Cyrus 780 - Tweeter/Treble issue - diyAudio
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Old 16th June 2007, 03:07 PM   #1
quaddo1 is offline quaddo1  Sweden
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Default Cyrus 780 - Tweeter/Treble issue

Hello, (sorry, longish post)

About two months ago my old Cyrus Power Amplifier broke dowm.
I was using it in a bi-amped system (with a Cyrus IIIi) driving four Cyrus 780 (made by Mission circa 1990, and not to be
confused with the Mission 780).
The Power Amp was driving the tweeters.
Opening it made me realize that repair wasn't an option. The PCB was badly burnt at one if its corners.
I contacted Cyrus in the UK for some advice. When I mentioned that the PCB was burnt, they basically could only offer me
an expensive upgrade-service.
So for a temporary solution I revertet back to a basic setup with only the Cyrus IIIi driving the speakers.
It sounded reasonably good. The tweeters didn't appear to have been damaged.

However, I recently got hold of a newer power amp, the Linkpower, to replace the old power amp.
The sound quality is not what it used to be. The treble is quite sharp/harsh and is not so nice to listen to.
The sound used to be considerably more "soft".
The problem is especially nocicable in the vocals of a song. The S's sound horribly poor/bad, and is more like three S's rather than one....
....especially if you're playing rather loudly..... ;-)
At the moment I have the Linkpower connected to the woofers (LF), and the IIIi connected to the tweeters (HF).
I have tried connecting the other way around, but that didn't make any audiable difference.

I have checked the components at the HF-input, and they seem to be OK.
Measuring the resistance of the tweeters in two of the speakers, gives a value of 6.2 to 6.7 ohms.
Since I couldn't find my own user manual I tried finding info about the speakers on the web.
Weirdly enough I haven't been able to find much, and neither Cyrus or Mission have any specs/manuals for it online.
No specs/info is located at the back either. From memory this line of speakers have an impedance if 6 ohms. I found someone
selling a pair of 780s at eBay, which confirmed this.
The Mission 760 is the "little-brother" in the series, and it has an impedance of 6 ohms.
Now. If the impedance is 6 ohms, the tweeters resistance shouldn't be any higher than approx. 5 ohms. Correct?

I've played around with the thought of reversing the polarity of the tweeters.
Either directly at the tweeter, or at the amplifier. Most likely that will make it sound even worse, or?

Have any of you any clues where to get hold of these tweeters?
The part.no is R761-HFU-D19. It's used in several other Mission speakers. Like the Mission 761 for example.

I have contacted both Mission and Cyrus, and only gotten a reply from Mission as of yet.
Strangely, Mission suggests replacing the bass driver (woofer). This sounds very weird to me, or are they on to something?

I've also found this: http://www.gvibes.com/parts/oldpartsinventory.txt
I contacted them as well, but have yet to hear from them.


Any help/tips/suggestions would be greatly appreciated.

Regards,
Daniel
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Old 16th June 2007, 11:18 PM   #2
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OK, Isn't there an equivalent Mission version of the same size?
Wouldn't a Mission 780 or 780se be the same as a Cyrus 780 of the same period? I know it is confusing because Mission use 780 for different speakers at different times.

Mission and Cyrus were the same company in those days and Mission usually share the same components throughout an entire range.

These two items are the same size:

Cyrus 780: http://cgi.ebay.co.uk/Mission-Cyrus-...QQcmdZViewItem

Mission 780se: http://cgi.ebay.co.uk/Mission-780se-...QQcmdZViewItem

It's probably too expensive to buy the whole speaker just for the tweeters. I don't know.

How does the tweeter sound with the 3i powering the woofer at the same time?

The 3i (I think) was made because the first Cyrus 3 sounded too harsh and brittle. That's what I read somewhere anyway!

I've had a similar problem with sibilance (sssss tttttt). It drove me crazy and I tried everything to fix it. Now, after a long time, I realise that I just need some more bass to balance the sound.

Could this be why Mission recommend a new woofer? Or is the crossover point very high on your speakers?

A lot of recent Mission speakers use Vifa drivers. Could you find a modern replacement? Maybe speak to Vifa and ask for a recommendation? Or someone around here might know. I am just guessing, sorry.

I will think again when I am more awake!

Anybody else got any idea?

Regards,
Martin
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Old 17th June 2007, 12:09 AM   #3
quaddo1 is offline quaddo1  Sweden
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Quote:
Originally posted by Sonusthree
OK, Isn't there an equivalent Mission version of the same size?
Wouldn't a Mission 780 or 780se be the same as a Cyrus 780 of the same period? I know it is confusing because Mission use 780 for different speakers at different times.
Interesting. I thought the Mission 780 looked like this:
http://oldsite.mission-hifi.com/prod...peaker_780.htm

The strange thing is that you can't find a user manual or any info about either the Cyrus or Mission 780 (old version), on either mission.co.uk or the old site.....


Quote:
Originally posted by Sonusthree
How does the tweeter sound with the 3i powering the woofer at the same time?
Do you mean when only using the 3i and skipping the bi-amping?


Quote:
Originally posted by Sonusthree
I've had a similar problem with sibilance (sssss tttttt). It drove me crazy and I tried everything to fix it. Now, after a long time, I realise that I just need some more bass to balance the sound.

Could this be why Mission recommend a new woofer? Or is the crossover point very high on your speakers?
It could be, but I don't get why the bass driver would be damaged after a failure of the amp I had driving the tweeters? Very unlogical.
Crossover-point? I have no idea since I can't find any specs for this speaker (other than that the impedance i 6 ohms)....


Quote:
Originally posted by Sonusthree
A lot of recent Mission speakers use Vifa drivers. Could you find a modern replacement? Maybe speak to Vifa and ask for a recommendation? Or someone around here might know. I am just guessing, sorry.
Don't be sorry. I'm thankful for any help I can get.
Contacting Vifa is not a bad idea....
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Old 17th June 2007, 09:57 PM   #4
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I've done some research today and here what I've come up with....


Tweeter:

Mission part.no. R761-HFU-D19.

The tweeter is a Vifa D19.
Most likely D19TD-05-08. Impedance 8 ohms, which would make my value of 6.2 to 6.7 ohms correct.

Problem is, there are several similar versions of this one. All with different impedances...


Woofer:

Mission part.no. R60 80-LFU-C13.

The woofers are Vifa C13.
It could be C13WG-08-08. Impedance 8 ohms.
That would make Mission's advice correct, since my woofers measure approx 3 ohms resistance (should be 5.5 ohms).

Different versions of this are also available:

C13WG-19-08: Z = 8 ohms
C13WG-08-04: Z = 4 ohms
C13WG-08-06: Z= 6 ohms
C13WH-09-08: Z = 8 ohms
C13MG-07-08: Z = 8 ohms
C13MG-08
C13MG-09-08: Z = 8 ohms
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Old 17th June 2007, 11:23 PM   #5
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Quote:
Originally posted by quaddo1
Tweeter:

Mission part.no. R761-HFU-D19.

The tweeter is a Vifa D19.
Most likely D19TD-05-08. Impedance 8 ohms, which would make my value of 6.2 to 6.7 ohms correct.

Problem is, there are several similar versions of this one. All with different impedances...
Like this? He posts worldwide too!

http://cgi.ebay.co.uk/Pair-of-Vifa-D...QQcmdZViewItem
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Old 18th June 2007, 12:51 AM   #6
quaddo1 is offline quaddo1  Sweden
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Yes, that looks like the same as the ones I have.....thx!

Although, I'm not totally convinced that the tweeters are at fault any longer....it could be worth a try though.
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Old 19th June 2007, 01:05 AM   #7
quaddo1 is offline quaddo1  Sweden
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I've been thinking....

Is it common practice to have different impedances of the drive units in a speaker?

If so then it's not impossible that the tweeters have an impedance of 8 ohms (approx. 6.5 ohms DC) and the woofers have an impedance of 4 ohms (approx. 3.5 ohms DC).

If the DC values are correct, then they aren't much use in helping with sorting out my treble problem.
Anyone agree?
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Old 19th June 2007, 01:31 PM   #8
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What are your views on "padding down" the tweeter by adding a resistor, or are there better ways of reducing the treble?


This is how the layout is by default at the tweeter input:

R = 3.9 ohms 7W
C = 4.7uF 100V DC
L = 270uH
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File Type: jpg 780_layout.jpg (21.9 KB, 282 views)
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Old 19th June 2007, 02:04 PM   #9
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I'm VERY confused.

You like the speakers with the first amp.
It broke.
It was OK with the second amp.
You don't like it with the third amplifier? So you think your tweeters are damaged and you want to replace them?
Now you think that you simply have too much treble?

Maybe it is logical to blame your new amp?

Have you tried changing the speakers position to get more bass? Try placing in a corner or against a wall and see what happens.
Try an EQ to give you more bass/less treble and maybe you will know what you are looking for. Even Windows media player will be OK for initial testing.

Sometimes reversing tweeter polarity can help with problems at the crossover frequency.

IMPORTANT: Are your woofers wired correctly. If one is out of phase then you will experience a lack of bass and, therefore, more prominent treble.

If you want to reduce the treble then you could try an L-pad attenuator. This reduces the level without affecting the crossover frequency too much.
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Old 19th June 2007, 02:09 PM   #10
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Quote:
Originally posted by Sonusthree
I'm VERY confused.

You like the speakers with the first amp.
It broke.
It was OK with the second amp.
You don't like it with the third amplifier? So you think your tweeters are damaged and you want to replace them?
Now you think that you simply have too much treble?

Maybe it is logical to blame your new amp?
I couldn't see any other way myself. Maybe we're both dumb
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