His Master's Noise: A Thoroughly Modern Tube Phono Preamp

I would be surprised if inrush is an issue, your main transformer should only be able to supply 100mA or so. Plus minimal soothing caps are needed.
One thing I did learn though when I built mine, it's really important to let the power supply discharge for 10 minutes or so before reconnecting the umbilical. I popped one of my regs doing that. Also, without the load in place the raw b+ went much higher than needed. Having the preamp connected to the raw supply acted as a soft start.
Have you put an extra switch in after the transformer like you might find on a tube guitar amp? Even if so, I would think that the regs would break first before the fets.
 
The DN2540 is indeed a sensitive device. The gate oxide layer is easily damaged in my experience. A few of mine are defective just from storing in a parts container (without antistatic protection).

OTH, I soldered up a cascode CCS and this didn´t fail even though I left it mixed with some other parts, unprotected.

(The cascode with DN2540 is an excellent choice of CCS. Over 110 dB of rejection up to 200KHz (as mesured by Walt Jung).)

-Alex
 
Hi Arno PF,
i build 4 amps now and never one current source died. i used someone DN2535.
I bought them by Reichelt in Germany.
Are you using the original circuit power supply from SY?
Which heatsinks are you using? Could you show a picture from your setup?

Did some extra checks today. Replaced the current source components and still measured a different current compared to the other side.
So, figured out a setting on the tube tester for the D3a...and one was indeed far gone....

So, I expect the current source was ok...but in the past I had some damaged ones...so going to change the heat sinks anyhow of the D3a current sources since these turn wayyyy hotter than the other two.

Eventhough it seems to go in the normal direction again...keep you posted if I discover anything new
 
Fairly sure not having a tube in wouldn't be a problem because there's no voltage drop on the current source.
However, if your tube shorted from plate to cathide (don't even know if that possible) then the ccs has to drop 260v. This means that it's will have a resistance of 13k to give 20ma this means that about 5w is getting disapated. I would expect a voltage drop of nearer 50v across the cca giving a disapatiin of nearer 1 watt or so under normal conditions.
What were your plate voltages on the d3a? If one seems abnormally low that could explain the extra heat.
It's also worth noting when you build your next cca on breadboard to set the resistor value, one position of fet is sensitive, to internal parameter the other isn't. Make sure you know which is which after testing. I usually use a trim pot then measure and solder a bunch of resistors together to match it.
 
Hmm, went to use my phono stage last night and turns out the main fuse has blown. I had a t500mA in there. I'm on 240v.
Have had a quick look inside but nothing obvious. I was wondering whether that's the correct value. It had been working fine. I did leave it on quite a bit longer than I usually do last time I used it so am wondering if 500mA was right on the cusp. Although 120w seems a tad excessive for a phono stage.
 
Hi Dave,
are you using a fast fuse? Or a slow type?
Post the voltage values of your transformer, please.
The init current of a transformer can be up to the 10th of the working current.
You can test with a littler larger fuse, 630mA up to 1A. If they will also blow up, your problem is a greater one.
regards
 
Hi Frank, ha, I'm an idiot. I've actually got a fast blow 500ma. I thought it said T but on closer inspection it's an F. I do have some vague recollection of only having f type fuses of that value in my multi box. Due to house move I'm struggling to find the box but that certainly makes me feel a bit more hopeful. I'll see if I can find another then I'll also measure the transformer voltages. Cheers.
 
Unfortunately I don't have the kit to do that, but it is dead quiet, it's only on the very last couple of notches on my impasse preamp you start to hear hiss. The gain on the hmn is sufficient to bring my benz wood sl (0.3mv) to around the same line level as my dac. My speakers are around 94db so it's very quiet. Impressively so.
I'm assuming it's the noise of the preamp you want a spectrum for, as you wanted one with the input shorted?
 
Unfortunately I don't have the kit to do that, but it is dead quiet, it's only on the very last couple of notches on my impasse preamp you start to hear hiss. The gain on the hmn is sufficient to bring my benz wood sl (0.3mv) to around the same line level as my dac. My speakers are around 94db so it's very quiet. Impressively so.
I'm assuming it's the noise of the preamp you want a spectrum for, as you wanted one with the input shorted?

I use a laptop with some free software and an usb audiocard