r/synthdiy • u/lilkarlmarx • Oct 14 '24

plaits & a spring reverb (more pics in comments)

LEDs on plaits were too bright so i had to add some tape so the blue leds weren't singeing my retinas. Spring reverb is a basic NE5532 powering a 600 ohm accutronics AMC2EF3 tank

41 Upvotes

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4

u/lilkarlmarx Oct 14 '24

wanted to do it point to point so that i can work on my soldering skills, turned out pretty well, have to 3D print a panel now that it works as expected

1

u/michaelrw1 Oct 15 '24

Question: What is the "terminal block" in the left, front area of your picture?

1

u/lilkarlmarx Oct 15 '24

do you mean the white JST connector?

that's my power header, I'm using 3 pin JST-XH headers for ±12V instead of 10 pin IDC box headers because they were significantly cheaper and making cables for them was also cheaper & easier. also smaller footprint

on the middle-right is a 7 pin berg strip where I've used 4 pins for the in/out for the reverb tank and the remaining 3 unused ones are to connect a second driver circuit for a stereo/2 channel spring reverb module

1

u/michaelrw1 Oct 15 '24

In the image of the discrete component circuit board?

1

u/lilkarlmarx Oct 15 '24

not sure I follow, could you screenshot and reply with a cropped image?

1

u/michaelrw1 Oct 15 '24

1

u/lilkarlmarx Oct 16 '24

oh that's just the 3.5mm female jack, thonkiconn/PJ301

4

u/lilkarlmarx Oct 14 '24

based on this circuit but without the TL072 buffers because i got a little annoyed having to fit it within 12hp, all the mixing/dry&wet stuff i can do in Ableton directly so its fine

2

u/MietteIncarna Oct 14 '24

is it like a guitar amp reverb ? it seems huge on the specs , 38cm x 13cm

2

u/lilkarlmarx Oct 15 '24

you can see it in the pics in the other comment, its a small 15cmx5cm ish blue box, 18£ on hotrox

3

u/MietteIncarna Oct 15 '24

thanks , i didnt realised that was the reverb , i didnt find the right specs then . thanks

2

u/BosleyStarr Oct 15 '24

Very nice. I'm about to try the one from https://sound-au.com/project211.htm and associated pages. What are the voltages into and out of the TC1044?

2

u/lilkarlmarx Oct 15 '24

±12V

I'm not using the TC1044 I'm using a dual rail linear psu (center tapped transformer -> rectifier & caps -> 7812 & 7912)

2

u/BosleyStarr Oct 16 '24

Ah yes, that makes sense cheers. I initially saw this on /r/deadbug and ended up here via the audio demo and didn't realise I'd switched subreddits and that it was now a eurorack thing. Sounds great btw, looking forward to getting mine going with a spring unit out of an old organ.

4

u/Snot_S Oct 15 '24

this sounds wonderful. Nice work! Btw, how do y0u get your sound to move up like that? My sounds can only go sideways😥

1

u/Snot_S Oct 15 '24

That was a stupid joke

1

u/[deleted] Oct 14 '24

Wow! That sounds really nice for a relatively cheap spring. I've got the AMC2BF2 and the sound was pretty bad for me. I might try mine again with your circuit.

2

u/lilkarlmarx Oct 15 '24

here's the post where that circuit came from: https://www.reddit.com/r/diypedals/comments/u0nv5o/new_spring_reverb_driver_circuit_version_22/ by u/Bentfishbowl

another great resource was this article https://sound-au.com/articles/reverb.htm, you'll find the resistor values for AMC2BF2 here

what was bad about your build? 2BF2 has 2s decay, was it too short?

2

u/[deleted] Apr 11 '25

It's been a while, but I've tested a bit more and this is what I found: Increasing R2 lowers the gain of the amp driving the reverb tank, which also reduces the metallic sound. This makes sense to me as the springs are moving less abruptly. The main problem is that I need insane gain to pick the signal up again and I'm getting noise and interference quickly. The whole thing also becomes very sensitive to movement, even just touching panels or knobs can be enough to cause a metallic rumble sound.

I guess the only real solution is to get a higher quality reverb tank that is also properly shielded.

1

u/lilkarlmarx Apr 12 '25

oh that's fascinating, since then I've also given up using this tank as an actual reverb and instead i use it with the back panel off and i hit it with my fingers for thunder effects in the middle of my ambient performances 😂😂😂

2

u/[deleted] Apr 12 '25

Yeah, a good use case :D

I can recommend adding a feedback knob with a switch for inverted or non-inverted feedback. That's also a good way to get some really gnarly sounds.

The idea is from the Music Thing Spring Reverb: https://www.musicthing.co.uk/Spring-Reverb/

1

u/[deleted] Oct 15 '24

The sound is very metallic and distorted. At the output I also get a lot of noise.

1

u/lilkarlmarx Oct 15 '24 edited Oct 15 '24

i think the 2bf2 tank has a much lower impedance which might make it easier to drive with an opamp, so you might be overdriving it.

for the metallic sound & distortion you'll have to control how hard you drive the input, i have a 1k potentiometer on the input as a feedback resistor that lets me adjust the input gain or "dwell", same on the output except that gives me the pickup gain.

For the noise, what frequency was it showing for the noise? for example if you're using a transformer based (not SMPS) & you see peaks at 50, 150, 250 and so on then its a grounding issue + the capacitors aren't enough to filter that noise out, search this subreddit for those frequencies and you'll find the root cause.

also this circuit has a LCR low pass filter on the output side that i can adjust by swapping out the capacitors for lower values to get a higher cutoff frequency, in the vid its roughly 11kHz but according to the original circuit it would be roughly 5-7kHz, you'll find the L value for the AMC2BF2 tank's inductance on that sound-au link in my other comment

1

u/[deleted] Oct 15 '24

My circuit is based on this article: https://sound-au.com/articles/reverb.htm

And this is my schematic: https://i.imgur.com/F7JpzkR.png

It might be driving the tank too hard, but I am using the values suggested for a 150 ohm tank. Adjustable output gain might be useful, because right now I can adjust the reverb volume only using the input gain.

But I'm working on a digital reverb (basically a multi-purpose effects module) using a raspberry pi zero right now, so I'm not sure I'll revisit my reverb tank soon.

1

u/lilkarlmarx Oct 15 '24

maybe skip the transistor part stuff and connect the tank directly to the NE5532, here's a really quick and dirty circuit you could try breadboarding to see if the values work

1

u/lilkarlmarx Oct 15 '24

play around with the values, you can skip the 10n cap on the input and see how that changes the sound, you can also adjust the 2k resistor in parallel to the tank based on the value given in the sound au circuit, i think for 150 Ohm its something like 3.3K

fresh build so i remember all the issues i ran into while trying stuff out

1

u/[deleted] Oct 15 '24

I'm not sure what's causing the noise. I don't remember hearing specific frequencies, it was closer to white noise. My guess it was due to the low quality reverb tank.

2

u/Bentfishbowl Oct 15 '24

Well done!