Groovewatt a DIY Vacuum Tube (Valve) RIAA Phono Preamplifier Project


Posted on Feb 5, 2014

This is a project that I always wanted to do, but managed to put off for a long time. It has been over a year in the doing. Partly because there are so many good phono preamps in existence and I was slightly concerned that it was beyond my design skills. It took over a year to get it up to my satisfaction. There were several iterations and lots of


Groovewatt a DIY Vacuum Tube (Valve) RIAA Phono Preamplifier Project
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frustration along the way. My goal was to make a preamp that would not embarrass the builder with inferior performance. I used a number of commercial products for comparison. My thought was why bother to design and build something that was already available for a lower cost. As it turns out, it was not as inexpensive nor un-complicated as I first hoped. I wanted response within 0. 5 dBV of the RIAA curve, low distortion, and a signal to noise of about -90 dBV. The first two were easy, the signal to noise was not. I did a lot of research on the RIAA curve and the various problems that are inherent in phono preamps. I tried active, passive and a combination of active and passive equalizations. All work and all have positive features and all have negative features. I tried several configurations and tube types. The final design uses things I am familiar with. The input stage is a symmetrical SRPP. It feeds the passive equalization network. The second stage is nearly identical with the first and is direct coupled to the third stage which is a cathode follower. I eventually used Gold Pin JJ ECC83S in both of the SRPP stages and half of a ECC81 (12AT7) for the cathode follower. Gain is sufficient at 45 dB for me to use a high output MC cartridge (I use a Dynavector 10X5 with an alternate of a Denon DL-110) to drive a passive volume control to feed a pair of Oddblocks. The initial design tried using other tubes but none had...




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