Landgraff Rat Mod

[guitarpkr76]

Okay, I was reading how the Landgraff Mo'd was just a rat clone with a few mod. I know it has a switch to switch between different diodes, but which ones? Also I read there is no inout buffer. Would I just remove the one in the rat. As you can see, I am quite a noob. Last question (for now), Is this a clone of the original rat or the rat 2? Thanks for any help you can give.

[Dragonfly]

...i havent seen a "landgraff MOD"  ...i thought they only made the "dynamic overdrive", which is based on the ibanez ts808....

for more info, search "grandlaff", "landgraff", and "dynamic overhype" ....

hope that helps,
   AC

[guitarpkr76]

The Landgraff Mo'd stands for more distortion. It is Landgraff's clone of the rat. There's probably only been about one thread on this pedal here. But I remember someone seemed to know what was going on inside it. I'm actually about to get started on a Dynamic Overdrive clone, but I'm also interested in the Mo'd. The Overdrive is definetly his most popular pedal, but he has made an overdrive, distortion, clean boost, and compressor.

[JHS]

The  D-Dist. is a stock Vintage Rat knock-off w CC-Rs and AVX metalfilm caps. 33p is 100p on 308N and there's a on/off/on switch for the clipping diodes (stock Rat, none, asym. Boss-style, diodes are 1N914). It has a o-buffer w 2N5458 FET. BIAS-R on IC and buffer are 1M, like in the original.

JHS

[guitarpkr76]

Thanks alot man. That was great help. I'm looking at a schematic but I can't see the 33p your speaking of. Is it the 30p or do I have a wrong schematic?

[Bernardduur]

It is the 30p

[Torchy]

Do a search for "Multi-Rat" - uses a rotary switch to select between diodes etc.

[guitarpkr76]

Thanks again guys. You all are a lot of help. I just how found out how little I know. I got some parts in to build the landgraff overdrive and the 51pf capacitor I ordered was about the size of a pencil head. You live you learn I guess.

[theman]

The  D-Dist. is a stock Vintage Rat knock-off w CC-Rs and AVX metalfilm caps. 33p is 100p on 308N and there's a on/off/on switch for the clipping diodes (stock Rat, none, asym. Boss-style, diodes are 1N914). It has a o-buffer w 2N5458 FET. BIAS-R on IC and buffer are 1M, like in the original.

JHS

Just curious on the 100p on the compensating cap. I tried it, and the sound is too bassy and woofy when the gain is maxed. And this is on the bridge pickup! Based on the datasheet of the LM308N, the response is very much tied to this cap value. I lowered it to 30p and it sounded much better, and even lower was better for my needs. You could easily hear the difference between these cap values.

I think it may be highly dependent on your guitar and amp. A bright setup with less bass response and higher treble might sound good with the RAT with a 100p comp cap.  But I was using a fairly neutral setup to test the pedal tone. And 30p and a bit lower was the best to me.

I would be curious to hear other people's comments on the tone when this cap is changed ...

[Mark Hammer]

Mr. Man and I have been discussing this off-line for a few days.

The compensating cap produces different open-loop gain/bandwidth products.  Look at the graphs for different compensating cap values and you'll see that at max open loop gain, a 10khz signal is 40db down from a 100hz signal under those conditions. 

At "normal" gain settings in audio circuits, large changes in that cap value would generally have little impact for the portion of the spectrum that guitarists are interested in.  The 40db drop would still be there but at frequencies much much higher than human hearing (i.e., all rolloffs are shifted "to the right" as gain is reduced) .  At the gain settings the Rat uses, though, the chip is being pushed to damn near its maximum.  Under those conditions, increasing the LM308's compensating cap can place serious limitations on the maximum audible bandwidth of the pedal.  Woofiness, indeed. A 100pf comp cap as much as tells the Rat that treble is essentially off-limits.

I am unfamiliar with the Landgraff, but it is quite possile that if the op-amp itself is changed in the pedal, increasing the value of the compensating cap from 30pf to 100pf may be just the right thing to do to achieve the desired rolloff with that IC.  A big part of the magic of the Rat is that a very modest op-amp (LM308) is being taxed to the limit.  In some respects, that is similar to the Distortion+.  Many builders/modders of that pedal report that completely eliminating the clipping diodes never results in a completely clean signal.  So, in each case, it is the weaknesses of the op-amp that are being exploited.

Might be a good time for folks to acquaint themselves with the open-loop gain bandwidth graphs from their favourite op-amps, typically found in datasheets.