Intermittent static/noise (more gremlins - have I made it even worse?)

[p_wats]

At some point a smarter man would give up on this ridiculously cursed build, but I just can't.

I've now had it boxed up and "finished" a half dozen times only for something weird to pop up.

In this case, I've now got an intermittent crackle/noise that interrupts the signal (doesn't seem to affect bypass). All effects/controls seem to work and affect this crackle. I hesitated before posting, as I thought it was clearly just a loose connection from all the boxing/unboxing, but I've reflowed all the joints and checked (and in some cases replaced) the connections.

With an audio probe I seemed able to trace the crackle back to C3 (not there on the way in to C3, but there on the way out). However, after replacing it it I still get crackle and now it seems to not appear until after the FV-1 (not there on pin 1, there on pin 28).

I've inspected and reflowed all the FV-1 joints and all seems well.

I swear, I've built complex, unique and fun pedals many times before, but this one is just doing me in.

 

[p_wats]

Hmm. My voltages coming off C3 seem wrong. 4.5v going in. Unstable and low (0.790-0.810v) coming off C3 to R3.

I just replaced C3 with a new 1u MLCC that I measured first, so it's a bit strange.

 

[phi1]

Maybe check the voltage coming off the 3.3v regulator? And check that it’s getting to the fv-1 pin 6&8.

I say this because of your C3 voltages. 4.5v going in is good (op amp inputs and output is biased to vref thru R2). But I’d expect the other side to read close to 1.75v since that’s what in the fv-1 input pins should be sitting at. (Fv-1 datasheet bottom of pg 5 states the inputs are internally biased to VDD/2).

 

[p_wats]

Maybe check the voltage coming off the 3.3v regulator? And check that it’s getting to the fv-1 pin 6&8.

I say this because of your C3 voltages. 4.5v going in is good (op amp inputs and output is biased to vref thru R2). But I’d expect the other side to read close to 1.75v since that’s what in the fv-1 input pins should be sitting at. (Fv-1 datasheet bottom of pg 5 states the inputs are internally biased to VDD/2).

Good suggestion. Thanks! Regulator measures fine and I'm seeing 3.23v on pins 6 & 8.

Hmm. If it internally biases and is receiving good voltage in, I'm hoping that doesn't point to problems with the chip itself (again).

 

[phi1]

Just to clarify you’re getting 3.23v while the static thing was occurring? What about directly on pins 1? I assume it’d be the same Voltage as C3 on that side. Can you measure C3 and pin1 while the static is occurring and while it isn’t to see if it’s changing?

sounds like you already replaced C3 with a measure good part, you could also replace R3 & C4

 

[p_wats]

Just to clarify you’re getting 3.23v while the static thing was occurring? What about directly on pins 1? I assume it’d be the same Voltage as C3 on that side. Can you measure C3 and pin1 while the static is occurring and while it isn’t to see if it’s changing?

sounds like you already replaced C3 with a measure good part, you could also replace R3 & C4

Thanks for the continued suggestions!

The regulator puts out 3.23v consistently, regardless of static or not.

The path between pin 1 of the FV-1 and R3 is where the changes occur.

Usually, it starts fine for a while, with 1.5v or so on pin 1, but if I leave it running long enough the static/sputtering starts and the voltage in that part of the path drops between 0.7-0.8v or so.

During this time, all controls, etc. work as normal and the static/sputtering noises are overlaid on everything.

I've now replaced C3, C4 & R3, to no avail.

The fact that it starts fine for bit gives me hope, but not sure where to go from here.

 

[phi1]

I’m afraid we’re starting to point to an unfortunate next step, replacing the fv-1 chip itself ?.

one other thought first though, as I understand it, the output pins and pin 3 should all also be biased to 1.65v internally. You could check if those pins are exhibiting the behavior as the input pins, and maybe try replacing C5.

 

[p_wats]

I’m afraid we’re starting to point to an unfortunate next step, replacing the fv-1 chip itself ?.

one other thought first though, as I understand it, the output pins and pin 3 should all also be biased to 1.65v internally. You could check if those pins are exhibiting the behavior as the input pins, and maybe try replacing C5.

Replacing the FV-1 has become a bit of a trend, unfortunately (I used to think these things were pretty robust, but I've got a growing, expensive graveyard of them now).

Checking the voltages again this morning here's what I found:

• After being left alone for a good 12 hours it started fine and stayed that way for a while
• After 10+ minutes the noise/static started and the voltages started jumping around
• Pin 1 jumps between 0.7-0.8v and 1.5v or so (ie, noise or not)
• Pin 3 jumps between 0.3-0.4v and 1.5v
• Pin 28 jumps between 0.2-0.3 and 1.5v

I can try replacing C5, as it's possible that became damaged while replacing/reflowing the FV-1.

While that's out I may remove/resolder the FV-1, just to be sure everything is making a good connection.

Thanks again for your continued suggestions!

 

[p_wats]

Well, I pulled C5, which measured fine, replaced it and resoldered the FV-1.

It all sounded and measured fine for about 20-30 minutes, but then started crackling/sputtering on its own after a while, so I'm back to the FV-1, I guess.

 

[p_wats]

I don't know if this is good news or even worse news, but I pulled the FV-1 and swapped it with one I know to be working and I'm getting similar, if slightly worse results.

I can occasionally hear the wet signal, but voltages on pins 1, 3 & 28 are all over the place (though seem stable on 6 & 8). Either I've somehow just fried another(!) one or there's something wrong with the rest of the circuit still that I haven't pinned down (I'm really hoping for the latter).

I have to remind myself that this was all working perfectly fine--I was just trying to track down a switch pop, but somewhere in my troubleshooting things descended further into madness.

I'm not really sure where to go from here---maybe I'm being stubborn, but I don't usually pitch a build, let alone several in a row of the same circuit.

I'll probably have to walk away from this for a while unless anyone has a bright ideas.

 

[Ariel Muñoz]

Hola amigo...sabes no sé si mi experiencia te pueda ayudar...yo arme un XB-MB y me pasó algo similar... después de unos minutos de operación se metía un ruido y chisporroteo en la señal ...el efecto y controles funcionaban ..este pedal no lleva fv-1 pero lleva dos ic...después de cambiar los condensadores electrolíticos y los transistores... perdistia el problema...y lo que procedí a hacer fue limpiar la cara de la placa soldada para eliminar todo resto de flux y suciedad en los terminales y repasar todas las soldaduras...una por una...y me di cuenta q uno de los ic...los pines inferiores no hacían buen contacto con los socket...y procedí a estañar los pines de los ic para aumentar la superficie y que entrarán más a presión ..con ambos ic...y las patas de los transistores también por qué le puse socket al final para intercambiar con diferentes modelos pensando que la falla podía pasar por ahí...pero después de todo lo narrado conecte todo ala caja y .... funcionó todo impecablemente....ningún ruido extrañó ni ninguna cosa....espero que te pueda servir de algo...buenas noches...

 

[p_wats]

Hola amigo...sabes no sé si mi experiencia te pueda ayudar...yo arme un XB-MB y me pasó algo similar... después de unos minutos de operación se metía un ruido y chisporroteo en la señal ...el efecto y controles funcionaban ..este pedal no lleva fv-1 pero lleva dos ic...después de cambiar los condensadores electrolíticos y los transistores... perdistia el problema...y lo que procedí a hacer fue limpiar la cara de la placa soldada para eliminar todo resto de flux y suciedad en los terminales y repasar todas las soldaduras...una por una...y me di cuenta q uno de los ic...los pines inferiores no hacían buen contacto con los socket...y procedí a estañar los pines de los ic para aumentar la superficie y que entrarán más a presión ..con ambos ic...y las patas de los transistores también por qué le puse socket al final para intercambiar con diferentes modelos pensando que la falla podía pasar por ahí...pero después de todo lo narrado conecte todo ala caja y .... funcionó todo impecablemente....ningún ruido extrañó ni ninguna cosa....espero que te pueda servir de algo...buenas noches...

Thanks! I've set it aside for now, to finish other projects and clear my head. I'll give it another shot later and check the sockets, as you've suggested. Sorry, I only know a little Spanish!