Using MOSFET amp module as a headphone amplifier

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TomS

Using MOSFET amp module as a headphone amplifier
« on: 4 Jul 2015, 12:55 pm »
Vinnie,

I'm not very headphone savvy, but since I'm going to trial the MOSFET Amp module (no balanced HPA module) I wondered about connecting headphones to the amp as single ended on the speaker outputs.

Is this even possible, where the L and R have a common ground on a TRS jack, or would it be 4-wire balanced only?

How would the MOSFET module compare to the HPA sonically?

Any disadvantages to this method other than not having the convenience of a front panel connection?

Tom

Vinnie R.

Re: Using MOSFET amp module as a headphone amplifier
« Reply #1 on: 6 Jul 2015, 03:32 am »
Vinnie,

I'm not very headphone savvy, but since I'm going to trial the MOSFET Amp module (no balanced HPA module) I wondered about connecting headphones to the amp as single ended on the speaker outputs.

Is this even possible, where the L and R have a common ground on a TRS jack, or would it be 4-wire balanced only?

How would the MOSFET module compare to the HPA sonically?

Any disadvantages to this method other than not having the convenience of a front panel connection?

Tom

Hi Tom,

You can't use the LIO MOSFET AMP speaker outputs to connect to a TRS jack, as you must not connect the L- and R- speaker
posts together (they are not internally tied to GND, and must not be connected or else you'll short out the amp).

So if you want to use LIO MOSFET AMP with headphones (and it should be headphones that like power, such as Audeze LCD-2, LCD-3, HiFiMan HE-1000, HE-6, HE-560, Sennheiser HD-650, Abyss, etc.), then you'll want the headphones terminated with a 4-pin XLR plug, and I can make a mating 4-pin XLR to banana jacks adapter to use. 

Or, I can make a custom cable that connects to the LIO MOSFET AMP from the inside, and connects to a 4-pin XLR jack on the front panel.   8)

Sonically, the LIO MOSFET AMP is more dynamic sounding, and just as musical. The only downside is that it might be too much power/gain for some headphones.  You definitely don't want to connect IEM's to it.  Feel free to email me if you have specific questions pertaining to your headphones. 

Vinnie

TomS

Re: Using MOSFET amp module as a headphone amplifier
« Reply #2 on: 6 Jul 2015, 12:46 pm »
Thanks Vinnie. I assumed that might be the case with the negative side connections, but thought I'd ask. I'm not thinking about any particular headphone just yet, so it wouldn't be any problem to pick a balanced option and go that way.



Blu99Zoomer

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Re: Using MOSFET amp module as a headphone amplifier
« Reply #3 on: 26 Jul 2015, 06:55 pm »
Hi Tom and Vinnie,

Would you mind if I interject a thought that came to mind while I was reading the ongoing saga of the headphone/amp/dac/wires shootout over on Inner Fidelity today.  I remember talking with Vinnie back when I purchased my Signature 15 amp from him as a closeout.  I had commented that the amp when turned on makes a popping noise out of the speakers.  Vinnie's comment was that this was a voltage not current noise?  Am I backwards on that Sir?  I believe this relates to Tom's use of a speaker terminal adapter.  But I am not sure.  Vinnie?  Further, Tyll  makes a comment on another manufacturer's amp being a current not voltage driven amp.

Tyll says, "I used to repair scanning electron microscopes, which have a bunch of electro-magnetic lenses and coils for scanning the beam. Because current through the electro-magnetic lenses determine the strength of the field, and not voltage, all the amps to drive the coils were current source amps.
For that reason I've long thought that's the way to drive a voice coil. The current drive signal is the one that's directly proportional to the driving force of the coil, not the voltage signal. It just kinda makes sense.


Read more at http://www.innerfidelity.com/content/big-sound-2015-and-running#hBBMkRdFxLRMQhIX.99


Is my thinking that all the above is related to Tom's original question way off on a tangent or what?  Cause it would be interesting to know how to safely use the speaker outputs on the LIO or another amp to drive headphones with authority. 

Which type of amp is the LIO?  Would either be better to adapt to headphone use out of the speaker terminals than the other? 

I will start a new thread if that's what I should do to ask my questions.  Thanks for your thoughts and consideration.

Best Regards,

Blu99Zoomer

Blu99Zoomer

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  • Posts: 203
Re: Using MOSFET amp module as a headphone amplifier
« Reply #4 on: 26 Jul 2015, 06:59 pm »
Now it seems to me that there is another spot on AC that someone talked about using speaker terminals to drive headphones.  Maybe it was another site and my old, too full mind is mistaken again?!! :duh:  And there I go having conversations with myself again.  Lol.

Best,

Blu99Zoomer

Vinnie R.

Re: Using MOSFET amp module as a headphone amplifier
« Reply #5 on: 27 Jul 2015, 03:12 am »
Now it seems to me that there is another spot on AC that someone talked about using speaker terminals to drive headphones.  Maybe it was another site and my old, too full mind is mistaken again?!! :duh:  And there I go having conversations with myself again.  Lol.

Best,

Blu99Zoomer

Hi Blu99Zoomer,

I read your post above, but that slight turn-on pop that you get with the Sig 15 has nothing to do with it being a "voltage driven" or "current driven" amp.  Nothing to do with TomS' question above.  The pop is just the result of DC offset on the speaker posts at turn-on.


Quote
Which type of amp is the LIO?  Would either be better to adapt to headphone use out of the speaker terminals than the other? 


To be perfectly honest, I'm not sure I understand Tyll's terminology there. 

LIO uses a Class AB MOSFET output stage with low output impedance.  It is perfectly fine driving speakers that are 4, 8, 16-ohm - or even headphones in the 4 - 1000 ohm range.  Impedance does not matter.  Sensitivity of the headphone does matter.  If it is a very sensitive headphone (e.g. like an in-ear monitor, IEM), I don't recommend using it with LIO, as there is too much gain and power.

For headphones that like a good dose of power (actually, what they really want is more voltage gain because they are not as sensitive) such as:

- Audeze LCD-2, LCD-3
- HiFiMan HE-1000, HE-6, HE-560, HE-500
- Sennheiser HD-600, 650, 800
- Abyss
- AKG K701, 702
- AKG K1000

The LIO MOSFET AMP could do a great job with them!

LIO does not have any turn on/off pop.  There is a 10-second delay that we implement while the LIO MOSFET Amp
powers up and stabilizes. 

All the best,

Vinnie

Srajan Ebaen

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Re: Using MOSFET amp module as a headphone amplifier
« Reply #6 on: 27 Jul 2015, 11:07 am »
I believe Tyll is talking about amps like the Bakoon which offer a current-mode output. For speakers there was one transconductance amp model in the FirstWatt stable. For signal transfer between components in the current domain (excluding speakers), Krell had their CAST protocol. Since speakers with standard crossovers rely on voltage-mode drive, that's what 99.99999% of all hifi amplifiers are.  With many headphones using a single driver sans xover, current-mode drive with its high output impedance comes to the fore. With Bakoon offering current and voltage outputs, one can easily compare the two. Particularly planars with their linear impedance really benefit. Dynamics with far more variable impedance meanwhile will get 'EQd' a bit. Whether the result plays to or against personal bias can't be predicted.

Blu99Zoomer

  • Jr. Member
  • Posts: 203
Re: Using MOSFET amp module as a headphone amplifier
« Reply #7 on: 27 Jul 2015, 11:15 pm »
Vinnie,

"The pop is just the result of DC offset on the speaker posts at turn-on."  You have said that there is no concern for my speakers with the noted DC offset.  Should I change polarity or is there something else that I should/shouldn't be doing?  Other than enjoying the great sound I already get from the amp with my speakers...

Srajan,

Thanks for the comment and sharing on current-mode versus voltage-mode drive amps.  I am not an EE and am relatively new to the hobby.  I appreciate the education sincerely.

TomS,

I am sorry if I subverted the thread.

Best Regards,

Blu99Zoomer