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I have a headphone jack in stereo amp, do I need a dedicated headphone amp?

Eddd

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My current equipment:
  • DAC: Cambridge Audio CXNv2
  • Amp: Arcam DiVA A85
  • Headphone: Grado SR325x
My considerations:
  • My A85 amp is from 2001, I've read somewhere that 'old' amps were actually doing fine with when driving headphones
  • I've read that impedance is key. The A85 manual mentions it accepts 8Ω - 2000Ω. The Grado 'Nominal Impedance' is 38Ω (not sure what nominal means in this context).
  • Sound is already a great step up from my previous Grado SR80
  • However, I'm considering adding a reasonably priced headphone amp like the Topping DX3
So long story short; would there be incremental benefit in adding a dedicated headphone amp like the Topping DX3. Would you have other ideas?
 

Spocko

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You need to try out the amp to compare the improvement, if any.
Now for a little extra ($249) you should try THIS because even if the improvements are minor,
nobody would blame you for keeping it because giant volume dial!
Screenshot 2023-04-07 at 6.36.07 AM.png
 

staticV3

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Many old amps with headphone out have very high output impedance, which can change the frequency response of some headphones (for better or worse).
You'd avoid that happening by using an external headphone Amp.

Btw, the DX3 is a DAC+Amp. It does not have analog inputs, only digital. So it might not work in the configuration that you're envisioning.
 
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Eddd

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Many old amps with headphone out have very high output impedance, which can change the frequency response of some headphones (for better or worse).
You'd avoid that happening by using an external headphone Amp.

Btw, the DX3 is a DAC+Amp. It does not have analog inputs, only digital. So it might not work in the configuration that you're envisioning.
Thanks! Ah, high impedance could be a factor then, any ideas how I could figure out if this is the case for my Arcam A85?

And good point on the DX3. Any suggestions on a reasonably priced headphone amp that I could add to my CXNv2?
 
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Eddd

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You need to try out the amp to compare the improvement, if any.
Now for a little extra ($249) you should try THIS because even if the improvements are minor,
nobody would blame you for keeping it because giant volume dial!
View attachment 277721
This does look way more cool than the DV3 :)
 

staticV3

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Thanks! Ah, high impedance could be a factor then, any ideas how I could figure out if this is the case for my Arcam A85?
You can measure output impedance yourself using a 1/4" headphone plug, a resistor (~30-100Ω), a basic multimeter, and a calculator like this: http://www.sengpielaudio.com/calculator-InputOutputImpedance.htm

Any suggestions on a reasonably priced headphone amp that I could add to my CXNv2?
Ideally you'd want a headphone Amp with XLR input so that you can connect the Arcam to your DAC via RCA and the headamp via XLR.
Here are some reasonably priced headphone Amps with XLR in:

Sabaj A20h
SMSL SH-8S
SMSL HO100
 

Zapper

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The schematics for your amp can be found here.

Here is the relevant bit:
Capture.PNG

The headphone jack is driven from the power amplifier outputs with a resistor attenuator on each channel. The resistor network reduces the output by 0.233 (-12.7dB) with an output impedance of 77 ohms. That is about twice the "nominal impedance" of your headphones, which will lead to some frequency response variations as the changing impedance of the headphones with frequency will translate into amplitude variations.

Many headphone amps advertise an output impedance of <0.1 ohms, which will eliminate the impedance dependency of the frequency response.
 

MRC01

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... The headphone jack is driven from the power amplifier outputs with a resistor attenuator on each channel. The resistor network reduces the output by 0.233 (-12.7dB) with an output impedance of 77 ohms. That is about twice the "nominal impedance" of your headphones, which will lead to some frequency response variations as the changing impedance of the headphones with frequency will translate into amplitude variations. ...
From what I read online, the Grado sr325x has peak impedance around 80 Hz, and width of this peak goes from around 40 Hz to 160 Hz. Thus, the amp's high output impedance will boost this frequency range. This is typical - most conventional dynamic driver headphones have peak impedance in the mid-upper bass frequencies. So an amp with low output impedance may sound tilted toward less warm / more bright.

In days of yore, it was common for headphone amps to have an output impedance of 120 ohm. This was documented as IEC standard 61938 from 1996, but it never became popular and is not recommended anymore. The modern standard is for amps to have the lowest possible output impedance, typically around 1 ohm. However, some headphones that sound too bright can be tamed by amps having a high output impedance. Some headphone amps have two outputs: one having 120 ohm output impedance, the other have < 1 Ohm.

All that said, any audible change in FR from these effects is usually subtle.
 

wwenze

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There's always the option of adding a 10ohm or whatever ohm resistor parallel to your headphone to bring the output impedance down. 10ohm is close enough to what some handphones and gaming consoles have so I'm used to living with that.

You waste a lot of voltage and efficiency in the process but it is easy and quick.
 

DVDdoug

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There's always the option of adding a 10ohm or whatever ohm resistor parallel to your headphone to bring the output impedance down. 10ohm is close enough to what some handphones and gaming consoles have so I'm used to living with that.

You waste a lot of voltage and efficiency in the process but it is easy and quick.
Yeah... It may not go loud enough.

If you have a smart phone, try the Grados with it. The phone will probably have lower impedance so the frequency response should be flatter and more-like with a headphone amp and more-like how the headphones were designed to sound. If you hear less bass as predicted, you can decide which sound you prefer.
 

Zapper

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From what I read online, the Grado sr325x has peak impedance around 80 Hz, and width of this peak goes from around 40 Hz to 160 Hz. Thus, the amp's high output impedance will boost this frequency range. This is typical - most conventional dynamic driver headphones have peak impedance in the mid-upper bass frequencies. So an amp with low output impedance may sound tilted toward less warm / more bright.

In days of yore, it was common for headphone amps to have an output impedance of 120 ohm. This was documented as IEC standard 61938 from 1996, but it never became popular and is not recommended anymore. The modern standard is for amps to have the lowest possible output impedance, typically around 1 ohm. However, some headphones that sound too bright can be tamed by amps having a high output impedance. Some headphone amps have two outputs: one having 120 ohm output impedance, the other have < 1 Ohm.

All that said, any audible change in FR from these effects is usually subtle.
This set of measurements shows the impedance rising from ~38 ohms to 98 ohms, which would produce a 4.6dB boost in amplitude at the 65 Hz resonance if driven with the 77 ohm source impedance of the amplifier headphone jack. So it would give a modest but noticeable bass boost, which many would find enjoyable.
 
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Eddd

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This set of measurements shows the impedance rising from ~38 ohms to 98 ohms, which would produce a 4.6dB boost in amplitude at the 65 Hz resonance if driven with the 77 ohm source impedance of the amplifier headphone jack. So it would give a modest but noticeable bass boost, which many would find enjoyable.
I'm in complete awe with this incredibly detailed and clear answer. Many thanks Mr. Zapper!

Thanks for the other replies as well. The internet can be a beautiful place.
 
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