The BSTRD - Class A Tube Pre and PSU, with Eagle Project Files

[skrodahl]

There was a strange little thing that appeared in Danish magazine Ny Elektronik (New Electronics) in 1989. A very simple preamplifier that used two L63 tubes in Class A with no feedback and it operated pretty much badly out of spec. (It was supposed to though, that was the whole angle of the article.) The article is available here (20MB PDF), for those who understand Danish: http://www.nisbeth.dk/carrotman/files/Bastard.pdf

It was called The Bastard, and gathered quite a following (it got the name because it was a hybrid. The phono stage used transistors for better SNR), and somebody suggested I should try it.

The Bastard was tested by some Danish guys and was found to have 6% THD+N or more. They upped the voltage and added some feedback, and it ended up having 0.185% THD+N.

I made PCBs for this pre that incorporates the higher voltage and feedback, and designed a regulated power supply to go with it. Both have been built and tested, and the preamp is sounding pretty sweet.

The Eagle project files are freely available. Etch, order or change them to your liking: https://hackaday.io/project/16944-the-muffsy-bstrd-valve-preamp

 

[knockbill]

Looks like a nice little project to try, however I can't open the modified links for the pre amp and PS...

 

[skrodahl]

@knockbill: Do you mean this link? https://hackaday.io/project/16944-the-muffsy-bstrd-valve-preamp

The Eagle files (.sch and .brd) for the Pre and PSU are zipped here: https://hackaday.io/project/16944-the-muffsy-bstrd-valve-preamp#menu-files

The Eagle software (the project can be opened in the free version) is available here: https://cadsoft.io/

 

[knockbill]

Yes,,,
I can DL them but can't open them...

 

[skrodahl]

I just downloaded them and tested with 7-Zip, they extract just fine and they do open in Eagle.

 

[knockbill]

OK,,
I don't have those programs,,, have to look into it..

 

[skrodahl]

You need 7-Zip, WinZip or some other program that can extract zip-files. Once they have been extracted, they can be opened in Eagle (link in my previous post, there's a free version so you won't have to buy a license) which is the software I have used to design the schematics and PCBs.

Both boards are within the limitations of Eagle's free version.

There's software for extracting zip-files for all operating systems. Eagle works on Windows, Mac and Linux.

EDIT: Come to think of it, Windows 7, 8 and 10 can open zip-files natively. https://support.microsoft.com/en-us...39-824c-b5be-6dda11b5075e/zip-and-unzip-files

 

[skrodahl]

How does this thing measure?
Well, it's got some prominent harmonics (mainly 1st harmonic, 2nd and higher are near or below the noise floor). The frequency range is 10 Hz to 30 kHz, and it's got an SNR (1V output) of >90 dB and a THD (1V output) of 0.35%. The tests were done with Russian 6S2S tubes.

Note that my audio analyzer picks up 50 Hz from my computer through the USB cable. This doesn't have a lot to say for the measurements.