AC30cc2 & C2, also AC15C1: my mods

[Jay]

I modded my ac30 by buying a laney vc30 instead.

really juicy cleans once I chucked a eminence legend in.

Did that amp turn up or did you tell the sender it didn't and then offer it for sale at a later date?

No second chances?

[TmcB]

Today I got a few things cooking, and it’s interesting having now modded and tinkered with many things since the first post.

Firstly, there’s a lot less magic reading the schematics - I’m largely aware of the building blocks now and where to find good things. Secondly, far less imbibing of the snake oil
- I’m more of a can-I-be-arsed-doing-this with some tinkering (particularly caps in the signal path) because I know how to do things properly and nicely now, and it takes me longer.

Never the less, today I installed jacks for the speaker and reverb, rather than having speakers hard wired. Rather than building a junction box outside and screwing it to the wood, so had a far more elegant solution using the three existing holes in the chassis. Had a mare getting the reverb going because solderer of the year here managed to connect the hot and ground of the rca output together with an errant solder blob…

Anyway, that worked out beautifully eventually, and I fixed the tremolo speed, made the reverb marginally nicer (still sucks), got more gain in the normal channel, and preamp plate resistors out.

Tomorrow I’ll switch out the grid and plate resistors for something not batshit crazy from stock - didn’t really want to be faffing in the power section last thing tonight.

Wharfdales don’t suck as much as I remember but blues are incoming anyway. Tubes are awful and stock from
factory so hopefully that’ll perk this thing up a bit.

[Bg]

I modded my ac30 by buying a laney vc30 instead.

really juicy cleans once I chucked a eminence legend in.

Did that amp turn up or did you tell the sender it didn't and then offer it for sale at a later date?

No second chances?

On this occasion no, I did poll both Molly and the mods but from my messaging with him that it became obvious he wanted to be buying selling etc along with other randomness

[TmcB]

Because apparently I’m blogging, tonight I changed the screen grid resistors from 100ohm to 1k because modern el84’s can’t handle that madness, and grid resistors to 3.3k. I also swapped the tiny fx loop cap to a big one so no low end loss happens any more there.

Had some nice Panasonic caps about so replaced the coupling caps for the hell of it whilst I was in there.

I also swapped out all the trashed black screws and replaced with nice new stainless ones on the back panel.


Next couple of days I have a blue coming, some silver mica caps for tone stack/bright cap faffage, and finally a new set of tubes.

[RectifiedAmps]

Did you hear a big difference after changing the screen resistors? It should make a big difference to the operating state of the EL84s but I’m curious to know how it sounded.

[TmcB]

Haven’t noticed much yet - old valves are pretty knackered but seemed not to make much difference tonally, which bodes well!

[TmcB]

Last night I changed out the lil’ caps to different values with silver micas. I’m unsure the mojotasticness of micas is a thing but the values sound nice. I have to point out that you need to put the cap across lugs 2 and 3 of the normal pot, not 1 & 2. That’s the reason you hear people say the brilliant switch doesn’t make any difference after the mod - it’s never actually worked properly

Also the little decorative collars are secured with loctite, and you just need to use a little acetone and it’ll come loose easy. Wish I’d known that last time I did this and had to get a new faceplate made from scratching the hell out of it. Not this time though!

Today I installed a fresh set of tubes, which thankfully sorted out an intermittent popping noise that was happening.

Also, blue from Ben arrived today and paired with one I had sitting around.

Right now I very much wish I had taken a before photo. The back panel was inexplicably covered in vinyl, no machine heads, vinyl coming off, wharfdales installed upside down with random wires and chocolate blocks. Lots of cleaning and rejigging was required.

Last thing left to do really is to convince my wife to make another reverb bag, and to get another reverb tank as the decay is waaaaaaay too long.

Total cost would be $480 for amp, $300 for tubes, $50 parts (caps and resistors), some amount for blues. Sounds like a bit but this will stand toe to toe with the best AC30’s made since the 70’s

[TmcB]

Whilst I’m at it, why not add some AC15C1 mods?
They’re all the bloody same vibe anyway

R1 Jumper (more gain on normal channel)
R5 & R6 220k (v1 & v2 plate back to vintage spec)
R24 & R25 360k Schems are weird here - there is a 360k instead of an 820k in my AC15c1 so there might be a field revision.

C4 68pf or remove (normal bright cap)
C8 remove (normal bright cap)
C13 47pf (old Top Boost value)
C32 & C34 47nf (trim bass before PI
C67 remove

Wire from south c67 pad (ground) to lug 3 ( left when looking at the back) of bass pot (there’s a small hole in the board next to it you can use. Bonus points - put on switch in the middle of the wire to go between new tonestack style and vintage - vintage makes the mids scoop out at certain settings

Another cool thing would be to put a 20k resistor on a three way switch so it goes vintage - normal - mid boost

[Reg18]

I kinda want to buy another AC15/30 and do these mods just for fun, glad you have documented it. I feel this might come in handy one day, if a AC30cch was available cheap locally I might just do that.

[vyfster]

I've been following these mods that you're making as I have a AC30C2 (or cc2 - not entirely sure which). I have zero confidence in doing any of these mods myself and probably too expensive to ship the amp to you (if you were willing to make the changes - obviously paid).

Anyone in Auckland able to make these mods to my amp?

[TmcB]

Right, just had a bit more of a tinker and I think I’ve cracked the ac15c1 code.

Switching the tonestack to vintage gives you more interactive controls and a small bass boost.

Switching the plate resistors from 100k to 220k changes the tone from being bright and a bit plinky (100k is more like a fender tone) to having a lot more gain and a lot more bass.

I was having a bit of a trouble with the amount of bass until I swapped c32 and c34 from 100nf to 47nf. Really sorted it out and gave it fullness but without it being too much. This was the final piece of the puzzle (other than a blue)

I also changed the 3spring short reverb tank to a 2 spring mojotone large tank and it sounds so much better! I changed R60 to 27k to increase the reverb tank output level a bit and it sounds nearly Fenderish.