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4s tube pre build.

After seeing some of the wonderful tube pre-amp builds here I wanted to build one for myself. Ordered all the parts for the solid-state power supply version and the parts should be here Monday or Tuesday.
I know that there are a lot of versions of this and other 12a*7 tube pre-amps. The reason why I settled on this one is that I felt like I was in constant analysis paralysis.
If someone knows of some simple modifications that are well documented I am willing to consider them as long as it doesn't lead back down the road of endless analysis.
Thanks for the input, I will try to document the build with lots of pics.


  • Your build was definetly one of the key insperations!
    My build wont have that big sexy transformer on the top but I think I can do something to add some sex apeal.

  • Like Craig mentioned, the circuit is not optimum for all the tubes it is capable of utilizing, but, now that I'm playing around with another tube/mosfet preamp which also uses the tube as a distortion/tone device ... well, who cares as long as it pleases the ears. I feel this point was driven home when swapping a Raytheon 12at7 (thanks Tom) in the unmodded 4sUniversal and listening to Natalie Merchant and Diana Krall. It was one of ThEm moments. Bass weak, treble weak, and come to find out the tube was probably on its last legs, but female voice was frelling awesome. Probably the best I've ever heard. Point is, the tube had to be adding all kinds of distortion and my ears absolutely loved it.
    IIRC, they spec a .47uf output cap. Go way bigger or the bass will start rolling off around 100hz. Also, use a good cap here. Depending on the caps used, the difference in sound can be easily noticeable. Also switched the volume pot to the input side.
    Curious about your observations when the tube rolling begins.
    To be stuck in constant analysis paralysis, you sure picked the wrong pre as this thing likes to be modded.

  • I hope to have a similar experience. I have for the most part avoided tubes because of their poor measurements.
    I keep trying to explore all there is to offer in the world of hifi. I have been intentionally picking projects that fit in different catigories so I can diy as I explore.

  • edited January 24

    Take a look at a tube pre-amp build thru tubes 4 hifi
    I took one of their boards and built the box (set mine up as a single stage buffer / pre)


  • Got the heater circuit on a breadboard. The B+ is not too far behind.

  • B+ looking good.

  • I looked at the bridge on your boards and thought, "Uhh, those are way too small." But then I remembered you are building a preamp, not an amp! Are those PCBs from Amazon? I was just looking at those before dinner.

    Lookin' good!

  • The pcbs came from banggood or aliexpress. They work great for these smaller projects.
    The rectifiers are very cute and still rated for more than double what the max curent draw should be.

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