SOLVED Mini heterodyne receiver is very loud

[neiltheseal]

Hi everyone. I just built the mini heterodyne receiver and it seems to generally work well. Although it's hard to tell as it is just so weird (I forgot why I decided to build this one).I followed the build docs with no modifications although It is possible I made a mistake somewhere along the way.

However I seem to have two minor issues:

1. The volume is extremely loud. The three top pots being oscillation, square wave fuzz and sub octave, are just very loud. Each seems to be at about unity volume with my guitar when turned about 1/8 of the way clockwise. There is a jump from barely audible to ear-splittingly loud.
   
   The pots seem to work correctly otherwise, they just go from unity volume at one end to needing hearing protection at the other end.
2. The other issue is with the oscillation rotary switch. On the third mode the effect is just a loud squeal which doesn't react to guitar input. Here is a link to a very short video. I can record another tomorrow when the kids aren't asleep.

Does anyone have an idea why this might be? I don't know where to start with the volume issue. For the oscillation whistling it sounds like I might be having a similar issue to the person in this post. I will try re soldering my connections and maybe try something like in that post. I assume the issue is with IC7 but not sure which of the pins to look at.

The build docs are here. Here are some pics of the pcb. Any guidance will be appreciated.

p.s. I am so chuffed that it worked on first try. I was convinced that I would make some massive mistake with all of this SMD soldering! Although now I have 19 CD4017 SMD chips from ebay that I have no idea what to do with.

 

[neiltheseal]

I have been thinking about the volume issue and replacing the pots with an a taper pot wound assist somewhat.

The pots are b100k. Would I be able to reduce the volume by changing the pot value?

 

[neiltheseal]

I changed the b pots for a pots. It does help a little, but this pedal is still ludicrously loud.

I might try putting a trimpot before the output to act as a volume control. I see the larger version of the pcb has that.

 

[gonzo]

A trim pot or just add a pot from the output, center lug to the output jack, last lug to ground. I added one to my mini. It's a big help.

 

[Audandash]

I have seen a few folks talk about the volume issue with the mini. Based on the schematic the mini is using a 100k resistor for fixed volume. You could either use one of the pedal pcb trimmit boards to add a trimmer (100k) in its place (r24) or socket r24 and try different values to find a volume you can live with. You could also add a pot as stated by gonzo. I like the trimmit method personally, especially if you are using the faceplate just to keep it tidy, but you have options.

 

[gonzo]

You can squeeze it in on the bottom sides and not put a job on it. Keeps it out of the way and it's harder to move by bumping it.

 

[neiltheseal]

I have seen a few folks talk about the volume issue with the mini. Based on the schematic the mini is using a 100k resistor for fixed volume. You could either use one of the pedal pcb trimmit boards to add a trimmer (100k) in its place (r24) or socket r24 and try different values to find a volume you can live with. You could also add a pot as stated by gonzo. I like the trimmit method personally, especially if you are using the faceplate just to keep it tidy, but you have options.

Thanks.

I ended up socketing the resistor and trialling new ones. Ended up with a 120r which seems really low compared to the 100k that was there. It’s still loud but manageable.

However I broke the trace from r24 to output so had to put a jumper there.

Now I just need to solve the weird whining issue. I might do a new post for that.

 

[neiltheseal]

You can squeeze it in on the bottom sides and not put a job on it. Keeps it out of the way and it's harder to move by bumping it.
View attachment 52676

Thanks. This is a really good idea.

 

[BrainDrain]

I have seen a few folks talk about the volume issue with the mini. Based on the schematic the mini is using a 100k resistor for fixed volume. You could either use one of the pedal pcb trimmit boards to add a trimmer (100k) in its place (r24) or socket r24 and try different values to find a volume you can live with. You could also add a pot as stated by gonzo. I like the trimmit method personally, especially if you are using the faceplate just to keep it tidy, but you have options.

If adding a 100k pot to the output would it be a good idea to get rid of the 100k resistor in r24 and jumper it or would leaving it be ok with the 100k pot coming after it?

 

[neiltheseal]

If adding a 100k pot to the output would it be a good idea to get rid of the 100k resistor in r24 and jumper it or would leaving it be ok with the 100k pot coming after it?

I think you would just omit r24. The only difference in the schematic for the super/mini heterodyne as far as I can tell is R24 in the mini is replaced with a 100k pot in the super heterodyne.

 

[BrainDrain]

I think you would just omit r24. The only difference in the schematic for the super/mini heterodyne as far as I can tell is R24 in the mini is replaced with a 100k pot in the super heterodyne.

Leaving r24 in place would just decrease the overall max volume I’m guessing?

 

[neiltheseal]

Leaving r24 in place would just decrease the overall max volume I’m guessing?

I’m no expert on this but I think it would increase the volume.

I managed to decrease the volume in my build by using a much smaller value than 100k.

Although maybe it’s already at max volume and leaving it there will have no effect. It’s worth a try.

 

[BrainDrain]

I’m no expert on this but I think it would increase the volume.

I managed to decrease the volume in my build by using a much smaller value than 100k.

Although maybe it’s already at max volume and leaving it there will have no effect. It’s worth a try.

So I finished it up with the 100k volume pot and.... no sound. Lol. It passes signal in bypass and the LED turns on and off as it should. All the ICs are getting voltage. I took the pot off for now and hooked the output up the regular way just to troubleshoot and not have that be a factor. So instead of fully omitting R24 I used a Zero Ohm resistor and now realize I probably should have left it empty. You said that when you lowered the resistor value of R24 the level decreased right? So I’m wondering if that Zero Ohm resistor Is somehow grounding the output signal in a way it shouldn’t be? Figured I’d ask before I remove it. Looking at the schematic I think I probably should have just left R24 empty and added the 100k pot on the output for it to be the same as the Super Heterodyne. Everything else in the pedal looks good and the LED turning on and off seems like a good sign (I think).

 

[neiltheseal]

that’s right decreasing the value brought the volume down. 100k was too loud but 120 ohm seems about right.

I’m surprised it doesn’t work with a 0 ohm resistor in r24. Have you tried an audio probe to see where the signal cuts out?

If r24 is a short the signal should stop there.

 

[BrainDrain]

that’s right decreasing the value brought the volume down. 100k was too loud but 120 ohm seems about right.

I’m surprised it doesn’t work with a 0 ohm resistor in r24. Have you tried an audio probe to see where the signal cuts out?

If r24 is a short the signal should stop there.

Gonna try the probe next. Hoping it’s just the zero ohm resistor I used.