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Fosi Audio ZA3 Amplifier Review
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morejazzplease
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I can't find this specification anywhere either. Extremely weird that it is never mentioned in any specs page, youtube review, article or forum thread!
HalSF
Active Member
I've seen this unanswered question about the ZA3 input impedance raised in a number of forums and threads. Why is it important to know this?
This area of engineering is far beyond my understanding, but I'm trying to comprehend why this number, whatever it may be for the RCA or XLR inputs, could be a problem or a significant thing worth knowing.
Impedance bridging - Wikipedia
Jimster480
Major Contributor
Simply for compatibility with certain other source gear and an understanding of the potential level of volume when paired with a specific source gear. For most people the spec doesn't matter, I've seen lots of amps with 60k ohm input resistance. It doesn't affect anything most of the time, as long as the value is safe. Which it obviously is here.I've seen this unanswered question about the ZA3 input impedance raised in a number of forums and threads. Why is it important to know this?
This area of engineering is far beyond my understanding, but I'm trying to comprehend why this number, whatever it may be for the RCA or XLR inputs, could be a problem or a significant thing worth knowing.
Impedance bridging - Wikipedia
en.wikipedia.org
Sokel
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As long as the x10 rule of thumb is in place, voltage transfer is unaffected.I've seen this unanswered question about the ZA3 input impedance raised in a number of forums and threads. Why is it important to know this?
This area of engineering is far beyond my understanding, but I'm trying to comprehend why this number, whatever it may be for the RCA or XLR inputs, could be a problem or a significant thing worth knowing.
Impedance bridging - Wikipedia
Now, high input impedance may offer immunity to the source before that but can also mess nice measuring figures to a point.
Keeping in low along with low gain and you have a happy chart.
But it's way better to be on the safe side, you never know the source you may connect to it.
Edit: a practical example why one may need high input impedance is the use of passive attenuators.
At some point of attenuation they can present a significant rise at output impedance, this combination must be always calculated before hand.
Last edited:
somebodyelse
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It's needed to judge compatibility with DACs and preamps in exceptional circumstances. The usual rule of thumb is to make sure input impedance downstream is at east 10x output impedance upstream. This should avoid too much change of frequency response if impedances change with frequency, and avoid excess distortion that the source output stage may generate if the input impedance is too low. Typically this isn't a problem because most modern sources have a low output impedance (around 100R) and don't start distorting unless the load they're driving is low (maybe 1k), while input impedance is typically 47k, so there's a lot of spare margin. One problem is that recently some manufacturers chasing small improvements in SINAD have started to take advantage of this by making devices with unusually high output impedance, or unusually low input impedance. The combination of two such devices could be a problem. It could also be a problem if you're trying to drive more than one amp from the source as the load seen by the upstream output is halved when driving two of the same sort of amp, or a third with three. Pairing with older sources may also be a problem as they may not be able to drive low loads without added distortion.
morejazzplease
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So I take it, nobody knows? haha
I have a pair of ZA3s in my system and I am evaluating new preamps. I want to make sure I stay above the x10 "rule" of preamp output impedance vs. power amp input impedance. I think it is absolutely wild this spec can't be found anywhere online! I figured if anyone knew, ASR would!
I have a pair of ZA3s in my system and I am evaluating new preamps. I want to make sure I stay above the x10 "rule" of preamp output impedance vs. power amp input impedance. I think it is absolutely wild this spec can't be found anywhere online! I figured if anyone knew, ASR would!
HalSF
Active Member
All I can contribute is that I’ve got a Schiit Saga 2 preamp feeding a Fosi ZA3 amp in stereo mode, powering MoFi Sourcepoint 8 speakers with no problems or apparent issues in terms of adequate power. I did a lot of reading on the ZA3 before buying and the only serious warnings I encountered pointed out that very hard to drive speakers might be too challenging for this amp. The implication I draw is that the input impedance of the ZA3 is well within a conventional range in terms of not posing difficulties for preamps also in a normal range for home audio.
The absence of this spec is frustrating, but I suspect that if and when the number emerges it’s not going to reveal a lurking outlier problem.
To be fair, SourcePoint 8 isn't a very hard load. I have the exact same speakers.
HalSF
Active Member
Voila! I just emailed Fosi Audio Support and received this prompt reply:
The input impedance for the ZA3 is as follows:
- RCA Input: 47kΩ
- XLR Input: 20kΩ
I'll be interested to see if others more knowledgeable than I am can offer any insight on these specs.
HalSF
Active Member
Uh-oh, received a second somewhat cosmic response from Fosi that leaves my poor non-engineer brain even more muddled:
ZA3 Input Impedance
- RCA Input Impedance: 47 kΩ
- XLR Input Impedance: Approaches infinity, so a specific numerical value cannot be provided.
morejazzplease
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Infinity? Haha what are they smoking? I continue to lose faith in this company...
Losing faith in Fosi because they listen to their customers to make innovative products that test well without breaking the bank?
I don’t know what they’re smoking either, but hope they keep at it.
Hi,
Question if I may and if you wanted a Fosi mono setup, would you get two ZA3 or V3 monos?
Question if I may and if you wanted a Fosi mono setup, would you get two ZA3 or V3 monos?
Dual V3 Monos would provide PFFB for load-independent frequency response. Dual ZA3s do not.
I prefer V3 mono because:
- Real mono amp (doesn’t have switch mono/stereo)
- Doesn’t have that f’k single hole sub-out. I hate it so much
Thank you
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