I experimented with four chips in my SD-1 from left to right; RC4558P, OP275, LM833 and JRC4558D.


Please note that all of the below writing is my opinion and you may prefer different chips over my choices. I suggest you buy all four chips yourself and try them out. They aren't too expensive and give quite a wide range of options.

The RC4558P
This is what used to be used in the old Ibanez Tube Screamer 808's, and it is quite obvious to see why! I really like this chip, it isn't transparent - and in this case that is a good thing! I like this pedal for a boost but it really shines on the clean channel! This is going to sound really subjective, but the sound is quite tube-y, sounds fuller and more 'alive' than the other chips. Probably a tie favourite with the OP275.

The OP275
This is what I consider to be my favourite at the moment. It isn't overly transparent, but not too much of a 'cloth over the speaker' type of tone either. This chip to me is a good all-rounder, not ideal for using the SD-1 as a boost but still provides a very good sound when used as one and the overdrive tone is good too. I find this chip to have a little more bass than the other ones.

The LM833
This is probvably my least favourite chip of them all, I find the tone quite thin when used as both a boost and overdrive. When used as a boost it seems to take away all the bass and leaves you with a weak tone. The overdrive isn't terribly bad, but it isn't as nearly as good as any of the other chips and gives a cheap solid state-y type tone.

The JRC4558D
This is the standard chip in the new SD-1s (well apparently it has the JRC4558DD, but most people I've talked to can't hear the difference between the two). This unit has a little more 'gain' in my opinion, sounds a little more aggressive than the other ones, which isn't a good thing or a bad thing nesisaraly. The tone of the chip seems to have more treble and a bit more 'bite' but this is my second least favourate of all of them. It is similar to the OP275 in the sense that it isnt either very transparent or not transparent at all, it is in the middle of the road in this sense. I do find the tone of this chip quite boring after a while.