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PhAttbox compressor cabsim

Started by phatt, March 20, 2022, 07:51:14 AM

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At the request of member *TassieViking* here is the schematic for my little black box. The PhAttBox is a compressor and a cab sim with a few extras.
Now if you want to build this I strongly recommend that you bread board it before you heat up the iron. you may want to tweak the cab sim to suit your sound.
If I was to build this again I would likely change a few things but it's been working fine for the past 7 years and played many gigs with it, so I'm not about to reinvent it again.

I run mine on 18V for that little extra head room but 9 will work just watch for big signals.

You can make the LDR by using 2 green low power leds, an LDR and a bit of shrink tube. Don't use hi brite leds.
In Australia Altronics and Jaycar sell cheap LDR's you may have to experiment with other types in your part of the world.
Check FSB for other LDR options here; https://www.freestompboxes.org/viewtopic.php?t=8581&sid=18c2603e67d802c43c8f08b2b3b38269

If you have insane hi output PU's you may need to up the value of R4
My PU's are low output and this works out fine.
Some builders have complained about a bit of hi end loss and loop a small cap around R4 but I've had no issues with my build.
Have fun,, Phil.


Thank you so much for that phatt.
Its joining the build list, might even get nudged towards the top of the list.
There are no stupid questions.
There are only stupid mistakes.


No worries chum, 8)
 Just a couple of things that may help if you try this.

1/ The Master out has a very simple level shift foot switch. In use the trick is to adjust the master to balance the amount of volume lift you need.
Should be obvious that with the master full up there is little difference in volume, while with master at low level the volume jump is likely too much.
You just adjust the master to a point where the level shift suits your need.

If I was to build this again I would change the switching sequence so that the trim section remained on all the time.
You just need to reconfigure the position of SW2.
Depending on how bright or dark your Guitar/Amp system sounds you can play around with the cab sim values to fine tune it.

R3,R43 are there to drain the caps when switching.
Also add them on at C20 (switch side).
Sorry forgot to add them to Schematic. I think I added them on S3 as well. I forget  exactly where I put them but I assume most folks will bread board this before jumping in.
One day I'll try to get a video of my gear in action but my little camera has built in compression on the audio which does tend to slew what you hear.