the_grumpy_gnome
Active member
They made several tweaks across versions, however the most important to me is the ability to self-oscillate with the extended 'Dwell' control. This change was made going from V2 to V3 in mid-2017.
Which version of the Ghost Echo (1, 2 or 3) does the Spirit Box most resemble?
- Thread starter the_grumpy_gnome
- Start date
Devoureddeth
Active member
Judging from the PCB it looks like an older version but you could probably make like V3. Upgrade the opamp to one of the low noise op amp like maybe OPA134? And the ocillation sounds like either a pot value change on a resistor addition to prevent it from going full feedback but hard to tell from what it says. Do you have a demo describing this effect?
the_grumpy_gnome
Active member
Devouredeth: I'd be perfectly happy modding this circuit. In addition to wanting one of these pedals, I really want to learn more about reverb and delay circuits for future custom projects. I can eyeball distortion mods but I'm just learning about PT2399, so this would be a great learning experience.
Hearsay is is that V1 and 2 are pretty much the same, but EQD enumerates the changes between the 2 & 3 here. Differences listed include:
Hearsay is is that V1 and 2 are pretty much the same, but EQD enumerates the changes between the 2 & 3 here. Differences listed include:
- “Attack” control adjusts 30ms-150ms of pre-delay - this was not available in V1, it was always set to minimal pre-delay. I can probably figure out how to increase this range in both directions.
- Upgraded op-amps for better performance and lower noise - yep, that OPA134 or a NE5532 would be perfect.
- Stronger reverb signal with 2x the output
- Accutronics Reverb Tank
- Recalibrated “Dwell” control capable of self-oscillations when all the way up - this is the main thing I'm chasing. Want to be able to get it to self-oscillate (probably a very easy value adjustment in the "Dwell" control and I'll be able to figure it out). The link above has an embedded video in it. Here's the link to the spot in the video with the dwell cranked. Also, here's another similar circuit that's even closer. It's the higher-pitched parts the the reflections I'll be focusing on, with the longer-term goal of developing something very similar to the Mr Black 'Eterna.' Though, that's digital and incorporates octave effects, I'm going to very much enjoy learning how to develop a similar analog version.
Devoureddeth
Active member
I would get a breadboard and try some things out. If I had some time I would give it a go a bandmate has been wanting one for a bit. Just looking at the schematic try some different values at R8. This is where I don't know my shit so take it with salt and experiment, decreasing R8 would cause it to feedback easier and increasing R8 should do the opposite. You could probably also mess with the value of the dwell pot. If someone of more knowledge knows how the stuff works take a stab. I would just mess with R8 and maybe the pot.
ChrisSchwarzkopf
Member
Hey there, any updates on this? I just finished building my Spirit Box, sounds great but modding it so it can oscillate would be great. So have you tried changing the pot or the resistor?
the_grumpy_gnome
Active member
No, not yet. I have a stack of several pedals that I'm trying to get done. However, when I get to this I'll post.
ChrisSchwarzkopf
Member
Perfect, thanks. Really hope that it can be done by just replacing the pot as the Brick now covers most of the backside and I really dont feel like removing it again 
robinton03
New member
start simple and just jumper R8 and replace the Dwell Pot w a higher value pot like 20k or 25k. its an easy mod and easily reversible if it doesn't work. Dont start with the dwell control dimed!! Work it up slow and see what happens. The Dwell control is really just the feedback control for the PT2399. Go check out the build docs for the Cataclysm, the Sea Horse, The Magnatron, The Chalumeau, and the Pitch Witch for some more ways the PT2399 Chip is hacked to create glorious tone.
the_grumpy_gnome
Active member
I'll try this with my Pitch Witch
ChrisSchwarzkopf
Member
Please let me know when you have done the mod
ChrisSchwarzkopf
Member
Just a little update on this: I rehoused the thing and also swapped R4 for 1 15k I had flying around for Unity Volume and I feel as if the oscillation is now finally there or maybe just more audible! Now it's perfect
ChrisSchwarzkopf
Member
Thanks
no you are the first one that asked i used white laser decal paper (bought it on Ebay) for the first time and it came out pretty nice.
Thanks
Can you share your ebay source? I've been wanting to try this but there's a million different laser decal paper versions.
ChrisSchwarzkopf
Member
daeg
Well-known member
Whatever version the PedalPCB is cloning, it already gets you that. The 10k 'Attack' pot will give you 1k-11k at Pin6 of the PT2399, gets you about 40ms-160ms of predelay. You wouldn't want more than 150ms for this type of effect and getting down to 30ms is only safe if you use an anti-latch circuit. I doubt the v3 really does that; more likely they're just fudging the numbers a little bit to look nicer on paper (3-15 is just more aesthetically pleasing than 4-16).
Source: https://www.electrosmash.com/pt2399-analysis
daeg
Well-known member
The consensus over at FuzzDog is that lowering R8 from 25k to 12k, then swapping that 5k 'Dwell' pot with a 25k pot is the perfect solution.
daeg
Well-known member
Also from the FuzzDog comments; try changing R5 from 10k to 17k. That's supposed to solve the volume drop issues and probably gives you a little extra when 'Depth' is fully cranked. If you make the that change, you might as well also use a 5k pot for 'Depth'. No reason for that special value pot except to bring the gain slightly up.
Disclaimer: I haven't tried these mods yet.
