[Armaegis]

How much was your build cost on those Ncores? (roughly)

 

[Chris J]

   
My gripe with it is the silliness of using amps with too much gain and high noise floors that are unsuitable for headphone usage, then jury rigging a solution by chopping down the output.
 
Well just speaking in generalities, amps have various "sweet spots" (best THD/noise/whatever specs) in their operating range, be it voltage or current delivery or load impedance. A headphone load is not going to come close to any of those. Doing some trickery with L-pads might work (a three-resistor network might get you closest) but that's not a true solution and you're wasting energy as heat (but if you're a class A proponent, then you don't really care about that anyways). At least planars don't have to worry about damping factor as much. Using resistors to adhoc output impedance sorta works, but isn't a proper solution either.

 
I would argue that when using power amps with headphones, the big elephant in the room will almost always be signal to noise ratio: excessive hiss and/or hum.
Speaker power amps are never designed to be used with drivers that output 96 dB when driven from 1 mW.
And 26 dB or even 32 dB of gain is a bit much for a headphone amp.
Hence the need for resistors.
 
As for voltage and current ranges, usually irrelevant in a well designed amp, as the THD will be low enough to be academic, unless you are approaching clipping.
Remember, you are often listening to a power amp deliver a Watt or less to your loudspeakers.
The idea that a transformer coupled vacuum tube power amp must see an 8 Ohm load if you are running off the 8 Ohm taps is grossly exaggerated.
 
In a perfect world, it would be nice to A/B one of the megapower headphone amps (like the Bryston and it's bretheren) against one of these resistor/power amp combos.

 

[potterma]

  ... snip ..
 
 
Well just speaking in generalities, amps have various "sweet spots" (best THD/noise/whatever specs) in their operating range, be it voltage or current delivery or load impedance. A headphone load is not going to come close to any of those. Doing some trickery with L-pads might work (a three-resistor network might get you closest) but that's not a true solution and you're wasting energy as heat (but if you're a class A proponent, then you don't really care about that anyways). At least planars don't have to worry about damping factor as much. Using resistors to adhoc output impedance sorta works, but isn't a proper solution either.

 
I have a difficult time believing charts that show a decreasing THD figure with increasing output power.  One is trying to measure extremely small signals with outrageous precision to make these measurements.  I'd wager its more about exceeding the capabilities of the measurement equipment (hence an artifact of the measurement) and not a real increase in performance.  You're "getting into the sweet spot" of the measurement equipment, not the amplifier.

 

[Chris J]

   
I have a difficult time believing charts that show a decreasing THD figure with increasing output power.  One is trying to measure extremely small signals with outrageous precision to make these measurements.  I'd wager its more about exceeding the capabilities of the measurement equipment (hence an artifact of the measurement) and not a real increase in performance.  You're "getting into the sweet spot" of the measurement equipment, not the amplifier.

 
No it isn't an artifact of the measurement equipment.
Typically it is caused by the crossover distortion in the Class AB output stage.
 
Try looking at some THD plots of SE Triode amps, THD drops as output power decreases.
 
OTOH, as I said earlier, the THD is usually so low that the actual value is often academic.

 

[potterma]

   
No it isn't an artifact of the measurement equipment.
Typically it is caused by the crossover distortion in the Class AB output stage.
 
Try looking at some THD plots of SE Triode amps, THD drops as output power decreases.
 
OTOH, as I said earlier, the THD is usually so low that the actual value is often academic.

OK, that makes sense.  I guess I was thinking exclusively Class A operation.  
 
What?  There's another class?

 

[Senn-Fi]

How much was your build cost on those Ncores? (roughly)

I think I spent about $1700 with all premium parts.

 

[robrob]

  Bottom line: if folks think their jury-rigged system sounds good, at a price they are willing to pay, then the world is a happier place for it... at least to them.

 
Especially if that jury-rigged interface has multiple headphone outs, switches and oscilloscope outputs 

 
 
We've got to keep in mind that what we like and what we think we like can be very different. Most audiophiles believe they prefer truly neutral sound reproduction--just like the artist and producer intended, but in reality our individual preferences vary in not-so-subtle ways. Vive la difference!

 

[Chris J]

  OK, that makes sense.  I guess I was thinking exclusively Class A operation.  
 
What?  There's another class?

 
Yes,  there are various classes:
The Proletariat, or lower classes
the middle classes 
and the 1%, hence the class struggles.
 
No wait.
I'm thinking about Karl Marx, Chairman Mao's Little Red Book, and the anti Wall Street movement.
Nevermind.

 

[ALRAINBOW]

Cris. Is there a general rule of sound signatures for different class amps. .?

Al

 

[Chris J]

Cris. Is there a general rule of sound signatures for different class amps. .?

Al

 
Oh boy.
Leave me out of this one!
Many will argue that Class A power amps are superior! They musy be better than Class AB because they have no crossover distortion!
Then others will say, well what about SE Triode tube power amps? They run in Class A! Butt hey have so much distortion they must be bad!
And what about Class _?
 
Continue, ad nauseam..................

 

 

[ALRAINBOW]

Ok I do see your point , my question was just SS amps . What about d class. It's use seems to be just subs and woofers. But I think genisis is making a class d amp now for the mids and tweeters . Any thoughts ?

 

[zilch0md]

  Well hey, I'm also the guy who says ditch the resistors and slap big autoformers on the ends of the amps. So I'm just a nutzo as you guys, but in a different flavour

 
Your flavor of nutzo is just fine by me! 

 

[Chris J]

Ok I do see your point , my question was just SS amps . What about d class. It's use seems to be just subs and woofers. But I think genisis is making a class d amp now for the mids and tweeters . Any thoughts ?

 
I have heard various Class D amps in various sub woofers have heard.
 
I once heard a Devialet for a few minutes. Based on that brief listen, I thought it sounded just like a good analog amplifier.
 
So I'm not much of an expert.
 
I suppose just like anything else, as they work the bugs out, the newer generations sound better and better.

 

[zilch0md]

   
I have a difficult time believing charts that show a decreasing THD figure with increasing output power.  One is trying to measure extremely small signals with outrageous precision to make these measurements.  I'd wager its more about exceeding the capabilities of the measurement equipment (hence an artifact of the measurement) and not a real increase in performance.  You're "getting into the sweet spot" of the measurement equipment, not the amplifier.

 
Interesting!  Most of the op-amps I've rolled in my iBasso PB2 Pelican have datasheets that show what you're talking about.  For example, the OPA1611 and 1612 allow a minimum supply voltage (Vs) of something like 4.5V (if I recall correctly) and a maximum supply voltage of 18V (I'm certain of this figure), but they show lowest THD+N at a supply voltage of 15V (and I'm certain of this, but too lazy to look up the datasheet at the moment).
 
So, yeah, lots of op-amps show an improvement in noise measurements until some peak is reached - always close to the maximum allowable supply voltage, it seems. That's had me scratching my head for a while, now. Your hypothesis makes sense to me, but I'll remain open-minded, especially since I've tried real hard to actually hear the difference, between 8.4V and 15V with the OPA1612 into HD800, for example, to no avail.  So, the whole subject is moot, with my ears and my gear, at least.  But...  I run at 15V because the output voltage increases better than linearly with an increase in supply voltage - and that I can hear, as improved dynamics and bass control, with inefficient headphones.
 
Mike

 

[potterma]

   
Interesting!  Most of the op-amps I've rolled in my iBasso PB2 Pelican have datasheets that show what you're talking about.  For example, the OPA1611 and 1612 allow a minimum supply voltage (Vs) of something like 4.5V (if I recall correctly) and a maximum supply voltage of 18V (I'm certain of this figure), but they show lowest THD+N at a supply voltage of 15V (and I'm certain of this, but too lazy to look up the datasheet at the moment).
 
So, yeah, lots of op-amps show an improvement in noise measurements until some peak is reached - always close to the maximum allowable supply voltage, it seems. That's had me scratching my head for a while, now. Your hypothesis makes sense to me, but I'll remain open-minded, especially since I've tried real hard to actually hear the difference, between 8.4V and 15V with the OPA1612 into HD800, for example, to no avail.  So, the whole subject is moot, with my ears and my gear, at least.  But...  I run at 15V because the output voltage increases better than linearly with an increase in supply voltage - and that I can hear, as improved dynamics and bass control, with inefficient headphones.
 
Mike

Supply rail voltage effect is not what I was speculating about.  Supply rail voltage changes will have dramatic effects on the quality of the signal coming out of the other end.  My hypothesis was based on Class A amps and trying to measure THD of sub millivolt input (signal) waveforms.