Eternal Burst (Lovepedal Eternity Burst)

[psb962]

Working to increase my collection of soft clippers I'm doing a build on this one. I like the design - a TS without buffers and some tweaks to the filtering and clipping. Not sure why the original TS needed transistor buffers anyway, given that the input impedance of an op amp stage is huge. Anyway, I breadboarded it with the PedalPcb prototyping board to see what it sounded like:


...and was frustrated for a few days as I couldn't figure out why it had no gain. On about the the third attempt at checking the circuit I noticed that the negative feedback loop to the first op amp stage was connected wrong way around. Swapped two wires and wow - that was better.

I've now spent a few hours swapping caps and resistors to see what matter and what doesn't. Verdict: the cap in the tone control and cap in path to ground off the negative feedback loop in first stage both make a big difference. The tiny resistors don't seem to matter. I used a 20kB pot for tone like original TS vs 5kB for the E and it sounds great. Drive pot 250k seems to be overkill, 100k would work for a lot of players I think. I didn't try an A pot instead of the B specified but that might work even better. I also don't think volume pot size shouldn't matter at all as its a voltage divider. So there is a lot of flex if you don't have exact values.

I'll wait for my next mouser order to arrive and build it next week.

 

[spi]

I assumed the reason TS had buffers was because of buffered bypass switching.

 

[psb962]

I assumed the reason TS had buffers was because of buffered bypass switching.

Well that would explain it.

 

[psb962]

Been playing around with different values to better understand why this circuit has been modified so many times. The drive pot in the feedback loop stops doing much when you get past ~100k (hence the 100k in the Black version). I went with B250k due to stocks. Also, having 20k as a minimum drive resistor isn't ideal as the loop gain with a 20k resistor (and pot at 0) is still more than enough to clip. I put a 3k3 in there to reduce the minimum gain and now its possible to control the clipping right down to zilch if you like that sort of thing.

My main issue at the moment is the tone ie glass control. Per electrosmash analysis of the TS it functions as a treble booster. Schematic says B5k, TS was B20k, and I'm using B10k (again for stocks). Pot size doesnt seem to matter. However, the adjustment seems subtle at best.

 

[cdwillis]

Have you tried using a logarithmic drive pot? The difference between an a100k, a500k, and a1m pot is more noticeable plus it's a little more flexible at dialing in lower drive settings. Halfway on a linear 500k is going to be about 250k vs a logarithmic pot will be about 75k. B100k halfway is 50k of course while an a100k halfway will only be 15k.

 

[psb962]

Have you tried using a logarithmic drive pot? The difference between an a100k, a500k, and a1m pot is more noticeable plus it's a little more flexible at dialing in lower drive settings. Halfway on a linear 500k is going to be about 250k vs a logarithmic pot will be about 75k. B100k halfway is 50k of course while an a100k halfway will only be 15k.

I thought so too, but when I tried A250k the amount of gain / clipping in the middle of the sweep wasn't as satisfying as with a B250k. I'm anal about having the pedal sound 'great' with all at 12, and falling out the usable range after 3 and before 9. Getting there!

 

[psb962]

Posting the PedalPCB schematic as a reference:

 

[psb962]

I settled on A100k for volume, B10K for Tone, and A500k for Drive due to stocks of pots trading off against which pot values matter. I also found that I had no 150n cap so went with a 220n instead - which is what the original TS used so its acceptable I guess.

The offboard wiring was greatly simplified thanks to the excellent Workflow thread by Jovi Bon Kenobi here. Results:



With the pedal completed out of the box I decided to test it on the proto board before boxing it:



This was pretty easy, just a case of connecting the power and jack wires to the breadboard, then the breadboard to the I/O headers. It works!

Now I'll finish the enclosure but taking more time than I did for the Clarkster as I think the clearcoat coats needed longer to dry on that one.

 

[psb962]

I finished the enclosure and boxed it up. Sounds great. Not happy with the finish though - I've tried this 'clearcoat over waterslide decal' approach on both my pedalpcb builds and been far from happy with the clearcoat - this time it did a spectacular orange peel effect on me and looks like crap. The photo is very flattering. I have no idea what I'm doing wrong, these coats had over an hour to dry each time.

 

[Nic]

Try not letting it dry too much between coats.
5 min between the first two coats, then 15 minutes for a third and sometimes fourth one did the trick for me. Still, now I have them printed at Tayda.