Wired up this ampeg scrambler board I’ve had for a while. I’ve been trying to finish up all of the unfinished projects from the last few years.
Fired up first test. I used MPSA13 transistors. I got the PCB from John Lyons on DIYStompboxes. It’s the tone pad layout. The layout is set up for different transistor pin arrangements. The MPSA13s were working well, I was thinking to try some others before boxing this up.
After playing around with this for a while I find reducing the gain on the input stage seems to get rid of the harsh noise from a hot input. Not sure if this will work for every circumstance, but it did work for my guitar.
To make up for the reduced output I modified the output buffer. This also made for a better effect in my opinion. I feel the trem sounds better when unity gains falls in the middle of the trem sweep.
Here’s a few notes. Part numbers follow the original schematic from Stompboxology.
R14 was 470K. Make this 309K (or there about). Lowers the input gain
and clears up a lot of nasty distortion that shows up when the input
R16 was 3K3. Just remove this, or replace it with something really
large ~1M. This increases the gain at the output. Which makes up for
the gain lost by the first change and gives it a little extra gain for
a better tremolo effect.
R25 was 25K. Make this 100K. This decreases the lower end of the rate.
I like the slow tremolo sound. I’d almost like to make this a little
larger. But it might require a weird size pot 120K, 150K, 200K etc.
You can fiddle with C15 also, but this tinkers with the fast rate
which I like.
I had an idea to build another with a switchable rate cap for super
fast audio rate modulation and regular low frequency modulation. The
HF modulation might give a weird sort of “ring moddy” tone.
This is the Tremolo-Matic X from Stompboxology. I’m in the process of building this for “Jonny” who I met at the last DIY Swap meet. He gave me this box to put it in.This project is coming together nicely.
This is Tremolo-Matic X from the Tremolo Issue of Stompboxology by Nicolas Boscorelli. I have redrawn the schematic to make it easier to read. Hopefully this will be helpful to anyone attempting this project. This is Tremolo that pans between a treble and bass signal. It inlcudes controls to set the level for both the bass and treble, rate and depth.
I built mine from the PCB layout posted by Morocotopoat Diystompboxes here. This lay out worked well for me. Though it looks likes it isn’t finished as there are a few extra pads that don’t quite make sense. The layout does work. I have built it myself.
It sounds pretty good. I made a few changes. First I changed the Rate pot to 100K to get a more useable range of speeds. With the original 25K pot the slowest speed was not very slow. I like the sound of slow tremolo. The 100K pot is shown on my vsersion of the schematic. speaking of the rate, I’d like to get a slightly faster rate at the fast speed and a little slower at the slow end. I think I will be playing with R21, R25 and C15 a little more.
The other mod, not included in my schematic, is to decrease the gain on the input stage. Basically this comes down to decreasing the value of R14. With the original value of 470K you get a little bit of clipping with hot pickups. I haven’t decided on a value yet.
Note the, input stage is inverting. Which presents a lower input impedance than would normally be acceptable. But it seems to work OK here.
Also note that there are a few parts list as optional feed through bias or something like that. These parts include a 5V regulator and adjacent parts. I left these out of my build, and everything worked fine. I left these out of the schematic posted here.