away but decided the cabinets might be resurrected and/or I could use the tweeters and crossovers as spares, probably too generous but paid $50.
Well….the mids are fine but these have to be the best cooked crossovers I’ve ever seen!
I did what I could to trace the design, I was a bit worried the inductors would be damaged but they both read an identical 0.18mH/0.4 ohm so I might be lucky.
The crossover design looks interesting, first order only with some impedance compensation, nothing at all on the woofer.
Based on the sketch this would be 700Hz/5kHz, can anyone see anything wrong with my assumptions?
SEAS H086 tweeter, 10 F-M midrange and normally a 25F-EWX woofer has been replaced with a Plessey C100.
Interdyn P33 which is a nice unit, when I got there the mid ranges weren’t working and the woofers had been replaced. I nearly walked away but decided the cabinets might be resurrected and/or I could use the tweeters and crossovers as spares, probably too generous but paid $50.
Well….the mids are fine but these have to be the best cooked crossovers I’ve ever seen!
I did what I could to trace the design, I was a bit worried the inductors would be damaged but they both read an identical 0.18mH/0.4 ohm so I might be lucky.
The crossover design looks interesting, first order only with some impedance compensation, nothing at all on the woofer.
Based on the sketch this would be 700Hz/5kHz, can anyone see anything wrong with my assumptions?
SEAS H086 tweeter, 10 F-M midrange and normally a 25F-EWX woofer has been replaced with a Plessey C100.
Well, according to this info, the Plessy C100 goes up to 13 kHz and the original SEAS only goes to 1500 Hz.
Since there is no filtration on the woofer in your sketch, the Plessy may be too bright for the mids, which may explain why the midranges were not working.
Perhaps they were intentionally disconnected when the SEAS woofer was replaced.
Hope this helps.
Since there is no filtration on the woofer in your sketch, the Plessy may be too bright for the mids, which may explain why the midranges were not working.
Perhaps they were intentionally disconnected when the SEAS woofer was replaced.
Hope this helps.
Attachments
I'd first switch positions for the L-pads. Your upper cross might be a little lower than you've stated.
I have no history on theses speakers, I suspects the Plesseys went in because they were available, and coincidentally had a higher response - but they didn't sound good when I listened.
I'm surprised the tweeters worked at all because the crossover tracks were charcoal, and I still can't fathom how they got so burnt out without also damaging the speakers.
Re the L-Pads, that's not something I have a lot of experience with, but I'm pretty confident on the values and the layout that I've drawn up.
Eg
H085 woofer is 91dB. No series inductor either, so full output.
H084 mid range is 89dB. This design has ~13dB attentuation through 2x 5 watt resistors.
H086 tweeter is 89dB. This design has ~3.5dB attenuation, series 5W and parallel 10W resistors.
The tweeter has a recommend 6dB crossover at 4 kHz so 6.8uF is probably more appropriate, but looking at the 0.18mH inductor on the mid and the 4.7uF cap on the tweeter, it looks designed for 5.5kHz but to me there is no need for any attentuation at all given it is already less sensitive than the woofer.
The mid is also less sensitive than the woofer and has relatively flat impedance curve, so why would there be 13dB attenuation? Seems that's why the resistors got cooked...
I've asked the original supplier for the crossover design so I can check...
I'm surprised the tweeters worked at all because the crossover tracks were charcoal, and I still can't fathom how they got so burnt out without also damaging the speakers.
Re the L-Pads, that's not something I have a lot of experience with, but I'm pretty confident on the values and the layout that I've drawn up.
Eg
H085 woofer is 91dB. No series inductor either, so full output.
H084 mid range is 89dB. This design has ~13dB attentuation through 2x 5 watt resistors.
H086 tweeter is 89dB. This design has ~3.5dB attenuation, series 5W and parallel 10W resistors.
The tweeter has a recommend 6dB crossover at 4 kHz so 6.8uF is probably more appropriate, but looking at the 0.18mH inductor on the mid and the 4.7uF cap on the tweeter, it looks designed for 5.5kHz but to me there is no need for any attentuation at all given it is already less sensitive than the woofer.
The mid is also less sensitive than the woofer and has relatively flat impedance curve, so why would there be 13dB attenuation? Seems that's why the resistors got cooked...
I've asked the original supplier for the crossover design so I can check...
I think that’s what happened here. Do you have any thoughts on the values/high attenuation that would be happening on the mid range? I’m not sure if ai am missing something or not.
These were very well regarded speakers the time.
1.2 ohms against the midrange isn't very much attenuation. The 10 ohm resistor in that position wouldn't be doing much other than smoothing the impedance curve and changing the damping of the filter.
Maybe I’m misunderstanding something, but the series resistor for the midrange is 12 Ohms.
Interestingly all the big resistors still measure in spec even though the boards underneath were burnt out, but the 2.2’s measure as 1.4 Ohms.
Interestingly all the big resistors still measure in spec even though the boards underneath were burnt out, but the 2.2’s measure as 1.4 Ohms.
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I used the tool here to calculate it, but either way do you agree there is too much attenuation. Maybe it was meant to be 1.2 Ohms.
https://sound-au.com/articles/l-pad-calc.htm
https://sound-au.com/articles/l-pad-calc.htm
I always thought that Interdyn speakers were only sold by Encel Electronics - in Melbourne. Is this correct?
I have also always wondered about the people/team & place that designed and built them 😳
PS.
I think that by today's standards, most if not all Plessey cone drivers would be considered to be quite 'loud & low HiFi'.
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could be a Mhz oscillating amp, the tweeter inductance would prevent the blowout, with the paralell resistor taking the grunt .
Interdyn were by Aranmar Acoustics in Melbourne, for Encel.
And yes, I think the Plesseys are not up to the SEAS standard. I’ll be replacing them ideally with some of the originals.
Although, the Plessey factory apparently is still in business, now called Lorantz, which is what these woofers are labelled as.
ok, thanks. I wasn’t sure if you are suggesting I’ve drawn it wrong…I’ve triple checked and my schematic is correct for this crossover. So I’m not sure what that parallel resistor is meant to be doing but will wait and see if I get a reply from Aranmar.