Vox AC30 Cream Edition mod....

simonbeckwith

......is it possible/easy to mod the normal channel to be another top boost channel so id have two top boost channels?


Seen one of these on eBay which you can add to the older single channel versions (i assume)?


http://www.ebay.co.uk/ulk/itm/262128976698


I rarely use the normal channel but would definitely use two top boost channels.


Im guessing id need to check the spec of resistors etc on the existing top boost channel to make sure it reacts the same way? Although a slight variation might not be a bad thing?


Any thoughts?
@icbm, @4114effects or anyone else thats into amp mods?

ICBM

In theory you could re-route the amp so the Normal and TB channels mix before the tone stack which would give you two TB channels (although with one set of tone controls), and change the coupling cap value and add the bright cap on the Normal channel to match the TB, but I would need to see inside the amp with this in mind to see how feasible it is. I don't have a schematic or a layout and it's not something I've ever thought about when working on one. It will also probably change the sound of the TB channel at least slightly too.

But to be honest, if you want to use two TB channels so you can have one louder than the other, just get a booster pedal. That's really the only difference it will make since the first gain stage on each channel doesn't overdrive.

simonbeckwith

@icbm So, run a boost on the normal channel and then run one channel louder than the other? Didn't think of that! So simple! Haha! Thanks dude

paulnb57

Idiot!

simonbeckwith

Oi @paulnb57 !!!! Only because the normal channel is quite a bit darker than the top boost, if i can dial them in to sound the same or very similar I'll probably be on to a winner. If not, who knows!

paulnb57

Calm down dear! FFS! Get a Marshal and stop fucking about!

simonbeckwith

Yeh......the thought has crossed my mind on several occasions

paulnb57

I was joking, but hey-ho!

Cirrus

As far as circuit mods go, the normal channel is quite easy to make brighter - IIRC the original non top boost "Bright" channel is basically the same basic circuit as the normal channel, but with a smaller coupling cap, a bigger bright cap and a smaller cathode bypass cap on V1 so it has less gain at low frequencies. It won't have the same compression and midrange notch as the top boost channel but it'd be brighter.

ICBM

I meant simply use a boost pedal into the TB Brilliant channel, since the only effect of modding the amp to give two TB channels is to give two different volume settings with the same sound.

In fact, modding the Normal channel to a *non* TB Brilliant channel makes more sense, since they will still be different. The difference between the non-TB Brilliant and the Normal is very simple, it's just the coupling cap size and the bright cap. They share the cathode network. That should be a very simple mod.

The difference is that a non-TB Brilliant channel is *quieter* and slightly thinner-sounding than the Normal channel, whereas a TB one is louder and thicker, so the non-TB is a better rhythm sound and the TB a better lead.

simonbeckwith

@icbm the top boost channel I've been running with the gain flat out, so adding a boost would only add more gain, not give me an increase in volume. I would just like the same sound, but louder if possible. TK I'm just gonna have to accept I'll need to run pedals in to the amp running clean.

ICBM

Yes, that's right. If the TB channel gain is maxed out then you can't get more volume because the master volume applies to both channels. No matter what you do to the Normal channel it will be no louder. What you need is an attenuator with a bypass switch. Set the amp for your boost level with the attenuator bypassed.

simonbeckwith

Who makes one of those that isn't ridiculous money?

ICBM

Weber. The Mini Mass 50W is available with a footswitch option.

simonbeckwith

Cheers dude

simonbeckwith

And this sits inbetween the amp and the speaker? Think my speakers may be hard wired in so I'd have to disconnect and attach a jack to one end and make a new lead to attach to the speaker also with a jack to allow the mini mass to sit inbetween the two?

ICBM

simonbeckwith said:

And this sits inbetween the amp and the speaker? Think my speakers may be hard wired in so I'd have to disconnect and attach a jack to one end and make a new lead to attach to the speaker also with a jack to allow the mini mass to sit inbetween the two?

Yes, between the amp and the speaker.

I would need to check for certain, but depending on what order the External and Extension speaker sockets are connected in, you may be able to do it very simply. The *External* socket disconnects the internal speakers, and the *Extension* socket is in parallel with them - so you can use the External as the amp output and the Extension as the speaker *input* as long as they're that way round and the Extension socket is directly connected to the speakers and not the amp... if that makes sense!

Unfortunately I don't have a schematic or an amp to check it on, but you could try it - just plug a cable between the two and see if the amp works - at low volume only, in case it doesn't! If it does, you know the jacks are in the right order and you can simply connect the attenuator in there - making sure they're the right way round, with External to the attenuator amp input.

simonbeckwith

Excellent, many thanks!

simonbeckwith

.

ICBM

I hope that wasn't you thinking better of a post to say you tried it and the amp blew up :-O .

paulnb57

@simonbeckwith - one of the finest, most concise and well reasoned responses you have to ever made on the Fretboard, both informative AND entertaining! Well done yoof!