Getting a bit further.
Tomorrow I'll test the "compressor" circuit to see what it does to the signal.

Not exactly off-the-shelf, but my two main cabs use hi-fi speakers.

One is a 1x10 using a woofer off some generic cab, that the gym right in front of my house threw away many years ago, and I grabbed and got it fixed at a local speaker repair place:


The other is a 2x6 using speakers off an AIWA microsystem they threw away at work:


I also have a shoebox with a full-range 5-inch "ETM" branded "5EFR" model speaker, 25w 4R, that I bought to experiment with. Brazilian brand, seems to have vanished a couple years ago, but there's still speakers out there available to buy, and they're decently built.

You could probably replicate that tool in a 3D software and get it printed in some of the many services out there in metal, and have a decent tool for ages.

or even turn/mill it out of a solid metal cillinder.

More pics of the build.

Drilled some holes, routed and soldered some wires, now I'm wainting on another order of 1M Log pots (weirdly weren't available before today) and knobs, coming tomorrow.

The extra jacks are for using the P.A. with my headphone amps (Vox AP2-AC, Joyo JA-03B, Xvive GA-3). They plug on the top P10 jack, Phones out goes into the 3.5mm jack next to it, guitar cable goes on the jack on the back of the cab.

When these are unplugged, they connect back to the internal preamp.

Another thing I wanna do is add a power jack, and also have the original speaker contacts be a utility power out for pedals and such. Curently, it's the power input.

Lastly, I wanna see if this "passive compressor" on the last pic could help with the P.A. input overload. I'll put it on the protoboard and see how it does.

Quote from: The Dude on July 07, 2025, 07:40:25 PMSounds like you've already chosen a path, but another good option would be the Sansamp GT2.

I appreciate the suggestion, but that's way too complex to my taste, with way too many controls to fiddle with, and from the samples I've heard, I don't like how it sounds on Bass.

Also a bit of an update.

I had ordered a couple battery holders and they arrived yesterday. I drilled a hole in each to run the wires under them into the speaker box, and installed an LED on the original holes for the wires as an indicator for that pack being on.
Potentiometers and jacks for the build will probably arrive by the time I'm back home from work today.

I also did a layout. Yes, I cheated a bit by looking up pics of the original amp boards, but I changed a few things around to try accomodating it in a more compact build. Lastly, I show the changes needed to turn the same layout into the Lead 12 in red on the board.

Quote from: blackcorvo on July 03, 2025, 07:01:22 PMI just found out I can get symmetrical +/- voltages from those cheap DC-DC buck converter boards(...)

Update: it works! The negative side is not perfectly symmetrical with the diodes I have on hand (they drop a couple volts in comparison to the positive side), but it works.

Doesn't seem to have the same level of distortion from what I've seen on videos online, but it might be just that on those, the power stage is being pushed and overdriven.

In my case, it pushes it to the point I think some kind of overload protection kicks in and mutes it (I tried powering the PA from the positive side of my XL6009 buck converter board to see if the higher voltage stopped that muting issue, and while it reduces it, it's still happening on volume settings beyond like 50% at full gain).

Might need to add a limiter stage between preamp and PA or something like that.

I've also googled a bit more and found this traced schematic on Freestomboxes

https://www.freestompboxes.org/viewtopic.php?p=286640&sid=d31c63eb87f367e522040034f9bc9f15#p286640



And not only does it have different values from the one posted earlier on here, it also has clipping diodes. Thought it'd be interesting to share here.

[Edit]

I also found this video talking about it, but I forgot to add it here before.

Quote from: Tassieviking on July 03, 2025, 05:19:03 PMMarshall 12w Bass

Thank you!!!  this is gonna help a lot.

[Edit]
I just found out I can get symmetrical +/- voltages from those cheap DC-DC buck converter boards:


I'm gonna try this when I get home, because I fried one of my ICL7660 trying the circuit yesterday (max V+ for them is 12v and my PSU is delivering a tad bit more than that).

Also, I redrew the Bass 12 schematic and marked the different component values with the Lead 12, so when I eventually make a layout, I'll do it so you can build either one of them in the same board.

Thanks for the suggestions!

Quote from: Tassieviking on July 03, 2025, 03:18:38 AMIt all depend on what sort of music you are into, what exactly do you want to play ?

https://c2celectronics.com/
https://www.sushiboxfx.com/
https://aionfx.com/project/beta-preamp/

I'm looking for something that has both good clean and drive sounds with guitar and bass, but has simple controls. Doesn't have to be super eclectic as I mostly play hard rock and punk.

Quote from: J M Fahey on July 03, 2025, 10:06:46 AMMarshall Lead 12 is a KILLER little SS amp.
You can build just the preamp to drive your power amp.

I thought about that, but I just don't know if I trust that schematic. I remember seeing discussions in the past where the components on Marshall Lead 12s didn't match the circuit, but I haven't found any actually successful reverse engineering of the circuit yet.

Funnily enough I was looking for the Bass 12 schematic and couldn't find a readable one. I also can't find any videos except for ONE of it used with bass to know what it sounds like. In fact, I had to make a playlist to have some references for certain bass amps being used with bass, because people seem to only use them with guitar.

Quote from: J M Fahey on July 03, 2025, 10:06:46 AMDon´t you have a pedalboard? Or a Zoom (or similar) pedal?

Those can straight drive your chipamp.

I do have a selection of pedals (Marshall Guv'nor GV-2, FAB Distortion, FAB Flanger, FAB Echo + time mod, etc), a Zoom 505II, and an M-vave Cube Baby Bass, but I just don't like dealing with cables, especially if I made this a portable setup.

I was initially using headphone amps to drive the amp, and they work great, but I fear they'll break in case of a bump or fall.
Which is also why I don't think I'll use tubes, but I do have a good selection of them (I'd be here for a couple days listing them, but basically I have 7-pin, 8-pin, 9-pin, subminiature and "pencil/rod" submini tubes, to give you an idea).
I also have like a dozen or so J201s. In fact, I stayed up late trying to finish a Runoffgroove Eighteen on my protoboard to test, but had to stop mid way cus I was falling asleep doing it haha.

Quote from: Loudthud on July 01, 2025, 09:31:23 PMWell first thing you gotta know is what power supplies are available to run the preamp ?

Initially, I'm thinking just 12v, both for the power amp and preamp, as I already have a 12v PSU that works well with the amp, and I could easily add a 3x 18650 battery holder to it in the future.
I also have some XL6009 boost converters, so I could use one for higher voltages on the preamp if needed.
The TDA8932B board I have can work with up to 30v, but I'd probably limit it to 20v max just for the sake of not going over the speaker's max 30w rating.

A couple weeks ago, I was gifted a Frahm PS200 (8 ohms, 30W, 4" + tweeter, studio speaker), and installed a TDA8932B inside. It sounds great with my selection of headphone amps through it, both with bass and guitar, but I wanted to have a built-in preamp I could use and, potentially, turn it into a battery powered portable amp at some point.

I've been trying to find something simple, maybe that could get some dirt off of, if I wanted to. Gain-Tone-Volume is plenty good for me. Maybe even Gain-Bass-Treble-Volume. I just don't want a dozen knobs.

I've been looking around but haven't really seen anything that clicked, so I'm asking here in case anyone else can direct me to something interesting.

Thanks y'all.

Quote from: Loudthud on March 25, 2025, 06:25:20 PMWhat are the little circuit boards attached to the lid ?

Battery and charging board + MT3608 voltage booster set at 15v.

And, finally, the finished build in a Barkley's tin:



Unfortunately I fried my only 4049, so I botched an adapter to a 4069 to use it for now (thanks Runoffgroove!)

Finished build:



Used a tiny 12v bulb instead of a resistor (because it looks cool when the brightness changes with harder picking).

Tried a 10M resistor in parallel with the last stage (suggestion from someone on DIYStompboxes), barely noticed any changes tbh. Leaving it there cus I'm lazy.

Sample:

Quote from: Loudthud on March 22, 2025, 03:19:45 AMOperating the CMOS without feedback may emphasize higher frequencies where the impedance of the ear buds is higher. Try setting the gain of the output stage to something between 1 and 10.

That's a great suggestion, but I'm liking how the output stage is sounding as-is, and since there's volume to spare on headphones and earphones, I've decided to take an idea from the earliest Runoffgroove designs of a "cab sim" at the output of their many JFET amp emulator circuits, using a pair of RC low-pass filters. There's an alternate output (amp) bypassing the RC filters for use as a pedal.

I've also drawn a layout that I plan on fitting on a Mentos CleanBreath enclosure (the thin plastic ones).

Just in case the link dies someday, I'm adding the file you mentioned as an attachment.

Now one thing I wanna figure out is having a better sound on headphones. On an amp (or a higher impedance speaker, as I've shown) it sounds great, but on earbuds it can sound pretty shrill.

I'd like to try adding a small filter to shape the sound on headphones, but I'm not sure where to start.