Question about New York Dave's passive EQ

[Coldsnow]

HI,
The original thread and schematics are here. http://groupdiy.com/index.php?topic=45515.0
I was made a few changes based on things I have already and was wondering if it would work.
First of all, I thought I'd go with a t Attenuator followed by a 600:600 transformer for the input.  The reason is it is what i have already.  Should the resister change from a 2.2K to a 600ohm after the transformer as a result?
Also, do I want to conect the API 325 to the "low" output of New York Daves schematic?
Also, Let me know If I shouldn't post parts of the orignal drawing.
Thank you.

 

[ruffrecords]

NYD's designs are carefully crafted and an equal amount of care is needed should you wish to alter them. The EQ network needs to be driven by a source impedance of not more than 100 ohms and I suspect this is partly the reason NYD added a 10K:600 input transformer at the input so higher source impedance devices could drive it. If you use a 600 ohm T pad followed by a 600:600 transformer then you no longer meet the not more than 100 ohms requirement so the EQ will not work as intended.

As far as driving the gain make up amp is concerned, as the EQ has a 12dB insertion loss so it will need some gain make up. The hi and lo outputs in the original were intended for different types of laod via the output transformer. As the load you are presenting is relatively high you can use the high output.

Cheers

Ian

 

[Coldsnow]

Thank you Ian,
Will this inductor/choke work for the low frequency boost?
http://www.digikey.com/product-search/en/inductors-coils-chokes/fixed-inductors/196627?k=M8402

Also,
Is it going to mess up something to move the 5k boost from the hi band to the mid band?  I assume values would stay the same and it would be nice to boost both 10k and 5k at the same time. 

Lastly,
Can I leave out the minus reisters or band cut resisters if I want a boost only eq?
Thank you again

 

[shabtek]

that digikey inductors dcr is >10X what nyd specs...Q will be much lower
closer bands will interact more/ wider bandwidth will be less defined
'boost' only;sure
do it

 

[Coldsnow]

So the higher the dcr will only make q lower hence wider boost?

 

[shabtek]

~10x wider; 500 Hz>5KHz
read NYD's description, find an RLC resonance calculator and play around with different values, what is an L-pad?

 

[Coldsnow]

I found this
http://www.mouser.com/ProductDetail/Hammond-Manufacturing/159ZB/?qs=sGAEpiMZZMv126LJFLh8yzepz9DCdHPWG9U5iATHGd4%3d
It's 320mh instead of 330mh which will only make the 100ohm boost slightly higher I believe.  Very low dcr. 
I also found some new Panasonic inductors for the upper frequencies that have a low dcr as well.

 

[shabtek]

compare the frequency range each choke is intended for:
what range are you concerned with?
I think the one with the smaller core will also saturate/distort/suck sooner

 

[ruffrecords]

Thank you Ian,
Will this inductor/choke work for the low frequency boost?
http://www.digikey.com/product-search/en/inductors-coils-chokes/fixed-inductors/196627?k=M8402

For audio work you generally need to be looking for ferrite cored inductors to ensure they do not saturate and also have a constant inductance across the frequency bands.

Also,
Is it going to mess up something to move the 5k boost from the hi band to the mid band?  I assume values would stay the same and it would be nice to boost both 10k and 5k at the same time. 

Yes, it will mess it up.

Lastly,
Can I leave out the minus reistors or band cut resisters if I want a boost only eq?
Thank you again

No, you must leave them in even if you do not use them. They form part of a switched potentiometer and pots don't work if you chop their bottoms off. You can replace the series set of resistors with a single one of the the same total value.

Cheers

Ian

 

[Coldsnow]

Thanks guys.  Just to be sure, the 12 way level switches are just 1 x12 (or 2x12 in the hi band) passive switches correct?

 

[ruffrecords]

Thanks guys.  Just to be sure, the 12 way level switches are just 1 x12 (or 2x12 in the hi band) passive switches correct?

Correct.

Cheers

Ian

 

[jasavoy]

NYD's designs are carefully crafted and an equal amount of care is needed should you wish to alter them. The EQ network needs to be driven by a source impedance of not more than 100 ohms and I suspect this is partly the reason NYD added a 10K:600 input transformer at the input so higher source impedance devices could drive it. If you use a 600 ohm T pad followed by a 600:600 transformer then you no longer meet the not more than 100 ohms requirement so the EQ will not work as intended.

As far as driving the gain make up amp is concerned, as the EQ has a 12dB insertion loss so it will need some gain make up. The hi and lo outputs in the original were intended for different types of laod via the output transformer. As the load you are presenting is relatively high you can use the high output.

Cheers

Ian

Hey Ian, I have a related question. If i wanted to build a line-level passive midrange attenuator filter (ie. Pultec MEQ mid band only with no amplifier) with transformer in/out, how would i select input and output transformers?

 

[ruffrecords]

Hey Ian, I have a related question. If i wanted to build a line-level passive midrange attenuator filter (ie. Pultec MEQ mid band only with no amplifier) with transformer in/out, how would i select input and output transformers?

Well, for one thing it depends first on the drive capability of your source and the input impedance of your load. Let's assume your source can drive a 600 ohm load and that your output is loaded by a 10K bridging input.

Also, if you really only want cut (no boost at all) then you can probably do it without any transformers. The basic principle is shown below:


C1 and L1 set the resonant frequency of the circuit and R3 sets the amount of cut and the Q of the circuit. Of course you would need to add some extra bits to make it variable but that is basically it.

Cheers

Ian