Rocket pre amp help

[Tone Lover]

I made a rocket pre amp tucked into a two channel with a marshall power stage first cap instead of a 500pf I have a .001 that will be the first thing I change, everything else is to the schematic.
But the tone stack is too bassy i mean way to bassy , any thoughts on changes that might help.
Thanks Bill

[RJ Guitars]

Ah Yes... a common item in many Rocket builds. So much so that many of us have nick-named the Rocket as "The Fat Bottom Girl".

Coupling caps are the best place to start. Bring the .047's to .033 or even .022 and see what she sounds like. Also, if you have added the optional Bypass cap on the 2nd stage, try a 1.0uF or something else really small instead of a 22uF.

Also consider adding a bright cap.

Let us know what you find.

rj

[M Fowler]

Rotate the cut control to desired effect and play that should brighten the amp.

I always put in a DPDT bright switch, a boost switch for V1b, reduce the plate resistor of V1a from 220k to 120k to clean the amp up.

Mark

[Tone Lover]

Mark I have it married up with a marshall bright channel, so the cut switch affects them both i was trying to get a happy medium. lots of good places to start thanks guys.
Bill

[xtian]

RJ, you suggest changing coupling caps to reduce bass. Is that C8/9, prior to the PI, or C10/11 post PI?

Mark, which is the brite cap that you switch? Is that C3, the 100pF across the Volume wiper?

[M Fowler]

Mark, which is the brite cap that you switch? Is that C3, the 100pF across the Volume wiper?

Yes I remove that 100pf cap on the volume pot and add a DPDT switch center off. down is 100pf cap center no cap and up 500pf cap.

You could also leave the 100pf cap on the volume pot and use 47pf in down position, center is stock 100pf then, and up use 250pf or 350pf.

Mark

[Colossal]

Also, if you have added the optional Bypass cap on the 2nd stage, try a 1.0uF or something else really small instead of a 22uF.

RJ,

The boost feature of adding in a (switchable) 22uF is a good mod for the Rocket and provides a noticeable boost without changing the fundamental tone too much. How do you find lower values such as 1uF?

Thanks.

[RJ Guitars]

RJ, you suggest changing coupling caps to reduce bass. Is that C8/9, prior to the PI, or C10/11 post PI?...

I'd start with C8/9 and then give it a listen for the difference. You might have to go to an extreme in value change here to get the desired results... but I suggest baby steps.

While it seems like a good strategy, I haven't done the post PI part of this myself so it's an intuitive guess on my part... so let us know what happens. All of these ideas are basically attempts to throttle back some of the low end before it gets to the power tubes.

Also, if you have added the optional Bypass cap on the 2nd stage, try a 1.0uF or something else really small instead of a 22uF.

RJ,

The boost feature of adding in a (switchable) 22uF is a good mod for the Rocket and provides a noticeable boost without changing the fundamental tone too much. How do you find lower values such as 1uF?

Thanks.

This is something from Merlin's book of amp wizardry and it was completely counter intuitive to me. It's on page 25 for anybody curious... my extremely oversimplified version - a small value capacitor increases the gain of the high frequency component of your signal and serves as a treble boost. You can still get a decent boost effect with a 1uF and while the overall boost isn't as dynamic as it would be with a large cap (10uF or greater) it should help to take some more bottom off of this girl. It is also another occasion where an on/off/on switch will let you choose two values and A/B it in real time. I have started using tantalum caps here and have been pleased so far.. small size but plenty stout enough for the task.

YMMV

rj

[M Fowler]

On one of my Reverb Rocket amps I used a DPDT center off switch with 1uf and 10uf boost. This really allows you some great options on gain.

You could use whatever values you want 10uf and 22uf would get a higher gain.

[Zippy]

... it should help to take some more bottom off of this girl...

Maybe just a lil' off the hips...

... small size but plenty stout enough for the task.

We're still talkin' amps, right?

Coffee much today?

[MysteryFever]

Hi Tone Lover,
I'm curious about why you increased the value of your first-stage coupling cap if you think the amp is too bassy? That would be where i would start for bass attenuation. I might also recommend trying smaller caps to and from you phase inverter.
@MFowler, that's interesting about your plate resistor, I found that running ~100k at that point produced less gain but also more bass flab. I attributed this to the lower output impedance of the stage with 100k, reducing the effectiveness of the 500p cap for bass attenuation purposes. Just my guess.

[Cliff Schecht]

... it should help to take some more bottom off of this girl...

Maybe just a lil' off the hips...

... small size but plenty stout enough for the task.

We're still talkin' amps, right?

Coffee much today?

RJ's got something else on his mind today...

[M Fowler]

@MFowler, that's interesting about your plate resistor, I found that running ~100k at that point produced less gain but also more bass flab. I attributed this to the lower output impedance of the stage with 100k, reducing the effectiveness of the 500p cap for bass attenuation purposes. Just my guess.

No bass flab in my Rockets Try using Vintage 30 speakers if too dark.

Mark

[mickephoto]

I'd like to add a boost mod to my Rocket. Can someone tell me if the bottom layout is correct. Top shows stock layout as a reference. I realize I'm skating on thin ice here and could use some help

[mickephoto]

Perhaps this will work better...