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Fosi Audio LC30 Speaker/Amp Switcher & Meter

Rate this speaker/amp switcher and meter:

  • 1. Poor (headless panther)

    Votes: 26 20.2%
  • 2. Not terrible (postman panther)

    Votes: 22 17.1%
  • 3. Fine (happy panther)

    Votes: 57 44.2%
  • 4. Great (golfing panther)

    Votes: 24 18.6%

  • Total voters
    129

amirm

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This is a review and measurements of the Fosi Audio LC30 Speaker and amplifier switcher plus "power" meters. It was sent to me by the company and costs US $150.
Fosi LC30 VU Power Meter ZA3 stereo speaker amplifier selector switch review.jpg

As you see, this is a gorgeous unit, sporting prettier meters than a lot of what vintage audio gear used to have. I always considered a meter with flat line markings as cooler. :) Both the case and switchgear have a higher quality feel than what I expected. Hitting the selector buttons causes reassuring relay clicks internally. The on/off switch doubles as 3 steps of back light plus off. The gain control has wide range and seems to work better than some of the others I have tested.

The unit is powered by a USB-C connector:
Fosi LC30 VU Power Meter ZA3 stereo speaker amplifier selector switch back panel review.jpg

You have a choice of two amplifiers and two speakers.

I spent a few minutes to see if the meters show the correct power wattage and they are hopelessly wrong. I would calibrate my amplifier output to a wattage displayed on the meter but when I changed it, the amount of change on the display was wildly different. Contacted Fosi to see if there is an impedance they calibrated to and the answer was: it is not calibrated to anything. It is just for fun.

And fun it is to watch those beautiful meters move. Sensitivity seems good with decent speed.

Fosi Audio LC-30 Measurements
I spent two days trying to measure the impact of LC30 on amplifier performance. I used the Purifi reference design amp to drive the LC30. As I had predicted and feared, the Purifi performance is so good that even slightest change in the impedance of its speaker connection causes third harmonic distortion (seen below). I bought more connectors and built new short speaker cables. I tightened and tightened the connections. Swapped wires and ran a bunch of experiments. But at the end, the impact could not be avoided:
Fosi LC30 VU Power Meter Purifi Power Noise and Distortion Measurement.png


There is a dashed blue line which shows the performance of Purifi amp direct. The red mark is the impact of LC30 if you use it as a switcher by routing the speaker output through it. The so called "VCR" (Voltage Coefficient Resistance) shows up more and more as power increases due to resistance variations based on voltage applied. I tried the Topping B100 with same effect. Then I realized that you don't need to use the unit as a switcher. My speaker connectors have a rear banana jack (i.e. they can pass the signal through) so I connected that to LC30. With speaker cables now remaining on the amplifier, we get the performance in green that is overlaid on dashed blue, indicating no impact.

Notice how the noise level is not impacted at all despite the extra cables even in switched mode (the graph before 10 watts). So the issue is only distortion. I am using locking banana connectors above and still registered an impact. If you use anything else, expect a bigger hit. In one case, the connector was a bit less tight and I registered massive distortion and half as much power! So if you are going to use it as a switcher, with a high performance amp, you really need to go the extra mile to get an extra tight connection all around (connector and wire to connector).

Now, if you don't have such a high performance amplifier, then the issue is much less significant to the point of not mattering. Here is LC30 as a switcher in the output of Fosi's own ZA3 amplifier:
Fosi LC30 VU Power Meter ZA3 Noise and Distortion Measurement.png

As you see there is no performance hit even though I have all the extra cables and connectors. Also, some amplifiers will be less impacted by extra connections and cables.

For kicks, I also ran a crosstalk test with Purifi using LC-30 as a switcher:
Fosi LC30 VU Power Meter Purifi Crosstalk Measurement.png


But note that I did not make an attempt to separate my jumper speaker cables so some of this may be due to that.

Given the passive way you can connect the LC30, i.e., not using it as a switcher, I don't see a reason to run other tests.

Conclusions
The LC30 from Fosi brings us a high quality fun meters with switching ability. If you just want dancing meters, I suggest tapping from the amplifier speaker binging to LC30 and not routing your signal through it. That's the way I would use it. If you are going to use it as an AB switch, you should invest in proper set of short cables. Be careful for any AB quality tests as there can be an audible impact here if utmost attention is not paid to wiring (no fault of this unit but in general).

And oh, don't try to use it as a power meter. It is not for that.

The build quality is excellent and the unit is one of the most beautiful of its kind.

I am going to recommend the Fosi LC30 meter and speaker/amplifier switcher for fun factor.
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As always, questions, comments, recommendations, etc. are welcome.

Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
 
A big thank you to Amir for the review.

Here is the exclusive 20% discount promo code for ASR members:)(it applies to either yellow or black meter version)

ASRLC30S

Official site; https://fosiaudio.com/products/fosi-audio-lc30-amplifier-speaker-switcher
Amazon US: https://www.amazon.com/dp/B0CZRMSHJB
Amazon CA: https://www.amazon.ca/dp/B07VHG2LR9
Amazon DE:
https://www.amazon.de/dp/B0CZRMSHJB
Amazon UK:
https://www.amazon.co.uk/dp/B0CZRMSHJB
Amazon AU: https://www.amazon.com.au/dp/B0CZRMSHJB
Amazon FR: https://www.amazon.fr/dp/B0CZRMSHJB
Amazon ES: https://www.amazon.es/dp/B0CZRMSHJB
eBay: https://www.ebay.com/itm/296282348992
Aliexpress:https://www.aliexpress.com/item/3256806475124737.html
 
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Contacted Fosi to see if there is an impedance they calibrated to and the answer was: it is not calibrated to anything
That's a shame, but understood it's a visual dancing meter bit of fun and not a serious meter. Good to see it tested anyway, cheers.

Some pics from Fosi marketing material on Amazon;

1727917728383.png


These further pics are from the other thread here and were provided by @Elgrosso;

1727917771718.png


1727917791619.png


1727917809595.png


1727917825108.png



JSmith
 
I want this, but including this into a digital system is not trivial…
 
Amir,

Thanks very much for the review and Fosi has been hard at work making this unit model for more transparent and that was the major complaint of the previous model. Fosi is listening to her customers and that’s a great sign and we all win in these types of customer dynamics. Congratulations Fosi. :cool:

Now build one that can take 500 watts @4 ohms please. Must admit I love the look and style here. Is it possible to give us led lighting option for variations of color selection for the backlighting. Or better yet an OLED screen with color selection and variations of vu meter styles. Of course charge extra for this. Like a Pro model.

Thanks Fosi for listening to your customers and delivering a superior performant revision model. Cheers Fosi!
 
I have the NEOHIPO ET30 still in the box from Christmas. Lol.

Guess I need to break it out.
 
Why only tests @8Ohm?
Because that is the measurement that has Purifi as a reference. 4 ohm results would likely aggravate the situation with extra cables/connections.
 
In one case, the connector was a bit less tight and I registered massive distortion and half as much power!
An interesting and useful lesson regarding quality of speaker connections when using high quality, high power amplifiers!
 
For kicks, I also ran a crosstalk test with Purifi using LC-30 as a switcher:
Fosi LC30 VU Power Meter Purifi Crosstalk Measurement.png


But note that I did not make an attempt to separate my jumper speaker cables so some of this may be due to that.

Did you have the dummy loads connected to the amplifier channels when running these two tests?
 
I spent a few minutes to see if the meters show the correct power wattage and they are hopelessly wrong
Hi Chief, what's the easiest way to measure power wattage sent from an amp to speakers? So that we know how much top wattage is actually being sent to a speaker at the given listening level? Thanks.
 
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Hmmm ... meters that don't measure and a switcher that may degrade performance (may, I get that) ... but it looks fun ... for $150

Not for me, I just don't get the point. It's better than a McIntosh light box though so, if it makes you happy then that's cool.
 
Did you have the dummy loads connected to the amplifier channels when running these two tests?
Yes. All the tests were run with dummy load as indicated in the Graph title.
 
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