So... yes, the post above looks correct. Saying that a different way: The front row of 3 pins is connected to the rear row and is for the left channel, and the two middle rows are connected and are for the right channel. So you can use either the front/rear for left and either of the middle...

The source impedance is basically the resistors in series with the output, between the opamps and output jack. You can replace R29 and R30 - now 10 ohms, 1/4W - with something smaller. A couple of notes and precautions: there is a 270uF capacitor in series with the output as well. At 20Hz this...

Yup, that is fine, if the caps will fit in the space available. Dale RN55 are fine too. Pete

That should work fine. Pete

An interesting discussion about the audibility of inverted polarity: https://hydrogenaud.io/index.php/topic,55323.0.html Pete

It is normal to hear a pop when the power is turned off. It's easy to delay the operation of the output relay to kill the turn-on pop, but when you power off, the voltage collapses fast and it takes some time for the relay to drop. I measure about a 1.5V pulse at the output that lasts about...

It should be OK. Pete

After quite a few requests, I finally designed a balanced (truly differential) headphone amp / line amp using the Korg Nutube. You can find details on my web site: http://www.pmillett.com/Nutube_bal.html It is a true differential amp, with the dual triode sitting on a CCS tail as a diff...

Sounds like WiFi. It can cause a ticking noise, especially if it's near a router. Pete

About 6.5V RMS into 30 or 150 ohms, or 1.3 watts into 30 ohms. Pete

Sorry about that, just updated it. (I assume the only dimension that was wrong was the height (should be 3.125)? Pete

The actual current draw of the amp is about 80mA. So that would provide plenty of current for this amp. Pete

One way to find out - try it! Try moving the bias up, and also down, maybe 2V at a time, and see what happens. You can't hurt anything... Pete

Sure. Korg quotes the lifetime at 30,000 hours. That's 3.42 years if you leave it on all the time. As far as I can tell, this is based on the lifetime of a vacuum fluorescent display as quoted by Noritake. The Nutube may actually last significantly longer, since the plate current used is...

What Tomb says :) You might be able to fit in the 10uF Wima MKS part. I used it on the class D hybrid. For a 10uF film cap it's pretty small. One goal with this design was to make it as affordable as possible. That's why I used the electrolytic coupling caps there and also the switching...

The carrier PCB has the pins duplicated on both edges of the board. So you only need to connect one side (e.g., JP3 and JP1). Carrier=Amp [Nutube pin #] P1=A1 [7], P2=A2 [10] (anode or plate) G1=G1 [4], G2=G2 [14] (grid) F1=F1 [1], F2=F3 [17] (these are the ends of the filament) FC (either...

They are high impedance nodes, so I would keep the wires as short as possible. Not more than a couple of inches... Pete

Sure, you can do that. The pins are fragile so be careful. Or, you can buy a little PCB for $6: https://www.ebay.com/itm/Blank-Carrier-PCB-for-Korg-Nutube-6P1/222598735398?hash=item33d3eb2626:g:wN4AAOSw~epZf0B8 Pete

There is always a little chance that an opamp will oscillate driving some headphones. Headphones are complex impedances, and if they present too much capacitance, the circuit can become unstable. I've not heard of it happening on this amp, but have seen a couple of cases with other...

Yup, that should work. Pete

I have two eBay stores... it's here: https://www.ebay.com/str/nutubeusstore Pete

Yeah, that relay seems to be perpetually out of stock. I know that the TE V23079A1005B301 works fine, and as it is a common footprintt I'm sure there are others. Nothing critical about the common mode choke, anything that fits in the holes will work. Higher impedance is actually better. Pete

The amp is fine with 1k, but the source that you're using it might not like it. It will present a 1k load to the source. Some sources are fine with 1k, others might distort a little more with a 1k load than a 10k load. And tube sources may not work well at all. I am guessing that phones...

Right - during normal operation, C3 and C6 are charged to wherever the bias is, normally around 11V. But you also have to consider what can happen at power-up, power-down, and if the output gets shorted. In some cases you may get more than that voltage applied. So the safest thing is to keep...

25V caps is close to the limit. If your power supply really measures 24V or less, it will work. Pete