It works well without pot between a Minidsp SHD Studio I use for volume control and power amp. The SHD has 2dB gain.
On second thought to be sure not accidentally get to high volume I put a 35kOhm resistor between + and - of both NuTube inputs and an extra 15kOhm resistor on both + inputs to simulate a 2/3 setting of a volume knob.
I have a hybrid power amp in which the B1K behaves as a buffer with no volume control. Others, perhaps Nelson himself even, recommended that I should implement a voltage divider on my inputs. I seem to recall the notion about it acting as some kind of regulator that the volume pot naturally imparted. You might want to search posts in this thread to read what more knowledgeable people said.
Of course the volume pot is what provides the input impedence as the B1K is normally built. I'm not sure what the input impedence would be without one. So you if don't want any attenuation, you should probably just put a fixed 50K resistor between the input and the ground. Or else, as @jaaptina suggests, some other combination that will add up to 50K, though I would think a 100K pot would work just fine, too. I'm using an ALPS 100K pot with mine now...
It might sound strange, but you can consider the two 221k resistors in parallel so you end up at 110k.
There are some text around on the web, e.g. FET and BJT Difference | Impedance at the FET Gate | Voltage gain
There are some text around on the web, e.g. FET and BJT Difference | Impedance at the FET Gate | Voltage gain
Hum question
I built the kit perfectly stock. I have a little bit of ringing, but only when the box is touched. But there is a hum. It’s not 60hz or 120hz. Someone in an earlier post said they heard a sound like an active cell phone near a radio. Not exactly crackling, but not periodic. The “hum” doesn’t go away when I change from input 1 to 2. And it doesn’t seem to be affected by the volume control. Any ideas where to start?
I built the kit perfectly stock. I have a little bit of ringing, but only when the box is touched. But there is a hum. It’s not 60hz or 120hz. Someone in an earlier post said they heard a sound like an active cell phone near a radio. Not exactly crackling, but not periodic. The “hum” doesn’t go away when I change from input 1 to 2. And it doesn’t seem to be affected by the volume control. Any ideas where to start?
My NuTube and amp hums and hisses loudly when the amp is connected to net ground. I removed the net ground connection. Now its completely silent.
In another room it doesn't hum and hiss while connected to net ground. So in my case it seems related to the shared outlet (with TV, modem etc). I did look for the ground loop in my 3 box stereo setup (streamer, dac and NuTube/amp), but could not find it. That is why I keep using it without net ground connection.
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Thanks, Jaaptina,
Can anybody tell me whether the board is supposed to be grounded to the chassis? The only way I see that happening is through the screws that hold the board down. The screws seem to be attached to a ground trace on the board, but then they attach to the chassis via threads through anodized holes. I don’t get any continuity from board ground to chassis other than by touching those screws. is that a problem? Should I have sanded the chassis before attaching the board?
Can anybody tell me whether the board is supposed to be grounded to the chassis? The only way I see that happening is through the screws that hold the board down. The screws seem to be attached to a ground trace on the board, but then they attach to the chassis via threads through anodized holes. I don’t get any continuity from board ground to chassis other than by touching those screws. is that a problem? Should I have sanded the chassis before attaching the board?