small tube amp for IEMs?

[jrebman]

So, that's what I'm looking for -- a small, not portable tube amp for use with IEMs. I'm figuring on battery power and a nice, quiet tube (6j6 for example.) Parafeed would be nice too, and I wouldn't be against using a good jfet voltage amp to drive the tube.

Any ideas or suggestions?

I really don't want to buy an off-the-shelf, portable amp.

Thanks,

Jim

 

[Alonzo]

The Quickie makes a nice little battery tube amp.  Less than an hour's work.  There's a sticky on it I think.
Alonzo

 

[Paul Birkeland]

IEM's are usually designed to not need amplification.

From my experience with IEM's, a SEX amp with a resistive voltage divider set for 4 Ohm operation will get you quiet operation with the reduction in output power that IEM's require.

I would try a 50 Ohm and 5 Ohm divider on each channel to start.  You can add an 1/8" headphone jack next to the 1/4" one and install the resistor network so that it is only active on the 1/8" jack.

-PB

 

[jrebman]

Hi Alonzo,

I gave that a lot of consideration but the microphonics could be a big problem. Aside from that, I gave away my collection of 3s4s.

PB, I'm not sure what you mean by IEMs not needing amplification. I'm confused.

In the mean time, I found what looks to be a really nice solution -- an active (*not* resistive) device to allow you to use IEMs with just about any headphone amp. The active device removes hiss but allows the full spectrum to come through without any attenuation of any part of the spectrum. It is also supposed to give an increased perception of dynamics and better bass articulation. The device is the iFi  IEM. Sorry, no idea of the cost.

The resistive attenuators always do bad things to dynamics and frequency response at the extremes -- just liike regular cans, but more pronounced.

This iFi device looks like what I've been waiting for -- and it now appears to be built into several iFi amps. IMO, this is the way to go.

-- Jim

 

[Paul Birkeland]

PB, I'm not sure what you mean by IEMs not needing amplification. I'm confused.

What is the power requirement of the IEM's you'd like to use?  Also, what is their specified impedance? 

Most IEM's require some tens of milliwatts, which can be gotten from just about any old headphone jack.

I'm not aware that resistive dividers have any effect on frequency response.  Most tweeters in most commercially produced speakers use resistive voltage dividers as a means to match levels, so I can't imagine any attenuation of the high frequencies.  On the bottom end, provided the resistive divider is of an appropriate impedance, bass damping shouldn't be affected.  We also do enjoy the sonics of switched resistive attenuators in our amplifiers.  Having said that, just using a series resistor will impose some limitations.

The iFi iEmMatch is a passive resistive voltage divider to reduce power and gain of your average headphone amp for use with IEM's.  This is the same solution that I'm proposing, but it costs a bit more and is external to the amplifier.  It is a selectable resistive voltage divider.

I don't currently see any active devices made to accomplish this task.

 

[jrebman]

Yes, only a handful of milliwats -- that's an awfully high SNR, which most amps simply don't have. I've plugged my Shure SE-425s into the s.e.x. and it was not listenable -- sure, music came through but the noise level was intolerable. Try it.

Even a good passive voltage divider now makes what is basically a straight resistive load into a complex serial/parallel network, and that has to change the frequency response curve.

You know for sure that the iFi device is fully and completely passive? I ask because it seems to me to be quite a trick to cut out the hiss, yet leave the frequency response alone, or increase the dynamics, or tighten up the bass.

I've had a number of both tube and solid state amps with headphone outs, and not one was acceptable with IEMs. So, like you would do, I built a couple of different voltage divider attenuators, and every single one of them left the bass washed out and attenuated, and severely rolled off the highs.

You really can't compare IEMs to room speakers, or even more standard cans... first there is the nearly direct coupling to the ear canal (plus a huge drop in ambient noise, and also because the moving mass of IEM drivers is so infinitessimally small even compared to standard cans, and this makes everything you use to drive IEMs far more critical when it comes to background noise and frequency response.

Yes, probably most amps that can handle an 8 to 120 ohm load (typical being about 16) ohms, will indeed play the IEMs, but the background noise will be intolerable to most. Believe me, I've done this more times than I can count, and the iFi device (whatever it is) is the first and only "attenuator" that takes away the unwanted stuff and leaves the rest intact (or possibly improved.

Believe me, if it were truly as simple as a couple of resistors, my search would have been over a long time ago. As I said, I've done this more than a dozen times and with both tube and SS amps. Hell, even many of the portable headphone amps are just too noisy to use with IEMs.

Somewhere somebody did a comparison of 10 under $200 portable (mostly) headphone amps and many of those did not make the cut with IEMs, and it would have been a very simple matter to add an "IEM" switch and some resistors, but I've never seen that either -- and you have to know that a good number of people that buy shirt-pocket size amps are going to want to listen to IEMs with them.

Bottom line is that I've done this many times and each time that the hiss was eliminated, so was  the enjoyment of the music and always with the FR severely compromised -- sometimes to the point that you'd never recognize the sound as being that of the untouched IEMs.

When the listening is that up close and personal, and background noise is 20-40 dB below ambient, there isn't much room for noise and non-linearities.

-- Jim

 

[jrebman]

Ok, I'll admit to this being a passive device, even with a resistive voltage divider, but I'll bet there is more than that in there -- passive compensation network, maybe a transformer or two -- I just don't know but I do believe there is more than a couple of resistors in there.

-- Jim

 

[Paul Birkeland]

Ok, I'll admit to this being a passive device, even with a resistive voltage divider, but I'll bet there is more than that in there -- passive compensation network, maybe a transformer or two -- I just don't know but I do believe there is more than a couple of resistors in there.

-- Jim

There absolutely isn't enough room in there for a pair of transformers.  There isn't enough consistency in IEM's to select one passive compensation network that will work with all IEM's.

What resistor values did you try when padding the output of the SEX amp?  Were you using dividers or just resistors in series with the output? Reducing the hiss in the amplifier is a function of one of these devices, there's no magic there.  This is the same recommendation that we give with folks who have very high gain amps with very sensitive speakers and complain of having noise issues.

If the iFi sounds good to you on the SEX, try a 15 Ohm and 1 Ohm resistive divider on each channel. 

 

[jrebman]

Paul,

There is more than enough room in there for even a couple of multi-pole filters and a common mode choke -- I've seen the size of a fingernail.

This box is almost 4 inches long, 2.x wide, and 1.1 tall -- plenty of room for a pile of circuitry. It also has only two settings -- not many as one would guess with some many different IEMs and headphones.

My friend who told me about this has super sensitive IEMs and listens to IEMs most of the time and he said this little box is a must. He's tried all the other attenuators that he could find and none of them could do anything like this box.

As I don't have an assembled s.e.x. amp, I cannot try anything, but the input impedance of the thing is 16 ohms and the output impedance is 2.5 ohms in sensitive mode, and less than 1 ohm in super sensitive mode.

Actually, I don't want to analyze this anymore -- a very trusted friend with  ultra sensitive IEMs, who has found nothing else that works, uses this and believes it is a must-have for IEM (and sensitive headphone) users.

Whatever it is, they wwouldn't put it in that big a case if it were only a couple of resistors, especially knowing that IEM users really want portability as part of the system -- I know I sure do, and with my Dragonfly Red mounted to the back of my iPod, there is simply no way to add this device to my portable listening setup.

I actually don't even know how my IEMs sound with the dragonfly, but people say it's not the best for sensitive IEMs.

Well, even if the box is packed with floobydust, I'm getting one.

!

Take care,

Jim

 

[Paul Joppa]

We appear to be talking about different products. The one I see is here:

http://ifi-audio.com/portfolio-view/accessory-iematch/

The circuit appears to be in a cylindrical aluminum tube, about the same diameter as the foam earplugs and a bit less than twice as long.

iFi seems to make many other products in different cases and sizes, so perhaps we are not looking at the same product?

 

[jrebman]

That could well be -- the pictures all look the same to me .

Still, what I really want is the iDSD Micro, which has this gadget in it, plus 3 selectable power output modes.

Without dissecting one of these things, we're all really just speculating -- I have it from a trusted source that it works as advertised, along with a recommendation that everybody with IEMs needs one of these. That is the sum total of what I know about this and have never heard one myself.

-- Jim

 

[johnsonad]

Music Direct Jim and you can return it if you don't like it! Let us know what you think of it if you purchase one.

 

[jrebman]

Hey Aaron,

I had the Nano for a while and liked it, but this one has so much more, and the fact that it will now work directly from my iPad or whatever, is a huge bonus.

As I said, I will get it, but I really do have to save my money first. Maybe it will be a christmas/birthday present -- that would be nice.

Take care,

Jim