Beefy

Quick question...... I bought a Sovtek 6AS7G for my Crack from Parts Connexion, and it rattles round a bit when I handle it. My Crack isn't built yet, so I have no way to test it. Being my first experience with 'real' tubes, how high should my concern level be when I receive something like this?

Always remember that building it yourself makes it sound 62.7% better.

6J6 is a 7-pin jobbie, compared to the 9-pin 6DJ8. Might be pretty tough to allow both without an external board/converter.

Well I'm not a prototyper and am a relative toob noob...... but as a prospective builder and tinkerer I like the idea of option two or four. 6DJ8/ECC88/6922 are ubiquitous are there seems to be plenty of inexpensive options for tube rolling. If people want to go stupid with NOS tubes, let them. 6J6 doesn't seem as widely available, with fewer rolling options. Lower heater current of the 6DJ8 might cool things down a tad? For option 3, futzing round with daughter boards seems like a lot of unnecessary effort. Between 2 and 4, I'd vote for the option that gives smaller parafeed caps. So 2 would get my vote - if I even have one.

I've always like this one......

630-HLMP-6000 Regarded as being excellent LEDs for biasing tubes.

Yesterday was Postdoc Appreciation Day. So we had a science journalist come and give us a talk, as president of the postdoc society I gave a rousing speech, and we had free food and wine. Its nice to be loved - even if only for half a day Today, I build flexi shelves!

I like parts of her.

The B22 does tend to pick up more magnetic noise than other amps, so it would need to be handled differently from most other commercial designs. I still maintain that in your case, magnetic noise it isn't an issue. You are WAY overthinking this. Steve nailed it pretty well, I think. If you have a really difficult load then balanced makes more sense. For most headphones, there is little benefit. But it really seems to come back to your source again, and how it handles balanced versus unbalanced. If one of the outputs it 'better', that will make much more of a difference than any of the other factors like a fraction of an ohm on the output impedance.

Ah, thanks for the correction!

Yeah, I read that before I purchased, but I don't think it will be a problem for me. I rarely sit and play with the volume while I listen...... Seriously though, I would consider steppers, but I listen at such low volumes that fine control of volume would be non-existent.

Partsconnexion also has the 2CP-2511 for $72. I ordered one just yesterday for my Crack.

Percy claims to have balanced CP-2511 for $76, but that doesn't make sense considering the stereo is $72. Maybe a typo for $176?

Lets say gain of 5 from 1VRMS unbalanced. Each amp board produces 5VRMS. Lets say gain of 5 from 1VRMS balanced. Each phase is 0.5VRMS. Each amp board produces 2.5VRMS. 5VRMS across the driver.

That sounds reasonable.

Well, it really depends on your source. The balanced output on some sources is twice as hot as the unbalanced output; in this case, the balanced output will indeed be louder if the gain is kept the same. But if your balanced output is the same voltage as unbalanced output, then the volume will be the same.

If the noise pickup is coming from a Blackberry polling the local tower, I really don't think that the transformer is the root cause......

Ouch, but now you know for sure. Certainly better to deal with it early before it becomes a major problem!

I suppose that if the Vf aren't perfectly matched, you can have problems......

The Kindle I bought as a surprise for my lady friend FINALLY arrived yesterday, after ordering on August 5th. Stupid Amazon. Anyway, the device is really fantastic. Light, compact, and the screen is just incredible.

I've got a pile of -6dB Goldenjacks that were pretty cheap. Many people poo-poo them, but they worked fantastically for me. Even so, a single 50k resistor right before a 50k pot will do almost the exact same thing, without the added cable bulk.

No, that isn't how it works, because the attenuator is a voltage divider. You get the same attenuation range regardless of the size of the attenuator, it just depends how much voltage the amp sees and how much goes to ground. Look at it like this...... a 100k attenuator has a maximum effective attenuation of -60dB, and you go from -60dB to 0dB in a full rotation. A 50k attenuator with a 50k resistor in front of it still has a maximum effective attenuation of -60dB, but at full rotation you can only get as high as -6dB; you can't get up to 0dB. It limits the overall range, but effectively gives you more precision per angle of rotation between -60 and -6dB.

This is good to know. I had heard some criticisms that the gain was fairly high. My plan was to use a 50k attenuator with 50k resistors in front of it. Should give an additional 6dB attenuation for a bit more usable range.

Well, that is the whole benefit of using an LED isn't it? That the voltage across it is always the same regardless of current. Thanks for that, it helps immensely

I've read a fair bit that the 'best' LEDs for biasing tubes are older style, low illumination red units, Vf approx 1.5V. As you get up into the green and blue units, they become less suitable. Would there be any potential benefit in two red units in series?