Adding mid control to Rocket?

[steeve_a]

Not that the Rocket *needs* a midrange control but I thought it might be interesting to rewire a Crate V18 pcb to the basic specs of a Trainwreck Express. The V18 does have a mid control labeled as such and it seems like a waste not to use it...

I see one way to wire up the mid control would be to bypass the whole tone stack (like the Texas Tea control on Kendrick Climax amp). Of course you would want to replace the 20k pot with 1M or even higher...

But I would rather have the mid control act more like a mid control, without screwing up the whole Rocket/AC30 vibe...

Thanks!

Steve Ahola

[Zippy]

Hah! I've been pushing RJ to add a mid control to his prototype Rocket build As I see it, the Rocket already has a mid control - it is just set at a fixed value. Rj has already done a few simulations of the change in response of the Rocket with a mild adjustment of the mid control's resistance value. Perhaps we can push him a lil' bit more to get that mid pot active!

RJ?

[Fischerman]

That 10k resistor to ground could be replaced with a pot. 25k linear up to 100k linear. Don't know how it would sound but it will work. Plug it into Duncans Tone Stack Calculator and see.

[steeve_a]

That 10k resistor to ground could be replaced with a pot. 25k linear up to 100k linear. Don't know how it would sound but it will work. Plug it into Duncans Tone Stack Calculator and see.

You know I was thinking *exactly* the same thing myself before getting up at the crack of noon today. I was wondering about the Rocket drawing here that showed a 1k resistor instead of 10k (like the AC30) and a 0.0022uF mid cap instead of 0.022uF... I'll snoop around some more since I believe that might have been a preliminary drawing with some errors in it.

In any case, while molesting the Crate V18 schematic with pen and ink, it looks like AC30/Rocket conversion could be done, just by changing parts and jumpers on the circuit board. (Musician's Friend has been blowing these amps out for $150 although they are currently out of stock.)

Thanks!

Steve Ahola

[steeve_a]

dbl

[Zippy]

That 10k resistor to ground could be replaced with a pot. 25k linear up to 100k linear. Don't know how it would sound but it will work. Plug it into Duncans Tone Stack Calculator and see.

As I wrote, RJ and I have already been looking into that - a 25k is about as much as I would choose.

[tubedogsmith]

That 10k resistor to ground could be replaced with a pot. 25k linear up to 100k linear. Don't know how it would sound but it will work. Plug it into Duncans Tone Stack Calculator and see.

You know I was thinking *exactly* the same thing myself before getting up at the crack of noon today. I was wondering about the Rocket drawing here that showed a 1k resistor instead of 10k (like the AC30) and a 0.0022uF mid cap instead of 0.022uF... I'll snoop around some more since I believe that might have been a preliminary drawing with some errors in it.

In any case, while molesting the Crate V18 schematic with pen and ink, it looks like AC30/Rocket conversion could be done, just by changing parts and jumpers on the circuit board. (Musician's Friend has been blowing these amps out for $150 although they are currently out of stock.)

Thanks!

Steve Ahola

The amp with the .0022 mid cap had a 500pf treble cap too. It makes for a real middy sounding amp that seems to break up sooner. Isn't really the rocket/AC30 sound but it's kinda cool. Two Rock used this on the two rocket type amps of theirs I've seen.

[jaysg]

That 10k resistor to ground could be replaced with a pot. 25k linear up to 100k linear. Don't know how it would sound but it will work. Plug it into Duncans Tone Stack Calculator and see.

Huh! I had never noticed that the early 80's Dumble stack looks so much like this Vox stack. Put your pot there for midrange and connect the Bass wiper to the bass pot, not the junction of the cap & resistor. Voila.

An alternative use for the Midrange hole would be a multi-position switch that switches different treble-pass caps in.

[steeve_a]

That 10k resistor to ground could be replaced with a pot. 25k linear up to 100k linear. Don't know how it would sound but it will work. Plug it into Duncans Tone Stack Calculator and see.

You know I was thinking *exactly* the same thing myself before getting up at the crack of noon today. I was wondering about the Rocket drawing here that showed a 1k resistor instead of 10k (like the AC30) and a 0.0022uF mid cap instead of 0.022uF... I'll snoop around some more since I believe that might have been a preliminary drawing with some errors in it.

In any case, while molesting the Crate V18 schematic with pen and ink, it looks like AC30/Rocket conversion could be done, just by changing parts and jumpers on the circuit board. (Musician's Friend has been blowing these amps out for $150 although they are currently out of stock.)

Thanks!

Steve Ahola

The amp with the .0022 mid cap had a 500pf treble cap too. It makes for a real middy sounding amp that seems to break up sooner. Isn't really the rocket/AC30 sound but it's kinda cool. Two Rock used this on the two rocket type amps of theirs I've seen.

I checked Mark's layout drawing and saw that it listed a 0.022uF mid cap and a 10k resistor to ground.

Yeah, I thought that the 500pF treble cap sounded pretty high- you would think that a 50pF cap would be very thin, but I believe that the difference in ESR between a typical 50pF cap and a 250pF balances things out a bit. (ESR being Equivalent Series Resistance). In other words there is much less signal going through the 50pF cap so that the mids and lows overpower it a bit (at least compared to a 250pF treble cap).

If you're going to go up to 500pF, I figure why not make it 720pF? In many of my amps I like using a 330pF treble cap and will wire up a switch to bypass it with a 390pF cap for a mid boost.

Thanks for all of the suggestions! Now I just have to wait for the stork to deliver another V18-112 to my doorstep...

Steve

[RJ Guitars]

Hah! I've been pushing RJ to add a mid control to his prototype Rocket build As I see it, the Rocket already has a mid control - it is just set at a fixed value. Rj has already done a few simulations of the change in response of the Rocket with a mild adjustment of the mid control's resistance value. Perhaps we can push him a lil' bit more to get that mid pot active!

RJ?

it's in the works... for now I am using an 18K resistor rather than the 10K to boost the mids a bit more. No doubt it would be handy to have that variable option... look for the next iteration of the "Roc Kit" to have a mid control. If you played through one of these it's fairly clear why we haven't heard anybody asking for bright switch yet.

rj

[Ron Worley]

I was wondering about the Rocket drawing here that showed a 1k resistor instead of 10k (like the AC30) and a 0.0022uF mid cap instead of 0.022uF... I'll snoop around some more since I believe that might have been a preliminary drawing with some errors in it.

Steve- If you mean the drawing in the files section on the Rocket, the values are taken off of a real Rocket and were verified by Allyn. Of course, Ken Fischer may have used varying values on different Rockets, I obviously don't know. Using the AC-30 values does however make lots of sense- but I'd listen to both sets of values to determine which you like best. It is a different amp than the AC-30, so who knows...

Ron

[steeve_a]

I was wondering about the Rocket drawing here that showed a 1k resistor instead of 10k (like the AC30) and a 0.0022uF mid cap instead of 0.022uF... I'll snoop around some more since I believe that might have been a preliminary drawing with some errors in it.

Steve- If you mean the drawing in the files section on the Rocket, the values are taken off of a real Rocket and were verified by Allyn. Of course, Ken Fischer may have used varying values on different Rockets, I obviously don't know. Using the AC-30 values does however make lots of sense- but I'd listen to both sets of values to determine which you like best. It is a different amp than the AC-30, so who knows...
Ron

I was looking at the "Schematics and Layouts" thread- Omar's post from 1/1/7/05: Rocket Schematic by Mark Abbott

Can you provide a link to the thread with the schematic that you are referring to?

Thanks!

Steve

P.S. With my intended conversion of the Crate V18 amp I was mainly going to rewire the preamp section and PI, and for those sections of the circuit the Mark Abbott schematic looks identical to the AC30.

[Ron Worley]

Steve, it's in the TW files section, a sticky calle4d Rocket Documents or something to that effect....

Ron

[steeve_a]

Steve, it's in the TW files section, a sticky called Rocket Documents or something to that effect....

Ron

Would that be the file titled:

taylor_schematic_updated_6_345.pdf

I was looking at the October 26, 2004 date when drawn by Matt Taylor but I guess you revised the drawing on June 5, 2008...

A question about the BOM.XLS file in that thread: is there information in that file that is more current than the 6/05/08 drawing?

Thanks

Steve

[dehughes]

An alternative use for the Midrange hole would be a multi-position switch that switches different treble-pass caps in.

Now THAT'S a creative, cool idea. Thanks....I just might do that...