ASTROSIM (cab simulator)

[deadastronaut]

iain...nice one..

mike, pcb is on its way to you... 

ive been using mine all the time on my bench into my mixer, haven't turned my amp on at all for the last few months...been recording a lot through it with guitar and bass...and electro acoustic

double tracking guitars is awesome...no noise or hiss, and very little post EQ too...
so am well happy...especially with the vintage/modern switch..very handy for metal or overdrives...

[drumminkiger]

Hey guys, I just finished building an Astrosim revision 2 board with the XLR and Headphone output. I'm having a little trouble with the tone on/off/on switch when using the headphone amp and the XLR out. The normal guitar level output works as expected when flipping the switch and sounds great, but the only way I get output on the headphone and XLR output is when the switch is in the off position. If it's not, I get a really awful screeching and buzzing sound with no output. I tried playing with various schemes of grounding the outputs to eachother or the case, but there's not a lot of change. When I plug the guitar line out into something with the headphone out connected it still buzzes on both, but once I disconnect the headphones the buzzing goes away on the guitar line out. Any thoughts on where I should start looking? It almost sounds like it's ground looping somewhere but I'm not too sure where to look. Thanks for any help

One thing I discovered as I tinkered with it some more, the problem clears up if I max out the high tone control pot, but once you raise the resistance up just a tad it comes back. It's the correct B5K Pot and seems to be in spec.

[deadastronaut]

HI man, thats weird, as the tone control is only switching in and out a couple of caps and should have no effect on any of the outputs like that....hmmmm...

did you do the XLR 'bridge' mod as in the the bottom of the pdf?.

[drumminkiger]

I've added and removed the bridge a couple of times, there's not really any change in the circuit at the moment thought I'm sure I'll want it in once I get past this problem. I noticed someone earlier in the thread mentioning that they were leaking VB through a pot, so I pulled out my multimeter to check and sure enough when the tone caps switch is in the off position, I can manipulate the pot's and the VB stays consistent, but when I put one in the circuit VB varies as I manipulate the pot. What's the correct wiring for the pot's? Maybe I'm just getting it wrong or something? I'm currently just wired Square pad to the 1st lug, middle to middle, and furthest left to the 3rd lug on all 3 of them.

[deadastronaut]

pots should be , when looking at the back of the pot.. (not the shaft side)

3    2    1 (1 being the square pad. )


same as looking at the top of pcb...

3 2 1 (square pad)


'' but when I put one in the circuit ''   ? 

[drumminkiger]

Yeah, that's how mine are wired, so I guess that's good then. I mean't one of the tone caps on the on/off/on switch. When I use the switch to put either cap in the circuit the VB starts changing. When it's plugged in through the normal guitar jack only the VB is consistent through all the switch positions, but I do get a little noise when the high pot is wide open, as soon as I plug in the phones the noise comes back on both the headphone out and the guitar line out. I haven't tried the XLR in a little while, but the behavior was the same as the headphone jack earlier.

[deadastronaut]

strange, i use mine all the time i have it on my bench right now, i have just tested with line out, and headphones simultaneously at the same time and switched the tones,

no problem.......i cant see how just switching caps would cause screeching.......hmmmm....

my headphone socket is a plastic socket...not that it should matter...hmmmmm....just thinking aloud...

[drumminkiger]

So is mine, I'm using an amphenol cliff style jack for all of the 1/4" I/O. It's especially strange because you would think if it was working on one output the remaining outputs would either not work at all or work normally at that point.

[deadastronaut]

Have you got any pics.....just curious.

Many eyes on it might spot something.....

[drumminkiger]

Sure, here's a photo. Nevermind the cap that I just melted a little with my soldering iron last night as I was remelting my off board connections to make sure they were solid, seems to be holding up but I'll likely swap it out when I can get another. Nothing really changed after that happened. Today I bypassed the XLR out  by removing the XLR volume pot to try and limit the problem down and everything is working great except when I get to the very end of the high pot, it starts to trip out. I'm thinking I'll try a different pot of the same value, maybe this one is just crap? I have one on hand that's probably too big to fit in the pedal physically, but is the right value.

[drumminkiger]

Did some more messing with it tonight. Tried another 5k pot in the high tone stack and nothing changed. I tried it with a quieter amp than my Marshall clone, and found that there is a bit of noise on the guitar output too when the high tone is wide open, but it's less pronounced than the headphone out. If I raise the resistance in the high pot above 6 or so ohms, the noise goes away, the pedal is dead quiet, and everything works great on both outputs. It's almost like flipping a switch and there's a big squeal if I go lower than that, and then at 0 ohms the squeal goes away but it's all hiss and and a super distorted version of the guitar tone. I'm almost thinking I should add a 10ohm resistor to the pot so that it never drops low enough to cause the squeal, but that seems like I'm just covering for something else wrong with my build somewhere. The XLR pot is still out of the circuit to keep it simpler till I get this part dialed in. Maybe theres a resistor somewhere that's too far out of spec?

[GibsonGM]

Hi Drumm, you'll get it working...umm, pic of the other side of the board if you can?  Wondering how you melted that cap when the serious stuff happens on the other side

I built this and it was fine (Great project in fact!  Lots of fun to use), but at first I had a build error. When probing, I got a squeal at one of the lugs of the "air" pot IIRC.  The cure was to notice I'd left out a load resistor (R20 probably).    These things are typically mistakes we make in assembly, just a matter of finding them!

[PRR]

.......I raise the resistance in the high pot above 6 or so ohms, the noise goes away, the pedal is dead quiet, and everything works great on both outputs. It's almost like flipping a switch and there's a big squeal if I go lower than that, and then at 0 ohms the squeal goes away but it's all hiss and and a super distorted.......

It squeals. When C11 C13 are direct connected to IC1_A, it squeals radio waves. You don't hear that but it messes-up the opamp's audio performance, hiss and distortion.

The abrupt shift depends on pot quality, a pot with large end-resistance may not get it into trouble. Yes, 47-100 Ohms series to the pot seems wise.

But it seems it also squeals audio. That is often layout, long wires and sneak-back from output to input.

[drumminkiger]

I'll grab a shot of the backside when pull it apart again. Lol, this is one of my first stomp boxes, but I've built lots of balanced audio circuits like mic pre's and compressors so if there's something wrong with it I know it's something I goobered up and need to hunt down This thing sounds awesome aside from this issue though, it is indeed a great project, and I enjoy it much more than plugging into an audio interface and a laptop to get a cabinet simulation.

If it's sneak back from output to input, could it be my foot switch wiring? Or perhaps my use of insulated cliff style jacks when maybe I should be using something like a switchcraft 11 jack so it's grounding to the chassis at the input and output by default? I've tried grounding them with alligator clips for testing and didn't find a lot of change, but I'd be happy to be wrong. I've also grounded the input and output jacks to the board, in the photo's Rob hasn't connected the input to ground it looks like on his initial post, but mine sounded like a ground lift when it wasn't grounded so I added it. Maybe my leads for the pot's are too long? I've tried to keep them at a practical length to accommodate getting them installed in the box with the board not mounted yet but not any longer than necessary. Thanks for you input guys, I really appreciate it.

[bluebunny]

Here's mine:



Added a ground lift switch and a second 3.5mm headphone socket.

[vigilante397]

Here's mine:

It can be hard to make those knobs look good on a build, but they absolutely work there. Looks great

[bluebunny]

Thanks Nathan, I thought the same.  I've bought a bunch of smaller knobs for Eurorack builds, but the majority use 9mm pots and mine all have smooth 1/4" shafts - these tiny knobs tend to be T18 splined.

[deadastronaut]

 

looks great marc.... like the added hp socket , handy , and ground lift too....neato.  .

[bluebunny]

Thanks mate - it's a neat little project.  Keep 'em coming!   

[cab42]

I have found myself playing more with headphones recently and at the same time I have got a pretty powerful computer I can use for experimenting with recording. As I could need a cab sim for this, I searched for an AstroSim vero layout as this is my preferred medium. To my big surprise no one seems to have made one. A couple of weeks ago I had a cross country train ride (only 3 hours, Denmark is a very small country), and spent the time trying to make one.

It is my biggest vero layout to date, but it was pretty easy. I omitted the XLR out, mostly to keep the complexity down, but also because I do not have any equipment with XLR's.  As an afterthought I also made a separate XLR out board.

The layout is not verified, but I have checked the nodes a few times, and it looks OK.

Here they are, freshly uploaded to the gallery. Let me know if you find something.




https://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=53899&g2_serialNumber=2
https://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=53902&g2_serialNumber=2