Hey guys, I am building a phono amp for my favorite beogram 2000. It includes a MMC4 cartage and its time to adjust the pickup load on the preamp. The input resistance is 47K ohms, thats for sure. However the capacitance is killing me, Beoworld product page recommend 220pf, I have read 100pf or 400pf in other places. The preamp is now working with 470pf, as you guys are much more experienced than me, shall i change it?

Yiangos :)

For the earlier MMC20 series the correct capacitance was 220 pF, so perhaps try with something smaller than 470. But in the end, let your ears decide!

Tnx :) just orders some 220pf caps. I will try a 220in one channel and 470 in the other so I will be able to decide which is better . Am going to post my results later:)

Hi,

Just to make your decision a little harder, I use 330 pF...

Oh another cap to test! Just a quick one, how does the sound gets as capacitance is decreased?

yiancar:

Oh another cap to test! Just a quick one, how does the sound gets as capacitance is decreased?

Well usually the response falls down, resulting in a dull top-end. But on some cartridges, the increase gives a horrible lift at about 10 kHz with makes up for a livelier, but more tiring sound. Experimenting is the only way to find out. With B&O MMC series, I settled for 330 pF, although B&O goes for 220pF which gives a flat response, lacking a little in life for my tastes. With SMMC 20EN 220pF is just right! With a Goldring 1022, I also increased the load to 56k to flatten the response.

A can of worms, this.

Thanks :)

Guys just realised that i made a huge mistake, in my original trt i used 4700pf insted of 470pf, thats why it sounded so bassy and dead :), Tomorow I will try the 220pf . I also couldent find any 330pf with <5% tolerance :(

yiancar:

Guys just realised that i made a huge mistake, in my original trt I used 4700pf instead of 470pf

Oh dear, it must have sounded dreadful!

Well it was REALLY bad, everything sounded darkish. It was bad, "stop me now before i burn your ears" bad

In order of preference, make sure you use NP0 or C0G MLCC ceramic caps, for experimentation. They are the most stable of the "cheap" capacitors. Murata or TDK here.

Once you've decided on the correct value, you can install Polypropylene film caps of the same value for added smoothness in sound. Try Wima, Nichicon or Panasonic here.

Menahem

Finally guys . the amp is cased up and fully working . I settled with the 220pf and some wima caps. It sounds very very full and balance i can say. Also the RIAA curve of the amp must be dead accurate as the pops have soften out.

Thank you for all the knowlage you gave me :)