Looking to get some confirmation on the crossover cap values in the original Super Towers. My friend's already fried the original MB Quart tweeters and has subsequently fried the Morel MDT 30S's recommended by Madisound.
In the HF section there are two large Solen radial caps that are clearly not original, one is 4.7uF and the other is 15uF. From what I've read about the Studio 1, which uses the same drivers in single-woofer bookshelf format, the crossover point should be 2.5kHz and both HF crossover caps should be 4.7uF. The 15uF cap would lower the crossover frequency, and my tests with a mic show the tweeter is passing signal down to 1kHz. That can't be right since the original MB Quart MCD25M is only rated down to 2kHz.
So as I'm borrowing one 4.7uF cap from one speaker to replace the 15uF cap in the other for testing, if anyone has any intel on the proper cap values I'd feel more comfy because my friend will wantonly unleash his Hafler DH220 on these puppies upon their return.
In the HF section there are two large Solen radial caps that are clearly not original, one is 4.7uF and the other is 15uF. From what I've read about the Studio 1, which uses the same drivers in single-woofer bookshelf format, the crossover point should be 2.5kHz and both HF crossover caps should be 4.7uF. The 15uF cap would lower the crossover frequency, and my tests with a mic show the tweeter is passing signal down to 1kHz. That can't be right since the original MB Quart MCD25M is only rated down to 2kHz.
So as I'm borrowing one 4.7uF cap from one speaker to replace the 15uF cap in the other for testing, if anyone has any intel on the proper cap values I'd feel more comfy because my friend will wantonly unleash his Hafler DH220 on these puppies upon their return.
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No idea why but this gent has edited out the values. weird.
If he keeps destroying tweeters from abuse, I'd put a polyswitch on the tweeters
No idea why but this gent has edited out the values. weird.
If he keeps destroying tweeters from abuse, I'd put a polyswitch on the tweeters
The tweeter may have a third order Butterworth high pass filter. If so, the capacitor connected to the tweeter is triple the value of the capacitor on the input side of the filter. The values 4.7µF and 15µF appear about right for a 2k5Hz Butterworth crossover for an 8Ω tweeter.
3 Way Crossover Design Example
Is the amplifier oscillating ultrasonically? That would pre-heat the tweeter and make it vulnerable to blowing.
3 Way Crossover Design Example
Is the amplifier oscillating ultrasonically? That would pre-heat the tweeter and make it vulnerable to blowing.
Sounds like a knob-junky that doesn't know what clipping is. Could add a 1A slow blow fuse at input.
You might just tell him if he breaks them again that you aren't fixing them, or poly switch them.
Yes, sounds like a 3rd order electrical filter to me as well, and the 15uF is likely fine.
If you do polyswitch, run a 12-20 ohm resistor across the limiter to allow the tweeter to play at a lower output until it cools and reopens. This way you know the tweeters still work.
Wolf
You might just tell him if he breaks them again that you aren't fixing them, or poly switch them.
Yes, sounds like a 3rd order electrical filter to me as well, and the 15uF is likely fine.
If you do polyswitch, run a 12-20 ohm resistor across the limiter to allow the tweeter to play at a lower output until it cools and reopens. This way you know the tweeters still work.
Wolf
A 1A slow fuse does nothing for the tweeter, heck, you could even burn up the bass drivers before it goes off. If you want a protection for the tweeter, put a 12V 3-5W bulb in series to the tweeter. That works and after it cooled down, the tweeter comes again, no need to replace anything then.
A bulb is likely cheaper because you don't need an additional resistor. Plus, you've got a visual indicator for free if you want. 😉
bulb sounds like a cool feature, how do one calculate the size of the bulb to protect a very fragile tweeter?
Here’s one specifically for that, I’ve seen them a lot on pro stuff and years ago I had a pair of Boston acoustics two ways that came with one built into the crossover. Speaker Crossover Tweeter Protector Lamp
Based on what wasn't obscured on the label the large inductor "0066" is an Intertech 2.7mH / 15AWG. LU78/2.7/140 | Intertechnik Components - your competent partner for business scale hifi audio parts - Shop
The values of the capacitors and resistors can be read off by anyone who has the actual crossover in their hand.
That is were i was going to go. Tweeters mst often fail due to an ampifier clipping hard.
Amplifier?
dave
It is a bit disingenuous to claim that a light bulb in series with the "protects tweeter without affecting the sound"! The bulb will modulate in resistance thus shifting the crossover frequency and tweeter level as it heats up and cools down. Back to back 3 watt zener diodes across the tweeter is an alternative where there is a series resistor in the tweeter feed, say 3.3 volt volt / 3W https://au.mouser.com/ProductDetail/ON-Semiconductor/1N5913BRLG?qs=y2kkmE52mdMaB8%252B0DLi8ZQ%3D%3D
Leave as much of of the copper leads on the zener diodes as possible as they act as a heatsink.
Leave as much of of the copper leads on the zener diodes as possible as they act as a heatsink.
Someone else had a DH200 that oscillated because of a faulty capacitor:
"Years ago I had a DH200 that was oscillating because of an open electrolytic on the power supply. An oscilloscope would tell you that. If it was oscillating above the audio range you would probably have blown tweeters."
Hafler DH-220 Buzz
"Years ago I had a DH200 that was oscillating because of an open electrolytic on the power supply. An oscilloscope would tell you that. If it was oscillating above the audio range you would probably have blown tweeters."
Hafler DH-220 Buzz
You mean it may vary non-linearly, or over time.. to which we'd want to know the thermal properties. Varying of the crossover point isn't necessarily going to be the result.
In the case of using a light bulb to limit power delivered to a tweeter, the light bulb in series with the tweeter voice coil are jointly the load seen by the high pass filter. It is an inescapable consequence of physics that if the terminating or load impedance on the output of a passive filter network changes, then the nominal turnover frequency of the filter network will also change. Whether that is significant in the context of the circuit under consideration is another matter.
Early Bose 802 professional loudspeakers contained a light bulb in series with a crossover capacitor to limit power to the four of the eight transducers that handled the high frequencies (the four transducers had high frequencies bypassed to prevent the dispersion of the system narrowing). At the beginning of a stage musical that I worked on in the early '80s which used 802s for the front of house PA, the orchestral overture caused the lightbulbs to heat, and the thermal inertia of the bulb filaments was enough for that the dispersion pattern versus frequency was affected enough to impact the intelligibility of vocals through large parts of the auditorium for a period after the overture. This was because the crossover filter cutoff frequency shifted downwards for the HF/full-range drivers whilst simultaneously pushing the cut-off frequency upwards for the LF drivers, thus narrowed the vertical dispersion of mids and highs from the loudspeakers.
This is a tweeter protection circuit used by Electro-voice in the 1980s. The resistor would normally be the attenuator to match the tweeter sensitivity and sets a minimum load for the amplifier when the limiter is activated. The zener types here are selected for a PA speaker, not a domestic loudspeaker. From memory the zeners were in a T03 package and mounted on an aluminium heat sink.
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This is incorrect. You've stated information that is inaccurate if the xover is other than a 1st order. Changing the impedance will shift the Q of the filter, not the xover point in higher than 1st order networks.
The rest I have no issue with, and agree. Yes, the varying attenuation is not an audible plus.
I've not heard of the double-zener arrangement on tweeters before. Are these kinds of TO3 chassis'd parts still available?
Wolf
EDIT: Looked them up, and that is a no for the TO3 zeners. They are either $160 each, or largely unavailable.
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I've called him out on that comment before, Allen, but he just seems to ignore me.
Either way, he's wrong,
Wolf
Either way, he's wrong,
Wolf
This site provides a handy calculator which allows one to choose the correct polyswitch (PTC resistor) to match a tweeter according to its dome diameter:
Loudspeaker Protection Components