Capacitor Identification

[oltern8]

Hi

recently I managed to lay my hands on a citronic sm650 dj mixer which is considered by many to be a good sounding dj mixer.
Unfortunately I am finding the mixer a bit too bright and wonder weather this is caused in part by the capacitor used in RIAA op amps feedback loop.
I am relatively new to electronics and haven't seen a capacitor of this type before it is a 22pf cap (C45) on the schematic and wondered what its dielectric is. The only caps i can find at this value are either ceramic (not recommended for audio) or mica which by all accounts can sound a bit bright. i realise that the brightness could be caused by many other things but the mixer was cheap and i am having fun experimenting with different components.

Since owning the mixer i have replaced the smoothing caps with panasonic fc's they are not burned in yet but yielded a small improvement.
I have also tried changing the op amps from 4558 to TL072 or OP275. I am undecided which ones i like best but both are an improvement over the 4558.

So if someone out there could id this cap for me i'd appreciate it.

thanks

oli

Phone Board Version PC 1141 / 1

 

[rayma]

It's doubtful that a 22pF capacitor is part of the RIAA network, but COG ceramic capacitors are good enough for audio.
Do you have a link to the schematic?

 

[oltern8]

schematic

Hi

Thanks for the reply. Here's the relevant page of the schematic. It's not on the web as far as i know. If you want i can send you the complete schematic it's too big to upload here in its entirety.

I was under the impression that ceramics were a big no no especially in place that have such a bearing on the overall sound of a circuit.

I thinks I might have solved my initial issue with the brightness by installing a NE5532 in place of the op amp responsible for the riaa amplification. I know its not really a suitable alternative as far as the data sheet info says but sounds a hell of a lot better.

thanks for you help

oli

 

[rayma]

I thinks I might have solved my initial issue with the brightness by installing a NE5532 in place of the op amp responsible for the riaa amplification. I know its not really a suitable alternative as far as the data sheet info says but sounds a hell of a lot better.

thanks for you help

oli

That's not an RIAA stage, just a 1.5 times gain stage. The 22pF/33Ohm feedback parts are a stability compensation network.

 

[oltern8]

feeling stupid

thanks I have found the riaa network on the schematic and it makes more sense although i haven't seen one like this before. the cartridge is loaded at 56k so that probably is contributing to the bright sound.

thanks for your help.

oli

 

[rayma]

thanks I have found the riaa network on the schematic and it makes more sense although i haven't seen one like this before. the cartridge is loaded at 56k so that probably is contributing to the bright sound.

You might also need some shunt capacitance, check the cartridge specs.