Author Topic: Windbag issues: R1 resistor causes LPF/muffling of audio signal & volume drop  (Read 1070 times)

Bobb_Lobblaw

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Hello all,
I'll try again...
I'm having a hopefully simple issue with the Windbag. https://www.madbeanpedals.com/projects/_folders/VFE/pdf/Windbag.pdf.
 It works, but I get a steep volume drop and an angry LPF/muffled under-the-blanket sound when the pedal is engaged.
Tracing the audio signal it hits the relay which then sends to R1. The signal going in to R1 is strong..coming out the other leg the vol. is severely dropped and muffled and flows through the rest of the circuit at that unusable volume.
 I reflowed R1, I switched R1 out for another 220K, and then reflowed that one too..and the same vol. drop/muffle happens.
If I crank the amp, I can hear everything else on the pedal doing their respective jobs; delay, reverb, envelope, etc, and sounds cool! It's just at a very low volume.
If I reduce the value of R1 to around 10K, the audio signal reaches unity, but the LPF sound on the alleged "dry" signal remains.

I checked the voltages, and they are a bit off, but I don't think they're show-stopping bad. I subbed a TL072 for the OPA2134 and a TC1044SCPA for the 7662B. My DMM doesn't do mV, so my TL072 voltage measurement is incomplete. sorry.

Any help/suggestions are greatly appreciated.

Thanks.
« Last Edit: August 01, 2023, 02:40:44 PM by Bobb_Lobblaw »

nimbleswitch

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Did you ever solve this?

Maybe there's an error in the parts list? I wonder if it's meant to be 22k instead?
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Bobb_Lobblaw

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Thanks for the reply....I thought the same thing about the R1 value.
What I figured out was that if I lower R1 (orig.220k) to around 10K I can get the audio signal to unity/a usable level. BUT..even if I turn the Reverb/Delay Mix knobs all the way down, the alleged "DRY" signal still has the muffled LP filter sound.
I thought perhaps R1/C1 are actually doing their job correctly and the opamp they feed or something else in the circuit is supposed to clean that LP filter mess up, but I sure can't figure out what other part of the circuit that is..It's Frustrating, it's a cool pedal.     

nimbleswitch

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I had the same issue on a different delay: the Sonomatic.
It was inexplicable how I probed loud audio signal on one side of the input resistor, but muffled deadness on the other side. Like you, I lowered the value just to hear the effect better. But it was never quite right.

The only thing these projects have in common is the use of PT2399. (In the case of the Sonomatic: 4 of them.)

Now, the PT2399 is nowhere near that resistor. But I wonder if it's creating an impedance issue that reflects back to the beginning of the audio chain.  I dunno, I finally gave up on the Sonomatic, even though every feature works, just at a hushed volume.

If I find a known good source of PT2399s, I'll try swapping them out and seeing if it makes a difference.  Good luck! Windbag is on my to-build list so I'll be on the lookout for that problem.
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Bobb_Lobblaw

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Oh man, that sucks. It's very frustrating to have a cool pedal MOSTLY work
Good luck with your Windbag build, curious to see if you experience the same issue.

nimbleswitch

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I will let you know!
I've got one hand in my pocket, and the other one is waving a dildo.