Project Ember

Thanks Frans. Seems there's a bit to this than I thought...

Yes, the info for that cable is lacking as you say and a google search reveals nothing more. Not worth the gamble if results may be no better than the Ember's H setting (not good with the Pandora).

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Although -24dB does sound a lot I don't think it'd be overkill for the Pandora.

Not sure what the 'sweet spot' on the vol pot is but with output R set to M (-15dB) I find 1/2 way between 8 & 9 o'clock is comfortable whereas with it set to H (-24dB) a little under 10 o'clock is about right.

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Knocking a cable up myself isn't an option sadly. I have zero soldering experience (ignoring one botched attempt) so I'll either need to wait patiently for the Garage1217 cable to materialise or find a stop-gap solution....and I may have found something that looks a bit more promising.

iFi Audio have or will shortly be releasing their own attenuators and spotted this quote from them on HF:

"One common recommendation is the 1/4 rule. The nominal HP impedance should be at least 4 times the output impedance. The 12dB Attenuator is around 3R output impedance, so 12 Ohm or higher minimum impedance IEM's should not experience audible issues.

The 24dB attenuator is 1Ohm Z Out, so it is not likely to have any sonic impact.

The 1/4 rule = response variations (absolute worst case) are less than +/-1dB, which is usually classed as inaudible."


From this it looks like 2 questions are answered. The output resistance of the -24dB attenuator is 1 ohm (I think..not sure what the Z means though?) and it is suitable for low impedance IEMs. 

They've designed it in-house and are clearly thinking about sonic impact so that's another positive sign.

I'll have an ask on the thread and see if I can get the input R and also an indication of how they are achieving attenuation, assuming it's something they're willing to divulge.

Thanks again Frans for all the help!

Cheers Gordon.

I'd read the same thing so I've always applied 1/8 when buying amps. Just to be safe I used both rules & figured that cable should be fine either way

I know some folks buy amps that break those rules and like the what they hear, so I suppose it's more of a guide than a hard & fast rule. I know I find the K7XX much nicer sounding on mid R (roughly 1/2) when low R (something I can't work in my head lol) would seem the more logical choice. Works for me tho' so that's good enough.

I was following the Nighthawk too but it doesn't sound like it's ben setting the heather on fire...

Trust your ears, that is all that matters Don't ever let anyone tell you what sounds good. Take a listen and if you like it, then you like it!

I found the k701 and k612 were better at 120 ohms output.

The surprise one was the Grados. To me, they sound quite a bit better at 120 ohms.

Below a table which shows the relation to output level reduction for different headphone impedances on Medium (35 Ohm) and High (120 Ohm) output settings.

In the left column you look for the impedance of the headphone in question.
The columns on the right give you the attenuation you get in the M and H setting in dB's compared to the Low output R setting.



The damping factor has always grasped the imagination of many folks.

There once was the 1/10th rule where it was said the output impedance should be 1/10th of the driver impedance.
In the old days tube amplifiers could have substantially high output resistances but nowadays most speaker amps are well below 0.1 Ohm.

Most headphones (those with 'flat' impedance plots) rely on mechanical/acoustical damping and don't need electrical damping.

Nothing gets past you Frans

I wasn't sure if the response I got from iFi would be adequate for you to assess the attenuator as they appear to be working on the (incorrect) assumption the Ember's output R is fixed at 120 Ohm. I therefore delete the post and was intending on going back to them to explain the various output R options, in the hope that might result in them being more forthcoming. 

However, based on your comment above regarding 16 Ohm load am I right to infer that if it's offering around a 16 Ohm load the attenuator should be okay? Or would it still be better to get details on the Input R and resistor(s) used before coming to a conclusion?

Here's the reply in full in case it is of help:

"Hi,

Asked one of our senior tech people who said.

We do not think the attenuators are suitable for something like project ember.

They were designed to work with modern "high drive, low impedance" amplifiers and simply emulate modern iEMS's for impedance. So they offer around 16 Ohm load (precise numbers depend somewhat on the headphone) to the driving amp, just like an IEM would.

Looking at "Project Ember" it seems this has a 120 Ohm output impedance setting. This, would give some substantial attenuation, at the cost of some frequency response variations. Otherwise best talk to the designer, however we would generally not recommend our attenuators for this product.

Sorry we could not be of more assistance."

Thank you again & apologies for my ignorance.

Thanks Frans.

I think whoever at iFi made that statement just took a quick glance at the Ember specs, saw 120 Ohm mentioned and came to the wrong conclusion. I've pointed this out to them and quoted the various output output resistance options that are available.

If the iFi cable is reasonably priced (i.e. not more than it'd cost me for a soldering iron & parts) then I'll buy one, but otherwise may look into making my own. Although your idea of easy and mine may differ markedly (I'm a hamfisted klutz).

Either way I think your guide will prove invaluable to others who wish to make one. Appreciate all the help!