Hello, I just joined, primarily for the audiophile products. Looking at purchasing the NHT C3 speakers for our new living room. Space is about 15 feet wide by 33 long and they will fire long ways. Space is just for general listening, music room with all equipment is downstairs, so hoping they will fill it with sound nicely. Cheers.
Mar 18, 2024
*O2's input stage will overload when set to high gain of 6.5X with SDAC's output at max, which may cause the sound to become distorted but it won't harm the O2.
THE DISASSEMBLY
*Before disassembly "...wait at least 15 seconds with the power turned ON(in) after the power is removed to let the capacitors discharge."-NwAvGuy
FRONT PANEL: *turn CCW to unscrew any of the screw or nut -Remove the volume knob by removing the hex screw securing it to the pot's shaft. -Remove the nut securing the potentiometer to the front panel. -Remove 4 Phillips screws on the front. by now the front panel should be able to be come off with the jack attached and you should be able to see if the resistors are of right values (R19, R23) and left out(R17, R21) if they aren't contact MD's support.
BACK PANEL: -Unscrew 4 Phillips screws and 1 Torx screw on the back. The back panel should come right off.
THE PCB: -Slide PCB out the back of the enclosure (it will get stuck if you slide it out through the front because of how the SDAC is mounted)
THE GAIN RESISTORS
"Resistor Values – The O2’s gain (for one channel) is: Low Gain Ratio = 1 + R16/R17 High Gain Ratio = 1 + R16/R19 Voltage Gain in dB = 20 * Log(Gain Ratio) …For 1X gain just leave out the gain resistors"-NwAvGuy
Switch out: R17and R21 needs to be left out for 1X gain (gain switch pushed out) but 1K ohms resistors are installed. So the gain is 1+1500/1000 = 2.5
Switch in: R19 and R23 needs to be 665 ohms or 649 ohms (closest standard resistor values) but 274 ohms resistors are installed. 665 ohms: 1+(1500/665) = 3.26 (~3.3X) 649 ohms: 1+(1500/649) = 3.31 (~3.3X)
274 ohms: 1+(1500/274) = 6.47 (~6.5X)
THE "FIX" *this is done at your own risk
Method 1(no soldering required): Clip off or desolder the "high gain resistors" (R19, R23) and leave the "low gain" resistors intact(R17, R21).
Now the gain switch be the following: SWITCH IN = LOW GAIN (1X) SWITCH OUT = HIGH GAIN (2.5X)
Method 2 (soldering required): Do the same as the first method so while you get the resistors you still have high and low gain(1X and 2.5X). Clip out R17, R21 and solder in the "high gain" resistors in R19 and R23.
Links O2's gain resistors: http://nwavguy.blogspot.com/2011/08/o2-details.html#circuitboardconstruction in "THE GAIN RESISTORS" section
O2's maximum input: http://nwavguy.blogspot.com/2011/08/o2-details.html#maximuminput
The teardown post on Reddit: https://www.reddit.com/r/Massdrop/comments/7ny0vj/massdrop_o2_sdac_dacamp_teardown/
SDAC measurements on ASR: https://www.audiosciencereview.com/forum/index.php?threads/review-and-measurements-of-massdrop-x-grace-design-sdac.2495/
https://i.imgur.com/e2BrxsU.jpg
Is there any other way how to find out the gain configuration without opening the unit?
Modifying it, well that's another story, currently trying to find out what to do from massdrop support.
I don't exactly trust myself with this kind of handling electronics, and I'd prefer potentially having a product with a wrong configuration over potentially electrocuting myself, especially by accident.
Hence my question about how can I tell differently.
You'll need to measure O2's output voltage with O2 and SDAC's* volume at max using a multimeter or a voltmeter. *SDAC will need to play back a 60Hz 0dBFS sine wave during testing which you can create one in Audacity (Audacity > Generate > Tone > Sine) since most meters are not as accurate at higher frequencies.
O2's output voltage should measure ~2.15Vrms with gain switch out("low gain") or the same as SDAC's output if the gain is 1X, for 2.5X it will be ~5.38Vrms. As for 6.5X gain the O2 will max out at ~7Vrms.
Vout / Vin = Gain
Generate menu in Audacity: https://manual.audacityteam.org/man/generate_menu.html
NwAvGuy on gain(there is a section on measuring the gain of an amplifier): http://nwavguy.blogspot.com/2011/09/all-about-gain.html
I will try to desolder the resistors and see how it goes.
As for Massdrop saying only 5 people complained about the problem, I'll admit I didn't complain because I was too new to audio gear to know the distortion I was hearing was a problem with the amp.
I'm a complete electronics noob so bare with me, I've opened mine up and it pretty much looks like what Stephen has, so if i want to fix it i just have to cut/de-solder the two resistors nearest the volume control right?
So can we just follow your advice on swapping the resistors to get 1x (switch out) and 3.3x (switch in) gain? - R17 and R21 (next to the gain switch) left out - R19 and R23 (next to the volume knob) 2 x 665 ohms (metal film resistor < 3.9mm, 1% tolerance) .
Or would it be more complicated than just soldering?
It's also funny how my cheap thin hex screw driver just snapped in half while I was trying to unscrew the screw in the dial. So I have no way of getting it open.
@Jiv_au that’s all you need to do for 1X gain (in) and 3.3X gain (out) some soldering and clipping leads, and don’t forget 1% tolerance or better for the resistors.
Same thing happened recently with VE Clan Cables. A complete mess up. Even that they offered a full refund.... And this O2SDAC a 15 dollars.... hmm And that is only IF I buy something from MD again...
I joined R2R Dac but now I am thinking should I pull out or not.
Not so much of trust raising events keep repeating...
It would have looked better if MD QA team found this themselves and took proactive measure instead of giving a 15 dollars voucher.
There should have been an effort to fix the units instead of giving out vouchers.
What if I received R2R Dac at the end of this year and same thing happens.... I know I would be given a voucher again..... Maybe another 15 dollars...
sigh
With this and the 15 dollars coupon, at least for myself, I would consider this issue resolved.
Edit: Yep. MD must fix it. They must provide free shipping back, fix the flaw and send it back to me free of charge. Until then, this is not resolved and I will not buy anything from MD. Still thinking whether I should cancel R2R DAC.
On another note, I've now started asking myself whether I really want 1x gain?
I've been using 2.5x gain (unknowingly) with my 35, 40, and 300ohm HP without much issues, as best as my ears can tell. I would assume 1x gain isn't enough for 300ohm (HD6xx) since I often have it at 12 o'clock volume. 9 o'clock for 35ohm (Fidelio X2).
3.3x gain is something I would like to have, as that is the max power possible without distortion through the SDAC + O2 combination. But do I need it if I don't own, or intend to own, a much higher impedance HP (e.g. 600ohm)? Some people think 7volts (3.3x gain) into 300ohm to produce 120dBSPL is needed, but that isn't for me.
6.5x gain combined with SDAC is the problem (distortion). But I'm wondering if I might need it when using the amp section only (O2 amp-only version comes with 6.5x gain option).
So for me the dillema now is choosing which gain combination I want. In fact, leaving it AS IS is also an option.
2.5x/3.3x or 3.3x/6.5x or 2.5x/6.5x or 1x/3.3x or 1x/2.5x.
Yes, last year. Fiddlesticks.
I do turn it down to 10 o'clock volume when on Skype.
@OpasTanti Thanks, I'll look into the SIP sockets.
Is 1x gain same as listening directly to the SDAC via RCA (e.g. using RCA to 3.5mm stereo adapter).
They should also be sending warranty cards with what they cover for each product, for example in this case they didn't state they would refund if there are issues. I'm not sure if this is against FTC regulations, but I snipped my resistors at this point
Regarding Massdrop's warranty, I'm unable to find any info of it on their terms and conditions page (except for the RETURN POLICY).
"Is 1x gain same as listening directly to the SDAC via RCA..." Even though output voltage will be the same, DAC's output have high output impedance and it might not have enough power to drive headphones from my understanding.
Power, Gain, Noise and Dynamic range : http://nwavguy.blogspot.com/2011/09/
To answer my own question: Is 1x gain sufficient for HD6xx?
Hell yes.
YMMV if you like your music loud, but I think prolong exposure at 1x gain with max volume would cause hearing damage even with the HD6xx.
Here's my mod. Apologies for the poor picture quality. (Note: I'm using 680ohm instead of 665 or 649 as I couldn't source them locally)