Hi, A couple of questions...how were you measuring it. They tend to be not as easy as would appear. The signal input can mess stuff up. If the impedance is not right it can cause issues, same for the output loading. I use a real time Bode plotter on a digital scope to do mine with a 1% reverse RIAA front end. Anyhow, your schematic is not the latest version. Later ones changed the .03 to a 0.027 and the 71K resistor to a 65K. Cathode resistors on the first stage to 910R and second stage to 820R. The changes reduced the distortion a tiny bit and because the change in cathode resistors in the first stage altered its output impedance it forced the change to 65K and the 0.027 capacitor. In a passive equalization arrangement like the one used the impedance of the driving stage and any series resistance to reach the RIAA components are inter related. The response in mine (I have three still here) measure less than 0.5db off at 20HZ and 20KHZ. I attached a plot of one of the preamps. The simplest change you could make to yours would be to change the 0.03 to a 0.027 capacitor it would give a slight increase on the top end. However ...the key band is 50HZ to 15K. If your data is correct then you are less than one db off at those points. Very little music is below 50 or above 15K and few of us can hear anything in those regions. The bottom end roll off may be a good thing depending on your turntable as it will act like a rumble filter.
Good listening
Bruce
Attachment:
L CH RIAA.jpg
Login
Register
FAQ
