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Old 3rd September 2010, 07:43 AM   #541
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Default 66's Crossover

Quote:
Originally Posted by LucasAdamson View Post
Hi Wayne,


Alan has contributed extensively to not only this thread, but also two others on the same theme of these excellent speakers. Do a search for Ditton 66. He (and others) go into great detail with their experiences of changing caps in the various models of 44 & 66. Alan, in particular, gives great advice on replacing these caps and also compensating for the ESR, present in the old electros but absent from the modern polyprops.
Hi Lucas

Thanks, yes I have been looking at some of these older threads. It's just a matter of getting everything in one place to make it as simple as possible for someone like me!

Regards

Wayne
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Old 3rd September 2010, 09:35 AM   #542
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Dloper did a schematic revealing the extent of his cap changes and ESR resistors. He said it was pretty much there as I remember...it's a good starting point.

Click the image to open in full size.

Certainly the caps should be changed for as close a value to the original as you can find. Here's the places Alan told me about:. Read post 71 and follow the links. He was helping me with my 44s, but the principles, and indeed most of the design and parts are the same. Awesome cap advice!

Good luck!
Lucas
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Old 3rd September 2010, 09:52 AM   #543
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You could also look at my schematic. It's for the 44s, which have a different midrange speaker and circuit, but it shows a better way to lay out a crossover schematic, in three sections for bass, mid & treble.

Click the image to open in full size.

I have replaced the tweeter with the Seas 19TFF1, the tweeter caps with a 4uF and a 6uF, no resistors (as old caps were film type, low ESR anyway)

The mid I have replaced with (2R7 4W) at 6uF to earth and (2R2 4W) at 33uF to earth. Both caps are polypropylene Jantszen, so I have ESR resistors in there.

The bass circuits are unchanged, but I replaced the 72uF with Alcaps (modern bipolar electros.)

There, that's all I can tell you....
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Old 3rd September 2010, 10:26 AM   #544
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Quote:
Originally Posted by LucasAdamson View Post
You could also look at my schematic. It's for the 44s, which have a different mid range speaker and circuit, but it shows a better way to lay out a crossover schematic, in three sections for bass, mid & treble.
Hi Lucas,

Thanks great! thanks a lot for your help. It's all becoming a little clearer for me now. I have just received a new Multi-meter through the post so I can take and post the necessary readings Alan requested.

Best Regards

Wayne
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Old 3rd September 2010, 11:57 AM   #545
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Quote:
Originally Posted by alan-1-b View Post
Wayne,


I can calculate you 2 resistors to make a suitable fixed L-pad for adequate attenuation.

I do need to know the DC resistance of the Realistic tweeters.
A good multimeter would be a more useful purchase than some other things,
and can be used more in diy to come.
Hi Alan,

I have purchased a multimeter so I can now give you the readings, and any future readings you require.

One Realistic tweeter measured 6.5 ohms, the other measured 6.2 ohms.
The mid range speaker in my Celestion 66's are model 'MD500 2" dome, impedance 8 ohm, range 0.5 - 5kHz, Nominal loading 80W, Din 45 500'.

I hope this helps with your calculations. Please see my previous posts regarding the use of these Realistic tweeters, Please ignore trying to make them suitable for interchanging between systems. I would much rather you were able to match them to my 66's, so that I can the best out of them.

Best Regards

Wayne
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Old 3rd September 2010, 06:04 PM   #546
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Default Multimeter brand and Accuracy spec ?

Hi Wayne,

I'm sorry, but I'll have to be brief today.

What is the Brand and Model Number of your multimeter ?

Also, look in its User Manual booklet - what is the Accuracy Specification for the Resistance ranges ?

... and there may be different Accuracy for different Ranges
-{such is common, and mid to high resistance ranges are usually greater accuracy than the lowest range and the very highest range}-
thus look to see what is quoted for Less than 10 ohms, or Less than 5 ohms, or whatever the case may be ..?

I do mean Resistance range - the brief Specification that advertisers state for multimters is usually only the DC Voltage accuracy,
as that is the easiest measurement to make reasonable accuracy for.

The Resistance Specification may state a +/- Percentage {%} AND a +/- number of Counts, or something else ...

I estimated from the Realistic data on the pamphlet you posted, using both the 2.2uF and .27mH and the dB drop around 5kHz wrt above 10kHz that the Impedance in the useable bandwidth is likely a little below 8 ohms, and that usually indicates a DC resistance of approximately a little over 6 ohms, thus so far it seems to be close ... but let me know the Accuracy, and I'll calculate 2 resistors for you to make a simple L-pad so that you can hear the tweeters in close to correct level wrt the 66's mids so that you can decide better their possible applications.
Currently as the tweeters dominate the sound so much, you really will not know what they can be usefully used for with any of your speaker systems.

I'll address the other matters when I have time available,
BUT do NOT buy 4uF and 6uF for new tweeters,
because about 3.6uF and larger than 10uF is likely what such will require,
if you want to keep the .14mH inductor, and that will be quite OK.

***************

Hi Lucas,

thanks for helping here !

Hey, if you can stand listening to the SEAS tweeter not well matched whilst you are making other components that is your business, but I will be posting about a crossover which will suit it and other similar tweeters as soon as I have time, but do Post in the 44's relevant Thread if you do decide to continue with where you left off there.

An Active crossover can work well for between bass and Cone mid-drivers, but such can be a problem to tweeters and dome mid-drivers because
DC Offset voltages from the direct coupled power amps hold their voice-coils out of the optimum locations in their magnets' space,
thus earlier distortion and compression.
Active for the lower section and passive for the higher section can be got to work well more simply - Post in the other Thread if you want to pursue that.

***************

Hi sba,

sorry, all this stuff and I haven't got back to your very interesting material yet !
I will ... eventually ...
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Last edited by alan-1-b; 3rd September 2010 at 06:07 PM.
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Old 3rd September 2010, 09:39 PM   #547
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Default Accuracy of new multimeter

Quote:
Originally Posted by alan-1-b View Post
Hi Wayne,

I'm sorry, but I'll have to be brief today.

What is the Brand and Model Number of your multimeter ?

Also, look in its User Manual booklet - what is the Accuracy Specification for the Resistance ranges ?

... and there may be different Accuracy for different Ranges
-{such is common, and mid to high resistance ranges are usually greater accuracy than the lowest range and the very highest range}-
thus look to see what is quoted for Less than 10 ohms, or Less than 5 ohms, or whatever the case may be ..?

I do mean Resistance range - the brief Specification that advertisers state for multimeters is usually only the DC Voltage accuracy,
as that is the easiest measurement to make reasonable accuracy for.

The Resistance Specification may state a +/- Percentage {%} AND a +/- number of Counts, or something else ...
Hi Alan,

My new multimeter was purchased from Maplins. The model is 'UT50A Manual ranging Digital Multimeter'. Regarding it's accuracy it states the following:-

'The test leads can add 0.1 ohm to 0.3 ohm error to the resistance measurement. To obtain precision readings in low resistance, that is the range of 200 ohm, short-circuit the input terminals beforehand and record the reading obtained (called this reading (x). (x is the additional resistance from the test lead. Then use the equation:
Measured resistance (y) - (x) = precision readings of resistance'.
I measured (x) to be 0.2. So I deducted 0.2 from the actual readings I obtained and gave you the results, (6.5 & 6.2 ohms).

The accuracy specification reads as follows:
Range Resolution Accuracy
200 ohm 0.1 ohm +/- (0.8% + 3) <--- I used this range
2k ohm 1.0 ohm +/- (0.8% + 1)

I hope this helps, I must admit I'm not exactly clear on this last part!.

As far as everything else is concerned I will not order any items until it becomes clear exactly what I need. Thanks very much for all of your help, I know you have gone through all of this in previous Threads but I really appreciate your efforts in this case, bringing it all together. I know this probably sounds simple but why wont an 'off the self' L-pad be OK? The explanation will probably help me to more understand the basic principles involved. It's all good stuff!!

Best Regards

Wayne

Last edited by WayneSwann; 3rd September 2010 at 09:53 PM. Reason: Tidying up
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Old 3rd September 2010, 10:44 PM   #548
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Default Speaker Clamps for Celestion 66's

Hi to everyone reading this Thread!

Does anyone know where I can obtain speaker clamps the same or very similar to the small triangular ones used on the 66's?. I have ordered several different types but they have all been too big for the job! I am missing just one.

Thanks

Wayne
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Old 4th September 2010, 07:41 PM   #549
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Default more about accuracy, and where can you buy from ?

Quote:
Originally Posted by WayneSwann View Post

My new multimeter was purchased from Maplins. The model is 'UT50A Manual ranging Digital Multimeter'.

The accuracy specification reads as follows:
Range Resolution Accuracy
200 ohm 0.1 ohm +/- (0.8% + 3) <--- I used this range
2k ohm 1.0 ohm +/- (0.8% + 1)

I hope this helps, I must admit I'm not exactly clear on this last part!.

I know this probably sounds simple but why wont an 'off the self' L-pad be OK? The explanation will probably help me to more understand the basic principles involved. It's all good stuff!!

Wayne
Hi Wayne,

in 200 ohm range, {that is Maximum 199.9 ohms measureable} ,
with +/-(0.8% +3) accuracy
a 6.5 ohm resistance could display anywhere between 6.1 and 6.9 on one of those meters, depending on the particular sample.
Worse is that a 1.5 ohm resistor, {which you will need 2 of at not less than 1.5 ohms each},
could display anywhere between 1.2 and 1.8 ohms,
thus you will need a Calibration resistor to allow you to use your meter for more accurate low ohms measurements.

The 1.5 ohm resistors themselves are specified +/- 5%, thus greater uncertainty via that meter to between 1.1 and 1.9 ohms.

Do not worry, because a 10 ohm/ 0.1% accurate resistor can be bought for 32p. , albeit via mailorder from Farnell,
and that can be used for Calibration comparison very easily.
I will explain how, if you choose this option.

Can you buy from Farnell's UK branch ?
It is accessable via:- Farnell / Electronic Component Distributors / Suppliers / Electronics, Electrical Parts, Electrical Components and Wholesale Electronics.

The resistors you will need for the L-pads can be bought from there at the same time, all for 50p. , or less, each.

Maplin do not stock suitable resistors in the required values.

Alternately, is there a local parts shop you can visit which stocks wirewound resistors in 1.5 ohm/5watt and 3.3 ohm/10 watt ?

+/- (0.8% +3 counts) really only becomes accurate to better than +/- 1% when the resistance is above half of the full scale,
and that will be from 100 ohms with that meter in its 200 ohms range.


A variable L-pad will only match Resistance for the single resistance it is made for, usually 8 ohms,
but to use your Realistic tweeter with the .14mH inductor in the crossover the resistance will have to be reduced to about 4.4 ohms.
I don't see any point in spending money on different inductance values for this experimental circuit when you do not know whether you will even like the sound from a heavily attenuated tweeter, thus I am advising to do it a cheaper way, for you to hear before you commit larger money.

A Calibration resistor will be useful for other purposes with that multimeter,
thus money not wasted.
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Old 5th September 2010, 05:52 PM   #550
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Quote:
Originally Posted by alan-1-b View Post
Do not worry, because a 10 ohm/ 0.1% accurate resistor can be bought for 32p. , albeit via mailorder from Farnell,
and that can be used for Calibration comparison very easily.
I will explain how, if you choose this option.

The resistors you will need for the L-pads can be bought from there at the same time, all for 50p. , or less, each.
Hi Alan,

I see! I don't know why these multi-meters cannot be more accurate? This amount of deviation is rather a lot. Anyway that being the case I will gladly purchase a 'Calibration Resistor' from Farnell Electronic Components!
I have had a quick look at their web site and I see one for 0.32p '(Ref 1353330) Thin Film Chip Resistor', is that the one you are referring to? Also which others will I need to order for the L-pad. Are their any other items I need to order from them now in order to save time in the future?

Best Regards

Wayne
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