Necessary with input capacitors on EQ?

[hansibull]

Hi!
I just got THIS NE5532 based EQ form Ebay today, and I immediately sat down and started soldering.

I discovered this kit had a pair of cheap 4.7uF input capacitors, but my amplifier already have a 1.0uF cap. is it necessary to have input caps on the EQ too?

 

[indianajo]

Random sound sources put out a little DC voltage which can bang op amp outputs into the power supply rail if there is any gain at all. I've had trouble with tantalum input caps (popcorn noise from the store, 92% failure rate) and aluminum electrolytic caps are generally unreliable after 15-20 years, 5 for the really cheap ones. If you have room use a plastic film cap. If you don't have room I have been using 4.7 uf CPO ceramic caps with a 50 V rating. Yeah, they are non-linear, but the excess voltage rating straightens out the curve some; I really like them better than the tantalums with the popcorn noise. They are right next to the speaker in a power amp so I don't think the Aerovox gold ceramic caps I bought (which at >$5 each are not "cheap" caps) are not microphonic. If you are willing to put up with non-function of the EQ when the source device is at fault, you can remove them.

 

[hansibull]

I have a pair of expensive 3.3uF caps, but the problem is that these have very short leads, and is twice as big as the mounting holes on the PCB.
(same size and value as THESE)
I may try to fit in these, so I don't need to replace them after some time 🙂

 

[hansibull]

Do you have any recommendation for input capacitors for OP-amps?
How does electrolytic caps affect the sound versus mylar caps?

 

[Refugee1]

If you connect a magnetic cartridge to the input any biasing currant for the OP amp will be grounded through the low impedance coils in the pickup.