Landtone DIY DoD 280 compressor (on Amazon) build

[Blue Jinn]

I recently purchased on of these from Amazon. Thought I'd share, as someone at Freestompboxes took the time to trace out the schematic. If you search for "Landtone DIY compressor" you should find it. i wish I took pictures of my build. the kit right now is US$27. If you swap in a Vactrol add another US$8-15. Still a bargain.

A few observations:

1. It's a DoD 280A clone. The schematic attached is almost the same as the ones found at GGG and Tonepad.

2. It comes with what appears to be a random LED and a LDR with no shrink tubing, so I decided to use a Vactrol instead. I had a VTL5C2 on hand for another unfinished project so used that instead. The GGG has a variant with a NSL-32 which are cheaper.

3. Soldering to the small pins on the pots, and soldering two wires to "PWC" is a little challenging. I wound up putting a blob of solder on the pot pins and "spot welding" the wires to them, and then using some shrink tubing to keep it connected. Same with PWC, used leftover component lead, twisted the two wires, and hooked the leftover lead, soldered, and held that with shrink tubing, So shrink tubing is necessary IMHO. You also have to cut off the tab on the pots.

4. I've never used a "real" DoD 280 so can't compare. But based on reviews, this acts the same. With guitar and higher levels of compression it does crap out and drop the signal initially quite a bit. But with lower levels it is pretty subtle and musical. I'm using it on a Rhodes with inconsistent action, right before a phaser and it seems  pretty good. The GGG and Tonepad schematics call for a LF358 OpAmp. This comes with a 4558. I swapped in a 1458 for the heck of it, and it still sounds OK but I'll try the LM358 at some point.

I also put in a pin header for the resister in parallel with the LDR. The Tonepad schematic has it a 1M, the GGG at 3M and there are reviews about that as well.

5. It's an easy build. The VTL5C2 is about US$13 plus shipping from SmallBear. The NSL-32, Macron, and NOS CLM6000s about US$5-7. It only looks like they are SOS or OS CLM6000s though. But overall cost with the "upgrades" is still a bargain.


Pics are shamelessly lifted from that other thread.

[anotherjim]

In a general sense, a TL0x2 opamp series is a closer match with any LFxxx part as they are JFET input opamps. A TL062 might be a good substitute but TL072 may also be fine.

[duck_arse]

The GGG and Tonepad schematics call for a LF358 OpAmp. This comes with a 4558. I swapped in a 1458 for the heck of it, and it still sounds OK but I'll try the LM358 at some point.

as jim sez, besides nigg, opamps. the LM358 is crappy for audio, good for driving leds. the LF353 is a jfet input dual, good for audio, but don't tell pinkjimi. the LF358? unknown.

and as jim used to never say - welcome aboard.

[anotherjim]

I'm just tenure blind.

LM324=LM358

This is Bob Pease talking about it from 7mins in.
LM358 distortion gets fixed after 17mins in.

[GibsonGM]

A little more on this. I don't see any single supply 'solutions' (if the added resistor could be called a 'solution' lol).  I have a bunch of them that just sit in their tube, unwanted...

https://sound-au.com/articles/lm358.htm

[anotherjim]

Single or dual supply has nothing to do with it. 10k from output to the negative supply pin of the chip - done. I'd call it a solution. Although it does seem kind of "loose" to call for one convenient resistor value - at what supply voltage? Any, apparently.
The tests done in the video prove it. This though was some time ago when Nat Semi was still a thing.
No, it is not an audio part, but the Foxx phasor for one, required an opamp that could work close to 0v on single supply and the Roland/Boss Jet Phasor had dual batery supply but presumably wanted the low power - there are no pull downs though and it goes through 8 stages of these lousy opamps.

I found an app note I hadn't seen before...
https://www.ti.com/lit/an/sloa277a/sloa277a.pdf?ts=1673606302266&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FLM2904B
This avoids mentioning 10k re xover distortion and speaks only of pull-up or pull-down resistors.
One nugget, the 358 has slower slew rate than the 324. I always thought they were dual or quads of the same thing.

[Blue Jinn]

As an aside, the original DoD 280 schematic has a TL022 (still available) and a CLM-50 opto, which appears to be unavailable anywhere.

[PRR]

10k from output to the negative supply pin of the chip - done. I'd call it a solution. Although it does seem kind of "loose" to call for one convenient resistor value - at what supply voltage? Any, apparently.

No. You design this like any resistance-coupled amplifier. For good swing the resistor is 5X to 2X the load. If swing may be smaller the resistor may be larger. Fer example 12V supply and 3V peak swing into a 10k load. For THIS case 10k DC bleed is the answer. But try to drive 600r this way (as I did the first time I used LM324) it will stink. 470r hasty-solder got me to the show and finished without shame (but near-flat battery from the huge class-A current).

There ARE better chips. LM324 was never intended for audio and I quiver every time I see it used. It happens that the 50uA internal bleed will put 2.5Vpk into 50k, which covers a LOT of guitar-cord work, so it don't stink. But if you mis-read your load, a TL072 will hump it down to 2.5Vpk in 1k, dead-clean, at hardly any more battery load.