Help With DSOTM? (Solved)

[Chuck]

Boxed up the dozen pot monster, plugged it in and the volume is very low – initially I thought I had wired the in/out jacks wrong. At the normal amp level I have to have all three effects on and crank all three volumes to get some sound but that results in a lot of distortion (not in a good way). Cranking my amp up is an option but I’d have to figure out the correct volume for all my other pedals. What should I be looking at for potential issues? I’ll try to get photos up tomorrow.

Chuck

[Barry]

Each circuit functions on its own. I would be surprised if all three circuits acts that way individually. Try to narrow it down.

If for some odd reason all 3 are low volume (individually) then I would use an audio probe to find out where something is wrong. If it is just a single circuit then less troubleshooting. Otherwise, do the normal reflow, check for firm Mosfet placement, orientations, etc..

Look for bad resistor values such as K values when it should actually be R (ohm) values etc.

(common mistake)

[Billy]

Low volume could be caused by a few things

As Barry says using an audio probe is probably the quickest route to finding your problem area

I’d start at the input jack tip to its 3PDT lug to circuit in 3PDT lug, circuit in pad etc to make sure audio’s getting into the first circuit at a decent level then do the same for output to next circuit input and so on

Hopefully that’ll narrow it down to whichever circuit is causing it or if it’s something external to the circuit

[Chuck]

Thanks Barry and Billy. Here are the photos I promised earlier. I first checked continuity of the DC, and In/Out jacks finding no issues there. Used my multimeter to check the pot values on all the Volume and Gain pots and they look to be in spec and functioning correctly. I usually search the build document for odd resistor and capacitor values and install those first so I don’t screw up 24+ resistors into a build – but I don’t always do what I plan to do so I’ll check those. Got to find that audio probe I made years ago and figure out how to use it again. Think it’s just a bad LED but just in case it might mean something – the yellow 3mm LED for the Luna Fuzz isn’t working. The red and green LEDs I used for the WattAmp and Phaser are working fine and the 5mm yellow LED is positively mesmerizing.

I’m off to poke and prod some more.

Chuck

[Chuck]

Haven’t found my audio probe yet but I did check the resisters Barry listed and they were correct so I did some more probing with the multimeter. I get nice chirping tones between the input tip and each of the ins on the board and stomp boards. The output tip has nice connection with the top of the board and the WattAmp but not to the Luna or the Phaser. While the Phaser and Luna have good connections between the switches and the bottom of the board there is no connectivity between the Out at the top of the board and the Phaser/Luna connections at the bottom.

Chuck

[Barry]

I need you to clarify a few things. It is best to rule out anything possible up front.

• Do any of the circuits work on their own with adequate volume etc? Explain for each.
• If the Wattamp does not work explain which type of Mosfets used, give voltages for all three, and details for what specifically is wrong. Low volume, no sound at all, noises, etc.
• If the Fuzz does not work give voltages for all 3 transistors and explain the details. Low volume, no sound, noise, etc.
• If the Phaser does not work give voltages for the transistors, and both IC chips, and details.

Keep issue specifics, voltages, and details separated for each circuit.

List any substitutions made.

You may need to dig that probe out.

Lastly, be careful to avoid excessive bending of the ribbon cables/foot switches. You can sever a connection without realizing it.

 

[Billy]

I can’t clearly see some of the resistor colour bands and the odd one partially hidden behind transistors etc even when I zoom in, which might be an age thing, the image is a little bit dark in places I’ve checked all your polarized components which all look correct apart from D3 which I can’t see

Here’s the audio probe PDF for when you find yours for a little refresher

https://drive.google.com/file/d/1T9OsJ0riQhm1QFWPfNQ5q5guikuFKDRN/view?usp=drivesdk

I’d personally start at the first send pad on the left with only the first circuit active if it’s OK there probe the return pad to make sure it comes out of the circuit OK I’d do this for all 3 circuits individually

Once you find a volume drop you’ll obviously know your problem area and its just a case of probing that particular circuit

In the meantime as Barry says post voltages that might indicate where the problem is

 

 

 

[Chuck]

Okay, I found the audio probe. Not going to use it though. Was getting ready to populate a spreadsheet with voltages and write a description of what effect was or was not doing when decided to put the board back in the box so I could hook it back up and sort out my impressions. In the process I remembered that I’d pulled the BS170s and replaced them with 2N7000s so I put the 170s back in making sure they were firmly seated and gave the 108Cs next door a good poke as well. Put everything mostly back in the box, hooked it up on my board, turned my amp volume way up, turned the amp on, and immediately had to crank it back down. With all three volumes and the WattAmp gain maxed I’m pretty sure that deaf people way down the street said “What’s that noise”. I want to pretend that reseating the Mosfets and transistors fixed it but I can’t. Got to pretty this one up and post it with the done stuff.

Chuck

[Barry]

I am glad you got it sorted out. 🙂

The circuit is not biased for 2N7000.

Now get a good and proper Show Off post done!

[Chuck]

“The circuit is not biased for 2N7000.”

The build document says “Q6-Q8 2N7000”. I assumed that the BS107s were offered because you were out of 2N7000s.

[Barry]

I did make a mistake when I released the DSOTM with regard to Mosfet choice.

I discovered the error not long after and updated the build document and sent out multiple emails with the subject as Urgent Update disclosing the change over the following week. If you download the build document again you will see the change.

Regrettably, you missed the update and the email notifications. I apologize for your inconvenience.

[Anonymous]

I’m building this as well. Everything is in, i’ve connected to my test box and looper and all 3 circuits worked fine. Put it in the box, and the Phaser isn’t working. It’s very, very quiet. I pull it out of the box, connected back to the tester and probed. It would seem the issue is between TL072 ic and the output.  But…. not being able to clearly identify any issue, i unplug everything and take a break.  I come back, plug it in, and probe the output and it works!.  I click the switch off and back on, and… nope, not working. I unplug it all, let it sit for a bit, plug it all back in and it works! turn the volume potentiometer and it stops working.

I’m guessing there’s something shorting out perhaps?  Why would unplugging and waiting 10 minutes reset anything? Capacitors discharging?

The other two circuits work fine on their own.  Thoughts?

[Barry]

I would re-flow Volume pot lugs, and C2. You can also replace C2 if that does not work.

If you need more assistance after that create a new thread with clear pictures and description.

[Anonymous]

Figured it out.  C1 needed reflowed and all was good. Thanks!

[Author]

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