Build Your Own Clone Message Board

I am building a "Shred Master" pedal, the PCB was purchased from Tayda. Along with that they offered a 3PDT PCB to make the build easier and not so cluttered with wires. My question is, I am getting a 3v drop on the supply voltage that goes to the effects PCB. I have included a picture of the schematic for the 3PDT PCB and the component values listed on the schematic. Would a 3v drop be "normal" the way this is designed? I'm am having some issues with the pedal operation and this was my first spot (starting from the 9v input) that didn't seem right to me. I removed the D2 and added a jumper to D1, as per instructions, if the effects circuit didn't need reverse polarity protection.
Thank you, in advance, for your time!

-=SteveO

p.s. I found out today that Tayda doesn't have a schematic for their Shred Master board, so I am going to have to wing from here.

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“To know, and not to do, is not to know”

I admit I don’t know what's going on here, but I just popped in to say that if you're going to get into building without kits, you should definitely build a breakout box. It's a simple device that you can make in a spare enclosure or even an electrical junction box. It has a 3PDT switch, input and output jacks, a DC jack and battery snap, and four wires that terminate with alligator clips: PCB IN, PCB OUT, 9V+, and GND.

The beauty of this device is that you can populate your circuit board and then test it to make sure it's working before you do all the offboard wiring. Then if you wire it up and it doesn't work, you know the problem is not on the board anywhere. It would be really handy in your situation, I think. And it's an absolutely indispensable part of my workbench.

If you're interested in this and want more details about how to make it, I can shoot you some photos of mine.

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Scott

My band, Austin Hollow

Absolutely Scott! I'd appreciate it. Anything to make this process easier.

Thank you!

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“To know, and not to do, is not to know”

What voltage drop do you see across D1? Across R2? How much current does the effect allegedly draw? Can you disconnect the effect and then see what the voltage is at "2 PCB V+" ? (I presume the 6.2 V is with the effect drawing current/power.)

EDIT: oh wait, I guess you meant you put in a jumper instead of R2, so then the drop across D1 is inferred to be 3 V ... have you measured it directly?

I just now checked it without the effects board attached and the voltage is correct (9.2v). So I can assume (hate the word btw) that the board is drawing the other 3 volts? When I checked the voltages at the IC's, the input voltages on both (pin-8) was at 6.2v. Being relatively new to this, and only having build BYOC kits, the input voltage on every IC I've checked has always been the same as the supply voltage, so I just 'assumed' that there was an issue. And without any schematic at all from Tayda makes it a little tougher. I have downloaded a couple of other Shred Master schematics from the internet but am struggling to make the comparison.

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“To know, and not to do, is not to know”

So does the pedal sort of kind of work? Tell us more.

Have you checked the voltages at the other pins? I am wondering whether there is a virtual ground, typically half of the voltage diff between pins 8 and 4, that might show up at pins 3 or 5 (the non-inverting inputs). It seems a bit odd that the parts list for the Shred Master only contains one cap (C7) that is 1 uF or above. I would expect two, if the circuit includes the creation of a "Vcc/2" virtual ground. You can look for example at the diagrams on

https://www.scribd.com/doc/282668500/ShredMaster-Guero-En



where it appears that two 41 k (yes, that's what it says) resistors (R1, R2) form the voltage divider that attaches Vcc/2 (orange trace) to the pins 5 of the two TL072's. It uses 100 uF and 47 uF to support that divider, which is typical--100 uF at Vcc and 47 uF at Vcc/2.

I suppose the same scheme would be used in the Tayda PCB but where is the support? I see that R14 and R15 have matched values (33 k) that are typical for the voltage divider, and sit next to each other and near C7 positive terminal, at 10 uF the only large-C cap in the list. Maybe the Tayda scheme expects you to supply a robust, well-behaved DC voltage of somewhere in the 9 - 18 V range and it only bothers to put the cap in for the Vcc/2 vs. GND, rather than also putting one across V vs. GND. So if you check some more voltages (or can check some continuity), you might want to see whether R14 / R15 / C7+ all join together, and see if any of pins 3 or 5 of either IC have the same voltage as C7+ (there would likely be components in between, so checking continuity might not tell anything).

None of that really explains the 3 V drop, but if the +V you supply goes to more places than just the pins 8, then possible explanations might include shorts, or wrong-value resistors being used in the Vcc/2 creation.

I'd be curious to try starting with a blank PCB and tracing with a continuity checker to reverse engineer it, just to understand it ... but I have an Echo Royal to finish (my enclosure-decorating skills are kind of lame) and I haven't yet even started that Analog Vibrato kit yet (much less the flanger and chorus mods we discussed) and there's more Tru Oil to put on this Tele body I've got so I don't need a new project quite yet.

Update:
I got tired of messing with the Tayda foot switch PCB and replaced it with one from GuitarPCB. I also double checked all the component values and their placement just to be sure I didn't drop the ball in that area. After replacing the Tayda switch PCB I now have 9.2v going to the effects board.
I have sound when bypassed. When I engage the switch, the LED comes on but there is absolutely no sound at the amp.
See attached for IC voltages etc. Definitely something going on with IC 1, but without a schematic I am lost. Lesson learned... never buy a PCB board without
any schematic. No support from Tayda for sure. Thank you again for the suggestions!

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“To know, and not to do, is not to know”

I wonder what the point of the Tayda switchboard is. It says it will trim 3 volts off.


Sent from my iPhone using Tapatalk

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Pedal building is like the opposite of sex. All the fun stuff happens before you get in the box.

Please post top & bottom photos of the Shred Master PCB, Steve. Maybe we'll see something you've missed.

BTW, I'm going to move this thread over to the DIY discussion forum, since we like to keep the Tech Support sub-forums focused on just BYOC products.

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“My favorite programming language is SOLDER” - Bob Pease (RIP)

My Website * My Musical Gear * My DIY Pedals: Pg.1 - Pg.2

Pictures as requested...

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“To know, and not to do, is not to know”

How's chances for a photo or diagram of the unpopulated PCB with the components labeled? If the component values aren't shown directly on the PCB silkscreen, could you post a BOM showing those values?

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“My favorite programming language is SOLDER” - Bob Pease (RIP)

My Website * My Musical Gear * My DIY Pedals: Pg.1 - Pg.2

I think you'll find it here on (web) page 2 of the Tayda instructions:

https://www.taydakits.com/instructions/shred-master/pages/designators-and-components--33

After looking at a couple more ShredMaster schematics online, and the BYOC Shredder schematic, I'd say the two Tayda 33 k resistors I mentioned earlier probably play the same role in Tayda as they do in other implementations, connected not to the 47 uF electrolytic cap but instead to the yellow 47 nF cap, and related to the Contour control. It seems more likely now that it's R6 and R8 (47 k each) that are the Vcc/2 voltage divider, if there is one. Unfortunately in SteveO's photos, which show the traces that Tayda doesn't show, the four power/signal wires obscure a lot of the real estate where there might be some observable traces!

At the least, it seems that the U2 (the TL072 on the left in the photos) pin 5,6,7 op amp is the output op amp, and seems connected to the Volume control in the same way that the various available schematics show. Again, I can't quite tell which things connect to GND and which might connect to a Vcc/2 in the photos.

It's a shame that the "Guero-En" schematic I linked to earlier is so hard to read, since its BOM and the Tayda BOM are nearly identical.

Ask and you will receive!

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“To know, and not to do, is not to know”

This one has less glare...

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“To know, and not to do, is not to know”

Two things:

• I would suggest inspecting the solder side of the PCB very carefully (use magnification!) and see if you have any solder bridging/shorts or other anomalies that need to be cleaned up. It is SO easy to send your audio signal to ground this way. With the light reflection from the melted solder mask, it's impossible to tell from the photos.
• C11 in the Tayda documentation is shown as a 22n, but you appear to have a 220n installed there, unless this is a mod you did on purpose. In any case, I can't believe that it would cause your problem. Just thought I'd mention it.

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“My favorite programming language is SOLDER” - Bob Pease (RIP)

My Website * My Musical Gear * My DIY Pedals: Pg.1 - Pg.2

Yes, it looks like one end of R6 goes to +V (and pin8 of U1 nearby) and its other end connects with R8, and that connection also goes to C7+. So R6/R8 should be the "Vcc/2" creator, fortified by C7, but no obvious on-board high-C bypass cap for the applied DC. It's still not clear to me how the other end of R8 connects to ground, but perhaps it's connected to a large-ish ground plane section.

The C11 220nF vs. 22nF thing seems to be a cap in the treble & bass network of R's and C's; other schematics do show 220n in one spot and 22n in the other, so that's probably C10 and C11 on the Tayda board. Their junction also meets one end of R10 (6.8 k) the other end of which meets one of the D1/D2 junctions that one sees in various shredmaster schematics.

SteveO, do you have one of those audio probe thingies? You might want to just check with it at the 1 and 7 pins of both IC's just to see how far into the effect the input signal is getting.

My mistake on the 22n and I have now corrected that. I also cleaned the PCB with some alcohol and it is a little easier to look at. Picture attached.

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“To know, and not to do, is not to know”

Problem solved!
After taking the suggestion from WMP1 to check the signal at several locations, the only thing consistent in my findings, was there was no consistency. Pin 7 on IC2 the signal would be okay, go back and check same pin a bit later and the signal was either very weak or not present at all. My signal generator has a switch for low and high volume and switching to the higher volume I could hear a faint signal at the output terminal, occasionally. My past experiences with electrical inconsistencies almost always involved a poor connection, somewhere. I pulled the PCB out of the box and re-flowed all of the connections, again. I then gave the PCB a good cleaning with alcohol and a nylon brush. Put it all back in the box and I now have a functioning pedal. Big thank you to WMP1 for all of your time in finding a very close schematic and helping make since of it all. I also would like to say thanks to duhvoodooman for the suggestions regarding the soldering. I swear, they all looked good, even under magnification.
I will post pictures in appropriate group later on.
Almost forgot to say thanks to sjaustin for the suggestion for building a breakout box to help trouble shoot these PCB's. I have in the works already!

-=SteveO

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“To know, and not to do, is not to know”

Excellent news! Persistence pays off!


After seeing that last photo, I would completely agree! But a weak solder joint isn't necessarily visually discernible (even though many are!).

_________________
“My favorite programming language is SOLDER” - Bob Pease (RIP)

My Website * My Musical Gear * My DIY Pedals: Pg.1 - Pg.2

I was ready to shelve this one for a while. And by shelve I mean use as a "parts donor", I was tired of looking at it.

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“To know, and not to do, is not to know”