Sabaj A20h Balanced Headphone Amplifier Owner's Thread

[solderdude]

so a series resistor doesn't affect the output impedance ?

It defines the output resistance.

What would you guess the output impedance is for the 3.5mm headphone out on PHA2 ?

Based on a review of the PHA1 I would guess 150ohm.
BUT.... they could have used different values but in any case it will be well above a few ohm for certain.
Needs to be measured or a high res picture of the PCB is needed.

 

[solderdude]

and you are saying the 6.5mm output on PHA2 has the same output impedance as A20d ? What is A20d's output impedance ?

I am saying that it appears that the PHA2 has the same circuit as the headphone out of the A20d.
Archimago did measure the output R of the A20d (6.3mm / 1/4") and it was close to 0 ohm (it really does not matter if it is 0 ohm or a few ohm)

https://archimago.blogspot.com/2022/08/sabaj-a20d-2022-part3.html

 

[LegionOfHell]

Based on a review of the PHA1 I would guess 150ohm.
BUT.... they could have used different values but in any case it will be well above a few ohm for certain.

Isn't 150ohms too much for headphones with high sensitivity and low resistance ?

what does a few ohm means ? what is the minimum ?

 

[LegionOfHell]

I want to use the 3.5mm out on Sabaj PHA2 with the following headphones:

Jvc HAS160
Sony MDRZX110
Koss KSC75/35
CAL! SE & 2
Sen PX100-II

what do you think ?

 

[solderdude]

150ohms would be too much for some headphones.
Also it is not verified that the output R is 150ohm.

In any case I would use the 6.3 output + adapter for 3.5mm headphones, not the 3.5mm output.

The minimum required output resistance is headphone dependent.

 

[half_dog]

I am saying that it appears that the PHA2 has the same circuit as the headphone out of the A20d.
Archimago did measure the output R of the A20d (6.3mm / 1/4") and it was close to 0 ohm (it really does not matter if it is 0 ohm or a few ohm)

https://archimago.blogspot.com/2022/08/sabaj-a20d-2022-part3.html

@solderdude thanks for your inputs!
I had guessed Sabaj PHA2 might had been designed following the guidelines from TI because it was released before the Topping L30 and was common to adopt resistor values around 10 ohm or higher mainly for low impedance headphones. And the high impedance output might not have any resistor - probably it would be enough to avoid the op amp oscillates.

 

[half_dog]

Isn't 150ohms too much for headphones with high sensitivity and low resistance ?

what does a few ohm means ? what is the minimum ?

The problem with high output impedance is that will change the frequency response of the headphone according to its impedance curve. At the resonance frequency there will be less attenuation while at the other region with lower impedance will be more attenuated. At the end you might perceive as a boost at the Fs. Anyway, to avoid it usually is expected a value equal or bellow 2 ohm (for 16 ohm headphones). But with the trend of headphones with even lower impedance (DCA Stealth, Moondrop Para, Truthear Zero (Red) etc.), a near zero ohm value is appreciated.

 

[LegionOfHell]

Alright, I think my priority is the O2 amplifier now, Since I have a bunch of lower impedance everyday headphones that I want to use while gaming and the fact that O2 has 0.5ohm output impedance.

Does the O2 spec better than Sabaj PHA2 ?

Is the Mayflower version of O2 set to medium or standard gain ? out of the two, which gain is more suitable for my headphones ? the headphones you see in my signature plus Jvc HAS160 and Sony MDRZX110 ?

Does the O2 distort when set to 6.5x gain ? is there a way to fix the distortion by inputting a lower Vrms from the DAC ?

Does the O2 pair well with lower impedance headphones at 2.5x gain ?

 

[half_dog]

Sorry for my late reply.

Does the O2 spec better than Sabaj PHA2 ?

I can't confirm 100% because I can't find any independent measurement to compare.

About the O2 in general. It is a good amp but you can get better gear today. If you don't need batteries amps like Atom Amp (a beefer desktop O2 version better in all departments), Magni Heresy or other version, Topping L30 II, SMSL A10H (that's ridiculous cheap now) etc. All those will fulfill your needs.
Honestly, for the quoted headphones a dongle like an Apple dongle, Sonata HD PRO, Meizu HD is enough. All those headphones are easy to drive (low impedance and high sensitivity).

 

[Veri]

@amirm are you aware, is anyone still getting you a Sabaj A20h?

 

[mc.god]

I'm not really confident in interpreting electronic circuits and excuse me if I'll say some nonsense but it seems to me that PAH2 is totally different to PAH1 and even to A20h\A10h.

PHA1 uses different opamp and has high output impedance (150 ohm as Solderdude says) at the 3.5 out probably as an easy way to cut voltage on low impedance loads, not having a gain switch. ( http://dieselpowered.ca/2018/sabaj-pha1-teardown/ )
A20h\A10h use TPA6120, that for TI specs needs a minimum of 10 ohms output impedance for avoiding oscillations, but they use an architecture similar to L30 that permits lowering that to near 0 ohms (as measured in Amir A10h review).
PHA2 uses the same TPA6120 but seems more an implementation on TI guidelines, I suppose it can have about 10 ohms on the 6.3 out and probably similar to PHA1 at the 3.5 out.
It remind me a lot a very basic diy board i bought times ago just for toying with:

https://it.aliexpress.com/item/1005003728321132.html

It has 10 ohm resistors at the output and I measured accordingly with a multimeter applying 10 ohm load.
Just as a side note, I enjoyed assembling it in an aluminium case with a dual 12v transformer, it would even perform well if not for a great flaw in the circuit: they didn't use a servo buffer before the tpa6120 and connect the 50kohm pot directly to it, resulting in high and variable DC offset (200-400 mV) and terrible rustling when turning the pot due to dc flowing into it. As you can see in the PHA2 pictures, it has a proper servo with on opamp before the tpa6120, so at least it should not suffer for this problem...

 

[Audioboxer]

Am I correct to assume that one of these has a bit more power than a topping L50 when using balanced? My L50 has been playing up a bit and I can snag one of these for £76 and it seems like a fun pickup if anything before they go extinct (stock wise).

Funnily enough the cables at the rear setup would work quite well for my at my PC desk given I currently route my headphone cables behind the desk and under.

 

[Roland68]

Am I correct to assume that one of these has a bit more power than a topping L50 when using balanced? My L50 has been playing up a bit and I can snag one of these for £76 and it seems like a fun pickup if anything before they go extinct (stock wise).

Funnily enough the cables at the rear setup would work quite well for my at my PC desk given I currently route my headphone cables behind the desk and under.

It will only have about 2.4W at 32ohm as it contains 2 x the A10h's amplifier. That's about 1W less than the L50, but more than twice as much as the old L30. It should have enough headroom for most headphones, I haven't had a pair of headphones here that didn't have enough.
However, the relay-based volume control with absolute channel equality is worth more than the price.

 

[Audioboxer]

It will only have about 2.4W at 32ohm as it contains 2 x the A10h's amplifier. That's about 1W less than the L50, but more than twice as much as the old L30. It should have enough headroom for most headphones, I haven't had a pair of headphones here that didn't have enough.
However, the relay-based volume control with absolute channel equality is worth more than the price.

I'll be running the A20h on Sundara's so they are balanced output, from my reading so far I know the single output on the A20h isn't great and that's where the L50 has it beaten. But it seems if you're running balanced the A20h should be a bit more powerful? (unless I've got that wrong!).

No Amir review for this one so I've just been picking up info from the forum users so it's possible I've read things wrongly.

edit - You might be right, is it L50 3.2w at 33ohms?

 

[bilifen]

I thought I will use it again while I am at the desk and the noise is back. Scraping the paint from the corners of the back plate and outer shell did not fix it. Well it might have fixed lack of corrosion problem but the noise is still there.

Did you find any fix for the phone noise problem?

It has been a while since I used my A20H but when I had it hooked up it was on a shelf where my phone and several other cellular capable devices lived and I never had a problem. I'm *not* saying you're wrong, but I'd check the U7 or cabling first. Perhaps run the A20H off another source and see if the problem persists.

I changed my Xonar U7 to a M300 SE (v1.1), it was not my (dying) Xonar U7.
With a "different source", do you mean a different power outlet? If so, not possible in this situation, unless I run extension cables through the whole room.

My A20h picks up noise if I place my phone directly on top of the amp. Move it a few cms away, just to the side of the amp and it's gone. So it does appear more susceptible than it should be, but not excessively so that it presents a problem as such. Obviously sticking a phone on top of it is not a good idea anyway.

I remember this aspect of its design being questioned quite early on in the A10h review thread, and those concerns appear to have been pertinent
considering a few users on ASR have reported interference issues subsequently.

I still get noise at ~120cm/ ~4ft, end of my table. Even if I put my phone in to the drawer (which is also at the end of my table), I sometimes hear the noise.

 

[Joel]

Did you find any fix for the phone noise problem?


I changed my Xonar U7 to a M300 SE (v1.1), it was not my (dying) Xonar U7.
With a "different source", do you mean a different power outlet? If so, not possible in this situation, unless I run extension cables through the whole room.


I still get noise at ~120cm/ ~4ft, end of my table. Even if I put my phone in to the drawer (which is also at the end of my table), I sometimes hear the noise.

Are you running everything balanced? Amir still has my A20h so I can't be too helpful.

 

[Joel]

@amirm are you aware, is anyone still getting you a Sabaj A20h?

I sent one to him. Tracking says it arrived. It may not be high priority because they are out of production now (and were never very popular).

 

[bilifen]

Are you running everything balanced? Amir still has my A20h so I can't be too helpful.

Yes, everything is running balanced.

 

[Davywhizz]

I've just discovered the A20H online and have ordered one for delivery tomorrow. £76 from Amazon UK. I've got a pair of almost new Chord RCA cables, but will get some XLRs soon.

I'll be using some Meze 99 classics and a Topping DAC. Just curious to see what the Sabaj can do. The reviews seem too good for the price.

 

[Davywhizz]

Well the A20H arrived, looks great and was easy to set up. But I'm hearing a background noise on all gain settings, louder as the gain increases. It's not a buzz or a hum, more like a constant rapid ticking.

Apart from that I like the sound.

I'm using the DAC from a Topping EX5 in preamp mode with mid price RCAs to the Sabaj, then a good, balanced headphone cable. I've tried cables with both XLR and 4.4 plugs. The DAC output is set to 0db.

All advice welcome. Maybe balanced input would be better; I've ordered some XLR interconnects, but from Ali Express so they will take a couple of weeks.