Very nice. Makes me want to put a bit more effort into tuning mine 
3 Likes
I have just started the pcb and l have noticed l’m missing the 4K7 resistor, is there another resistor that l can replace it with?
Many thanks.
Remember you can wire two 10k resistors in parallel to make 5k, which may be close enough to 4k7. I’m not familiar with the circuit in question, but it’s worth a try. Just piggyback the second resistor across the terminals of the first.
5 Likes
Thanks, l will give it a go.
This is the relevant part of the circuit. I think you should be fine with any value in the neighborhood of 4.7K.
2 Likes
The datasheet for the LM386 shows a 10k pot there acting as a signal attenuator — so at least as far as the chip’s concerned, that resistance obviously isn’t critical. I’m not sure what the fixed 4k7 to ground is for, here. It pulls the amp input to ground if MIX isn’t well defined, which I wouldn’t think would ever be the case, but maybe it could. Or maybe it’s just supposed to be the bottom of a voltage divider with the parallel 1M (or 1m, ahem ahem) resistors at the top. Anyway, I’d bet anything in the few to 10k range would work.
1 Like
Please ignore the double sided velcro, it’s a means to an end just now while I figure out how I want the case. At the moment, fits nicely with the rest of the rack! Super simple build, I thought, relatively new to soldering though, so I still sighed a sigh of relief when it powered on and started angrily buzzing.
11 Likes
Thanks for the information, this is a big learning curve for me.
this resistor R9 was to bring down the headroom even further. you can not bother putting a resistor in there just leave it empty, it makes it really loud!!! but it also means it distorts to the point of silence near the low end of the CV. so by all means mess around, I found going lower with the resistance which made it quieter which was good for the machine as it increases the headroom but you can go for something like 10k, or even 100k but at the bottom of the CV pitch it will be silent. experiment!
3 Likes
thats absolutely awesome!!! literally sounds like THX ha love it.
2 Likes
wheeyyy!!! great to see some completed ones!!!
I have a half finished build video in the works, ETA some point next week. if anyone has anything they would like me to cover in it please let me know!!!
3 Likes
awesome!!! glad its working
1 Like
So it looks like a voltage divider to bring the oscillator voltage down to well within the ±400 mV input range. 1005k/5k = 201× so if the transistor avalanches at 8 V or so, you end up with around 40 mV in, well below the limit.
But the LM386 is configured for 200× gain by the capacitor between pins 1 and 8 (this shorts out an internal resistor), so we’re back to where we started… and then the output is fed into 10-20k so there’s very little voltage drop on the output level, so how does this thing end up with guitar level outputs? I might have to build one to figure out what I’m missing 
3 Likes
Live this! What did you do for the power supply in your standalone?
The board has a space for a barrel Jack, but I also soldered in the 2*5 box header.
2 Likes
Oh my bad, didn’t realise it had space for a dc jack on the panel. That’s awesome, I may build a stand-alone one too!
1 Like
indeed!!! the main reason its got certain parts and done the way it is was because I wanted to be able to power it with +12v. as opposed to synth power. it just made the 1000 oscillator mega drone much simpler to make. also in the back of my head when I was doing this I sort of wanted to make the project accessible for people who dont want to delve in with synths too much, as I know the power supply is always such a stumbling point to getting proper into it! So yeah it can be either powered with the barrel jack, or the eurorack power input! the eurorack power input only connects to the GND and the +12v on the power rails.
2 Likes
Hey all, I’ve been patiently waiting for the postman for 2 weeks to deliver all the parts for this project, then this morning a quite literal tsunami of little packages came through my letterbox, yay.
This is my first synth project, so I want to gather all the information on it that I can before I start…
Other than what has been mentioned in this thread and on Sam’s videos is there anything that I should watch out for or be careful with?
… I know that I can wait till next week for Sam’s build video but I’d really like to get my teeth into this.
(As I was writing the postie came again)
Ahh, I may now have to wait until next week as the postie has just been again and I’m minus OSC Caps, LEDs and jack sockets and he’s let me know there are problems at the depot and they are only delivering when they can… Last post was last Thursday, off topic but is anyone else having trouble with their post.
Rambling a little sorry but thanks for any advice in advance.
2 Likes
My fets are here aparently…
Yeah brilliant. I am into eurorack world, I’m currently converting the Triple Splashback to fit turned around on its side, but my eurorack case is full and I don’t want to start another case lest I spend all my cash!
1 Like