Originally Posted by dcheming
I recently got my two turntables out of storage after three years. Since I gave my old DJ mixer to a friend a while back I needed a cheap solution for a phono preamp. Eventually I want to build my own mixer but for the time being I chose to simply build the $15 Velleman K2573 Stereo RIAA Correction Amplifier.
I substituted some of the low-grade parts included in the kit with the best I could find at Norvac Electronics: the signal caps are mylar bypassed with Dayton film/foils instead of the stock polar electrolytics, the equalization capacitors are silver/mica instead of the stock ceramics, and all the resistors are NTE metal oxide.
The sound of this is actually pretty good surprisingly. Overall I like it better than my friends slightly modified NAD PP-1. The only area the NAD beats it is the deep bass extension but we're planning on putting polypropylene caps in the NAD soon though which should turn the tables. Next up will be a Bugle phono preamp from Hagtech.
Well if you do a spice-analysis, the amplifier has more than 3 dB deviation from the RIAA curve. The response peaks at 10 kHz and has its lowest value around 110 Hz (more than 3 dB), so no wonder there is too little bass.
Component values should be: (only one channel shown)
Unchanged:
R5 = 1M
R6 = 2.2k
R8 = 3,3k
Change:
R4 from 100k to 76.33k
C4 from 680pF to 1.06NF
C5 from 3.3n to 2.95nF
This will give a response within +/- 0.1 dB. You will have to find suitable parallel combinations for this yourself.
In my experience it is almost impossible to make a phono preamp with standard component values.