EQ for headphone amp output?

[nielsk]

A friend wants to have a tone EQ between the headphone amp output and the headphones (he likes the internal amp in his high end monitor station, and finds the bass response a bit much on most headphones).
He does not listen very loud so some signal loss would be acceptable.
Anyone seen something like this? A passive EQ to work on a powered signal that won't act too much differently with various headphone loads?

 

[Meathands]

A passive EQ to work on a powered signal that won't act too much differently with various headphone loads?

Seems almost like a contradiction in terms, no matter what the headphones will form part of the filter circuit. Why not put the filter before the monitor station with a bypass switch?

 

[nielsk]

That would be too awkward, as it would equalize the signal to the monitor speakers, and having to constantly switch in / out is cumbersome...

 

[mjrippe]

Well, you could add a buffer stage after the EQ so it has a constant load.  But then it's not a simple passive project anymore!

 

[MagnetoSound]

No reason why this can't be done.

You need to open up the monitor controller and insert the EQ between the monitor line out and the headphone amp (I'm assuming that the headphone output is driven independently).

You could build a dedicated, fixed HPF inside the unit, or maybe put a TRS jack with break contacts on the back of the unit to accomplish a send/return at the right spot in the circuit? Then you can use whatever external EQ is at hand at any any given time.

 

[nielsk]

Of course at line level this is easy and in the good old days it was not too difficult to get inside & interrupt the signal to tap in, but now with everything SMT and no one giving out schematics it just aint so...
the question is equalizing a powered signal. anyone been there & done that?

 

[JohnRoberts]

The only way to make a passive output filter relatively independent of load, is to passively load it down more heavily than the expected load. This will not completely eliminate load interaction but will reduce it. Of course you now waste power in the dummy load.

JR

 

[MagnetoSound]

Of course at line level this is easy and in the good old days it was not too difficult to get inside & interrupt the signal to tap in, but now with everything SMT and no one giving out schematics it just aint so...

I can't [don't want to] believe it isn't possible. Difficult maybe, squinty? for sure, but still doable, Shirley?

John is right - if you use say 8Ω power resistors and 400Ω cans you can go after the amp, but will the amp still deliver the goods in terms of required level?

 

[SkunkFunk]

Can't you just get around the headphone impedance problem by having a rotary switch that changes some component values optimized for different ranges of loads?

 

[CJ]

one thing to consider is that headphones usually have a pretty good variation in sound, AKG vs Sony, etc,

now i know what your sayin, unenjoyment figures are still up near 8 percent, unless you live in Detroit,  :  and we want to go Cheap! we do not want to buy another set of bones,

hey wait, don't Bones cost  like 10 bucks?

why not just stick a cap in series with the hot lead?

you could also EQ by stuffing some cotton inside the headphones, or "ear goggles" as one of my out of country co-workers use to call them,

 

[MagnetoSound]

why not just stick a cap in series with the hot lead?

See?  Lateral.  Frickin' genius simple.  :

 

[CJ]

well, make it an inductor to ground then,  :

 

[MagnetoSound]

No no, I'm with you CJ! It's so simple I didn't think of it. Series cap is all it takes, provided you always use the same cans.

(My 'roll eyes' was at my own reply two posts up.  ;D)

 

[CJ]

ahh, i see, thought it was a bad sheapards pie or something,  ;D

 

[MagnetoSound]

No such thing mate.  8)

 

[PRR]

>> bad sheapards pie or something
> No such thing mate.

You didn't go to my school.
______________________________

 

[nielsk]

Well that sure looks worth a try... what will the roll-off slope be? Basically a (1st 0rder?) cross over, so 6 dB per octave?
The desired effect here is tone control, not filtering "out"
And yes, this is a "golden ears" guy (with more platinum albums to his credit than you can shake a stick at) who has tried every set of headphone out there, and wants to tweak the only pair he found that works for him

Thanks!

 

[mjrippe]

If you can fit the cap and resistor into the 1/4" plug shell, each pair of phones can have it's own EQ built in.

 

[SkunkFunk]

Or put a potentiometer in parallell with the cap to get a shelf-ish response?

 

[ricardo]

And yes, this is a "golden ears" guy (with more platinum albums to his credit than you can shake a stick at) who has tried every set of headphone out there, and wants to tweak the only pair he found that works for him

If he only wants to tweak a single type of headphone, he can play with EQ at line level and measure the response he wants.

We can dream up a passive circuit that does exactly what he wants with the said phones.

I did this for Sennheiser HD414 using a bridged T but I was working on H/P design in dem Jurassic days.