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RE: But here's a commercial preamp kit that uses your favorite tube

92.2.65.104

In Reply to: RE: But here's a commercial preamp kit that uses your favorite tube posted by Frihed89 on October 29, 2014 at 01:29:01

Any comments? Well, I don't have the circuit to hand. Anything with the 4P1L will be a good idea. The best way to use it is in filament bias and with a really good interstage or OPT, so that takes my design out of the area of the more simple variations. More complex but worth it sound wise. Otherwise you get most of the quality with an active load and a good coupling cap, which is a typical implementation. As long as you eliminate the cathode bypass cap with some kind of solution in the cathode circuit and provided you have a really clean filament supply, one for each tube. Mine is very elaborate. Schematic details below in thread.

But the point of 4P1L into PSE 4P1L is that you have a DHT 2-stage solution due to the higher gain of the 4P1L so you don't have to resort to inferior input tubes to make up the gain for a low mu output like the 45.

Follow Ups:

High gain appears to be a problem with this preamp - Frihed89 04:09:49 10/29/14 (1)
People with sensitive speakers hear a lot of noise.
Observe, before you think. Think before you open your yap. Act on the basis of experience.
- It's not a high gain tube - andy evans 07:57:00 10/29/14 (0)
  People with sensitive speakers hear a lot of noise.> >
  
  The mu of the 4P1L is only 10. That's pretty low for a small tube, though higher than most DHTs. So more likely to be the ratio of signal to noise, which is stated at 88db and that's respectable, so may be anecdotal.
  
  The circuit has 150v (0D3) on the top of the plate resistor of the 4P1L and LEDs in the cathode. The filaments use an L200C regulator. Capacitor output. That's what I see from the specs.
  
  I don't know if people with sensitive speakers are having problems with microphonics rather than noise. The tube is microphonic, so needs special treatment to dampen the potential for vibration (like a massive chassis or some rubber-ish decoupling) and starving the filaments helps too.

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