AC30 top boost tone stack

[jfutral]

While I wait for my new PT, I've been playing around with this amp with what I have. I am wanting to utilize a Vox top boost pre since I've never had a Vox. I got it wired up, but it is such an unusual sound, I think I may have wired it backwards... but I can't tell! I know it is a bit of an odd duck... I mean, a typical Fender or Marshall tone stack, I can tell when I turn the treble down or the bass up. I feel like I wired wired it up correctly, but this is... confusing? Should it be?

I tried to find something online that might talk about how it might be different. I found a nice PDF on the history of the top boost. It does say it will behave differently, but I didn't think it would be this different.

Thanks?
Joe

[jfutral]

Just to add to this Vox discussion, any thoughts on how to incorporate a post PI MV on an AC30 style build, particularly with that Tone Cut circuit in the same location? Would it go before or after the tone control? Either? What might be the difference if either works?



Joe

[jfutral]

OK. Maybe visuals are needed. Here is the wiring per Hoffman's website. I assume this is looking at the pots from above with the terminals on top.



Joe

[Jazz P Bass]

Read this discussion.
It may help you understand the top stack weirdness.
Link: http://www.vintageamps.com/plexiboar...=94991&start=0

[jfutral]

Wow. That was a great read. The grounded bass is NOT an error. Hmmm.

However I do think the Hoffman wiring does have the bass wired backwards. Looking at the pic of back of the mod unit here, it look like the bass control would be grounded on the left terminal if they were on top. Hoffman's diagram has it on the right if the terminals are on top. If Hoffman's drawing was meant to be seen with the terminals on the bottom, then the treble pot would be backwards... I think.

Joe

[Pedro Vecino]

Is common to find old AC30´s with the controls wired backwards.

[jfutral]

Well, there you go! With the way it behaves, it is kind of hard to tell which way it _should_ be. I flipped the bass end-leads and it SORT of makes more sense, but it is still weird! Seems to affect volume, too. If I have bass and treble full open, it is softer than at 12 o'clock. I guess straight up is about as close to a flat response as you get, from what the articles seem to say.

Joe

[Pedro Vecino]

In a standard AC30 when raised from 8 to 10 the bass, there is a drop very noticeable in the mids.
The tone circuit wired backwards is disconcerting even if you are familiar with the AC30´s.

[pdf64]

The 4 AC50s that I've worked on have had the tone controls wired backwards. Pete.

[imaradiostar]

I've built a few AC30 style preamps and always ended up rewiring the tone stack to something akin to a marshall or older fender.

jamie

[jfutral]

Well, I had to see what all the fuss was about with the Top Boost. And since I am not likely to ever be able to afford/justify a new Vox, much less a vintage AC-anything, I thought I'd wire my own. This is definitely a unique breed, assuming I am wired and equipped properly. I do like variety, so I'll keep it for a little while.

Still need to figure out that MV question. I'm thinking post Cut for the MV. Kind of makes a linear, logical sense in that "adjust the over-all volume of the tone" vs "adjust the over-all tone of the volume" way. I don't know about electronic sense, though.

Joe

[MikeM]

I'd put MV after the cut control as well.

[jfutral]

I'm kind of worried about any unwanted interacting. I mean, really, if I put the MV after the coupling capacitors and before the grid resistors, it is effectively kind of ganged together with the Cut, right? Is there some way to separate the two controls so they are more like stages? Doesn't the Cut sort of act like a frequency centered MV?

Joe