Thanx for your tips guys, received my LDR's yesterday, so will start experimenting.

Alright, drawing stuff here. Noticed i had some 100k digital pots, so will try them out while i wait for my LDR order to deliver.

If i want to "emulate" a gain pot for example that is 1M, but the digital pots and ldrs are only up to 100k, and jfets even lower. the pot is located between 2 gain stages, 1 to GND, 2 to stage 2, 3 to stage 1.

The only solution i came up with (and i'm not even sure that it's a usable one) was to connect a buffer in place of 2 with a 1M resistor to GND, and another in place of 3 with a 100k attenuator after it, in order not to mess up the impedance of the circuit. seems a bit clumsy... How would you guys that actually know what you're doing go about this?

Hey.

Preparing for a few gigs and the very late album release, i've noticed that even though i'm down with a 4 button pedal i've built (distortion, gain boost, delay and volume boost), there's just too much stomping. I would like to mod my pedal to be programmable with presets instead. using an mcu, display and momentary switches instead to switch on/off multiple effects, but also change tone, delay and volume.

I can get the digital part off easily, and i already got the analog part. Now interfacing them in a convenient way is where i've hit the brick wall.

I know about digital pots, but i've also heard lots of arguments against them. i dont really need insane resolution, but it wouldnt hurt to get atleast a few possible variations, which kinda rules out the string resistor solution i experimented with, as i need 1 resistor per setting. i also found a forum thread about using LDR's, the way mesa boogie does in the triaxis amp.

But i'm really not sure what route to go here, something that wont enlarge the casing by a factor of 10 would be nice.

i did connect a jfet shunt to GND with a R2R ladder to set the level for the gain and volume, and well, it seems to work. But not tested enough yet. The tone stack though is where i'm entirely lost. Any suggestions are welcome

Hey guys, my preamp project still on hold. :/ too much work for me with stuff for the band and the upcoming album release, a friend of mine though is in need of help. His Rocktron rampage SS amp is acting a little wierd. It takes numerous power cyclings to get running, the power led is on every time, but the sound is not. occasionally volume starts fading and the amp gets silent during play aswell.

I inspected the board, and everything looks fine, power resistor and all, entire board looks unheated in every way, electrolyte caps looks fine too, no bulging, although, i have no meter to check them. :/

Any hints on what to look for? there's not really much to the circuits in it, so i might just try and replace some stuff if somebody got a hunch here.

Hey.

Currently working on som high priority stuff for the band, so going a little slow with the amp project. I had to make a better backing track solution than our current mp3 variant, the new backing tracks from our producer really need to be stereo (or preferrably 4-8 channels), so i've made a small pic-controlled remote control with a display and buttons that controls a computer through the serial port running a minimalist microcore linux (6 mb iso) to play multichannel Flac-files.

The reason i did not go with +-15 for the opamp in the cab sim is that the one i found, and liked was made for single supply. The tone stack will be tweaked later on. The cab sim + tonestack i posted here is something that i use as a "plugin module" to test the actual preamp circuit while designing and experimenting without having to make a huge breadboard circuit just to test a couple of gain stages etc. There will be +-12 for the jfets though in the preamp itself. I've been looking quite alot at the Rod elliot project, but i really like the sound i get from jfet circuits i've been building and want to do a PROPER design with those. No trimpots, doing correct biasing etc.

Going a bit slower than i anticipated, but getting forward. Installed the transformer, did all the wiring up to the bridge rectifier and figured out where on the heatsink i want to mount it later on,a used LOTS of heatshrink tube. Love that stuff. Now i'm going away over the weekend, so probably wont get much done. But i need some mounting materials anyway, so might aswell go away while waiting for the delivery.

By the way, Roly. what's up with electronics and Australia? Is everyone a pro engineer over there?

Stumbled across this guy (Dave Jones) a few days ago.
http://www.eevblog.com/episodes/
That stuff is excellent! i've learnt so much just watching those teardowns and of course his PSU design project, and on top of that, you also got Rod Elliot, and you seem to know quite alot yourself.

Waiting for my goldsmith Girlfriend to make the front panel for the PSU as she offered to. Will be a brass plate.

Before i start soldering the boards i did some measurements while moving around the guts of the supply to make sure my board wont get too big. I also put in a small DC fan, not sure if i will need to use it, but, hey. when did you last hear of a power supply running too cool? ^^ Also got my 2000mA transformer, so i figure the 150 mA used by the fan (well actually i think i'll just pwm it and get it down some more) wont be a problem. Now the fancy way to do this would be to let the pic read a temp sensor and adjust the fan accordingly, but that means i will have to redesign a little, and pick a bigger Pic, no spare pins atm. I think i'll probably just run this one of a potted 555 if at all.

Also looking at fabricating a small enclosure that will seal the input jack + switch. i dont want any mains points touchable at all, especially with the small hole array at the back panel of the ATX case. inserting a guitar string or wire by mistake would be bad. So i will make some sort of bracket to make sure it cant get nasty.

Attached pictures of the "mockup" placement and the LCD, Terminals + knobs, still in bags.

Oh, and the plate which the transformer secondary wires are resting at on the picture will be the front. Gonna cut it into a frame for attaching the front panel when i get it.

Tried a different approach writing the firmware. Tried out FlowCode, microcontroller programming without actual programming. Really fun to work with, but terribly optmized code. My program got 250 words too big at first. managed to optimize by hand down to 3 words+, but realized this is a no-go as i need to add offset voltage compensation and so on.

So i guess i will make a rewrite from scratch in C, I do work as a programmer, so it's my cup of tea. But for anyone wanting to experiment with MCU's, and dont care about using a bigger chip with the benefit of no coding, i highly recommend flowcode.