Converting a simple preamp to Nuclear Fire

[Robert8192]

I am building a simple preamp, but I would like to add
a simple circuit to add extra umph.. on one side- on the
other side.. NUCLEAR FIRE.. Total distortion mayhem...
As the included schematic shows..



If you have simple circuit ideas, like a circuit using 2-JFET transistors or
other types of Add-ins, I would try them out.

Thanks.

[wizard333]

Most designs accomplish that by switching in a gain stage, or 2. Going from say 2 gain stages to 3 can get you from clean to melt-down. I've never completely understood the need for 4 or 5 stages unless you're throwing away a lot of gain somewhere and using them for tonestack recovery or a clean boost stage or something like that.

Given you have 4 to work with there, it should be pretty easy to do what you're describing. 2 stages could keep you very clean, then you could switch in another 1 or 2 for total melt-down mode.

If you want to accomplish that with solid state add-ins, you may want to check out the schematic for the Blackstar HT-5, which makes liberal use of solid state goosing on the gain channel.

[Enzo]

One can use 4 or 5 gain stages because it gives you 4 or 5 opportunities for tone shaping. If you get the same gain total from one stage, you get only one shot at tone.

There are only three gain stages on this page, two are switched in for dirt channel.


It is Monday after all, but I don;t get the caps across your cathode follower. WOn;t those squash your tone?

[wizard333]

I was just counting triodes not really looking at the schem.

If you check the schematics request forum and take a look at the Marshall MHZ15 schem Enzo posted for me recently, you'll see that they use 2 stages on the clean and 3 on the gain, then have a cathode follower tone stack similar to what you have going. I can tell you, that thing has a serious wall melting amount of gain, but will stay nicely clean on the cleans.

If you take a look at how they are doing their switching and gain staging, it may give you some ideas.

The tone is a different matter; the gain channel has too many bleeder caps and comes off too dark, but that is of course a subject for a mod.

[Robert8192]

Those Caps I have handdrawn in are going to be
somewhat of a presence switch. Maybe a 8.2n Cap
and a a 2.2n Cap for HI/LOW switch. with the switch
ON- OFF- ON style. So it can be off too.

There is a lot of good ideas so far, but none I didnt already
know. If someone comes up with something else, please post it.
And A small schematic also. Is there a simple circuit out
there that mimics JAZZ- BLUES- FUNK - ROCK..??? and is a
switchable Type thing Like the H&K Tubeman ver2.

Thanks.

[J M Fahey]

Sorry, but

I don;t get the caps across your cathode follower.

either.
A little math tells me those 8n2 and 2n2 caps will cut highs above some 20kHz and 80kHz respectively.
I wouldn't call that a presence control, although it might cut some RF interference.

[guitician]

I would reverse your V1a and V1b circuits. The 220k circuit is better for distorting and the 100k is better for cleans.

[Robert8192]

Using some info from previous posts, I
looked into the Marshall MHZ15 schematic,

and found it more pleasing and elegant.

I redrew it.



If anyone sees any errors, concerns, or improvements, please
let me know.

Thanks.

[wizard333]

I have the mhz15, which is why I originally requested the schem from Enzo. It sounds great with the bright switch on and the treble dimed on the gain channel, but that makes the clean channel WAY too bright. The clean channel sounds great with treble around 5 and bright off, which makes the gain channel way too dark.

If you look at the schem, you'll see a lot of bleeder caps to ground that dump the high end of the gain channel. They went overboard. When I get some time from fixing other people's crap and working on other mods, I'm going to address that. Its a great basic idea, it just needs a brighter gain channel.

If you were going to use that circuit, you should address that issue as well.

[Robert8192]

Yeah,
Good point. As I look at this schematic, there are
two places where a 470K and a cap are in parallel and go to
ground. One where the cap is a 2n2 and another where the
cap is a 220pF. Both look like they will remove the highs
from the tone. I will probably leave some of these caps
off completely.

Rob.