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Thanks, all.

Tayda have 10M ohm 1% in stock. I'll get a couple on my next order.

Copied from some random web site about MOSFET amplifiers, the second part is most applicable here:

"it is desirable to make the values of these two resistors as large as possible to reduce their I2R power loss and increase the mosfet amplifiers input resistance."

Interesting, thanks for that! Wonder what "large as possible" means? 10, 20, 30 M ohm?

10 Billion Ohms

LOL! 

Copied from some random web site about MOSFET amplifiers, the second part is most applicable here:

"it is desirable to make the values of these two resistors as large as possible to reduce their I2R power loss and increase the mosfet amplifiers input resistance."

Interesting, thanks for that! Wonder what "large as possible" means? 10, 20, 30 M ohm?

OK, thanks. But why does it use such a high value?

OP07 datasheet: http://www.analog.com/media/en/technical-documentation/data-sheets/OP07.pdf

The OP07 does not need the 30 pf external compensation capacitor. It uses those pins for offset nulling (which is something that never gets used in pedals AFAIK), and the cap probably won't do anything if you leave it in.

Yep, you're right, thanks. The 30pF cap does nothing if I leave it in. Wonder if it will do any harm leaving it in, just in case I ever slot in a LM308 or TL070?

I'm building the Giant Hogweed fuzz circuit. R19 and R20 are both 10M ohm. I'm wondering why the value is so high and could I use 4.7M ohm instead?

So I built the Giant Hogweed circuit here - http://tagboardeffects.blogspot.com/2015/10/giant-hogweed.html

The schematic is here - http://www.davidrolo.com/wp-content/uploads/2017/07/GiantHogweedSchematic_zps445f5a36.png

I still haven't found an LM308, so I popped in an OP07. The pedal works, but so far I don't know how it compares to an LM308 or a TLO70. Also, I'm not sure whether the 30pf compensation cap between pins 1 and 8 of the OP07 needs to stay, be removed, or the value changed.

This is good timing.  You can see the effect of different bypass caps on Daves oscilloscope:

Brilliant! This video and Dave's other one on bypass caps explains thing nicely. Thanks for the heads up.

(Side note - some of the vero layouts at tagboardeffects remove the additional small-value bypass caps. Probably not a good idea then!)

Sure, but there are 4 caps in parallel - 100uF and 3 100nF. Thus a total of 100.3uF and where these are physically placed will make no difference to this. Yet the text talks about them as if they are separate caps for each of the three ICs:

"It's followed by three 100nF caps which are used to filter the power between pins 8 and 4 of each of the ICs"

Wouldn't a 100uF and a 300nF cap be the same?

Don't understand this part about the power supply:

"C20 is smoothing the majority of any DC ripple that existed in the power supply. It's followed by three 100nF caps which are used to filter the power between pins 8 and 4 of each of the ICs to prevent any noise in the signal path."

Surely running these caps in parallel just gives 100.3uF total capacitance?

And the three connections U1, U2, U3 are all coming from the same rails.

What am I missing here?

I just did an ET pour which was going great until about 2 hours in and I noticed a few micro bubbles had appeared. Put a BBQ lighter over it, but messed it up because by this time the ET had started to harden and ended up with pucker marks from the flame instead.  Next time if bubbles appear after about an hour, they can stay. 

Those looks good, Willybomb.

Datapol seems to be an Aussie thing, can't find that in the UK.

What clear coat do you use?

I wonder if it would be possible to print on shiny or satin paper with a colour laser printer and then just glue it to the top of the enclosure? Does the laser ink need to be protected with a clear coat or some kind of lacquer? (I'm looking for simpler alternatives to Envirotex or spraying clear coat on decals).

I use water slide decals. I like the white as opposed to the clear, the colors are more vibrant. I get it off of eBay, as it's nearly impossible to find around here. Sticky back is ok, but you only get one shot at putting it on.

And I guess you don't need to coat it before putting it in the water?

Nope, no need to, that was one of the attractions for me.


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How adhesive is a water slide decal? If it's covered with Envirotex the whole lot has to be stuck to the enclosure by whatever's on the back of the decal paper.

I use water slide decals. I like the white as opposed to the clear, the colors are more vibrant. I get it off of eBay, as it's nearly impossible to find around here. Sticky back is ok, but you only get one shot at putting it on.

And I guess you don't need to coat it before putting it in the water?