AC 30 tremelo mods?

soundmasterg · Post by **soundmasterg** » Fri Jul 25, 2003 10:47 pm

Is there a way to modify the reissue Korg AC 30 tremelo/vibrato so that instead of preset values, you can have a pot that rotates like a Fender so you can get any settings in between? I figure the hard part has got to be integrating the new parts with the PCB? Thanks!

toneman · Post by **toneman** » Thu Jul 31, 2003 5:52 am

Yes, It can be done. I've done it. You take a 1 meg audio taper pot and replace the 3-way switch and remove the resistors on the pcb and add a wire and a resistor in a spot and it's there. Easier to show you than explain here. But can and has been done.

kennyhowes · Post by **kennyhowes** » Thu Jul 31, 2003 6:53 am

Man, someone did that mod in my AC30st head before I got it and it TOTALLY rocks, verrry versatile.

My friend Chris has a JMI AC30 combo wherein the Vib/Trem buisness is wired into the Brilliant channel. (I think it's a back panel TB.) Now THAT'S a cool mod.

soundmasterg · Post by **soundmasterg** » Thu Jul 31, 2003 11:00 pm

Thanks Don. I'll take a look at the schematic and my amp the next time I have it apart and see how hard it is. I may end up having you do it for me at some point, but we'll see.

toneman · Post by **toneman** » Fri Aug 01, 2003 8:41 am

Greg; Hi! I can tell you how to do it but would be best in a phone call as it's very lenghty to write out here. Easy to do if you've got electronic experience.
Basically it involves removing the 3 resistors from the board(1 meg, 510K & 330K) and taking a wire from the pcb to a 1 meg pot and putting a 220K resistor on one side of the pot to ground(I like a 220K as it slows down the speed a bit. you could always use a 330K though if you like that faster slow speed.)
Anyway, easy easy!

soundmasterg · Post by **soundmasterg** » Fri Aug 01, 2003 11:43 pm

Hi Don. Thanks for that last tidbit. I can probably do it with that added part, but it will have to wait. I've been working on modifying an old Conn organ power amp( 3 amp sections on it ), adding 3 new preamps in a seperate chassis( BF Fender with princeton trem, Vox/Marshall style preamp, and 2203 preamp), and having it all in the same head. So when I get done I'll have 3 new amps. I've been working on it for like 5 years and am getting close to finishing it, so that has to come first!
And I may send my AC30 speakers to Ted Weber also to get rid of some serious ghost noting that they've done since the amp was 6 months old. I've heard all AC30's do it, but then I've heard they don't too. Who to believe?

toneman · Post by **toneman** » Sat Aug 02, 2003 2:14 pm

Ghost notes....I get them from the speaker in my old AC-15 when I crank it. I also have an Alnico Celestion in my `62 brown Deluxe that gets ghost notes and cone cry.
Now ghost notes from the amp and not speaker can be resolved by going up to a dual 32uf filter for the first filter stage in place of the dual 16uf in an AC-30. I look at it this way; if you're going to play loud with an AC-30 then use the 32uf's. If you are just going to play clean then use the 16uf's..

soundmasterg · Post by **soundmasterg** » Sat Aug 02, 2003 4:07 pm

Hi Don. I guess I should have said cone cry, as that is what it is. If I use a 2x12 cabinet with 2 70w Celestian modern lead speakers in it, the cone cry noise goes away. As soon as I plug in the Vox Blues again, I have cone cry. Of course it only happens when the amp is approaching half way up and more, but I do play often there. If the cone cry is still there, but not so prevalent after Ted gets through with them, then I'll be happy. I just hope I don't lose too much of the aliveness of the speakers....
My AC30 is a '93 Korg reissue, so it doesn't have the 2 16uf caps. In fact, I had a guy mod it about 5 years ago with larger caps to get rid of what I thought was ghost notes, but it didn't make a difference. One of these days, I'll take them out and go to some 32uf or 16 uf. I need to find some good GE EL84's to use for recording purposes. The EI's sound just as good as the GE's but they don't last as long and don't quite make as much power.

toneman · Post by **toneman** » Tue Aug 05, 2003 7:10 am

Have you tried the new Ei Elite EL-84's with the gold pins? These are a better built tube, tested better, last longer and sound great!
On your amp use two 22uf's for the first two sections and then 10uf's for the other four cans in that amp. This seems to open them up and they sound great. The amp breathes a bit more. Cone cry can be mistaken for ghost notes. They are, as you know, two completely different things.

soundmasterg · Post by **soundmasterg** » Wed Aug 06, 2003 10:30 pm

Hi Don. I haven't tried the new EI Elites yet because I still have a stash of the older ones to go through. Next time I do buy EI's though, I was planning on getting the Elites. I would like to have a quad of GE's to use for recording only however.
Two 22's and the rest 10's? Sounds good to me. I like having less filtering in the preamp anyway. As I said before though, it will be awhile before I start to tweak the AC30 again. Got to finish my other project first!
I am almost positive the problem with my AC30 is cone cry, as it stops when I go to different speakers. I suppose it could be a cabinet rattle or something along those lines too, since when I use the other speakers, they are in a different cabinet altogether. I have to do something to get rid of it though because it is so annoying I can't play much in the way of leads when the amp is up loud or it drives me crazy!

admin · Post by **admin** » Thu Aug 07, 2003 10:06 am

Don: Either than the gold coating used in the pins of the new Ei Elite EL-84's, is their construction any different from the Ei Elite EL-84's that have the standard pins? In other words, would expect any perceptible difference in sound between the two types?

toneman · Post by **toneman** » Sat Aug 16, 2003 9:23 am

Peter; it's a bit sturdier than the normal tubes.