Audio Research SP16 annoying volume control

Is it happening in the lower part of the scale ?

Audio Research has a taper volume kit...or whatever they call it. It allows more steps at lower range so it doesn't get too loud too quick. And you can reduce gain of this preamp. Call ARC and talk to them. Reducing gain will solve that issue. It may also have a positive effect on overall noise floor of the preamp, have smoother highs and less forward mids, but at a possible expense of overall bass drive. bass may become a bit softer.

Mating a preamp with an amp, you need to consider several things, such as gain of preamp, gain of amp, amp sensitivity, preamp output impedance, amp input impedance.

What you're experiencing is not unusual. it isn't a design flaw of an ARC preamp. It's a simple mismatch between your preamp and your amp.

Hello Elberoth2
Yes its happening at the lower part of the scale, the volume increments seems to be one press, then 2 press, then 3 presses but its already loud at around the 3rd or 4th light.
I think the further up the scale then there are 4 presses to each light increment.
At the moment I am not using a ARC amp, so maybe its a mismatch of the gain of the amp or CD as Audphile1 points out.
But there are serveral reports from other users that the volume on the SP16 is not very adjustable at the lower volumes.
It just seems to me as a way to differentiate between the more expensive ARC gear, they have dumbed down the functionality which to me seems very stupid as they have marred what is otherwise a great piece of equipment.

I had similar issues with my ARC LS-15.
I swithced to LS-25 that has more volume steps and it helped, but the solution was delivered by adjustable gain of LS-25. I used it only on lower gain setting. That really helps. That's why I suggested lowering the output gain of your SP-16. Or get another preamp. One of the best volume controls I've seen on a preamp is on Sonic Frontiers. You really can not ask for a finer adjustment. I think it has 180 steps or close to that number anyway. You can fine tune that volume control. It's really nice.

The problem you identify is one I also experienced, mostly because I am using high efficiency speakers. There simply was not enough flexibility when listening to high output sources (i.e. CD's) at low volume levels. The good news is that it is an easy problem to solve. Send your unit back to ARC and have them do their "gain modification" which simply involves dropping a high quality resistor in whichever source you would like to shelve down the preamp output. I only did the CD input so the mod was called the "CD only gain modification". Now I have much more flexibility when setting the volume during CD playback, particularly at low listening levels. A secondary effect is that the volume is now matched for CD and LP playback. It cost around $60 if I remember correctly and they did a thorough check up on the whole unit while it was there.