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Old 17th June 2012, 01:35 PM   #11
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IP=intellectual property, but I found it under the link, my mistake.

I took another look at the schematic, and I think it will be unnecessarily noisy. Under this link you will find everything you need to know to do it in a better way: Active Filters

The basic problem in the setup you posted is that in the input stage Vin is reduced, and subsequently re-amplified again in the filter stages. About this input buffer: most audio opamps are unity stable, that is, they will not oscillate if gain=1. I have never used an opamp to give a gain lower than 1, because I always thought this could lead to stability issues. Dunno for sure, but better to prevent it.
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Old 17th June 2012, 02:57 PM   #12
AndrewT is offline AndrewT  Scotland
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Default XLR in balanced impedance connections

The non-inverted input is PIN1 & PIN2, if not balanced (unbal). PIN1 is the audio ground in this unbal case.

If balanced then the extra PIN3 becomes the inverted input. Thus PIN2 = Hot = non-inverted and PIN3 = Cold = inverted. This time PIN1 is chassis, not audio ground.
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Old 17th June 2012, 04:32 PM   #13
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Quote:
Originally Posted by vacuphile View Post
IP=intellectual property, but I found it under the link, my mistake.

I took another look at the schematic, and I think it will be unnecessarily noisy. Under this link you will find everything you need to know to do it in a better way: Active Filters

The basic problem in the setup you posted is that in the input stage Vin is reduced, and subsequently re-amplified again in the filter stages. About this input buffer: most audio opamps are unity stable, that is, they will not oscillate if gain=1. I have never used an opamp to give a gain lower than 1, because I always thought this could lead to stability issues. Dunno for sure, but better to prevent it.
Thanks, but I already have the xover, I just want to add a notch filter. I understand there may be better circuits, but this is what I have, and I don't have the time or mental energy to start over!
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Old 17th June 2012, 04:38 PM   #14
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Quote:
Originally Posted by AndrewT View Post
The non-inverted input is PIN1 & PIN2, if not balanced (unbal). PIN1 is the audio ground in this unbal case.
That is what I have. The problem is my inability to alter the drawing! It seems I will have to draw my own symbol, but don't yet know how to. The xover DOES work, it's my ability to post that doesn't.
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Old 17th June 2012, 05:05 PM   #15
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Ok, this is the speaker, and I want to cut the shallow peak at 2kHz. If I have a circuit for that, with variable cut, then I should be able to recalculate for different frequencies. But I need help with the original design.
Click the image to open in full size.
I plan to put the xover point at 4kHz with 24dB slope, so the 6kHz peak will be tamed to some extent. Anyway, that is on-axis, and I will toe them in to suit.
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Old 17th June 2012, 07:21 PM   #16
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Hi Awkard,

I would go quite a bit lower than 4Khz for xover, more like 2-ish, depending on the tweeter you are using. What is the manufacturers recommendation?
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Old 17th June 2012, 09:06 PM   #17
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Are you suggesting that because of the 6kHz peak? I can alter the xover point any time I like, but a notch filter would let me play around. Any way, I may change the midrange driver for a different wide range unit. Maybe the L. Cao 8".
At the moment the HF driver is the Jordan JXR6HD, but I also have a Shackman electrostatic panel to try. So I want to make the xover more versatile before I go 3 way.
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Old 17th June 2012, 09:36 PM   #18
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Yes, I prefer to stay away 2 octaves from a break up peak like that, so that would give you even less. Anyways, slipped my mind you are designing a 3 way, so that means there should be no problem. You would cross over the bass driver not any higher than 500 Hz to the mid anyways, and than mid to high somewhere between 2 and 3 Khz.
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Old 18th June 2012, 05:08 PM   #19
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Quote:
Originally Posted by vacuphile View Post
Yes, I prefer to stay away 2 octaves from a break up peak like that, so that would give you even less. Anyways, slipped my mind you are designing a 3 way, so that means there should be no problem. You would cross over the bass driver not any higher than 500 Hz to the mid anyways, and than mid to high somewhere between 2 and 3 Khz.
Bass/mid crossover point is 134Hz at the moment. KEF B139s in isobaric configuration, they break up at just above 400Hz, so low xover point.
I still need the help with a (preferably) single opamp notch filter design. I have NE5534s, OPA132s, OPA604s, AD825s and OPA627s. In the xover itself, I prefer the sound of the AD825s, so would like to stay with them if possible.
As for the Jordan JX125s, the 6kHz peak is on axis, the same as the JX92s, so toeing in sharply minimises that. Anyway, the 24dB/octave slope will also reduce it effect on the sound. I appreciate your good advice, but that is something to consider another time. I want to keep the xover point as high possible at the moment, I may change that at a later date, but not now.
Linkwitz's site doesn't really help me, I don't have the skill to make use of it, I am more a hand/eye type of person, so although MAKING the circuit is not a problem, working it out is. I have made valve preamps (Croft, Concordant, Paragon) by measuring and copying, they worked fine. But if they developed faults, I was in trouble, no theoretical knowledge.
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