"The Wire" Ultra-High Performance Headphone Amplifier - PCB's

[sek]

Originally Posted by qusp

I see no reason at all to use a 5 pin

Agreed, not necessary. But some manufacturers do it and some DIYers might want to be compatible...

with no way to terminate the shield at both ends for me it causes more issues than it solves.

Why would you have to termintate it at both ends? What would you gain by doing so, sound quality wise?

One reason to still connect it at the amplifier side might be safety. Not all headphones have low voltage (dynamic) transducers.

Another one could be shielding from RMI. Not all amplifiers are immune to a long antenna at their output.

If you wanted to terminate at both ends, I'm shure you'd find a metal structure in many headphones. Grilles, frames, bows ... things that could even contribute to safety and shielding.

reasons not to use 5 pin XLR: well for starters CMMR will be superior if you use a connector that has the pins closer together

A 5-pin XLR connector has the exact same physical size as a 3-pin or a 7-pin XLR. Due to this, the pins are even closer together the higher the number of pins get. According to your argument a 7-pin connector would improve CMMR... I doubt it.

Actually, I consider 4-pin XLR the optimal choice for the general public (safe, reliable, convenient, cheap, readily available). Shielding via the connector housing is optional. Take a look at an application from Violectric.

plus its larger than needed overall.

Which is why I mentioned mini-XLR.

But you bring up LEMO. Those are preferable, thanks for the link. They're standard in mobile applications like lavalier microphones, in-ear monitors and many battery supplied transmitters/receivers in the professional audio industry. Sennheiser would be an example, Shure is another one.

other than that i'm good as long as its not 2 x 3 pin.

I second that.

TRRS shorts the inputs on the way in and out and are generally of poor quality, another dumb standard

A dumb standard indeed. But a standard...

I still stand to my recommendation for 4-pin XLR with 4-pin LEMO being second best due to higher price and more difficult availability (remember you always need parts quickly, on a weekend, out of town, etc. ).

[tommy thong]

Hi Owen,
How much is the price for SE-SE kit (unit+psu) and SE-SE pcb(unit+Psu)?
i want to order
- 1 set SE-SE kit (unit for stereo setup+PSU)
- 1 set SE-SE pcb(unit for stereo setup+PSU)
thank's
Tommy

[agdr]

It looks like Mouser has just added the Susumu resistor line, the ones OPC has specified for the Wire at Digikey. I don't recall seeing Susumu when I searched Mouser a week or two ago. They say "new" on the product listings. Mouser offers them in 1x qty rather than that 10x minimum at Digikey.

1K 0.1% Susumu, Digikey RG20P1.0KBCT-ND, Mouser 754-RG2012P-102-B-T5, $0.42 each, in stock

10K 0.1% Susumu, Digikey RG20P10.0KBCT-ND, Mouser 754-RG2012P-103-B-T5, $0.42 each, in stock

240R 0.1% Susumu, Digikey RG20P240BCT-ND, Mouser 754-RG2012P-241-BT5, $0.42 each, in stock

I saw a post where someone was thinking of replacing the input 10K with a 47K. That would be these, Mouser 754-RG2012P-473-BT5, $0.42 each, in stock

[opc]

Hi Guys,

Well, I finished measuring the SE-SE and the BAL-BAL version, as well as the PSU this evening. Tomorrow I'll measure the BAL-SE, then I'll be starting on the power amp.

In the meantime, I'll post what I've got so far. I'll toss them up here, and I'll compile them into a proper wiki and link to it from the main headphone amp wiki. In the wiki I'll discuss the significance of each measurement, and post up a more formal spec.

Let's start with the PSU:

1. I took an AC coupled FFT measurement of the output of the PSU while connected to and powering the SE-SE amplifier. You can see the 120Hz fundamental caused by the rectifiers, and the subsequent harmonics at 240, 360, 480 and 600Hz. The negative rail is the purple trace and the positive rail is the greenish trace. The fundamental is about 20uV on the positive rail, and about 10uV on the negative rail. Overall, the supply is very quiet and well behaved up the measurement limit of 80kHz.

2. This is the same measurement as above, except only up to 20kHz and expressed in dBV.

3. This measurement simply shows the two rails on the AP scope.

Next up is the SE-SE amp!

Cheers,
Owen

[opc]

Next up we've got the SE-SE headphone amp. This little guy far exceeded my expectations, and those of you going with SE inputs and outputs will be glad to know that you're not really giving anything up in doing so!

1. The first measurement is an FFT of the amplifier's output into a 50 ohm load with a 50 ohm load across the input which is disconnected from the AP. This basically eliminates the AP as a source of noise and shows the amplifiers true noise floor.

Thanks to the three layer board, the noise floor is about 10dB lower than the previous BAL-SE version, for a pretty stunning noise floor of between -160 and -164dBV. You can see the 60Hz noise and a few of the harmonics getting through, but they're all lower than -148dBV. This is the quietest amplifier I have ever measured.

2. The next 6 measurements are all FFTs at various voltages driven into a 50 ohm load. There's 0V (AP plugged in but no signal), 100mV, 1V, 2V, 5V, and 7.2V which is the most the AP can put out single ended.

3. The last three measurements are calculated SNRs at 100mV, 1V and 7.2V. The channels of interest are 5 and 6, the other channels are not connected. These channels are used because they happen to be the best performing of the 8 channels.

More to come!

[opc]

Continuing with the SE-SE amp we have:

1, 2, 3 = Calculated THD+N ratios at three different drive levels, 100mV, 1V and 7.2V all into 50 ohms. Again, channels of interest are 5 and 6.

4 = Gain linearity which is basically showing that the gain remains perfectly linear regardless of output level. If you had an amplifier with a high output impedance, this would be all over the map. The Wire, however, doesn't flinch at all from the lowest to the highest output level.

5 = Frequency response. Note the +/-1dB scale. The peak between 70 and 80kHz is the AP, not the amp.

6 = Frequency response zoomed in. This is probably one of my favorite measurements because it's almost funny how absurd it is. The 0.1% resistors mean that the channels match up better than 0.0001dB.

7 = THD+N ratio vs. Frequency - sweep

8 = THD+N ratio vs. Output Level - sweep

9 = THD ratio vs. Frequency - sweep

[opc]

Next for the SE-SE amp we have:

1,2,3 = DFD Intermodulation distortion at three different drive levels.

4,5,6 = SMPTE Intermodulation distortion at three different drive levels.

7,8,9 = Crosstalk at three different drive levels. As this is an SE output amp, this is where the BAL-BAL really pulls away. The SE amp hits the wall at about 100dB of channel separation, where the BAL-BAL, as you'll see later, does significantly better.

[opc]

1,2,3,4,5 = sweeps showing distortion product ratio vs. frequency. Each harmonic is shown separately so you can see the character of each with respect to frequency.

6,7,8 = Distortion product ratio at three different drive levels.

[opc]

Overall, this amp measures incredibly well. I personally have never seen anything that has such low distortion that you're basically just measuring the AP's generators. The noise floor is so low that this amplifier will be completely silent into even the most sensitive IEM's, and yet you still get enough voltage and current drive to run the hungriest headphones out there. The very low output impedance means you get superb linearity, and a perfectly flat frequency response regardless of the load. I couldn't be happier with this little amp! Keep in mind that there are no tricks here... no batteries, no filters, no fancy chassis or shielding, just the supply and the amp running off a transformer.

I've attached a few shots of the test setup below.

BAL-BAL measurements to follow tomorrow.

Cheers,
Owen

[HYPERTUNE]

All I can say is I'm REALLY glad I decided to hop on board this group buy

Congrats Owen