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Review and Measurements of Massdrop THX AAA 789 Amp

Veri

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FUN and CV2 are very noisy. How are they suddenly become low noise?? The only earphone that I can't hear the noise is er4b/s. Even with er4sr will have the noise. Many earphones are very noisy on burson. And FUN is even worse than CV2.
Perhaps with IEMs, with headphones not 'very' noisy from my experience. They're not the most silent, but quite powerful.
 

trl

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Your FUN is probably defective, so feel free to RMA it. My FUN is perfectly compatible with my 120dB/V IEM's.
However, none of the above amps were designed for IEM's.
 

JohnYang1997

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Your FUN is probably defective, so feel free to RMA it. My FUN is perfectly compatible with my 120dB/V IEM's.
However, none of the above amps were designed for IEM's.
I don't have FUN. But i had CV2 for very long time. According to Burson's website, Fun has similar SNR as CV2. CV2 is very noisy compared to o2 atom etc. According to calculation of specs from burson it has 283uV noise. What a joke. No doubt it's very noisy. Even attenuated it's still too high.
 
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I got my 789 and it's really awesome. I have a problem with it though: With my Fostex T20rp mk3 (sensivity: 91db) i can't turn it up to even a little high volumes because the protection switch turns on (if i'm right and that's a protection switch..) and shuts down the HP output for a second, comes back again, shuts down again, and so on. Also the LED turns red for that time. I can't really use it in daytime with higher ambient noise, so it's not that high of a volume. Is there any fix to this?
That was on the SE output, this headphone is not built balanced sadly.

With my other headphone, the Quad Era-1, i have no problem's.
 

trl

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I think it was another member having a similar issue, if I'm not mistaking. Are you sure the plug is perfectly plugged into the socket? Not sure how this protection works, but if it doesn't senses headphones internal resistance (DC-resistance) or if the plug creates a short-circuit, then protection might kick-off. I really think it's plug related issue and not headphones related, but I can't be 100% sure, because I din't know how this protection works.
 
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I think it was another member having a similar issue, if I'm not mistaking. Are you sure the plug is perfectly plugged into the socket? Not sure how this protection works, but if it doesn't senses headphones internal resistance (DC-resistance) or if the plug creates a short-circuit, then protection might kick-off. I really think it's plug related issue and not headphones related, but I can't be 100% sure, because I din't know how this protection works.
Thanks! I will check the plug (it has also an adapter), it was late night and full dark when i tried it. It was at a certain volume level when it kicked-off, i tried multiple times, on all gain settings. I don't think i reached the max output power, because that volume level can reach even a mobile phone, wasn't really that high.
Edit: in Joshua Valor's review, he had some similar problem, but he could avoid that by switching off and on the amp, if i remember correctly. I tried also that, but no effect.
 
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I think it was another member having a similar issue, if I'm not mistaking. Are you sure the plug is perfectly plugged into the socket? Not sure how this protection works, but if it doesn't senses headphones internal resistance (DC-resistance) or if the plug creates a short-circuit, then protection might kick-off. I really think it's plug related issue and not headphones related, but I can't be 100% sure, because I din't know how this protection works.
Oke, so it was either the plug not plugged in correctly, or the amp needed a full power off/on (plugging out from the wall).. now its working as it should, thanks! :)
 

AresHarvest

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Something to check when using those Fostex headphones is how secure the headphone-side plug is. Those twist-lock 3.5mm connectors tend to un-twist sometimes, and then you run the risk of having them come a bit loose. Which as far as I know could trigger the overcurrent protection if the plug's ring makes contact with the jack's sleeve tab, just like it can when the plug on the amp side comes loose.
 

zym1010

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I just received my THX AAA 789 and made some big mistake while trying to compare it with my existing JDS Atom: I plugged JDS Atom's preamp RCA output into 789's "SE Bypass" output (my bad; misunderstood the meaning of "SE Bypass" port). Turns out if you switch 789 to SE input you can hear the sound from the SE Bypass output provided by Atom... The output volume I hear from headphone (provided by Atom's preamp) is really low but I am still worried if this would permanently damage my 789...
 
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AresHarvest

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I plugged JDS Atom's preamp RCA output into 789's "SE Bypass" output. Turns out if you switch 789 to SE input you can hear the sound from the SE Bypass output provided by Atom..
The 789 has SE PASS connectors are wired in parallel with the SE INPUT. Think of it like a set of internal Y-cables... SE INPUT L and SE PASS L are ganged together, likewise with SE INPUT R and SE PASS R. So what you did is no different than plugging the Atom output into the 789 input.

I doubt there's damage, since you said your headphones weren't too loud. That means (unless you were using super low sensitivity headphones) that you weren't pushing too much current or voltage.
 

zym1010

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The 789 has SE PASS connectors that are wired in parallel with the SE INPUT. Think of it like a set of internal Y-cables. So what you did is no different than plugging the Atom output into the 789 input.

I doubt there's damage, since you said your headphones weren't too loud. That means (unless you were using super low sensitivity headphones) that you weren't pushing too much current or voltage.
Thanks. What I am worried is that Atom output has too much current/voltage. In terms of actual sound I hear from headphones (Senn HD800 S), the volume is really low.
 

AresHarvest

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If your HD800S wasn't that loud, then you have nothing to worry about. At 102 dB/V, your headphones would be deafening (119 dB SPL) by the time the output voltage of your Atom even made it to the clipping point of the 789 input in high gain. And you would have a ways to go beyond that before you hurt the 789.

So essentially, your headphones would probably break before the 789 suffered even minor damage. You're fine.
 
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Your FUN is probably defective, so feel free to RMA it. My FUN is perfectly compatible with my 120dB/V IEM's.
However, none of the above amps were designed for IEM's.
I don't have FUN. But i had CV2 for very long time. According to Burson's website, Fun has similar SNR as CV2. CV2 is very noisy compared to o2 atom etc. According to calculation of specs from burson it has 283uV noise. What a joke. No doubt it's very noisy. Even attenuated it's still too high.
I have FUN, and did experienced a strange noise issue with the headphone output. I raised the issue to Burson and they were not sure what was the problem but acknowledge that the noisy headphone output issue was indeed a problem (not normal working condition).

I found this issue during op-amp rolling, and the issue started when I plugged Burson V5i op-amp. FUN does exhibit higher noise with V5i than with other op-amps, up to the level that the level of noise is not tolerable. I was using IEMs for the op-amp rolling. So it seems the issue was with the V5i. I sent the V5i yesterday to Burson for investigation and replacement.

Using other op-amps, testing with my most sensitive IEM, the 1964 Ears V3 universal (Sensitivity: 119 dB spl/mW at 1kHz ) old discontinued model, there is some moderate level of hissing noise that for me is still 'tolerable' considering the high power output of the Burson FUN. Anyway I won't use FUN for such sensitive IEM, simply doesn't make sense. So in my opinion, considering the 2 watt output, that level of noise on a 119 dB spl/mW IEM, FUN can be considered low noise. Again in the context of a 2 Watt output amp. Using other less sensitive IEMs like DUNU DK-3001, the hissing noise is very low and didn't bother me at all.

I did SNR measurement of the headphone output using QuantAsylum QA401, and here is the result:
Headphone Ouput SNR on 33 ohms load (lowest measurement selected) @ 1kHz - 1Vrms (0 dBV) input:
At 2 Vrms (6 dBV) : 97.2 dBA
At 1 Vrms (0 dBV) : 96.8 dBA
At 0.5 Vrms (-6 dBV) : 94.8 dBA
At 100 mVrms (-20 dBV) : 85.6 dBA
At 50 mVrms (-26 dBV) : 79.8 dBA

I probably not very sensitive to hissing noise, for me, based on my own experience with SNR measurement using QA401:
SNR greater than 85 dBA: perceived as totally quiet.
Between 80 to 85 dBA: mild hissing noise might be audible.
Less than 80 dB: mild to moderate audible hissing noise.

So for a 2W amplifier with 79.8 dBA at 50 mV output, in my book it is pretty good. I guess the THX AAA 789 would be a lot better.

Sorry OOT in this THX AAA 789 thread.
 

trl

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V5i is incompatible with many amps, even with my Matrix HPA-3B where a noise appeared initially in one channel, then in the other one too.

Thanks for sharing the info!
 
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