Vini darko
Major Contributor
Thankyou for the reply @JohnYang1997 I'm still new to in depth measurements and have much to learn.
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WolfX700 Measurement of Topping L30 Headphone Amp
- Thread starter WolfX-700
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Thank you!
Tatteredmidnight
Active Member
Outstanding performance regardless of price, and at its target price point... unbelievable! Exceptional work @JohnYang1997, when you first announced your intention to develop these amps with Topping, I was skeptical, but the proof is in the pudding! Hopefully the channel imbalance issue is limited to this pre-production unit, as that would be a truly unfortunate blemish on what is otherwise an essentially flawless performance! There aren’t enough superlatives to express what you’ve achieved here, you should be extremely proud, and I’m excited to see what the future holds for you.
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What "channel imbalance" are you referring to?
The one mentioned on the first post?
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That one: https://www.audiosciencereview.com/forum/index.php?attachments/rms-level-jpg.70140/
Wich is pretty bad indeed. If the retail units perform similarly, that could be a deal breaker. 9dB attenuation sub 0.5% channel imbalance is bad. Luckily it has a -9dB gain setting.
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@ichonderoga yes, the dotted blue line is the difference in levels between the left and right channels while the red and blue line is the volume button decreasing the levels. It means that only the first 9 decibels of attenuation the channels are somewhat attenuated the same (Y axis left the red and blue decreased 9dB, Y axis right the dotted blue differ 0.5 decibel, which is somewhat the tolerable limit).
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DDF
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I was waiting for the other shoe to drop. Thanks for your generous efforts with this, very helpful.
I still wonder what it all comes to? It's great for filtering out complete junk, but reasonable vendors are now chasing meaninglessly low noise and distortion numbers but the stuff that really matters now gets nowhere near the attention it needs, and I think the focus on thd/noise gives them a place to hide behind:
channel balance vs volume is unspecedground isolation (risk of ground loops) is kept a mysteryfor DACs, driver quality and robustness (custom driver? what are benefits? Standard xmos driver?....)how it deals with dropped samples (overshoot/undershoot and how audible). One dac may sound very different than another when dealing with thisreliability cuts corners (what brand caps and what are temp ratings?)
I've had issues with all the above with various dac and HD amp equipment (all well reviewed). It made these equipments failures and the extra zero in the distortion decimal place couldn't begin to compensate.
Not just L30 specific, so moved to here https://www.audiosciencereview.com/...us-on-sinad-gives-vendors-hiding-space.14271/
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The dashed line belongs to the scale on the right, wich indicates the channel imbalance in dB. Ideally, you'd want to stay <0.5dB.
The solid red and blue lines indicate the volume of the output signal (of both stereo channels). From left (full volume, knob turned all the way up) to right (lowest volume, knob turned all the way down), they go with the scale on the right.
40dB of balanced attenuation would be what I'd call good.
Now to be fair here, this is a pre-production sample, so they might be able to fix that. Also, some channel imbalance is to be expected with analog volume control, at the lower price point that is typical.
On my particular Atom amp for example, the lowest 10% or so of the adjustment range are not really usable due to overwhelming channel imbalance, over that level, no imbalance is perceivable (though I'm sure it is measurable). JDS is using a fairly decent Alps potentiometer, and still there is some manufacturing tolerance.
The solid red and blue lines indicate the volume of the output signal (of both stereo channels). From left (full volume, knob turned all the way up) to right (lowest volume, knob turned all the way down), they go with the scale on the right.
40dB of balanced attenuation would be what I'd call good.
Now to be fair here, this is a pre-production sample, so they might be able to fix that. Also, some channel imbalance is to be expected with analog volume control, at the lower price point that is typical.
On my particular Atom amp for example, the lowest 10% or so of the adjustment range are not really usable due to overwhelming channel imbalance, over that level, no imbalance is perceivable (though I'm sure it is measurable). JDS is using a fairly decent Alps potentiometer, and still there is some manufacturing tolerance.
Channel imbalance is caused by the potentiometer, which is a part that they buy and use. It does not matter much if the rest of the board changes or not, the pot would be the same, and they differ from part to part. I know it is difficult for manufacturers of pots to build reliable and balanced pots on such low prices. The high end ones use volume steps connected to resistors, but this is a lot more expensive and impossible for the budget of a 100usd or so amp.
Vini darko
Major Contributor
This a spec sheet for a £40 high quality pot. Even it has expected imbalance. Its just a part of this type of component. Only a stepped attenuator or digital volume are gonna be close to perfect.
While the result is technically superior I just can't get onboard with feel of a clicky stepped knob over a smooth pot. Relay attenuators even worse from a user experience for me, very disruptive to critical listening. I'd argue that a very good mechanically designed rotary encoder + well implemented digital volume control is best.
Why is a channel imbalance at low volume usually expected for a pot? Does the imbalance at low volumes have something to do with the wiper mechanism?
Vini darko
Major Contributor
I think it has to do with the carbon tracks and how they are laid down.
Same pot is used for a90 and l30. This must be an outlier.
The imbalance between the left and right channels of D90 and L30 has a problem in selecting the volume POT.
The volume POT for volume control must use the taper A, but both use the taper B volume POT. This can be seen immediately by looking at the measurement graph. This is also the reason for the sudden change in volume with respect to the rotation angle.
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