Air 1-Band EQ - Ideas ?

[frejo89]

cheers and a happy new year

Iam currently searching for a solution to get a nice Air Band eq for my mastering chain - with the unusual availability of just this one band.
For example something like just the highest band of a neumann W492 or the air band of the EQ3D. But without the other bands.

Is there something existing pcb towards this direction or useful design?

Maybe I just could use the w492 pcbs for this idea - the question is, what I have to populate and what not - where will I be able to pick up the new place for ins and outs, ignoring the other bands.

I would be thankful for any input here,
whether you would like to

maybe its garbage, but for my thoughts it seems to be a good idea.

 

[ruffrecords]

Just to be clear, you are looking for a low Q peaking response around 16KHz or thereabouts?

Cheers

Ian

 

[frejo89]

Just to be clear, you are looking for a low Q peaking response around 16KHz or thereabouts?

Cheers

Ian

Hi Ian!

thanks for your answer.

yes, that is the target!

 

[ruffrecords]

OK, in that case you could use the high band section of my REDDPLUS EQ design. This is a multi-band extension of my original REDD EQ design. Here is the schematic:


It has a single resistor ladder (on the left) for boost and cut which is used by all of the bands. Each band consists of a LC section (with switched caps) connected between the EQ output and the wiper of its boost/cut switch. The 11 contacts of the boost/cut switch are wired to the resistor ladder. It can provide up to 10dB of boost or cut and the Q is deliberately broad as in the original REDD EQ.

You only need the high band section and if you just want boost then you can dispense with the cut part of the ladder and replace it with a single resistor. With the values shown the high band frequencies are approximately 9KHz, 15KHz and 19KHz. The switch is a SPDT toggle with a centre off position. In the centre position just the 1n5 cap is in circuit (19KHz). Switching either way from there adds capacitance and lowers the resonant frequency. So for 15KHz the 1n5 and 1n are in parallel.

It is a passive EQ so it would need to be followed by a gain make up amplifier with a high input impedance so as not to load the EQ. A FET input op amp is ideal. The EQ input impedance is approximately 10K.

Cheers

Ian

 

[frejo89]

OK, in that case you could use the high band section of my REDDPLUS EQ design. This is a multi-band extension of my original REDD EQ design. Here is the schematic:
View attachment 120350

It has a single resistor ladder (on the left) for boost and cut which is used by all of the bands. Each band consists of a LC section (with switched caps) connected between the EQ output and the wiper of its boost/cut switch. The 11 contacts of the boost/cut switch are wired to the resistor ladder. It can provide up to 10dB of boost or cut and the Q is deliberately broad as in the original REDD EQ.

You only need the high band section and if you just want boost then you can dispense with the cut part of the ladder and replace it with a single resistor. With the values shown the high band frequencies are approximately 9KHz, 15KHz and 19KHz. The switch is a SPDT toggle with a centre off position. In the centre position just the 1n5 cap is in circuit (19KHz). Switching either way from there adds capacitance and lowers the resonant frequency. So for 15KHz the 1n5 and 1n are in parallel.

It is a passive EQ so it would need to be followed by a gain make up amplifier with a high input impedance so as not to load the EQ. A FET input op amp is ideal. The EQ input impedance is approximately 10K.

Cheers

Ian

Wow, Thank you a lot. That is a good way to start

I have to admit, that Iam not really into OP amps - thats one of my bigger flaws..
you may have a recommendable schematic for this too ?

Which type of OP Amp would you choose?
The goal is to get the same output level as input level, so that bypassing the unit will have the same level.

 

[frejo89]

Will this supposed to work this way? I can hardly believe
The OP Amp approach might be the worst in history..

 

[ruffrecords]

That is basically it. However, you need some gain in the op amp. Here is the basic op amp configurations I recommend (but of course you could use s tube instead like I do!).



Cheers

Ian

 

[frejo89]

alright, appreciate. completely forgot about the opa2134.

I like the idea with 600:600 transformer in there. I assume R15 is the wiper for gain adjust? So in this case 4,7kOhms log ?

 

[ruffrecords]

alright, appreciate. completely forgot about the opa2134.

I like the idea with 600:600 transformer in there. I assume R15 is the wiper for gain adjust? So in this case 4,7kOhms log ?

Yes. Set the EQ to flat and then adjust R15 for unity gain overall. You should use a multi-turn trim pot for R15. I use 25 turn types. They are all LIN rather than log but the correct gain should be not far from the mid point.

Cheers

Ian

 

[frejo89]

multi turn LIN, alright =)

 

[JMan]

Ian, could R15 be safely substituted with a pot to create a front panel user adjustable gain knob, or would that cause problems outside of a certain range in either direction?

 

[Whoops]

Iam currently searching for a solution to get a nice Air Band eq for my mastering chain - with the unusual availability of just this one band.
For example something like just the highest band of a neumann W492 or the air band of the EQ3D. But without the other bands.

Is there something existing pcb towards this direction or useful design?

Not ditching what Ian has wrote,
but the best circuit to do what you want to achieve is really the Night EQ.
You can build just the Air Band of the Night EQ, people have done that in the past in this forum as there is a thread about that project. You can build just the Air Band or even ad just the Air band circuit to another project.
Forget the W492 for these duties, the Night EQ is the one that actually does it well

 

[Script]

the Night EQ.
You can build just the Air Band

A parallel path with RC filter into a summing amp on the Nite EQ. Inductor filter might sound different though.

 

[frejo89]

Not ditching what Ian has wrote,
but the best circuit to do what you want to achieve is really the Night EQ.
You can build just the Air Band of the Night EQ, people have done that in the past in this forum as there is a thread about that project. You can build just the Air Band or even ad just the Air band circuit to another project.
Forget the W492 for these duties, the Night EQ is the one that actually does it well

Thanks for your response.

to tell my story - I purchased the NEQ3D before at DIY Racked... But. After reading some threads and speaking with other members here I decided to refuse starting this project - sitting here with the PCBs and waiting for a rack case, that I will both not use (I would not really be able to have a clear conscience looking at that unit in my studio, thinking of what this guy did in the past..)

So I decided completely against this built and put this question here after that, because while searching this forum for a 1-band air eq, I was not able to directly find a working solution - maybe the chosen words for my searching approach didnt turn out to be that useful
so, thats were I came from.

I very much favor the approach by Ian so far - to have just one stepped control for each side with a fixed band (here at 15kHz).

maybe you are able to point out the according thread as Iam not able to find it
just that I know of.

thanks in advance

jonas

 

[ruffrecords]

Ian, could R15 be safely substituted with a pot to create a front panel user adjustable gain knob, or would that cause problems outside of a certain range in either direction?

Yes, you could use it as a limited range gain control. You would need to add a resistor in series with the pot to limit the maximum gain. I would suggest using 1K which means the maximum gain would be 26dB.

Cheers

Ian