Saturday, July 27, 2013

Thy Last Screamer

Landgraff's Tube Screamer Clone
Well, this was about to happen sooner or later. Once I started this blog I knew that one day I will build a Tube Screamer clone or something like it. However, I never, in my life, would have imagined that I would spend so much time choosing the best version for me and I sure never imagined that there were so damn many versions, variants and clones all built around the same basic topology. The original design was developed by S. Tamura in the late 70's for Ibanez and was issued after a few pilot versions as TS-808 in 1979. 

The schematic basically revolves around the operational amplifier which is hooked up with a diode clipping pair on the negative feedback loop. This is the overdrive section which is very common to all Tube Screamer offsprings. When the diodes go into clipping due to a drop in the forward voltage on the diodes, you get a saturated clipping tone. This is what happens when you crank the DRIVE knob. It increases the gain on a resistor hooked up in parallel to the clipping diodes and thus more juice is fed through to clipping. Various designs of clipping pairs can be used like 1N914 or LED pairs. Clipping can be symmetrical or asymmetrical. It means that if you run a sine waveform through the gain stage you get a distorted waveform which looks more like a  rectangular shape. There is also a clever chain of filters designed to get rid of some bass before clipping occurs and then stage.

Below you can find a schematic of the two stages: The clipping stage with its high-pass filter in front, and the post clipping EQ'ing. 

The clipping stage with its high-pass filter in front, and the post clipping EQ'ing with its lo-pass and hi-pass shelving filter.

The filter design is what makes the Tube Screamer cut so well through the mix and it always sound punchy. it's very mid range in terms of equalization. Also the original TS and most of its variants employ an input and output buffers. So, to sum things up the Tube Screamer overdrive style is a very sweet and warm one with plenty of mid-range not a lot of body. The complexity and success of its design made it possible to get a lot of different colors by implementing small changes to the circuit. A lot about the magic within the electronics can be learned from the links below:

Among the endless list of clones and variants you can find: BOSS OD-1, MJM Phantom Overdrive, Landgraff Dynamic Overdive, Green Machine, Little Green Wonder, MAXON 808, Retro Sonic eight o eight, Signa Drive, Maxon OD820, HBE Power Screamer, Toadworks Texas Flood, Visual Sounds Route 66, Xacttone Multi Drive, SBN Lil Screaming Eagle, Pedalworx Tejas, Lovepedal Burst Eternity, Cusack Screamer, Way Huge Green Rhino, Clay Jones OD, Fulltone Fulldrive 2, Love Pedal OD11 and many others, all categorized under the tedious label YATS (Yet Another Tube Screamer).

Scream-a-delic Dynamic Overdrive
After listening to loads of Youtube videos and reading endless reviews and recommendations I built the basic "skeleton" similar to the Runoffgroove "Tube Reamer" and started experimenting with various designs. I ended up really loving the versatility and tone of the Landgraff Dynamic Overdrive (LDO) which became sort of legendary, maybe because it was a boutique and expensive pedal, but maybe because it just sounds fantastic. I don't know. Anyway this baby rocks so well that I ended up giving it to our band's guitarist and he doesn't plan on giving it back to me. Along with the Boss BD-2 and a Wah-wah in front he has the most creamy and sweet sound you can imagine.  

I built the layout using the JRC4558D op-amp and a pair of 2SC1815 trannies for the buffers. A really nice addition by Landgraff is the clipping switch which let's you choose between symmetric LED clipping, asymmetric diode clipping (1N914) and no clipping at all which makes the unit act as a nice mid range booster. I didn't use any ready made layout and just built the entire thing according to the schematic from beginning to end. Got it right the first time...
If you want to imagine the sound of the screamer think of the SRV blues tone and the sweet Gibson sound of R.E.M. or Oasis. That's the sound. Being such a big psychedelia addict I named it "SCREAM-A-DELIC" to stay in context with the original Screamer but to give it some nice Scottish Primal Scream vibe (and yes, I noticed that I miss spelled the "Scream"...ooops).

Until I get my audio clip together, here's a review from the best in the business - the Gearmanndude. He's got a few of those videos featuring the LDO amd it's a killer pedal, even next to some boutique legends like the Zendrive and the original screamers.

Don't think twice. Built the LDO or another YATS, and yeah, it is that good! You can find the Clay Jones schematic with a nice layout here or here.

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