Gold Sounds (jimmybjj's Sparklehorn PCB)

[mgwhit]

Forum member jimmybjj was kind enough to let me try out one of the extras from a small batch of Sparklehorn PCB's he recently had fabricated.  One of my bandmates had been bugging me for a overdrive/delay combo for some time, and I had just ordered some PT2399s, so I was thrilled to get an opportunity to try this one.  As you can see, it came out looking pretty nice.  I'm not 100% sold on the overdrive yet, but that's probably because I haven't used the recommended op-amp.  I will fill in some extremely long-winded details in my next post.

[mgwhit]

There were a few mistakes on the PCB that Jim had caught and fixed before he sent it.  Nothing big -- just a couple of cut traces and a couple of jumpers -- but I'm glad I didn't have to debug those myself!

I took these (very blurry) photos so I could remember what Jim had done on the board:





I spent a couple of evenings populating the board.  I was missing a 15n cap for C16, but Bean assured me that a 10n would work just fine there.

When I had finished populating the board, I decided to do a power-up smoke test without the chips.  Good move on my part, as I was getting 6.41V on pin 1 of the PT2399 socket, 6.99V on pin 8 of the op-amp socket and a reference voltage of about 3.2V [I'm estimating these, as I can't find my notes.]

I spent a couple of days debugging traces (tedious work, especially on a populated board!) and going back and forth with Jim.  I was starting to be afraid that I might have a bad voltage regulator and I was not looking forward to bending the leads on the PCB-mount pots to get at the underside of the board to desolder it.  Finally I broke down and looked at the datasheet for the LM78L05 voltage regulator.  Then I looked at the board.  Then I looked at the data sheet.  Then I looked at my voltage regulator.  Was my voltage regulator backwards?  I took a spare over to my breadboard, set it up backwards and tested -- bingo!  6.99V and 6.41V.  I then tested to see if I had fried the regulator, and I hadn't.  I just needed to turn mine around.

[It turns out Jim had put the silkscreen shape of the voltage regulator on backwards, which left him wondering how his was even working.  He had lent his out for a couple of weeks and couldn't test it, but he confirmed that the PT2399 data sheet specifies the max voltage as 6.5V, so the 6.41V coming out the backwards regulator is just enough to not fry it.  Maybe it's the combination of maximum headroom on the PT2399 and low-voltage fuzzed out op-amp that makes yours sound so awesome, Jim! ]

Getting at the regulator was hard work.  I had to bend the pots and desolder another capacitor to get at it properly, but in the end, I got everything out and even reused the parts.  (I snipped the leads on the regulator as close to the board as I could, and then removed the remaining bits of lead one at a time.)  Once everything was back in place, I checked and I was getting proper voltages on the sockets.  I put in my chips, hooked up my test rig and got overdrive and delay.  Whew!

[jkokura]

Great story Matt! Would love to know if you like how it sounds...

Jacob

[jimmybjj]

Looks great! Glad we got through that my buddy loves his, says it number one his board now. I still need to get together with him to see if I installed that regulator right or if I just got really lucky

[mgwhit]

I wanted to get a build report up for Jim, who had donated an old 125B with some powdercoat flaws for this to go in.  Since this pedal is obviously inspired by the Golden Cello (and since I had some gold paint left over from a model rocket build) I decided to go the aesthetic route of the original.  It's a good look.

I sanded back enough of the flawed powdercoat to have a fairly smooth surface.  I used 80 or 120 grit, and in hindsight I probably should've finished off with something a bit finer, as there are obvious grooves in my paint.  I gave it at least two coats of white primer and a toast at 200F in the oven for an hour after each, and then a couple of coats of gold.  It looked amazing.  Shiny metallic gold.  I thought, "This is going to be my masterpiece!"

Then I put on a coat of clear and it all turned baby-poo brown.  Maybe it's still recognizably gold,  I'll let you be the judge.



(I think it looks much better in my first post.)

I originally mocked it up with some Radio Shack knobs, but they looked ridiculous so I cobbled together a Mammoth order and got some cream 1611 knobs.  At 15.7mm, they're a little too close to my label text, but I can live with it.

As I said in my first post I, I wasn't thrilled with the overdrive, but I also didn't have the right op-amp.  I started with a TL072 for no particular reason and thought it was uninspiring.  Next I tried an OPA2604AP, but thought it sounded too harsh.  I finally gave in a tried a 4558, which I thought sounded good enough.  I have since received a Mouser order with some TLC2272s in it.  I'm eager to try one, but the pedal is currently on loan to a friend.

Thanks MadBean for a cool circuit!  And special thanks to jimmybjj for giving me this opportunity and for all his help!  Thanks to the rest of you for reading all my nonsense....

[mgwhit]

Great story Matt! Would love to know if you like how it sounds...

I'll probably take a 2272 over to my friend's house this weekend and sub it in.  If I'm still not satisfied I might have to turn that voltage regulator back around!

Oh, and for the record my favorite settings were with the Repeats and Mix at 10:00, Delay at 1:00-2:00 and Tone 2:00-3:00.  I like the Drive at around 11:00 for smooth overdrive or totally dimed for saturated madness.

[mgwhit]

Looks great! Glad we got through that my buddy loves his, says it number one his board now. I still need to get together with him to see if I installed that regulator right or if I just got really lucky

Thanks, Jim.  I was only half joking about the "maximum headroom on the PT2399 and low-voltage fuzzed out op-amp"!

[nzCdog]

Dang! What a fine looking build and fine idea!  Wd!

[jtn191]

beautiful build! tell me the pedal's name is a Pavement reference!

[mgwhit]

beautiful build! tell me the pedal's name is a Pavement reference!

Thanks, and yes.  Pavement was my favorite band of the 90's, and I had been wanting to use that name for something.  When this one came along it was too obvious to pass up.  (I mocked up the artwork with the "z", but thought it looked dumb.)

Not that the pedal sounds like Malkmus or anything...but there might be a tiny bit of delay on that solo!