[davehutch]

There is something about OTL amps that needs to be taken into account.
OTL amps are Current Amplifiers.
That means, theoretically and upto their max current capability, the power goes up as load impedance goes up. SSD amps, standard tube amps with transformers are the opposite, as they are Voltage Amplifiers!
A voltage amplifier's output increases as the load impedance decreases, again upto their max current capability (can't escape that).
Examples:
- OTL amp with rated power output of 200mW at 20 ohms, will output 400mW into a 40 ohm load & 100mW into a 10 ohm load.
- SSD amp with rated power output of 200mW at 20 ohms, will output 100mW into a 40 ohm load & 400mW into a 10 ohm load.
That is all else being equal, under theoretical conditions.
OTL amps feeding transducers of varying impedances, will affect the tone, SSD amps won't. (inside their operating zones).
This could explain why you had such an experience.

I see. That makes sense. So in theory there is no reason to discount an OTL tube amp for planars as long as they have a relatively low impedance and a relatively high efficiency?

 

[Daniel Johnston]

Funny you say that about OTL amps. I tried the Feliks Audio Elise and although the output is quoted as 200mW, it played far louder and smoother and more impactufullywith my HEKSE than either the hybrid or the SS amp I tried.

That was one of the OTL amps I tried with the Mojo2. The Diana V2 and Utopia had a special synergy that was mind blowing good. Other than lack of bass, the Grado 3000 series I tried with the combo was quite good.

The Folkvangr/Mojo 2 combo is also crazy good with the Utopias. Loudness is tricky. It’s not just about SPL but distortion as well. Subjective loudness also is tricky. Good planar transducers with amplification can have fairly high SPL but not feel “loud”. Magnepans are famous for this.

 

[Daniel Johnston]

I see. That makes sense. So in theory there is no reason to discount an OTL tube amp for planars as long as they have a relatively low impedance and a relatively high efficiency?

Yes and no. Not that simple.

My go to is the Meze Liric with the Folkvangr. I think it’s tonally spot on with a wide soundstage and great detail. Someone else could hear quite different. The load presented by the planar to the OTL will significantly impact sound in terms of bass control (quantity and quality). Harmonic distortion can affect perception of soundstage.

The only thing you can infer from your experience is that you like the Feliks pairing with the HEKSE. In general, you get the best performance from higher impedance headphones with OTL. It doesn’t mean non ideal headphones can’t sound good. Oh yeah, your choice in music plays a huge part.

 

[Kentajalli]

I see. That makes sense. So in theory there is no reason to discount an OTL tube amp for planars as long as they have a relatively low impedance and a relatively high efficiency?

OTLs have a lowest impedance capability, below which, they should not be used. Indeed "rated output power" for an OTL is a little bit confusing. They should quote max. current and min. impedance.
OTLs don't like low impedances, so a flat impedance above their rated impedance handling is fine.
Their best use is indeed with a planar headphone of not too low impedance. That's where they are happiest. Getting them to stay balanced and have low noise is the ultimate trick.
They tend to go out of balance and become noisy. Also if they blow up, they take the headphones with them! But in ideal working conditions, they are sweet! sweeter than a standard tube amp.

 

[Daniel Johnston]

OTLs have a lowest impedance capability, below which, they should not be used. Indeed "rated output power" for an OTL is a little bit confusing. They should quote max. current and min. impedance.
OTLs don't like low impedances, so a flat impedance above their rated impedance handling is fine.
Their best use is indeed with a planar headphone of not too low impedance. That's where they are happiest. Getting them to stay balanced and have low noise is the ultimate trick.
They tend to go out of balance and become noisy. Also if they blow up, they take the headphones with them! But in ideal working conditions, they are sweet! sweeter than a standard tube amp.

I'm pretty confident modern well engineered and built OTL amps don't blow up headphones. Nor is noise an issue unless the tube is highly microphonic or going bad.

Also many will violently and vigorously disagree that planars and OTL are ideal parings.

A strong IMHO and YMMV need to be added to your otherwise sound thoughts.

 

[Kentajalli]

I'm pretty confident modern well engineered and built OTL amps don't blow up headphones. Nor is noise an issue unless the tube is highly microphonic or going bad.

Also many will violently and vigorously disagree that planars and OTL are ideal parings.

A strong IMHO and YMMV need to be added to your otherwise sound thoughts.

Well engineered ones surely are good.
But OTL by default need to be perfectly balanced in the output stage or DC currents will flow out into headphones. So well engineered ones need to have a balancing circuit.
OTLs (output transformer less) do not have an output transformer to protect both the headphones and the amp.
To keep DC at bay, OTLs need to be perfectly balanced on the inside.
Noise can also creep in if not balanced.
OTLs are more challenging to design and build.

 

[flyte3333]

Mojo2 has SNR around 82dB with 50mV output. Depending on IEM, you may hear hiss...

There are high quality amps now that have > 90dB SNR at 50mV which may result in no hiss with sensitive IEMs.

Safe to say an external amp may be better in that scenario unless someone prefers to hear hiss just because Rob said an external amp will make things worse.

Having said that, no hiss with Mojo2 and Hugo2 with my IEMs but there are much more sensitive IEMs out there than mine.

 

[SecretAgent]

Proud owner of Mojo2 here. Would you say is powerful enough for hd800s or maybe I should go for something easier to move such as lcdx or clear? Thanks

 

[Chibs]

Hey guys,
I'm AB testing the Chord Mojo against an other DAC that was sent to me and ran into a question. Now I normally have the Mojo 2 set to indigo when needing line out to my Amp but the DAC I'm comparing is fixed volume and runs louder. If I set the Mojo 2 to light indigo on left and white on the right I don't have to adjust volume on the integrated amp (making A/B faster) but I don't want the thing to clip. Am I better off volume matching after switching inputs and leaving the Mojo set to indigo?
I'm thinking the Mojo 2 is probably clipping at this volume and not optimal. I think i just answered this one myself lol.
On that note, hope everyone is enjoying their Mojo 2's!

 

[Chibs]

Proud owner of Mojo2 here. Would you say is powerful enough for hd800s or maybe I should go for something easier to move such as lcdx or clear? Thanks

Definitely, I have HD-800s and no problems there unless you're craving more base. But that's a different set of cans type of solution..

 

[SecretAgent]

Definitely, I have HD-800s and no problems there unless you're craving more base. But that's a different set of cans type of solution..

That's great news thank you

 

[joseluishs]

Proud owner of Mojo2 here. Would you say is powerful enough for hd800s or maybe I should go for something easier to move such as lcdx or clear? Thanks

The HD800s is ok with Mojo 2 but don’t expect the biggest stage. Thankfully the EQ in the Mojo 2 helps with the bass. Also, the slight sense of warmth of the Mojo 2 complements the HD800s very well.

 

[Kentajalli]

Proud owner of Mojo2 here. Would you say is powerful enough for hd800s or maybe I should go for something easier to move such as lcdx or clear? Thanks

LCD-XC or X surely. good headphones, almost no distortion or resonances, easy peasy to drive. Mojo2 is more than ample.
Though Mojo2 can drive the Focal Clears (is that what you meant?), The Clears are in no way in the same league as HD800 or either LCDs.

 

[rmkjr]

Mojo2 has SNR around 82dB with 50mV output. Depending on IEM, you may hear hiss...

There are high quality amps now that have > 90dB SNR at 50mV which may result in no hiss with sensitive IEMs.

Safe to say an external amp may be better in that scenario unless someone prefers to hear hiss just because Rob said an external amp will make things worse.

Having said that, no hiss with Mojo2 and Hugo2 with my IEMs but there are much more sensitive IEMs out there than mine.

Only thing I noticed when I tried this path to deal with very sensitive IEMs that I could hear the Mojo2's noise floor on, the external amp simply amplifies the hiss of the Mojo2

I picked up the new CA Fathoms, and they are the most sensitive IEM I have had to date. They pickup noise floor hiss on basically everything I have (only the Lotoo PAW S1 was quiet). And the Mojo2 was my worst offender in this case. When I connected my Mojo2 to a Cayin C9 (spec'd as 122 dB SNR on Low Gain SE) I heard the same hiss as Mojo alone if not a bit louder.

My end solution was to put a iEMatch+ 3.5 in between the Mojo2 and the Fathoms. The attenuation removed the hiss, and the 2.5ohm output impedance on the high setting actually works in the Fathoms advantage. Resulting in a very smooth, cohesive, and prominent vocal presentation. Where the low setting at 1ohm tightens up the vocal area bringing it less forward, and bringing the bass up a bit. Pair that with the Mojo2's EQ, and you can get things pretty much where you want them (ie bass shelf up and down based on the iEMatch setting and preference). Note, the OI changes are probably less of an impact with higher Z IEMs, but then so is the Mojo2's noise floor. I also noticed, while I have heard the iEMatch hit dynamics a bit on other sources, the Mojo2's high transient precision seems to make up for that quite a bit. The dynamics reduction is still there, but it is either something I end up liking, or small enough that I just don't notice it outside of A/B.

 

[flyte3333]

Only thing I noticed when I tried this path to deal with very sensitive IEMs that I could hear the Mojo2's noise floor on, the external amp simply amplifies the hiss of the Mojo2

Yeh in that case things are quite bad. Mojo2's SNR of around 82dB is too poor for such sensitive IEMs.

IEMatch gets rid of Mojo's hiss but now significantly increases the output impedance (as you noted) and probably affects frequency response for low Z IEMs, hence time domain response (since both are inversely related )