AC30 1979 Mods

[jimmyflanders]

Hi! I have a 1979 ac-30 - rose Morris but only just, if you know what I mean. It is PCB, but the one with 2 thin boards with the components set up in an accessible fashion and panel mounted pots. I got it from a friend for cheap as it needed a little work but I've rectified the actual 'issues' - new cliff input jacks, cts pots and new cap cans (f&h I think).
I love the sound of it, but am finding it a little spikey.

Has anyone here tried resizing the mid resistor (10k) to any other value to bring down the midrange fixed frequency, or done any time stack mods?

I have removed the cap across the tb volume (I think this is the standard 'bright cap' mod, but find the tb channel too fizzy and harsh, especially with dirt pedals.

I saw that lyle Caldwell came up with some normal channel mods for the cc, I had a go at converting these for this amp (he mentions the 330k resistor ahead of the volume pot, I have a 220k on this amp - I removed it, the normal channel gain increased considerably, but the tb channel then stopped working!
Any ways to fix the fizziness or ice pick highs?
Unfortunately funds are minimal and blues are out of the question. I've tried a graphic eq, which has helped, but I think I need to tidy up the issues at source really.

Any thoughts?[/img]

[Roe]

vox changed a lot of values over the years, but the holy numbers are mostly found in the early-mid 60s schems

[rooster]

It's funny how some versions of the basic amp can sound so different. A typical AC30 has so much bass in the TB channel that many people don't realize how bright the tone stack actually is. Your amp obviously lacks the bass of the trad build. So...

If it's too bright, sure pull the bright cap, but also replace the 50pf cap that controls the treble of the TB channel. Change it to 250pf and see what you think.

[Blackburn]

I think you really need to eliminate the speakers as a possibility before changing stuff internally. I once was fiddling with an octal Deluxe build and kept trying caps of different values here and there without even considering that some old alnicos might be the source of the 'spike' in highs. Sure enough, changed over to another cabinet and the amp was dark as hell, not at all clear. Don't think that Blues will be the magic ticket either, some report them being spikey in the high end. Maybe try the Scumnicos, as they are cheaper than Blues and people speak very highly of them.

Hard to get a 'good' alnico speaker cheap these days.