LND150 SHO variant (LND 'HO)

mdc

mdc

Well-known member
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I bought a bag of LND150 depletion-MOSFETs a while ago and have been entertaining myself by figuring out ways to use them. In case anyone needs an extremely low parts count boost, here's a SHO variant that takes advantage of the LND150s low input capacitance and internal ESD protection to drop 3 parts out of a normal SHO. Crackle-not-OK version included as well; the 1M series pot in the of CNO™ doesn't seem to work with the LND150, but a 1M voltage divider does the job in its place.

I haven't tried making a LND of Rock yet, but I'm hopeful this variant will sound as good stacked up as the BS170 version.
 
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Made a few tweaks to that schematic, there's a cap and a resistor in there that are probably redundant but aren't hurting anything I guess.

Here's some vero if you want to give it a go:

[EDIT: Updated vero below]

It's pretty straightforward, a SHO variant going into a an overdrive loosely based on the preamp stage of a Vox AC50 with a james tonestack and recovery stage following. Then there's a final boost on the output. The SHO and the final boost are on the same footswitch so you can control how hard the OD is slammed by the SHO and have some control over the final output.

There's a starve control on one of the MOSFETs which gets you into gated sputter territory. With the various gain stages cranked, the treble up, and the bass down, you can play with the starve control and get some nice J&MC style sounds.

The three sections (pre-boost, main OD, post-boost) are all on separate boards to make the wiring a little less chaotic and make stuffing it in a box a bit easier. 7 knobs is way too many knobs for a vero board imo, but here we are. The layouts are all verified but I haven't wired it all together, so there may need to be some extra RC networks tucked in if the switches start popping or anything. Time will tell.
 
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Finally got this boxed up and working properly. 7 knobs really is way too many knobs for a stripboard project, especially trying to cram it into a 1590B. I noticed a few mistakes on the schem and layout along the way so had to make a few quick corrections on the fly to make it work, thankfully nothing too serious. Most notably had a 4n7 and 470p cap flipped on the bass side of the EQ section, so there was a big mid hump and neither knob was doing very much. Easy fix and now there's a good range of adjustment on either side.

I added a 1M at the input (just tacked it onto the 3PDT) that's not reflected in the schem as there was a bit of switch pop once it was all together; the resistor didn't really do much so I assume it's LED-related, and as far as these things go quite minimal. I meant to tack another one onto the end but have yet to get around to it.

It sounds cool, has a big range of sounds, gets quite hairy, and the battery starve feature is nice at low gain as well as high.

The middle section is a decent low-to-medium gain OD (only 5 knobs!) if you don't feel like trying the whole kit and caboodle; you'd just need to build the larger board and add whatever power filtering you prefer.
 
Decided the EQ was a bit too scooped at 12:00 bass and 12:00 treble, so I swapped out the two 4n7 caps in the tone stack for 1n5 which flattened it out. the bit of extra low mids are helpful, it all sounded a bit too spiky without them. I usually cut a fair bit at 225hz whenever I'm mixing guitars so I tend to want to carve that out in pedals as well, but I think the circuit overdrives much better with them left in. I was going to increase the 47p cap on Q3 as well, but with the EQ adjusted there's no need imo. Feels much more balanced.
 
Also, tried to chase down the switch pop with some extra RC combos on the 3PDTs and it didn't improve the situation at all. Disconnected the LEDs and it went away. 😔
 
This is really neat! Any chance of some sound demos?
I've tried my hand at swapping an LND150 stage into different things with varying results. Most of the time it's rad, but occasionally I'll get some unwanted harsh clipping or fizz. I'll have to try this schem out!
 
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I went back to this and tried to hunt down the switch pop, trying to tack extra Rs and Cs into the already nightmare-ish tangle of wiring proved... frustrating... so, I gutted the thing, tweaked the circuit/schematic a bit, laid out the whole thing on a single piece of stripboard, and rebuilt it.

Schem:
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Vero:
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Pedal:
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It sounds quite nice! Typical mosfet chewiness, having control over the boost volume and gain is great. An A1M might be a better choice for the boost volume but I just used what I had on hand.

Built it for the drummer in my band's BF and I'm a bit sad to see it go. I don't think I'd want to build another on stripboard (7-knobs is WAY too many, it took a long time to wire everything and stuff it), but I might order a few PCBs and build another one.
 
Oh, also, I used optical switching for the main ON/OFF which solved the popping there completely. I left the BOOST as normal mechanical switching and there's a small amount of pop there (definitely LED-related), but I'd say it's well within the realm of acceptable.
 
Where are you getting your LND150s from? I didn't see any on Tayda or Stompbox Parts which are my two main supply sources.
 
I ordered a bag of 50 or so from mouser or digikey a while ago - they're about $.60 from there. I believe @Robert is stocking some for the spaceman pultec project too?
 
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