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Review and Measurements of Meier Corda Jazz Amp

MRC01

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Being a voltage source it does NOT have to work any 'harder'.
300 Ohm and 600 Ohm is not a problem at all for any amplifier.
...
My point was, maintaining the same voltage across half the impedance requires delivering twice the current. So in relative terms, when driving my HD580s the amp does have to work harder at 20 Hz than it does at 100 Hz.
Though in absolute terms, I agree, the impedance is high enough to make it an easy load. Portable devices can't drive the HD6xx well, so they get a reputation for being "inefficient". But they're actually not inefficient. They have low voltage sensitivity. But their impedance is high enough that the don't draw much current, making them reasonably efficient. Even though the LCD-2 plays louder at the same volume setting, it's actually less efficient than the HD6xx.
 

Soniclife

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I think JDS are missing a trick, they should put the Atom internals in a fancy metal box ballasted down to weigh a few kilos and charge $$$$$$$$$$$$$'s for it. Add wooden side panels, champagne gold finish and stick a couple of VU meters on the front and it'd be just tip top. Never underestimate the sonic benefits of champagne gold finish, wooden side panels and VU meters, some will try and tell you it doesn't make any audible difference but to the true golden eared audiophiles among us these things definitely add more pace and rhythm, lifting a veil and move you two rows forward.
I'm truth if there was a version in a nicer case, with a better quality vol pot, for double the money I think it would be very tempting for many people. I'd love to see the market tested with total honesty from the manufacturer, that they sound the same, but one is just a bit more luxurious, and see how the sales figures go.
 

Brianc

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I know they're probably not recommended on this measurements-oriented site, but a lot of people like OTL tube amps with higher impedance phones like the HD6xx. Is there possibly some measured shortcoming of those amps that actually improves the sound subjectively? I realize this falls under the "some people like distortion" explanation possibly, but, as someone new to the tech aspects, I wondered if there is a specific measured shortcoming that could be pointed to as an explanation for some people's preference for those amps. And though I assume this is less likely with solid state amps like the Jazz, could a solid state amp, in theory, have the same measured flaw that may cause some people to prefer OTL tube amps?
 

MRC01

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Almost 20 years ago, I had a tube amp that I could recommend now, if you can find one. Pete Millet's Wheatfield HA-2. It is everything a tube lover could want: SET and OTL. Well matched for high impedance headphones like the HD-6xx. For people who like that sort of thing, it's just the sort of thing they like.
EDIT: sorry, posted this in the wrong conversation.
 
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solderdude

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I know they're probably not recommended on this measurements-oriented site, but a lot of people like OTL tube amps with higher impedance phones like the HD6xx. Is there possibly some measured shortcoming of those amps that actually improves the sound subjectively? I realize this falls under the "some people like distortion" explanation possibly, but, as someone new to the tech aspects, I wondered if there is a specific measured shortcoming that could be pointed to as an explanation for some people's preference for those amps. And though I assume this is less likely with solid state amps like the Jazz, could a solid state amp, in theory, have the same measured flaw that may cause some people to prefer OTL tube amps?

Preference for something can be based on a LOT of factors (more often than not based on knowing/seeing).

OTL tube amps usually can supply a LOT of voltage in high impedance headphones giving it 'authority' in the lows. They can play a lot louder than most SS designs without clipping.
Also these tube amps also show mainly 2nd harmonic distortion and in much lower level 3rd harmonic when playing loud.
As most instruments have lots of harmonics these added harmonics aren't that sound degrading as one might expect.
However, aside from harmonic distortion there is also IM distortion which is not 'musical'.
At lower volume there is very little distortion added though.
Disadvantages could be noise levels, microphony and longevity of tubes.
Aging can go quickly, abrupt or take quite a long time.

Then there is the warm 'glow' of tubes together with it's reputation.
Don't forget the 'quality feel' you get handling/lifting these which adds to the idea you are handling 'something good'

And yes, one can get very low distortion with tube amps and also can build SS amplifiers with similar bandwidths and distortion 'character' as some tube amps.

What one rarely sees is that tube amps owners compare their amps in truly blind and level matched conditions.
If they did I am quite sure most goldeneared listeners may not be able to distinguish between quite a few amps.

As always aside from several gems, good performers there are also crappy designs both in the SS and tube amp camp.
This can be irrespectable of its price.


The strong point of the Jazz is crossfeed (some like this, others don't) usage with lower impedance headphones and sensitive IEM's.
Disadvantage is it won't attenuate all the way down to quiet which may be an issue with sensitive IEM's and it cannot supply a large voltage swing so high impedance headphones will not play loud and with 'authority'.
 

MRC01

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...
The strong point of the Jazz is crossfeed (some like this, others don't) usage with lower impedance headphones and sensitive IEM's.
Disadvantage is it won't attenuate all the way down to quiet which may be an issue with sensitive IEM's and it cannot supply a large voltage swing so high impedance headphones will not play loud and with 'authority'.
The Jazz has a high/low gain switch, and on low gain it attenuates down low enough for most IEMs. Unlike analog volume pots, it has perfect channel balance down to its lowest setting. If I understand how its unique volume control works, changing the gain/feedback loop instead of attenuating a fixed gain, the lower you turn down the volume, the less gain and more negative feedback it has, which should mean lower distortion and wider bandwidth. All this makes it one of the cleanest (best SINAD) amps Amir has measured, at low to medium volume settings.
The primary drawback to the Jazz is its limited voltage output; the HD6xx series is about the lowest voltage sensitivity it can reasonably drive. Anything lower and you'll need a different (higher output) amp.
 

Brianc

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The Jazz has a high/low gain switch, and on low gain it attenuates down low enough for most IEMs. Unlike analog volume pots, it has perfect channel balance down to its lowest setting. If I understand how its unique volume control works, changing the gain/feedback loop instead of attenuating a fixed gain, the lower you turn down the volume, the less gain and more negative feedback it has, which should mean lower distortion and wider bandwidth. All this makes it one of the cleanest (best SINAD) amps Amir has measured, at low to medium volume settings.
The primary drawback to the Jazz is its limited voltage output; the HD6xx series is about the lowest voltage sensitivity it can reasonably drive. Anything lower and you'll need a different (higher output) amp.
I've been using the Atom as a pre-amp for the Jazz, so I still have the crossfeed available on the Jazz. I'm getting robust output at 9oclock on the volume setting (12oclock with the HD650s). I assume this is because I'm getting extra gain from the Atom. Would there be other sonic advantages? Any disadvantages? I certainly don't hear any negative qualities. Newbie question, I know.
 

solderdude

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Yes, that will do the trick for the Jazz. The output stage has lots of headroom and can supply quite a lot of voltage, if it weren't limited by the gain and input voltage. As long as one does not overload the input amp circuit it can provide a higher voltage than one could normally get from line-level sources.

When you don't hear negative qualities it is no problem to use it this way. At least it will play a bit louder with HD650's. I have no idea how far one can push this though.

Another option could be to let the Atom drive the headphones and use software X-feed.
 

Brianc

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Yes, that will do the trick for the Jazz. The output stage has lots of headroom and can supply quite a lot of voltage, if it weren't limited by the gain and input voltage. As long as one does not overload the input amp circuit it can provide a higher voltage than one could normally get from line-level sources.

When you don't hear negative qualities it is no problem to use it this way. At least it will play a bit louder with HD650's. I have no idea how far one can push this though.

Another option could be to let the Atom drive the headphones and use software X-feed.
Thanks. This also allows me to use the Jazz's superior volume control.
 

solderdude

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Yep, and you can turn the volume all the way down as well if needed.
 

MRC01

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I thought the onset of distortion with the Jazz started at 3.7 V output. Does feeding it a louder input signal increase this level? Put differently, is the voltage clipping distortion caused by total voltage, or by gain ratio?
 

Brianc

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I thought the onset of distortion with the Jazz started at 3.7 V output. Does feeding it a louder input signal increase this level? Put differently, is the voltage clipping distortion caused by total voltage, or by gain ratio?
Beyond my ability to answer. But I can tell you this: if I turn the Jazz volume control past 1 oclock there is audible hum. I don't get anywhere near that setting using the Atom preamp outputs to feed it. I went back to the St. Vincent performance on ACL I mentioned in a previous comment, which needed the volume pushed well past 1 oclock even with the Atom. With the Atom as preamp, eleven o'clock is plenty of volume on the Jazz.
 

MRC01

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When I measured my Jazz several years ago when I first bought it, the onset of this distortion was at the 2:00 to 3:00 knob position, the same in low or high gain. High gain is about 16 dB louder. This suggests it may be a voltage limitation in the gain-feedback loop, and the gain switch changes the final gain applied after that stage. Indeed, Jan said earlier:
... Unfortunately multiplexer IC's have limitations with respect to their supply voltages and as a result the output voltage of the first amplification stage of the JAZZ is limited. ...
If so, and since the Jazz sounds cleanest its lowest volume settings, the ideal Atom-Jazz configuration would be to set the Atom to low gain, using a high volume setting, connected to the Jazz at a low volume setting. Set Jazz gain to low if that's enough, high only if necessary. I use Jazz low gain with my LCD-2 headphones and it is plenty for me, I rarely get it to 12:00. The HD6xx are only 3.5 dB quieter at the same volume position.
 

solderdude

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The input circuit of the Jazz is an inverting input with a so-called virtual ground.
The volume control circuit is only in the feedback loop and thus R feedback/R input determines the output voltage of the first stage.
This first stage is the limiting factor together with the op-amp circuits behind it (also inverting circuits).
More current in the input stage (= more voltage across the input resistor) = a higher output voltage which is limited by the power supply voltage, possibly the volume control feedback electronics and the gain of the following stage.
The higher distortion at higher output voltages makes me think that the volume control (the way it is set up) may well be responsible for the higher distortion at higher SPL.

The position of a volpot does not say much. One has to take into account the gain of the amp and the volume control type (there are various log-type tapers) and the applied input voltage,
 

MRC01

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When the distortion sets in, it kicks in hard and fast. It's not gradual or subtle, and it's easy to hear. Play a test signal with any 2 pure frequency components (say, 500 Hz and 1 kHz) and you can hear the differences tones (distortion) when the level exceeds the threshold. You can experiment with this: fix the input volume and slowly turn up the Jazz volume knob until you hear it. Or fix the Jazz volume knob and slowly increase the input level until you hear it.
All else equal, I'd expect the "best" sound below this threshold to be with Atom volume high, Jazz volume low.
 

Brianc

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When the distortion sets in, it kicks in hard and fast. It's not gradual or subtle, and it's easy to hear. Play a test signal with any 2 pure frequency components (say, 500 Hz and 1 kHz) and you can hear the differences tones (distortion) when the level exceeds the threshold. You can experiment with this: fix the input volume and slowly turn up the Jazz volume knob until you hear it. Or fix the Jazz volume knob and slowly increase the input level until you hear it.
All else equal, I'd expect the "best" sound below this threshold to be with Atom volume high, Jazz volume low.
I do indeed set the Atom input volume to max but on low gain. I have to use high gain usually on the Jazz, at least with the HD650s.
 

MRC01

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PS: the comment below regards the JDS Atom, not the Corda Jazz. I've owned the Jazz for 6 years of daily use with no problems at all.
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Speak of the devil (sounds great but build quality seems questionable) and he appears (the high/low gain switch is now stuck in low gain).
I don't mind much since I only use low gain. But it confirms that JDS Labs did get a bit too aggressive when making this amp inexpensive. I'd gladly pay an extra $100 for the same amp with higher quality knobs, switches and case.
 
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Silou

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I'd gladly pay an extra $100 for the same amp with higher quality knobs, switches and case.
I would not. No need to raise the price for something that does not increase the performance or lifetime of the product. Just appreciate the great value. Same goes for the Tone Board imo.
 

MRC01

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I would not. No need to raise the price for something that does not increase the performance or lifetime of the product....
I agree in principle, but the switch on mine actually broke only the 2nd time I pushed it (gently), making it hard to appreciate the value. ;)
 

Silou

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Where did you buy it? JDS Labs is known for their great customer service.
 
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