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Why is the Little Dot 1+ recommended for low-impedance cans?

post #1 of 21
Thread Starter 

Greetings audiophiles,

I am hoping you can shed some light on an acrimonious debate between my friend and me.  My friend is a fan of nwavguy, and he insists the 32 ohms output impedance of my Little Dot 1+ is disastrous for my Denon D2000's (which have 25 ohms impedance).  Sometimes I suspect the amp is overpowering the cans; rarely can I raise the volume past 9 o'clock.  I have seen people recommend a 1:10 ratio of output impedance to load impedance; if that advice is correct, it would seem terrible that the LD actually has a higher Z than the Denons!  And yet everyone highly recommends this amp for Grados, Denons, and other low-Z cans, so I am puzzled.

 

On a semi-related note, my friend and I listen to a lot of acoustic music, especially harpsichord recordings by Gustav Leonhardt, which I think tend to be closely mic'ed.  I hear all kinds of background noises on these recordings (performer moving/grunting), and on some I hear continuous, unpleasant low-frequency noise, almost like a dull roar.  Sometimes the bass noise comes across as a kind of pressure, more felt than heard - hard to describe; is it an effect of closed cans?  I am using Voskhod EF95 tubes, OPA2107, and the HRT Streamer 2 with lossless files as a source.  My friend claims he hears none of these problems, or he hears them so little they're not distracting.  He is listening to the same CDs, using Grado 325i, Grado RA1 and a portable CD player with line-out.  So, the essence of our debate: I believe these particular recordings are awful because I don't hear problems with any other ones, and perhaps his cans or DAC are obscuring details.  He claims the recordings sound fantastic to him, and there must be a problem with my setup: perhaps the bassy response curve of the Denons is revealing noises the recording engineers did not intend to be audible; perhaps the impedance mismatch is causing bizarre, unpredictable distortion or imbalanced response at certain frequency ranges, etc.  It is worth noting that the Grados and the Denons have opposite response curves in the midrange, so perhaps he simply doesn't have to turn the volume up enough to hear the noises badly.

 

There are perhaps 2 other things worth noting: (1) the low-frequency noise problems seem to be better with my new Voskhods (previously, I was using WE408a's which came with the amp, and one of them was quite microphonic), and (2) the problems I heard on Leonhardt's CDs were not any better when I tried a JRC cmoy amp, which should have near 0 output impedance.

 

So, can anyone explain this bizarre disagreement between us?  I would be delighted to hear other people's experiences of the LD 1+, the Denons, or especially both together.  And if anyone has listened to lots of Gustav Leonhardt and can settle the question of the recording quality, I'd be ecstatic!  On almost all my other records, the LD 1+ / Denon combo has sounded fantastic.

post #2 of 21
the LD I+ is 8ohm output.

- Suitable Headphone Impedance: 8 - 600 ohms

http://www.littledot.net/forum/viewtopic.php?f=9&t=819&sid=03eba24e612ff56ba1667c77011dddd1
post #3 of 21

yes and the denon D2k handles high impedances well in comparison, but still not well enough for my taste.

The midrange is unaffected, the high highs are elevated, and the subbass levels out at an elevated level, NwAvGuy did some measurements to show this.

 

Its a much bigger problem with the Asus Xonar Essence STX, because I suspect the JRC opamps compound on this resulting in the sound signiture, and way too much unnatural subbass.

 

So you will haveto look at the traits of the amp in question, it may counteract or amplify the problem.

post #4 of 21
Quote:
Originally Posted by sacheie View Post
Greetings audiophiles,

I am hoping you can shed some light on an acrimonious debate between my friend and me.  My friend is a fan of nwavguy, and he insists the 32 ohms output impedance of my Little Dot 1+ is disastrous for my Denon D2000's (which have 25 ohms impedance).  Sometimes I suspect the amp is overpowering the cans; rarely can I raise the volume past 9 o'clock.  I have seen people recommend a 1:10 ratio of output impedance to load impedance; if that advice is correct, it would seem terrible that the LD actually has a higher Z than the Denons!  And yet everyone highly recommends this amp for Grados, Denons, and other low-Z cans, so I am puzzled.

On a semi-related note, my friend and I listen to a lot of acoustic music, especially harpsichord recordings by Gustav Leonhardt, which I think tend to be closely mic'ed.  I hear all kinds of background noises on these recordings (performer moving/grunting), and on some I hear continuous, unpleasant low-frequency noise, almost like a dull roar.  Sometimes the bass noise comes across as a kind of pressure, more felt than heard - hard to describe; is it an effect of closed cans?  I am using Voskhod EF95 tubes, OPA2107, and the HRT Streamer 2 with lossless files as a source.  My friend claims he hears none of these problems, or he hears them so little they're not distracting.  He is listening to the same CDs, using Grado 325i, Grado RA1 and a portable CD player with line-out.  So, the essence of our debate: I believe these particular recordings are awful because I don't hear problems with any other ones, and perhaps his cans or DAC are obscuring details.  He claims the recordings sound fantastic to him, and there must be a problem with my setup: perhaps the bassy response curve of the Denons is revealing noises the recording engineers did not intend to be audible; perhaps the impedance mismatch is causing bizarre, unpredictable distortion or imbalanced response at certain frequency ranges, etc.  It is worth noting that the Grados and the Denons have opposite response curves in the midrange, so perhaps he simply doesn't have to turn the volume up enough to hear the noises badly.

There are perhaps 2 other things worth noting: (1) the low-frequency noise problems seem to be better with my new Voskhods (previously, I was using WE408a's which came with the amp, and one of them was quite microphonic), and (2) the problems I heard on Leonhardt's CDs were not any better when I tried a JRC cmoy amp, which should have near 0 output impedance.

So, can anyone explain this bizarre disagreement between us?  I would be delighted to hear other people's experiences of the LD 1+, the Denons, or especially both together.  And if anyone has listened to lots of Gustav Leonhardt and can settle the question of the recording quality, I'd be ecstatic!  On almost all my other records, the LD 1+ / Denon combo has sounded fantastic.

That is a long and complicated question(s), Maybe it would better to break it down into  4 or 5 separate questions, but still keep it in one thread.

Some (most?) on Head-Fi may just skip your thread/questions because it's just to much of a pain to take the time to deal with your thread.

I'm far from an amplifier expert....but.

As the Little Dot 1+ is a hybrid headphone amplifier, it may make it easier to drive Low Ohm/High Current headphones.
 

 

 

post #5 of 21

In my experience with D2000 I have been switching back and forth between E9 and LDI+ using an E7 dac.  I have found that the LDI+ (completely stock so far) sounds noticably better, especially in the low range.  I don't think anyone definitively knows the output impedance of the LDI+.  The website does say "Suitable Headphone Impedance: 8 - 600 ohms," but this doesn't actually tell us anything about the output impedance.  The website for my E9 says it is suitable for 16-600 ohm headphones, yet it was measured by a pretty popular blogger as having 10 ohm output impedance.

 

So until someone measures the output impedance of the LDI+ we will never really know if it is a good impedance match for low impedance cans.  I will be able to compare LDI+ and E9 to a Corda Arietta (0 ohm output impedance) next week.  I can post my impressions on that if anyone is interested, not that anyone would be (Arietta is discontinued, picked it up off the used forum).

post #6 of 21

As I have just purchased/traded for LD1+, I'd be interested in hearing more on this combination. I did a good bit of research on this forum simply to get actual owner impressions of this combination. The overwhelming majority regards this pairing as well matched. 

post #7 of 21

I love how my Little-Dot I+ performs with my Sony XB-700 headphones (24 ohm).  Great clarity, amazing amounts of power.

 

Interestingly, I've found that 408A tubes tend to give the amp more gain, perhaps because of their 20v heater voltage (compared to 6.3v with EF95, etc).  I would personally recommend giving some EF92/EF91 tubes, or CV4015/CV4014 a try.

post #8 of 21

I just picked up a LD I+ specifically for my Grados, and so far it's a great pairing. It's really an amazing piece for only $109. Built like a tank, fast shipping, the owner (David) provides excellent customer service pre-sale and post-sale, and from what I understand there are lots of cool tubes for rolling. I just added some Telefunken/AEGs last night..so far so good. This is my first foray into Chinese audio, as I typically prefer to buy American, Canadian, or German. But I have to say, it's been a really solid experience out of the gate...great little amp!

post #9 of 21
Thread Starter 

On this page (http://www.littledot.net/forum/viewtopic.php?t=868), David Zhezhe, AFAIK the owner of Little Dot, says the LD 1+ should have an output impedance of 32 ohms.  I understand that being a hybrid design, the 1+ will have lower output Z than most purely tube amps.  My specific question is why 32 ohms would be considered acceptable for 25-ohm cans like the D2000's if a 10:1 ratio is really ideal.  But like I said, the setup sounds good to me, so I can imagine a variety of answers to this question - perhaps the ideal ratio isn't really so important?

post #10 of 21

I'm interested in this. Anyone else care to chime in? 

post #11 of 21
If it's that high why would they say it's for headphones rated at 8-600 ohms? It's much lower than 32, my guess is it's in the lower single digits.

I have a good meter and I'd be more than happy to test it if someone will tell me how.
post #12 of 21
Thread Starter 

Saying that it's acceptable to use "for headphones rated at 8-600 ohms" says nothing about the output impedance of the amp itself; it sounds more like a marketing statement than a measurement anyway.  Since David Zhezhe himself says it's 32 ohms in the link above, I don't see a reason to doubt it, but I'd be happy to hear people's independent measurements.  I'm fairly unlearned in electronics and wouldn't know how to go about doing that.

 

To judge whether the impedance mismatch is a problem, I wouldn't want to rely on just technical measurements/theory, I'd want subjective listening.. but since I am listening for pleasure, I don't want to be hooking up the cmoy constantly for comparison ;)  Eventually I'm sure curiosity will get the better of me.

post #13 of 21
I can understand the LD III having an output resistance of 32ohms, it's an OTL design. However that is ridiculously high for a SS head amp, and that's basically what the LD I+ is. The tubes are in the pre-amp stage only for coloration.
Edited by Magick Man - 4/1/12 at 8:20pm
post #14 of 21
Thread Starter 

Magick Man, I agree normally an opamp should have lower output impedance.  My understanding is that the output transistors which come after the opamp, or perhaps the "Vbe multiplier," cause the elevated output Z.  Some discussion of the LD 1+ circuit can be found here:

http://mail.audiokarma.net/forums/showthread.php?t=274126

post #15 of 21

The D2000 is one of the cans that handles high impedances relatively well, but not well enough for my taste, it depends on the sound signature of the amp.

The subbass is elevated, and so are the high highs. It matches badly with the STX because (from my research) the JRC opamps inflate the bass aswell, and the entire card has a harsh sound signature (A combination of the JRC opamps, and the TI headphone amp.) So it sounds unpleasant.

 

If the LD+ is a little subbass shy, and handles the high high frequencies better, then it should sound good, I have no idea about at low volume levels though.

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