Re: do all LAZ EQN have an 18kHz notch?
« Reply #20 on: May 12, 2018, 12:14:41 PM »
From this, I can see High and Low-pass filters, a Bass (LF) control and a Mid control. How is this supposed to allow 25kHz EQ?
It seems like each band is handled by a separate circuit, so I would think that rules out interaction; the plot thickens...

Sorry I forgot to mention as I don't think Peter provided a full schematic of his final design but I believe he added in two pairs of appropriate capacitors to the high shelf section to allow for a 20kHz and 25kHz shelf. He also specified a mid-inductor that had the 9kHz value which also wasn't on the original. So these additions seem to be behaving in very unique ways due to possible limitations from the midband inductor going by what Ian said. And now that I think about it, I wonder if the addition of the 9kHz tap on the inductor could have added significantly enough to the parasitic C to move the inductor resonance into the audio band?


ruffrecords

Re: do all LAZ EQN have an 18kHz notch?
« Reply #21 on: May 12, 2018, 01:01:14 PM »
Thanks Ian for this insight. I was wondering if this were the case, if it would then make sense to move the high shelf section to the end of the signal chain instead of the beginning, in order to avoid the mid band inductor capacitance interacting with the boosted highs. But then of course you have the issue of boosting all the noise created by the other bands in this case?

in a linear system the order does not matter so it will be the same either way.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

abbey road d enfer

Re: do all LAZ EQN have an 18kHz notch?
« Reply #22 on: May 12, 2018, 01:20:12 PM »
Sorry I forgot to mention as I don't think Peter provided a full schematic of his final design but I believe he added in two pairs of appropriate capacitors to the high shelf section to allow for a 20kHz and 25kHz shelf.
Which I don't see, I mean I don't see a high shelf section; am I blind, or just dumb?

Quote
He also specified a mid-inductor that had the 9kHz value which also wasn't on the original. So these additions seem to be behaving in very unique ways due to possible limitations from the midband inductor going by what Ian said. And now that I think about it, I wonder if the addition of the 9kHz tap on the inductor could have added significantly enough to the parasitic C to move the inductor resonance into the audio band?
I would very much doubt a tap would change significantly the parasitic capacitance; adding turns to provide for a lower center frequency would, though.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

ruffrecords

Re: do all LAZ EQN have an 18kHz notch?
« Reply #23 on: May 12, 2018, 02:13:26 PM »
nothing else than expensive masturbation.

Please refrain from using such language. I find it offensive.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

abbey road d enfer

Re: do all LAZ EQN have an 18kHz notch?
« Reply #24 on: May 12, 2018, 02:25:15 PM »
Please refrain from using such language. I find it offensive.

Cheers

Ian
Poster's been warned once, then bit back. If he doesn't calm down, he'll be ousted.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

ruffrecords

Re: do all LAZ EQN have an 18kHz notch?
« Reply #25 on: May 12, 2018, 07:43:49 PM »
Poster's been warned once, then bit back. If he doesn't calm down, he'll be ousted.

Thanks Abbey.

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

Re: do all LAZ EQN have an 18kHz notch?
« Reply #26 on: May 13, 2018, 11:39:12 AM »
Which I don't see, I mean I don't see a high shelf section; am I blind, or just dumb?
 I would very much doubt a tap would change significantly the parasitic capacitance; adding turns to provide for a lower center frequency would, though.

High shelf is just above and to the left of BA205 in the original schematic. 10, 22, 33nF for the original frequencies.


abbey road d enfer

Re: do all LAZ EQN have an 18kHz notch?
« Reply #27 on: May 13, 2018, 12:05:44 PM »
High shelf is just above and to the left of BA205 in the original schematic. 10, 22, 33nF for the original frequencies.
Yes, I found out later.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

Re: do all LAZ EQN have an 18kHz notch?
« Reply #28 on: May 14, 2018, 05:32:18 PM »
So I've decided to leave well enough alone here as there's no easy way around the inductor self resonance but I wanted to just wrap up with a few findings for anyone who may come across this issue later.

I've attached a graph with the following:
yellow trace = 25kHz shelf @ full boost
red trace = 25kHz @ full boost & 9kHz @ full boost low Q
blue trace = 25kHz @ full boost & 9kHz @ full cut low Q

Basically if you want to use the high shelf without any HF pulldown above 10kHz you need to either not use the mid band or use it below 3.2kHz where it doesn't interact with the shelf at all.

Out of my four units the resonance averaged to around 16.5kHz and because of this resonance, as you use higher mid-band frequencies the slope to the right of the boost peak (or cut trough) has increasingly higher Q than the slope to the left.

If there's a dog you're trying to freak out you can amplify 40kHz by 20db no problem.

analogguru

Re: do all LAZ EQN have an 18kHz notch?
« Reply #29 on: May 14, 2018, 06:26:58 PM »
......
If there's a dog you're trying to freak out you can amplify 40kHz by 20db no problem.
The duration of the dog's freak out depends on how long your  tweeter feels comfortable with 100 times of the normal power....


radardoug

Re: do all LAZ EQN have an 18kHz notch?
« Reply #30 on: May 14, 2018, 09:32:46 PM »
Seems to me you dont understand that when you turn all the knobs up on an eq, the resultant curve is the sum of all the eqs you have turned up. There is no dip, its just the result of the eq's summing. Depending on the eq, it may or may not be smooth. Also, if you are putting this much eq on something, I am going to suggest it will probably sound like sh*t.

Re: do all LAZ EQN have an 18kHz notch?
« Reply #31 on: May 14, 2018, 11:13:19 PM »
Seems to me you dont understand that when you turn all the knobs up on an eq, the resultant curve is the sum of all the eqs you have turned up. There is no dip, its just the result of the eq's summing. Depending on the eq, it may or may not be smooth. Also, if you are putting this much eq on something, I am going to suggest it will probably sound like sh*t.

I understand what you're saying and I may have been abusing the word 'interact' so let me be clearer in my cause-effect statements here. There is a stop band in the midrange at 16kHz that would not be there on a IC gyrator EQ and certainly not a software EQ. It's an unexpected non-linearity that I was trying to figure out the origin of. There is a dip, and that dip is the inductor self resonance at 16kHz. Beyond that frequency the bell curve continues as would be expected up beyond 20kHz. Because the frequency is static regardless of the frequency boosted it makes for a really asymmetric slope which to me sounds 'weird' thus this whole ordeal.

Below I've attached the mid band graph for each frequency fully boosted from 360Hz - 9kHz. This is just the midrange control, there is no shelf included here even though it sure looks like it. You can see how the slope changes as it approaches 16kHz and how the frequencies above 16kHz could be construed to be a distorted continuation of the bell curve.

TBH I'm just so used to Pro-Q in linear phase at this point maybe inductors aren't for me...

abbey road d enfer

Re: do all LAZ EQN have an 18kHz notch?
« Reply #32 on: May 15, 2018, 01:35:25 AM »
TBH I'm just so used to Pro-Q in linear phase at this point maybe inductors aren't for me...
Don't jump to conclusions.
According to your measurements, the inductor, at its 9kHz position has an inductance of about 200mH and a parasitic capacitance of about 400p. I don't think that's how it was designed by Neve. You must have noted that there are two inductors in the original BA211, the second one being used for the 3 highest frequencies.
Am I wrong in guessing you use a single inductor with all the taps for the whole frequency selection? This certainly saves money but compromises performance to a point that is unacceptable for you. Only when you solve this problem will you be in a position to ascertain your position regarding EQ with inductors.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

EmRR

Re: do all LAZ EQN have an 18kHz notch?
« Reply #33 on: May 15, 2018, 08:18:38 AM »
I would look for another inductor option. 

You see similar notches with many audio transformers in certain configurations.  All the desirable UTC inputs exhibit some amount in single ended configurations, and it disappears if the same is used in a push-pull configuration.   In this case it's usually only a few dB, and slightly about 20k, but I've seen deep notches down around 12K with some other 'desirable' vintage types.   Not obvious if you aren't listening for it. 
Best,

Doug Williams
Electromagnetic Radiation Recorders

"I think this can be better. Some kind of control that's intuitive, not complicated like a single knob" - Crusty

"Back when everything sounde


 

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