Rocket treble cap preference

[Gaz]

I'm not sure if there's any sort of consensus on this, but what are folks' preferences for the treble cap in the tonestack?

My understanding is that it's either the standard Top Boost stack, subbing the 50p for 500p, or the weird 2-Rock stack found in Abbott's drawings.

I dig the 500p with single coils, and find the 50p way too scooped overall and fizzy in the high end, mainly when overdriven. With humbuckers I can go either way for OD, but definitely dig the 50p for cleans.

Thoughts, or link to other threads would be appreciated if this has already been discussed at length.

Thanks.

[skeezbo]

Are you talking about a Rocket?
Maybe you are already on this: the 50p tonestack from a vox usually has a 1M treble pot; the 500p from a Marshall has a 250k. Plug these values into the Duncan tone stack simulation software and you will see the huge difference if you don't change the pot value, too. In fact, the 50p cap 1M treble pot setup in Vox designs looks like it would sound very similar to the 250p 250k tone stack in the Fender tweeds (if the slope resistor etc. were the same). If you have a 250k treble pot, try a 250p cap to get a sound similar to what vox was going for, or switch the treble pot, too, for the real deal.

Skeezbo

[skeezbo]

Oops, I saw the title on the thread and of course you are talking about a Rocket, so you probably already have a 1M treble pot. You prefer the 500p, which must give a stiff mid boost compared to the standard 50p. I don't own a Rocket, but have experimented with these tone stacks in a similar circuit. I am interested to hear what real Rocket owners have to say...
Skeez

[rooster]

Use whatever you like, of course.

That said, I use the 50pf cap but also have a switch for the 100pf across the volume pot. Reading your post, and seeing the word 'fizzy', I think the 100pf cap across the volume pot can cause this at a particular rotation of the pot and a particular setting of the cut and treble controls. With me?

Another thing to think about is the volume pot itself. A typical pot made today is a 10% taper, even when it is called 'audio taper'. (Sad.) If you consider that the Vox/Rocket product was prolly running at least a 20-30% taper pot, then you would realize that the 100pf cap would behave in a different way. In other words, put the volume control on 12 noon on the 10% taper and you will hear some fizz. This is because the cap is conducting super treble freqs across a resistive value of 450K, and not letting much of the 'full' gtr signal thru. Consequently, the 30% taper pot has the 100pf cap bridging 350K - noticeably better.

(If you keep going down this path and next consider the treble pot and then the cut pot, you begin to understand why Ken's Rocket and the original VoxAC30TB sound different than what people are cloning these days. Well, unless of course you have sourced and used the vintage correct pots, and some here do. Well, and then there's coupling caps and speakers. But that's for another day maybe...)

All of which is to say, going back to the switch that would turn the 100pf cap off, if the pot/guitar needs or benefits from this, then consider adding it. I run a PEC audio taper pot that is a 10% taper and if I run my volume pot anywhere below 12 noon I might typically turn the cap off depending on the guitar. And then there's OD pedals that can add to the fizz as well. I run a modded TS and it likes the bright switch 'on' where my Plimsoul likes it 'off'. Hope this helps.

[Gaz]

Thanks for your experience, Rooster, and that's a good point about tapers. I can go either way with the bright cap depending on the speakers/guitar, but what I really meant by fizz was the range of treble the standard Top Boost stack controls.

To my ear, and what is apparent when modeling the stack on the TSC, is that the treble control only controls the very upper register, with very little upper mids/mids compared to the Marshall stack, or the Express for that matter. This seems just fine for cleans, but when the amp gets overdriven heavily turning up the treble yields a thin and fizzy response increasing very little 'meat' of the note, and mostly the distortion itself. I suppose this is why people like to run cranks AC30s with the treble and bass at 'zero', to accentuate the mids.

I've never built a Liverpool, but am even more suprised to see the 1M/50p combo in such a high gain amp. I need to listen to some more clips but it seems like it would be really 'scooped' sounding. I know the high-gain Badcat Hotcat has the same stack, and the distortion sounds pretty fizzy to me. Then again, maybe I'm just used to a more mid-rangey overdrive sound.

JM2C.

[johndandry]

Want to look further into this topic. I also find the 50p in the treble cap a little mid cut when cranked. Thinking about putting a 100p or 200p on a switch ala boogie mid shift. Any thoughts. On the tone sack calculator it looks like raising the cap value to 250p u get a mid boost and the highs and lows stay the same.

[Markusv]

On my 15 watt rocket I use a 100pf treble cap with the standard pot value
I feel it adds just a little girth
I have done this for a Vox AC30/6 TB owner too and he's very happy

Additionally, I find that adding a 25K mid pot instead of the fixed resistor gives me the opportunity to dial some fizz out. The Mid pot at higher settings seems to help the amp retain enough highs even with the Treble at a relatively low setting

YMMV
My 2 Canadian Cents


Markus

(BTW I failed to see the hype about the rocket until I built one. The sound clips sounded good, but didn't blow me away like a Liverpool does. That is till I built my own. Very special beast. The versatility is incredible and the sound is simply beautiful.)