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.

Quote from: Tassieviking on March 19, 2025, 07:51:09 AMLove it, its going into my to do list, I might even make a tiny PCB up for it.
I might even make one in a stompbox and use it as an effect pedal.

This made me think of trying something else: using the chip only wired as the output stage, as a "clean" headphone amp to use with pedals. Like a really beefed up buffer that can drive earbuds. Hmm.

v2



I figured I could use a 10k trimpot with a high value resistor from the taper to do the bias adjustment.
I also figured that I have like a half dozen of those 4M7 trimpots with the red knob, and that I'd like to use them on something, and they worked when I put them on the circuit, so I'm gonna use them in the final build.

Also V+ resistor reduced from 220R to 68R for even better driving output capabilities.

So, ever since I learned that these inverters we use for some of our pedals can deliver 5 to 25mA output, I wondered if it'd be possible to make a headphone amp out of them.

And early today, after not being able to sleep, I decided to see it for myself.



After tinkering a bit with the circuit, I ended up with the following schematic:



The trimpot for adjusting the bias for the output stage is actually an idea from Tim Escobedo's Circuit Snippets, specifically from the Calavera circuit.

I think it could do with a filter at the output to kinda "simulate" a speaker cabinet, but I'm terrible with filter stages. Wouldn't even know where to start tbh.


Sound sample:

https://youtu.be/8VQJ2Yj2IJ8?si=pFdULSaG7aHjAICO

I fixed it.


The main issue was the MT3608 DC-DC boost converter I was using. I think it was inducing high frequency oscillation into the circuit. Subbing it for an XL6009 solved it.
I also isolated the input jack from the panel because I think it was causing a ground loop with the output jack.

I'll try playing it through another speaker, I don't really want to mess with dismantling the build because I used the box from the old multimeter for the finished thing.

Just in case, I'll try swapping the J-Fet for another one today (I also ordered more, cus I only have like 2 of them left).

And here it is, finished!


Although I'm suspecting I should replace the MPF102 because there's some strange underlying distortion I didn't have before. I accidentally had the DC-DC converter board set to 25v and fried the first LM386 amp board, but I'm not sure if the J-Fet didn't also get nuked. I'll do it tomorrow cus it's midnight right now.

I had some free time at work today so I drew this perfboard layout for the buffer, and made it once I got home - worked first try.

Attached are the layout and some pictures of the project so far.

Only difference between the Hiwatt/Bassman mod I drew and the actual build is that I didn't have any 18nF caps (to get 15nF in series with 100nF for the Hiwatt mode), but I do have a bag of 33nF caps, so 2x of those in series gets me in the right ballpark (~14nF) for this mod.

Recently I got a handful of those LM386 module boards peeps seem to like turning into fuzz boxes, and got very dissapointed with how they sounded right away, but then I thought "what if I added the input buffer from the Ruby to it?", and went to work.


It's night and day. More gain, better dynamic response, and the "Hiwatt" and "Bassman" mods work as expected.

So, if you have one of these lying around, try adding that buffer to the input and see how it works for you.

For a "full Ruby conversion", on top of adding the input buffer, you can remove C1 on the board and attach a couple wires to it's pads to connect the 1K gain pot, remove the volume trimpot and wire up a 10K volume pot to it's pads, and change C3 from 100uF for a 220uF.

Quote from: Tassieviking on February 03, 2025, 01:27:07 PMWhere did you get the cassette adaptor ?
Whats the brand and model of it ?
A nice picture speaks a thousand words.
I really like to try this as I have some old cassette players somewhere.

I got it from MercadoLivre (a Brazilian marketplace, it's kinda like Amazon), but I found one available on e-bay .

The adapter is a Coby CA-M800 "cellular phone car adapter", there's pictures of it at the end of the first video, but I'll attach them on this post too. I'm pretty sure any modern equivalent will work just as well, but you might have to remove the insulation from the cable to make the cassette player/recorder door close properly (I ended up using some thin wire off of a broken laptop screen cable and made an adapter to connect it to pedals and such).I only got this one because it was the cheapest available for me, but the fact it has 3.5mm jacks instead of a built-in cable honestly makes it work better for me.

If you do get one, fair warning: the coily cable it comes with WILL crumble. Just cut it off and keep the 3.5mm tip (if you reuse those like I do), and maybe keep the mic it comes with. For some reason they made the mic cable insulation of a different material that won't crumble, so that part is okay. It even has a lapel clip!

Quote from: joecool85 on February 02, 2025, 10:43:54 AMWhat are you using for headphone amps?  Are these Vox amPlugs?

It's all in the videos. I used a Joyo Bass and an Xvive Classic Rock
I do have a Vox Amplug 2 AC30, but didn't like how it sounded as much as these other two.