Do I need a filter for preamp?

[obrien135]

Hello,

I recently built a preamp to increase the amplitude of a turntable output before feeding it into an AUX input of a cd player. It works pretty good , but I guess it emphasizes the higher audio frequencies because it exaggerates the hiss and *****le and every imperfection of the grooves in the records. Some records sound good and others don't. If I put a low pass active filter before the preamp, on the output of the turntable, with a cutoff frequency of about 15KHz and a steep enough rolloff, would that help? Or should I try some other cutoff frequency, or some other method?

George

 

[Prototyp_V1.0]

Just search for "riaa preamp filter" on the net. Google returns a lot of schematics

 

[obrien135]

Does an RIAA filter knock out some of the high end frequencies as well as the cartridge rumble?

 

[FvM]

It does not attenuate low frequencies.

 

[Audioguru]

Are you talking about playing old fashioned vinyl records?
The machine that cut the grooves could not move much so they added equalization to the recording circuit that decreased low frequencies at a certain standard rate then the preamp for a magnetic cartridge had reverse equalization that boosted the lows up to normal and cut the highs back down to normal. The equalization is called the RIAA curve.

The original RIAA curve boosted very low frequencies a lot which resulted in rumble on some cheap record players. Later equalization reduced low frequency boost below 50Hz.

 

[obrien135]

Thanks. I did a search for "RIAA preamp filter" and found a circuit on the link below in figure 5 which I modified a little and it works great . Thanks for the help.

George

**broken link removed**

---------- Post added at 10:20 ---------- Previous post was at 10:13 ----------

Thanks. I found one on the link below and built one similar to fig. 5 and it works quite well. Thanks for the info.

George

**broken link removed**