BAJA Splawn Quick Rod style Overdrive 160220

Ripthorn · Post by **Ripthorn** » 01 Jun 2020, 19:28

Alright, here is the quick video demo I promised:

bajaman · Post by **bajaman** » 01 Jun 2020, 21:14

It sounds like the buzz noise is from single coil unshielded pickups - otherwise it sounds great
cheers
bajaman

Ripthorn · Post by **Ripthorn** » 01 Jun 2020, 21:35

I used humbuckers, and the enclosure is grounded, so I'm not sure where the noise is coming in, but it does sound good. I may have done something weird with my layout that allowed some noise to get somewhere it shouldn't. I'll post the layout stuff soon.

jhergonz · Post by **jhergonz** » 02 Jun 2020, 03:00

that is so small, maybe I will start in something bigger if I use SMD parts

Ripthorn · Post by **Ripthorn** » 02 Jun 2020, 13:00

jhergonz wrote: ↑02 Jun 2020, 03:00 that is so small, maybe I will start in something bigger if I use SMD parts

This was my first project that was all smd. With a reasonably fine solder tip, it wasn't bad at all. I simply put a tiny dab of solder on one pad for each component, used tweezers to hold the component ($2 on aliexpress), and heated the existing solder while sliding the component into place. Then solder the remaining connections and away you go.

brianhujung · Post by **brianhujung** » 07 Aug 2020, 04:32

Hi Bajaman.. thanks for this circuit!
I Just finished build the true bypass version of this, using slightly modified layout from dirtboxlayout to accomodate latest schematic.. circuit was quiet, not as noisy as ripthorn smd version.. ballsy with tons of gain and low end for chuggy chuggy..

but I got oscillation/hi pitch noise after 2 clock on the gain pot.. this high pitch frequency heavily affected by mid control.. any suggestion for this? Change the pot to A50k or should I lower gain from the last op amp like the first schematic?

bajaman · Post by **bajaman** » 07 Aug 2020, 08:45

no oscillation problem with my layout

Ichabod_Crane · Post by **Ichabod_Crane** » 07 Aug 2020, 08:59

brianhujung wrote: ↑07 Aug 2020, 04:32 Hi Bajaman.. thanks for this circuit!
I Just finished build the true bypass version of this, using slightly modified layout from dirtboxlayout to accomodate latest schematic.. circuit was quiet, not as noisy as ripthorn smd version.. ballsy with tons of gain and low end for chuggy chuggy..

but I got oscillation/hi pitch noise after 2 clock on the gain pot.. this high pitch frequency heavily affected by mid control.. any suggestion for this? Change the pot to A50k or should I lower gain from the last op amp like the first schematic?

The board is still out of the box? Did you tried to move the wires, especially input and output? Myabe you can try to use sheilded cable fro input and output.

brianhujung · Post by **brianhujung** » 08 Aug 2020, 03:13

Thanks for the suggestion, and Yes the board is still in "testing jig".. i will use shielded cable for in - out and box it up.. i'm making a video and documentation for this build and planned to put voltage measurement just in case someone else need it for trouble shoot their builds.. any suggestion which point to measure? Also what is the proper way to measure the voltage, i mean did I have to measure it with some audio signal injected to it or it's enough to measure it without any signal injected? I dont have oscilloscope btw.. thanks again bajaman and ichabod_crane

brianhujung · Post by **brianhujung** » 09 Aug 2020, 10:35

Boxed the circuit today. Signal Straight in and out circuit without footswitch. put shielded cable for input and output, still have same response with the feedback after gain reach 2 o clock..

I dont have much experience with veroboard but I guess installing all pots in daughter board and connect some of them with exposed jumper is not a good veroboard practice, especially in hi-gain circuit.. I will try to tap signal from the last 1uf coupling to see if this daughter board is the problem..

Anyway, I actually i dont need that much gain, but now I'm curious to tackle this issue before I move to next bajaman's amp emulator..

Ichabod_Crane · Post by **Ichabod_Crane** » 10 Aug 2020, 08:17

I soldered pots directly through the wires, avoiding excessive length.
Sometime the layout makes the difference in the oscillation issues in high gain circuits. I built twice on veroboard a multi clipping Rat without any problem. Then I built a stock and smaller version getting oscillation in some setting. I had no other experiences about it, but I guess there's other example of it. It's not a schematic problem, because often (not always) a PCB version doesn't have this issue.
I found annoying to insert a second board not included in the original schematic, but a buffer (maybe depends if IC, BJT or JFET based) in front solves almost every time this issue. I don't know how exactly is possible, maybe the buffer roll off smoothly high end that caused the oscillation better than modify of the filter in the main circuit.

Ripthorn · Post by **Ripthorn** » 26 Sep 2020, 22:53

I was playing with mine again, and had a couple of notes:

1. The noise is not nearly as bad as on my clip I posted earlier. Must have been a noisy setup that day.
2. The bass pot would probably be better served with an audio taper. The linear taper hits a point at about 8:30 where it dramatically increases and gets super bottom heavy. Not a bad thing, but an audio taper pot would give a wider range of achievable settings.
3. I would probably lower the gain pot, personally. I find that there isn't any real noticeable change in the gain saturation after about 50%. Perhaps a 50kA would work better.

However, all told it's a fantastic hot rodded Marshall sound!

Also, I have a few extra boards for the surface mount layout. If anyone is interested, I'm happy to let them go to where they will get used.

brianhujung · Post by **brianhujung** » 07 Nov 2020, 02:21

Just a heads up.. adding boss BJT buffer solved my oscillation issues.. perhaps a simple ferrit bead in the input will tackle it as well.. anyway the oscillation most probably coming from my layout itself since i use veroboard.. I agree with ripthorn about gain saturation, in the end i stay with a50k gain pot..

Cheers

bcruzin · Post by **bcruzin** » 01 Feb 2021, 04:14

Once again Bajaman, you have peaked my interest, can hardly wait for a pcb layout , maybe it will move me I the direction of laying out one...

BAJA Splawn Quick Rod style Overdrive 160220 [documentation]