@Uklawyer, yes I am still taking the amino acids and being very careful to maintain a low free glutamate diet and my tinnitus is only loud when I first wake up in the morning, since all the stuff is no longer in my system. As soon as I get up I take my "cocktail" and within 30-45 minutes it's gone back down.
I still have tinnitus but the volume is about 3/10 instead of 8/10! I found this great website that I can look up the amt of free glutamic acid and aspartic acid in a food and that is helping me make better food choices. I know everyone's tinnitus is not caused by this malfunction of the glutamine neurotransmitter system, as mine is, but this is the same problem that causes focal epileptic seizures and also Alzheimers, Parkinson's and ALS.
By the way, like the person who posted just above you, the L-Carnitine caused me a big bad spike so I don't take it. My holistic doctor suggested Quercetin so I've added that (500 mg 1x) to the NAC and L-Theanine.
I still have spikes occasionally and I always assume that something I ate had too much glutamate, but the spikes don't last. I have about 75% or more of my waking time at very quiet level of tinnitus. I discovered dairy is a huge glutamate offender, I sure miss ice cream!
Here's the food data website: when you get to the Data page that looks like a spreadsheet, scroll down to "protein and amino acids" and click on More Details, it's in that chart.
https://nutritiondata.self.com
NAC has been taken off the market here in the US, I blame our Big Pharma of course. It's hard to find here now but it's still out there. The FDA caused a big brouhaha about it but it's just an amino acid! When I learned it was happening I snatched up every bottle I could find and have 14 months supply. You can probably find it easily in the UK, I'm assuming from your user name that's where you live. Let me know if this helps you, and good luck!