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Audio GD SA-31 head amp/ preamp . A powerfull Head Amp with Diamond Difference design . - Page 8

post #106 of 434
Originally Posted by Kingwa View Post

If the gain is 10DB, the source and the signal cable total have 0.1MV noise level, the amp will output around 0.3MV output ( assume the volume is on max position ).

If the gain is 30DB, the noise become 3MV .


The source noise is fixed, the good shield signal cable can have less noise while transfer the signal .



Nowdays, the amp design usually is refer the input signal level around 2V to 3V because most dedicated source have refer this standard  , if the source have quite low output , like 0.7V ,the amp can't have enough gain for the large power output .


If design refer 0.7V input level design, while connect with 2V output level source, the volume just turn several steps, the output have very loud .


This is different to the DAC built in amp , Its DAC output level is fixed  so can easy design the total gain  .


Ok thanks for the clarification Kingwa!


So will there be an difference if I connect it like this


Smartphone---NFB-16(DAC mode)---SA-31---HE-500/Pro 900/LCD-2s,etc


or just simple




Does the NFB-16 in DAC mode has any effect on incoming gain?


Additionally would you recommend me a custom gain setting for this configuration?



Edited by conquerator2 - 10/28/12 at 3:36am
post #107 of 434
I understand, but when I have used other amps of various sizes and power and can get an appreciable volume out of my headphones with the analog sources I use, and cant do the same with the SA31, its problematic, leaving me with being unable to use my expensive amp for anything but a few sources.

I would have to stick to very easy to drive headphones for my phone and other portable devices, or buy a secondary amp that WILL drive them loud enough. This is unnacceptable to me. I got rid of my other amps BECAUSE I thought the SA-31 would have both power and volume for all my devices. All my other amps (aside from the lowly E5, and E7) had the volume for all except the most demanding headphones in the same situations that the SA31 couldn't provide enough volume for. Even the E17 drove the 600ohm to appreciable volume levels off those weak portable sources.

Yes, power =/= volume, but what good is power, if I can't get an appreciable volume? If the SA-31 is THAT picky, then it's not for me. I may as well have gone back to the Lyr.

Now, I'm stuck in probably having to lose MORE money just to ship it back.

Even if it does miraculously drive the HE-4 louder than the 600ohm, it's still useless for my weak sources.
Edited by Mad Lust Envy - 10/28/12 at 4:34am
post #108 of 434

The phone, game player and the tablets usually have low output level because the battery voltage limit.

It need the amp have more than 20DB gain for well well but if connect to dedicated DAC or CDP, 20DB is too loud for normal sensivity headphones.


The NFB16 can have higher than 3V output in battery power supply model so it can connect to the SA 31 with enough power output . In USB power supply model its max output level low to around 1V .

post #109 of 434
Kingwa has been very helpful via email. Seems all I need to find is someone who can solder two resistors to bump up the gain. I believe my stepfather can solder, so I'll wait until he wakes up before I ask him. If not, I'm sure I can find someone that can do it.

I realized the E9K has a high gain of +18db. I had thought it was 10, like the SA-31, which was why I was confused as to why it went much louder, more easily than the SA-31.

If I get this done, I'll make low gain 8-10, which would make high gain 20-22. As it stands right now, I have no use for the default low gain and have been using high gain exclusively.

To fill you guys in...

See the photo, there are two resistors in the red panel, you don't need take off the board, just addition two 1800 ohm on the original resistors . ( each original resistor addition one 1800 ohm.).
If you want to buy the resistors I advice you buy 1.5K, 1.8K, 2.2K ,2.7K and 3.3K for test wich is better gain for modify.

I dunno what he means by addition two 1800ohm on the original resistors. I assume he means to add them directly to those resistors, and not replace them?

The original resistors don't need take off just addition the new resistors on it.
1.5K =24DB
1.8K = 22DB
2.2K = 20DB
2.7K = 19DB
3.3K = 18DB

Awesome. My stepfather says its easy. I just have to get the resistors. The 1.8K (1800ohm) resistors should bump the low gain to 10db and high gain to 22db). That should be all the headroom I need...though I may go with the 2.2k instead. I'd use Low Gain for my ODAC and Mixamp, and High gain for my weak, portable sources).

I want to apologize. For some stupid reason, I thought the E9K's gain was lower. Even the E17 has a higher gain than the SA31. Which is why I was having issues.
Edited by Mad Lust Envy - 10/28/12 at 6:28am
post #110 of 434

C/P from a PM to conquerator2:



So I tried the cowon with the SA-31 and HE-500. As I suspected, it does not play very loud even in high gain and volume maxed out. I would say it is an average volume even for me who does not listen to crazy levels so it's a no-go (even more so with the HE-4).


I think the portable amps that can drive full size headphones have much bigger gain. Paired with an IEM and its >100dB sensitivity it is never an issue but when you need to drive power hungry cans you need either a source that has line out or a bigger gain in the input stage.


Some integrated amps have a MP3 input jack in the front plate and I suspect this input has an additionnal gain to it to match the other line level inputs (CD, Aux, receiver...).


The thing is, if you ask Kingwa to increase the high gain to, say 25dB, you will never be able to use this gain mode with line level inputs. It can be dangerous if you accidentally swith the gain when the volume is not 0. Considering the gain button is just next to the volume one on the remote, it becomes even more dangerous. Personnaly I had the gain volume disabled on the remote, for that particular reason.


With my DAC I listen to either 45-50 in gain 1 or 10- 13 in gain 2. I don't want to imagine what 45-50 in gain 2 would do to my ears (and with 10Wpc headroom it definitely will reach very high volume!).



post #111 of 434
Basically, what everyone needs to know about the SA-31, is that it (by default) is made for things considerably stronger than portable sources. It sounds just fine off my ODAC.

If you plan on attaching weak sources like MP3 players or your phone (i.e. 3.5mm to RCA into one of the SA-31's inputs), it will NOT drive beefier headphones to an appreciable volume.

My SA-31's rear inputs look like this...

Input 2: RCA to 3.5mm which I'd use for my phone, mp3 player, 3DS XL, PS Vita, PSP
Input 3: ODAC (sounds fantastic)
Input 4: Mixamp (for gaming in Dolby Headphone, also sounds great)

For input 3 and 4, the SA-31 is PERFECT for the DT990/600 with good headroom. High gain only needs to be between 30-50 depending on the song, etc).

Input 2: No go. Moderately low volume even with the SA-31 maxed.

So bumping the gain to at 18db-20db for high gain will benefit my 5 current portable sources, leaving low gain to be identical to what I use now for my 3rd and 4th input.

Question, the top inputs look different from the bottom ones. Are they special in any way?
Edited by Mad Lust Envy - 10/28/12 at 6:53am
post #112 of 434

They are the same, Kingwa re-used the case for NFB-6 which has XLR connectors (balanced inputs/outputs) with bigger holes.


Edit: the same goes for the SA-1 DAC vs. Reference 5

post #113 of 434
Ah ok, thanks. I didn't wanna touch the upper inputs because they didn't have the red/white markings, lol. I was like "digital coaxials?" rolleyes.gif

I know it seems silly to use a desktop amp for portable gaming consoles, but I am a gamer first, audiophile second. These headphones NEED to be able to be used for those systems, so it was very important that I be able to use this amp for those sources. I wouldn't have been so vocal about the lack of gain otherwise. I know I have very peculiar needs.

I do tend to lay on my bed while playing these portable games with my good headphones. Since I've had the Fiio E9 for ages, it was never an issue. Then I swapped out temporarily for a Lyr, and then I had a problem with the NFB-5 not having analog inputs, which then I went to the E9K. I returned that which brings me to the SA-31.
Edited by Mad Lust Envy - 10/28/12 at 6:59am
post #114 of 434
The top inputs are higher end Neutrik RCA jacks
post #115 of 434
Stupid question (possibly), but wouldn't adding these resistors on top of the existing one actually LOWER volume?

This is why I stay away from the internal side of electronics.
Edited by Mad Lust Envy - 10/28/12 at 7:54am
post #116 of 434

Adding resistor "on top" of other resistor equals connecting them in parallel. You are actually lowering the resulting resistance, not increasing it... if this is what was bothering you.

post #117 of 434

Adding a resistor in // to the existing one will decrease the equivalent resistor, so increase the gain (the volume).

post #118 of 434
Thanks guys.
post #119 of 434
Okay, new issue...minor. What resistor? 1/2 watt or 1/4 watt? The 1/8 watt was very tiny, so I doubt it was that one. Would it be one that is the same size as the one im adding it to?

I went with 2.2k ohm, for 8db low, 20 high gain.
post #120 of 434
HE-4 works fine from the iPad albeit on max volume so I don't understand how some can experience lack of volume with those headphones. I know if I use oDac I must turn the volume way up on my amp while with AGD Ref 5 its on half the volume.
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