Vintage Receiver Reborn - Emotiva BasX A100

So this is another interesting product that I learned about that might interest a few people here, especially those who have a thing for vintage receivers for headphone use. This is a pretty cheap ($230) speaker amp that feeds its output through a 220hm resistor to a 1/4 Jack on the front. They guys at Emotive claim this thing is a modern take on the headphone out for classic hifi receivers from the 70's and 80's. I guess some people really like the sound of headphones through these things.

Here is an SBAF thread about it: http://www.superbestaudiofriends.org/index.php?threads/vintage-receivers-amplifiers.41/

The original MiniX A100 was a popular amp for the HE5 and HE6, back when people were making adapters for the speaker taps. Anyways, the new one eliminates the need for this by including a jumper in the box that, when installed, bypasses the 220ohm resistor, giving the 1/4 headphone out access to the full power this amp produces.



Anyways, Keith at Emotive posted an interesting discussion of the benefits of using resistors with speaker outputs for headphone use on the Emotive Forum:

"Exactly... they're 220 ohms (per channel).
And they don't typically DISSIPATE much power at all.

However, there are several different things going on here - and they're all cool.

1) The easiest one first. Some few planar headphones are VERY inefficient, and actually require three or four WATTS into 30 ohms or so to drive them. These are the ones you hear about people driving with "speaker amplifiers" - usually by building some sort of adapter cable that connects to the speaker terminals but has a headphone jack wired to it. Very few headphone amplifiers can drive them well, and they're not quite perfectly matched to speaker amps either, so they've always been a bit of a problem.

The BasX A-100 will work VERY well with these models. (Remember that you will have to put on the internal jumpers - which also prevents you from doing it unless you really intend to. And also remember that putting this much power into normal headphones would be dangerous to the headphones and your ears.)

2) Really high impedance headphones (like many 300 Ohm and 600 Ohm Beyerdynamic models) require a lot of drive VOLTAGE to really sing. They're actually quite efficient, and don't draw much POWER, but you need enough voltage to drive them. Many headphone amplifiers have trouble with these simply because they don't put out that amount of voltage. (The reason is simply that they aren't designed to. It's not that it's difficult to design an amplifier that can run them well, it's simply that most headphone amplifiers are optimized to run "normal" headphones - which are usually between 30 Ohms and 50 Ohms; and those simply require different optimizations.)

You could actually run headphones like these on the A-100 with the jumpers on or off. Most other amps would probably be too noisy to connect their speaker output directly to a pair of 600 Ohm Beyerdynamic cans, but the A-100 is very quiet, and very clean, so it works just fine that way. (However, you don't gain much by bypassing the resistor, so we don't really recommend doing so.)

3) The resistors also serve a very different purpose. In virtually all vintage equipment, the headphone output was derived by using resistors, like we do in the BasX A-100. Back in those days it was simply a matter of saving money; they didn't want to bother with a separate headphone amplifier. By using dropping resistors, the same amplifiers that you use for the speakers can run your headphones. The main drawback is that speaker amplifiers tend to be slightly noisier than good headphone amplifiers. That's not a problem with the A-100 because we've designed it to be really quiet.

Another thing is that, by driving the headphones through a large value resistor, the impedance of the headphones is allowed to interact with the signal. Most modern headphone amplifiers specifically aim to have a very low output impedance. This minimizes this interaction, and helps ensure that a given pair of headphones will sound very much the same with different headphone outputs and different headphone amplifiers. However, it is this variation that gives each headphone and amp combination its "distinctive personality", so wiping it away may not be a good thing after all. THIS is what contributes to the "great sound of vintage headphone outputs" that some audiophiles rave about so much (and we've brought it back).

The resistors also serve to "even out" the level between various headphones. While there's a lot of variation between both the impedance and the efficiency of different models of headphones, in general lower impedance models tend to be more efficient. If you work out the math, by delivering a certain signal level through a large value resistor, lower impedance headphones end up getting less signal. As a result, with the resistor, when you unplug and plug in different headphones, you are more likely to end up with similar output levels.

(You may be surprised to know that the "standard" for equipment back in the old days was for the headphone output to have a resistor..... often 120 or 220 Ohms.)

Check out the output power the A-100 delivers into headphones of various impedances (with the resistors).
You'll notice that it lines up VERY well with the actual needs of typical headphones.
Remember that these are MAXIMUM OUTPUT CAPABILITIES; so don't worry about "too much power for your headphones"."

Anyways, Some guys on Headfi (take it with a grain of salt) are posting positive impressions with this thing and the HD 650/800. For $230, it could be worth a try.

Headfi and Emotiva Lounge discussions:

http://emotivalounge.proboards.com/thread/48439/basx-100-amp-available
https://www.head-fi.org/f/threads/emotiva-a-100.825970/

 

That stupid amp was hyped to Niflheim and back. I have no complaints about it as a speaker amp, but it sounded like grassy turds with the HE-6.

 

The plot thickens.

I'm still pretty curious about the effects of 220ohm resistor on a speaker output. It basically becomes a headphone amp with 220ohm output impedance.

 

Regarding the points listed above...

#1: no problem here

#2: There's a bit of misleading here. All headphones require power. High impedance ones need less current.

#3: very conveniently steps around talking about impedance interactions causing FR deviations on headphones (most typically a midbass hump) and lack of damping factor, and disguises it under the pretense of "great vintage sound" blah blah blah.
3b) it's true that a high output impedance causes that FR variation, but a really really high one might potentially smooth out that variation... but this is really still not ideal

 

With the exception of some Marantz models and Fischer tube amps IME, vintage receivers/amps tend to be noisy for the majority of modern headphones and yes, dynamic cans do exhibit the midbass hump. However, planar magnetics can sound very very good from vintage gear: quiet and without FR distortion.

 

I now listen through the headphone port of my Cyrus integrated amp.

Whilst it was hearing problems that made me get off the hifi dream/upgrade conveyor belt (no point: not enough ear bandwidth) it was also this very amp that showed me how much better my 'phones were than I thought!

Maybe it's mid-fi... but, with my HD600s, it is fi enough for me. And, I'll stick my neck out and say... not a bad way to listen to music

 

I received one if these as a gift from my wife the other day.

A seriously fantastic piece of equipment. Listening to headphones through this is fantastic. HD6XX. I tried emailing Emotiva seeing how long it remains in class A. No response yet. Superb office equipment. Power elac debut 2.0 B6

 

I've had this amp for over a year now. Until the pandemic came it got used every day. Wonderful budget 2ch amplifier. Its driven Deftech 350s, Elac Debut 2.0 B6s, and HD6XXS. Now it's on garage duty with the Elacs. As an HP amp Its better then the Magni 3, but worse then the Asgard 2 and Ragnarok 2.

For a budget system though, you can't go wrong, and it has auto on, which is very nice..

Nearfield experience with the Deftec 350's was truly awesome, especially for the price. Great depth, imaging, detail. Does about 1/2 watt class A into an 8 ohm load per Emotiva. It has a fan, but I've never heard it turn on..

Dacs in play here have been Schiit stuff, Modi Multibit, Modi 3, Bifrost 4490, Bifrost 2.

 

I absolutely love my A-100. Gets some can use; but mostly speakers near field. So so clean. Is just good.