Random musings on hifi components from 20+ years of upgraditis

gibbsy

Moderator
Okay, I've just looked up the specifications of my Arcam FMJ A32 integrated and it says:

Headphone Output

Maximum output level into 600 ohms - 8V (volts?)
Output impedance - 100 ohms

Enough to drive a pair of Sennheiser HD 800S, @gibbsy?

Sorry this is OT, won't ask again!
Here's the Linear's figures. How it equates to the voltage signal of the Arcam I can't really work out. As a comparison the rHead has 130mW into the 300 ohms needed to drive the Senns. So the Lehmann is more powerful. Perhaps someone with more brains than me can work out the difference in figures between the FMJ and the Lehmann.


Output power400 mW/60 ohms
200 mW/300 ohms
Output impedancepre-out 50 ohms
phones out 5 ohm
 

dannnielll

Well-known Member
Hi Gibbsy. Auditioning for the brains trust. The figure for the Linear is that when driving 300 ohm loads, it will provide 7.7 volts at peak output power, but if the load is as low as 60 ohms ,it can due to its own internal resistance,, only generate a peak voltage of 4.9 V.
The rHead driving the senns at 300 ohms can manage 6.2 v
The FMJ..and using the figures quoted above will produce About 6.0 V .
...300/(100+ 300) * 8
 

gibbsy

Moderator
Hi Gibbsy. Auditioning for the brains trust. The figure for the Linear is that when driving 300 ohm loads, it will provide 7.7 volts at peak output power, but if the load is as low as 60 ohms ,it can due to its own internal resistance,, only generate a peak voltage of 4.9 V.
The rHead driving the senns at 300 ohms can manage 6.2 v
The FMJ..and using the figures quoted above will produce About 6.0 V .
...300/(100+ 300) * 8
Still lost, well maybe still wandering and thanks for replying. It seems that the lower the ohm rating on the headphones themselves then that has an effect on voltage. My Oppos PM1s are just 32ohm and was bought initially because I really wanted to try planars but was instantly smitten by their performance. The other reason was that I could easily use them with the low powered headphone sockets that are fitted to my Marantz players. Which is something they did quite well. Now that they have the power of Lehmann they really do sing.

Does voltage then, influence the performance of the headphones? I did audition the Senn 800s but they were being driven by an amp (Project Head), found them a wee bit bright for my tastes, especially on female vocals, plus the 300 ohm loading for the reasons above. Then I went and bought the Oppos completely blind.
 

Derek S-H

Distinguished Member
Christ, the Sennheisers are here! :eek:

Okay, simple question @dannnielll - is my Arcam amp's headphone output powerful enough or do I really need a separate headphone amp?

Thanks!
 
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dannnielll

Well-known Member
Christ, the Sennheisers are here! :eek:

Okay, simple question @dannnielll - is my Arcam amp's headphone output powerful enough or do I really need a separate headphone amp?

Thanks!
The Arcam quotes a 50 ohm output impedance, and it is driving phones of 300 ohms. This means that the Arcam is strongly controlling the phones. ..If the amplifier says jump, the phones jump ,if the amplifier says stop, the 'phones stop quickly . Whether you like this or not is a matter for yourself. One of the "attractions " of many valve amplifiers is that they do not control the headphone or speaker so if the amplifier says stop the speaker slows down at its own sluggish rate.
There is very little difference between 6 ,6.2 and 7.0 volts, and I expect that anything at that level will be blowing your ears off , and you will normally be listening at a level of 1.0 V. so No, in terms of power.
But it would be possible to get headphone amplifiers with 5 ohm or 1 ohm output impedances, and they would even exert greater control.
I am operating in a different league, but the same argument follows. I have reasonably good headphones in the Sony MDR1A,and have used them in a variety of situations over the last 5 years... With music players, PCs DACs ,Music Centres .They have a high efficiency and have 50 ohm impedance. They sound completely different when driven from a standard mobile phone than when driven with exactly the same music source but instead from a Cyrus Soundkey DAC Headphone amplifier. In all cases the sound is clear ,but in the case of the Soundkey it is dynamic, fuller stronger .. substitute your own positive adjective. It is not a volume thing as in all cases the volume can be brought up to excessive. No it is because the output impedance of the Soundkey is 1.1ohms, which means it controls the phones.
Now the Soundkey tops out at 1.7 volts peak, which is very low compared to your peaks of 7.0 volts!.
 

dannnielll

Well-known Member
Hi Gibbsy.. the following is an attempt of demystification...
A car battery output is at 12v. The little PP3 battery pack in the fire alarm is 9v. Sticking two of these together can produce 18V . .. obviously bigger than 12V.
A car battery can easily put 10 Amps into a car headlight and therefore a power level of 12V *10 A of 120 Watts of power..and do this for a number of hours.
Our two PP3s ,produce 18V but cannot drive more than 100mA even into a short circuit. ..so connecting a car headlamp would not even make it glow red.
We say the car battery has an internal resistance of maybe 1/20 ohm and our PP3 of probably 100 ohms.
When a voltage is applied to a circuit containing a resistance ,a current will flow and power will be consumed ,both in the resistance and also in any internal resistance inside the voltage source. The power in the resistance is P = V*I .the voltage difference across the resistance times the current flowing in the resistance . However because current depends on the voltage, there are a few math relationships we can swop around ...
power is also V^2/R or power is I^2 *R
. Unfortunately the headphone manufacturers keep rearranging the deckchairs,and quote power which is a useless measure. Since they have already decided on the size of resistance in their phones, what they should say is ..This phone needs X volts to generate Y dBs ,and never exceed Z volts ,
 

gibbsy

Moderator
@dannnielll Thanks for the explaination, brought it down to my level of intelligence.
 

Derek S-H

Distinguished Member
@dannnielll - thank you very much for your detailed reply, which I must confess I didn't understand entirely! :blush:

I think the upshot was that headphone manufacturers quote watts when it's more useful to quote volts, as you have?

Anyway, thank you for taking the time to reply and you have just saved me hundreds of pounds, though it would've been nice to own a piece of equipment called Schiit!

And I shall forgive you whenever you criticise Vinyl, whether in the past, the present and undoubtedly the future! ;)
 

dave48

Active Member
Thanks for flagging headphone amps - I think I completely forgot them. I had a Musical Fidelity X-Cans which looked cool but I couldn’t hear any difference to the headphone output on my old integrated amp (which was nothing special). Now use a fiio rechargeable amp which is pretty good (I’ve only got Sennheiser 600HD so nothing exotic to drive). Headphone outputs on Audiolab M-DAC and Hegel HD25 are both pretty good.
 

dave48

Active Member
Also forgot phono amps. Had a Musical Fidelity X-LP or something - like most of the other Musical Fidelity X products - I really wanted to like them as they looked so cool, but they all sounded tame and uninvolving. Upgraded to a Lehmann Audio Black Cube SE. I’m really happy with that - but it was only after spending quite some time with my hifi dealer tweaking the settings that it really came to life. It needed some experimentation - the setting that was theoretically right just didn’t sound as good. Now sounds even better with the Lyngdorf (this for me is THE revelation of the Lyngdorf). So happy with the Lehmann and v. unlikely to ever change it whilst it is still working.
 

dannnielll

Well-known Member
@dannnielll - thank you very much for your detailed reply, which I must confess I didn't understand entirely! :blush:

I think the upshot was that headphone manufacturers quote watts when it's more useful to quote volts, as you have?

Anyway, thank you for taking the time to reply and you have just saved me hundreds of pounds, though it would've been nice to own a piece of equipment called Schiit!

And I shall forgive you whenever you criticise Vinyl, whether in the past, the present and undoubtedly the future! ;)
.. Leaving aside the Vinyl slur..which we will both ignore.!!!!. ..😃 ,The low internal resistance in the amplifier is kind of important. Look at it this way. The amplifier squirts out a voltage to the headphone and the diaphragm starts to move. It was a cymbal clash and very short lived ,so the amplifier stops giving out voltage very quickly. However the diaphragm is still moving. Now. Things actually reverse. The head phone is a magnet with a coil of wire attached to a moving diaphragm, and it, instantly becomes a generator driving current BACK into the amplifier. If the internal resistance of the amplifier is low compared to the resistance of the coil, the kinetic energy of the diaphragm is instantly absorbed and it stops . Otherwise the diaphragm would continue moving and slurring the acoustics a little. Now with 50 ohm internal and 300 ohms in the Senns, you have a Damping ratio of 6:1 ..which is good. But in my case with the Sony and Cyrus the Damping ratio is 48:1 which is better.
Again you might well prefer a lower Damping Factor..many people do... One of the reasons why many people like Valve amplifiers is that they have a lower Damping Factor ..
 
For those who never took any electrical/electronics training, a very basic parallel to water delivery:
Voltage is analogous to pressure
Current is analogous to flow
Resistance is analogous to friction
Power (wattage) is SOMEWHAT analogous to volume (gallons/liters), in that the amount of pressure vs friction will determine the amount of water flow/unit time.

Tube (valve) amps are sufficiently different from semiconductor amps that it is comparing apples and pomegranates... both are fruit but neither is a direct substitute for the other.

Ah, back-Electromotive Force, (aka counter-EMF) is where the real "fun" in coil/magnet mechanisms interacting with electronics begins. Far too long and controversial a topic to be fully addressed here, or anywhere outside an engineering course, but one I'm sure any competent amp/speaker designer/manufacturer is well aware of.

Here's a good explanation, no sense reinventing the wheel... scroll down to reply #3 by Aether Audio. There are other instructive comments of his further down the thread too. This is from 2005, but as far as I know the Laws of Physics haven't changed much since then. :)
 

gibbsy

Moderator
For those who never took any electrical/electronics training, a very basic parallel to water delivery:
Voltage is analogous to pressure
Current is analogous to flow
Resistance is analogous to friction
Power (wattage) is SOMEWHAT analogous to volume (gallons/liters), in that the amount of pressure vs friction will determine the amount of water flow/unit time.
Ah, but. Does electrickery lose power as it goes up hill. Water does. Roughly one bar per storey. Got to give the branchman enough power to fight the fire.:thumbsup:

It's a good analogy for a dim wit like me. Remember peeps, water and electrickery does not mix.
 

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