Griffin Ricochet -SurfyBear clone

[ThisIsAlec]

I built them both with the improved mixer, and I think at least one other person built it without, and same issue, so it seems to me it's not the mixer circuit. What it could be I have no idea, especially since it has been successful built before...

I built this circuit and had the same issue with the improved mixer. Worked fine when I wired it up using the original wet/dry blend pot. When I traced my circuit I found - get this - pin 3 and 5 (VB) were coming in as clean signal, not a neutral VREF. NO idea how this could happen (maybe somehow running VA through the 2N5457’s caused this?) but it totally bonks the improved mixer stage. Tried a few things to isolate VB and failed. Any ideas are welcomed.

 

[Dan0h]

I built this circuit and had the same issue with the improved mixer. Worked fine when I wired it up using the original wet/dry blend pot. When I traced my circuit I found - get this - pin 3 and 5 (VB) were coming in as clean signal, not a neutral VREF. NO idea how this could happen (maybe somehow running VA through the 2N5457’s caused this?) but it totally bonks the improved mixer stage. Tried a few things to isolate VB and failed. Any ideas are welcomed.

You guys are using 12v Dc adaptors right?

 

[Bugeyed Earl]

You guys are using 12v Dc adaptors right?

In my case, yes. I've also used a bench power supply just to rule out the little wall wart as the source of the issue. I haven't made much progress since my last message, but I did start tracing the signal through the pedal. Too many projects, too little time...

 

[ICTRock]

assuming there isn't a physical defect (as in the pcb matches the schematic), are you using individual pots for the improved mixer or a single dual gang?

I ask because audio taper isn't the right taper for this application and becomes super wrong in a dual gang configuration that is supposed to be turning one gang down while turning the other up

 

[mybud]

You guys are using 12v Dc adaptors right?

Yes, same as @Bugeyed Earl, a dedicated 12V adapter for this purpose.

 

[ProfMagpie]

I'm in the same boat as several of you. Built with the improved mixer and exhibits the same behavior as @Bugeyed Earl is seeing. I've reflowed, traced the signal through the entire circuit, had 5.9V at TP1. I socketed my transistors and tonight was pulling them and checking them with my cheapo transistor checker. I pulled the BC557B to check it and for no real reason tried playing through the thing without it and now it seems to be working without that transistor. Stronger reverb from the wet control and the reverb is no longer intermittent when playing. My dwell control seems to be working in the opposite way that I expected (turn CCW for longer dwell), but it was doing that before I pulled the BC557B. The voltage at the test point increases a little less than 1V with the BC557B left out.

Anyone have any ideas as to why it would work better without that transistor??? I'm clearly way out of my league here. Below are pics of my build and the tank I'm using.

 

[Bugeyed Earl]

assuming there isn't a physical defect (as in the pcb matches the schematic), are you using individual pots for the improved mixer or a single dual gang?

I ask because audio taper isn't the right taper for this application and becomes super wrong in a dual gang configuration that is supposed to be turning one gang down while turning the other up

I'm using separate A taper pots for the wet and dry mix as specified in the BOM, are you saying linear would be a better option?

 

[Bugeyed Earl]

I'm in the same boat as several of you. Built with the improved mixer and exhibits the same behavior as @Bugeyed Earl is seeing. I've reflowed, traced the signal through the entire circuit, had 5.9V at TP1. I socketed my transistors and tonight was pulling them and checking them with my cheapo transistor checker. I pulled the BC557B to check it and for no real reason tried playing through the thing without it and now it seems to be working without that transistor. Stronger reverb from the wet control and the reverb is no longer intermittent when playing. My dwell control seems to be working in the opposite way that I expected (turn CCW for longer dwell), but it was doing that before I pulled the BC557B. The voltage at the test point increases a little less than 1V with the BC557B left out.

Anyone have any ideas as to why it would work better without that transistor??? I'm clearly way out of my league here. Below are pics of my build and the tank I'm using.
View attachment 69676View attachment 69677

Interesting observations, thanks for sharing! A bit off track, but did you detect any heat on the MOSFETs? I've seen reports from the Surfybear kit builders that they had to heat sink them, but mine don't seem to even get warm.

 

[Bugeyed Earl]

Last night, I pulled a handful of components to remove the improved mixer from the circuit (C17 & 20, R26, U1, RV4 & 5), I didn't have a B taper pot for the "original" mix control, so I used one of the A pots from the improved mixer for RV3.

Now I get no hint of reverb, and voltage at TP1 hasn't changed. I'm thinking I might have one or more bum transistors, I had them on hand from some old orders, and they probably came from Tayda or similar cheapo supplier, so my next step is to order some known quality parts from Mouser and try replacing all the silicon. They all tested ok on my transistor tester, but who knows...

 

[mybud]

I pulled the BC557B to check it and for no real reason tried playing through the thing without it and now it seems to be working without that transistor.

Since mine completely refuses to work, I am going to give this a try. What's to lose? Will report back on progress later this week.

 

[ProfMagpie]

Interesting observations, thanks for sharing! A bit off track, but did you detect any heat on the MOSFETs? I've seen reports from the Surfybear kit builders that they had to heat sink them, but mine don't seem to even get warm.

Yeah...mine are cool as a cucumber.

 

[ICTRock]

I'm using separate A taper pots for the wet and dry mix as specified in the BOM, are you saying linear would be a better option?

The provided "improved" mixer gives you what might be better thought of as independent level controls that then proceed to a summing amplifier that is a fixed ratio mixer. The ratio is set by summing resistors R28/R29. In this respect, the taper of the potentiometers is immaterial and I imagine an audio taper was settled upon because they're rightly thinking of them as level controls. I consider this too fiddly as you're messing with volume and/or mix as you mess with two knobs that were previously one.

What I would consider to be an improved mixer will dual-gang these level controls with a linear taper and possibly adjust the summing resistors so that "noon" on the control is representative of a 50% wet/dry mix with respect to perceived volume (if adjusted by ear) or by signal level (if adjusted by scope) . In this configuration you're keeping the original concept of a single Mix control but you're also getting the ability to reach 100% wet and 100% dry at the ends of the rotation if you configured the potentiometers' connections so that one gang is turning up while the other turns down.

But why limit ourselves to one approach?

Removing the "improved" mixer potentiometers' connections to ground turns them into adjustable summing resistors rather than level controls if that freaks you out less. You won't get 100% wet/dry as a tradeoff.

Configuring the dual gang potentiometer connections so that both gangs turn up/down at the same time turns the Mix control into a global Level control with a fixed ratio summing amplifier for the wet/dry mix. (which you could then adjust for your preferred mix ratio with the summing resistors)

 

[Bugeyed Earl]

The provided "improved" mixer gives you what might be better thought of as independent level controls that then proceed to a summing amplifier that is a fixed ratio mixer. The ratio is set by summing resistors R28/R29. In this respect, the taper of the potentiometers is immaterial and I imagine an audio taper was settled upon because they're rightly thinking of them as level controls. I consider this too fiddly as you're messing with volume and/or mix as you mess with two knobs that were previously one.

What I would consider to be an improved mixer will dual-gang these level controls with a linear taper and possibly adjust the summing resistors so that "noon" on the control is representative of a 50% wet/dry mix with respect to perceived volume (if adjusted by ear) or by signal level (if adjusted by scope) . In this configuration you're keeping the original concept of a single Mix control but you're also getting the ability to reach 100% wet and 100% dry at the ends of the rotation if you configured the potentiometers' connections so that one gang is turning up while the other turns down.

But why limit ourselves to one approach?

Removing the "improved" mixer potentiometers' connections to ground turns them into adjustable summing resistors rather than level controls if that freaks you out less. You won't get 100% wet/dry as a tradeoff.

Configuring the dual gang potentiometer connections so that both gangs turn up/down at the same time turns the Mix control into a global Level control with a fixed ratio summing amplifier for the wet/dry mix. (which you could then adjust for your preferred mix ratio with the summing resistors)

Thanks for your analysis, much appreciated! I think I'm going back to basics with this circuit, and will try to get it working with the original mixer before anything else.

 

[ICTRock]

holy shit I have to stop following this thread
also if you're reading this and you're not the OP and you're looking for help troubleshooting your ricochet build then go to the troubleshooting forum ffs and start a thread and, you know, mark it as resolved if you fixed it. it's like you all pee outside as much as the dog does.

 

[Milt_Mason]

I don't think this is just a build issue. I think there's an underlying problem with the circuit for the improved mixer section.

Here are the details:
I came here for reviews of the PCB and I ended up going down a rabbit hole. This issues people were having seemed consistent enough that I started to question the circuit itself. I simulated the design and now I'm not surprised that people are having issues. The simulations show a low overall output for the improved mixer with an especially low response for the wet signal.

That sent me down another rabbit hole and now I'm reasonably confident that I understand the issue. It looks like the design intent for the improved mixer was to create a summing amplifier. I included a shot from the Griffin schematic and a summing amplifier circuit from here:

https://www.ti.com/lit/an/snla140d/snla140d.pdf?ts=1712820627958

In the improved mixer, the summing amplifier has trouble since the wet and dry signals aren't buffered before they go into the amplifier. Because the signals aren't buffered a bunch of other parts contribute impedance. In the TI example, the impedance of the summing leg sourced by V1 is this:

In the improved mixer, the impedance of the wet leg of the amplifier is the following two sections in series:


This group of parts creates a complex impedance leading to low gain and frequency dependence. This low gain and frequency dependence seems to explain the issues that builders are having. The dry leg of the summing amplifier has fewer problems, but it still has relatively low gain.

I'll probably end up building a pedal with the ricochet board, but I'll stick to the original mix control. I've read some helpful posts here and this seems like a great community. This is my first post here so let me know if I should've put this on a different thread or something.