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Can someone help me with DIY hybrid preamp? 2sk170 - 6dj8 - cascode


2002-07-30 12:44 pm

I have been working on this preamp for a few days. I'm not really following any formulas because I'm not good at that stuff at the moment. However, I love tweaking wires and using jumper cables to get things working.

I'm making this mainly as a guitar preamp but hope to use it with other things as well. It can handle about 1 volt (ac) input without clipping. 1 volt in gets me about 18 volts out.

right now I just have one stage (2 - cascode) and things seem to sound really good. I'm just wondering if some of you more experienced people can let me know what you think or give some ideas of how i can make it better.

Also, how would i correctly put a volume (more like a gain control) in this thing?

Future plans are to capacitively couple to an EF86 (as a cathode follower), and then into the remaining 6DJ8... maybe as a mu follower of some kind. I then want to sample some of the ouput, rectify it (negative), filter, and run it into the EF86 to control the gain of the EF86 (hopefully resembling a compressor of sorts!).

Anyway, here it is. I hope some of you take a look and leave a few comments!!


Matt M.


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funny find this circuit idea from 2002, ten years ago, even when it is diagrammed wrong (output is from plate):
there is a DC feedback from plate to source, 2M/2k2= 60db amplification. Fixed. Not bad in concept.
60 dB bit hefty though and I think impossible to realize.
But 45db should be possible with this combo. [I did that without feedback].