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SMSL SH-9 THX Headphone Amplifier Review

gvl

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Will I be too far off saying a perfectly good female 4 pin XLR connector is wasted here?
 

PeteL

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Ouch... No XLR output! It would have been a perfect match for my newly acquired SU-9 but It would force me to use it via RCA if I want to keep it connected to both speakers and headphones. What a pithy... With that display and stepped attenuator would have been a perfect pre. ‍
there is no rca output neither, only headphones output
 

Rja4000

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Hi
Good review, as usual.
I have 2 questions:
- Did you measure output impedance(s) ?
- How is SINAD evolving with attenuation?
With the type of attenuator, we should see a better performance at lower output level (higher attenuation) then with a more classic attenuator, shouldn't we ?
 

YSC

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One question though, how do they manage a 256 step resistor ladder inside such a small case
 

wasnotwasnotwas

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Ouch... No XLR output! It would have been a perfect match for my newly acquired SU-9 but It would force me to use it via RCA if I want to keep it connected to both speakers and headphones. What a pithy... With that display and stepped attenuator would have been a perfect pre. ‍
It has an xlr output. It's just not balanced, so the same as the 6.35mm in terms of power.
 

wasnotwasnotwas

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PeteL

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One question though, how do they manage a 256 step resistor ladder inside such a small case
I would like to rephrase that. Where is the state of the art in term of signal relays for such applications. It is one component that didn't evolve that much over the years, they have been big and clunky. The resistor ladder don't take much space but I'd like to know what's proper nowadays fr such applications. Amir said quiet. This is good, and yes the smallish case suggest smaller than the usual as well. Do we know what's the go to, reliable, smallish and quiet model to do something like that nowadays?
 

peng

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I did not. It is not a DAC so I usually don't measure that.

Thanks, but are you implying that DACs are more prone to IMD whereas preamps are not, or not a factor typically speaking?
 

boXem

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One question though, how do they manage a 256 step resistor ladder inside such a small case
Probably vertically stacked PCBs.
It's 8 signal relays. And 16 SMD resistors. Doesn't seem that difficult keeping it on the main board.
I had another question on how they would manage to get a fast volume setting with that many steps, and indeed it's slow.
 

PeteL

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It's 8 signal relays. And 16 SMD resistors. Doesn't seem that difficult keeping it on the main board.
I had another question on how they would manage to get a fast volume setting with that many steps, and indeed it's slow.
Are you sure of this? 256 steps? would lead me to think at least 16 relays... 8 per channels...
 

kn0ppers

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In total we are most likely looking at:

16 Relays, 16 Flyback Diodes, 16 MOSFETs
32 SMD Resistors
+ maybe a separate 7812 for all the relays or something

I still think they probably put it on a daughterboard.
 

boXem

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Are you sure of this? 256 steps? would lead me to think at least 16 relays... 8 per channels...
My first reaction was oops, Saturday afternoon. :facepalm:
Then my internet-fu showed me the internals of the beast and it actually seem to actually have 8 relays for the volume control. These are Omron G6K-2F-Y, very small (5.2 x 6.5 mm), and DPDT. So 2 channels can be managed with one relay.
1605366025009.png
 

ZgSTar

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It has an xlr output. It's just not balanced, so the same as the 6.35mm in terms of power.

Yes, what I meant is that to keep both an speaker amp and a headphone amp connected in the same setup starting with SU -9 as DAC it would require one amp being connected to XLR out of the DAC and one to the RCA of the DAC. In my case I would keep the AHB2 on the XLR so this would leave RCA only for headphones amp use. Maybe they are about to come up with a PREAMP in the same series?
 

Labjr

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In total we are most likely looking at:

16 Relays, 16 Flyback Diodes, 16 MOSFETs
32 SMD Resistors
+ maybe a separate 7812 for all the relays or something

I still think they probably put it on a daughterboard.

I think they would need liquid nitrogen cryocooling for all of that!
 
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