Rod Elliot Spring Reverb [LAYOUT VERIFIED]

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artilect99
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Rod Elliot Spring Reverb [LAYOUT VERIFIED]

Post by artilect99 » Fri Aug 14, 2020 12:42 pm

Hi all,
I need a second pair of eyes on this layout. It seems to be "working" but I'm getting a lot of squeal/hi-frequency noise on the output, which is maybe the op-amp oscillating? Does anyone notice anything conspicuous about this layout that would cause that?

It's a relatively simple circuit, so I'm hoping I've just made some dumb mistake. Any suggestions would be appreciated.

EDIT: It was a dumb mistake. There was a single trace cut missing from my original layout, causing the input signal to feed into the output of the opamp. With this fixed the circuit is working great and the layout is verified. I'm posting the revised layout in case anybody else wants to build this, as Rod Elliot is not currently making PCBs for it.

The 4.7nF cap (changed from 22nF) puts the corner frequency of the EQ boost at about 5Khz, which is personal preference. Lower values will move the freq down and give more bottom end, making it more boomy.
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Last edited by artilect99 on Mon Sep 07, 2020 11:23 pm, edited 1 time in total.

jorg
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Re: Rod Elliot Spring Reverb

Post by jorg » Fri Aug 14, 2020 12:46 pm

I suspect some phase-compensation feedback is needed; I don't see any here. I think this is current-drive, which I don't have much experience with so I can't get much more specific than that, I'm afraid.

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artilect99
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Re: Rod Elliot Spring Reverb

Post by artilect99 » Fri Aug 14, 2020 1:41 pm

yeah it is current drive. I'll look into phase compensation, thanks for the suggestion.

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EATyourGUITAR
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Re: Rod Elliot Spring Reverb

Post by EATyourGUITAR » Fri Aug 14, 2020 4:33 pm

Did you move the corner frequency of the rc low pass on the input of the recovery circuit? I see 22n changed to 4n7. That moves the corner frequency up two octaves. If the resonant frequency of the tank is not dampened by the recovery circuit maybe the crosstalk on the PCB creates a feedback loop. If you make R1 a 5K trim pot maybe you can wiggle the phase and the frequency at the same time so that it gives you more damping at the frequency of the oscillation that you are hearing?
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artilect99
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Re: Rod Elliot Spring Reverb

Post by artilect99 » Sat Aug 15, 2020 5:39 am

Yeah I did change the RC corner freq. 4n7 was intended to put it closer to 5Khz. I will try changing the value and see if anything changes. thanks!

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Re: Rod Elliot Spring Reverb

Post by wuff_miggler » Sat Aug 15, 2020 5:47 am

hey artilect, did you join the ESP forums? i got some really good help there (even a phonecall from a member) to help me work out what i had done wrong.

( you're in good hands here too though ofc )

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artilect99
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Re: Rod Elliot Spring Reverb

Post by artilect99 » Sat Aug 15, 2020 2:39 pm

no, in fact I didn't even know there was one! I'll check it out.

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Re: Rod Elliot Spring Reverb

Post by artilect99 » Sat Aug 15, 2020 3:21 pm

In another version of this circuit he recommends a 100n bypass between the power pins of the NE5532, so I'm going to try that as well.

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Re: Rod Elliot Spring Reverb

Post by wuff_miggler » Sat Aug 15, 2020 6:28 pm

Sorry i should have mentioned - i havent built this spring reverb, and am next to no help to you (apologies) but i wanted to just let you know about the forums just incase you dont get a resolution here! :D

[my diy skills are fucking SHITE - and i dont know how i managed to pull off building the ESP phono amp (using 3 ESP PCBs) that works and sounds brilliant]

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Re: Rod Elliot Spring Reverb

Post by artilect99 » Mon Sep 07, 2020 6:35 pm

Just in case anybody does run into this same problem, I tied a 100nF cap across the power rails and that seems to have sorted it.

The circuit is still *VERY* susceptible to EMI hum from positioning, nearby devices, and even my own proximity to the board. I'm thinking enclosing it in a metal box is going to help in this regard.

It is a very nice, hi-fi sounding spring reverb -- prob. one of the nicest I've heard!

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