Rat Distortion Schematic Analysis

[@gunslingersymphony5015]

This video was exactly as much explanation as I needed to bridge the gap between my knowledge bases. I'll feel much more comfortable now in my endeavors. Thank you!

[@xanataph]

The JFET is wired is source follower mode, so it cannot add any voltage gain. It does contribute some current gain, so really it's purpose is an impedance converter. I'm sure I've seen an older schematic for the RAT where there is actually a similar circuit on the input before the op amp. One thing about the RAT is that LM308 opamp. It's listed as a "precision op amp" and off the shelf at many suppliers it's fairly expensive. However, it is considered in integral part of the tone of the Rat. The clipping diodes are pretty ordinary.

[@theandromedacorporation]

You're right about the JFET. Did I get the name flipped around or something in the vid? I read somewhere that the LM308 has poor stats compared to contemporary opamps, the slew rate is supposed to be especially low, but check the datasheet before you quote me on that. I'm about to do a deep dive on opamps in my Circuit Vlog series and I'll be sure to include a proper investigation of the LM308 when I do that.

[@Drewofthetube]

i wish for you to not be so upset with yourself by the end. your doing a great job and all your videos are so helpful, just take your time and have fun!

[@themadkraken1912]

Thank you! I’ve been wanting to try building myself a rat clone for a while, and this really helped me understand what’s actually going on. My end goal is a double rat with both LED and normal diode clipping running in parallel, with a knob to control the ratio between both clipped signals. This is helping a lot :)

[@theandromedacorporation]

Yes! Have you checked out the Sibriex Distortion Pedal that we make? Because you've just described something very similar the "mutate knob" on it. I recomend yellow or blue LED's. We went with yellow LED's in the Sibriex, but blue was a close second.

[@grannemaneten]

Thanks for making this video. Came in with very little knowledge about this stuff and you really explained everything I was wanting to understand. Excellent work!

[@josiahgagnon4598]

I learned a lot from this that would be hard to read through, keep making these.

[@zeki2515]

Thanks for the video! Good and clean explanation. Easy to understand.

[@Xa2arra]

Very clear and helpful!! Keep posting videos like this! Thank you!

[@carsonyuh]

You rock. Keep doing these.

[@theandromedacorporation]

no, u r.

[@ryanmelvey8764]

thanks for this one. very helpful breakdown

[@madf00bar15]

What is the +4.5 volt supply for ? I don't see a connection point, just the +9 volt at 2 points.

[@theandromedacorporation]

4.5V is the middle point between 0V and our 9V maximum. That gives the opamp the room it needs to swing the audio up and down. If the circuit were biased to 0V instead of 4.5V, the opamp would be able to make the peaks of the waveform, but the troughs would get cut off, as the opamp wouldn't be able to go below that 0V.

[@ResidentEyebrowAppreciator]

Above R2 it feeds into the lm308's non-inverting input

[@artysanmobile]

It, with +9v and 0v ground a virtual bipolar supply of ±4.5v for the opamps which require it.+4.5v plays the part of ground in this scenario. The opamp outputs are biased to 4.5v above ground and large capacitors block the DC for other components to operate as ground referenced.

[@codelicious6590]

So, where might one hope to find the foundational knowledge requisite to understanding most of the language and elements of this video?

[@dahmc59]

im barely grasping the gyst myself... watching jhs videos helped me. basic electronic class will probably get you these tools

[@theandromedacorporation]

Georgia Tech has some great free online classes. I also find this type of circuit Analysis really helpful to develop intuitive understanding. Some good things to start reading up on: - Components (resistors, capacitors, diodes, etc.) - Voltage Dividers - RC filters - Opamps - BJT’s You can do a lot with just those few elements.

[@noahbeyer2518]

What Georgia Tech course would you recommend? Thanks for the info!

[@dahmc59]

being a begginer in electronics, i am only able to get the gyst and cannot converse fluently or articulately in these things.i have a question about that section you went over after the opamp and after the diodes. i think you said resister and capacitor where freq. begins to drop. Could you split that say into 3 seperate differing resisters to move the frequency fulcrum to 3 different spots for cascadeing drops?

[@theandromedacorporation]

Short answer is yes. In fact, that's happening in the feedback loop of the opamp in the rat here. The two pairs of caps and resistors are acting as a pair of highpass filters to give the bottom end a unique filtering curve. There are some issues with simply stacking filters serially without buffering between them, but there's lots of cool filtering tricks you can to by combining different configurations. The Big Muff filter comes to mind as an example of a highpass and lowpass that are both controlled and blended together on a knob.

[@generalleigh7387]

J fet also gives a more rounded less harsh tone from the rest of the silicon.

[@christopherwagley5426]

Dude sounds like Butthead when he says “uhhhh” 😂

[@darwindewilde]

Amazing!

[@theandromedacorporation]

No u r

[@martynharveythepoet5114]

Brilliant video - Thanks!!! I'm newbie developer and at the very beginning of the learning curve but this was just what I needed to start to understand Distortion pedals. (Thanks again!) One question: I understand the LM308 is an OpAmp... I'll try and get hold of one but, as I've been building small battery amps, I have a load of LM386s laying around: Could I use one of those instead? Many thanks :-)

[@koonsickgreen6272]

thank you!

[@foobarables]

I don't know what you find wrong with an LM308. It's not such a bad choice for a ultra low input bias current op amp. The signal is being distorted by D1 and D2 anyhow and and the JFET output stage is easily outperformed by the LM308.

[@theandromedacorporation]

The short answer is the LM308 has a crummy slew rate. If you're interested in more details, you should follow my "Circuit Vlog" series. I'm about to post a deep dive into opamps including the LM308, the very popular TL07x, and others. We'll compare the stats off datasheets, prices, availability, etc.

[@foobarables]

@@theandromedacorporation According to the data sheet the slew rate is 4 V / µs with a 30 pF compensation capacitor which is about 10 times more than required by a circuit powered from a 9 V battery. Also, the input signal is low pass filtered by 1 K with 100 nF which equates into 16 KHz - 3 dB. Of course there are better op amps with even lower quiescent current specifications today. But my choice would not be a TL071because of the quiescent current in the range of 1 mA. Also people might prefer the sound of the LM308. The sound in this case is determined by how the LM308 saturates and comes out of saturation.

[@theandromedacorporation]

Yeah, that's all good info that I'll explore in depth in my circuit vlog this month. And to be clear, I'm not saying, "install TL071's in your Rats." I only mention the TL07x as another opamp to be included in my opamp deep-dive. The TL07x seems to be the most popular by far in the synthesizer DIY scene.

[@spentron1]

The op amp contributes quite a lot of distortion and all the "fuzz". The dynamic range between it and the diodes clipping is only about 12 dB and with an actual guitar seems tiny.

[@theandromedacorporation]

@@spentron1 opamp clipping is real, I've even used it in my own designs, but I worry you're downplaying the effect the clipping diodes have. There's loads of character to be had from using different types of clipping diode. Those diodes do plenty of fuzzing up the sound.

[@nah3]

do the guvnor next🙏🙏

[@Microtonal_Cats]

the power section is almost as complicated as a whole Fuzz Face.

[@redpillcommando]

I've been hoping the Electrosmash store would come back. What's the deal. Does anyone have any news? Did someone die or end up in federal prison?

[@theandromedacorporation]

I heard their website is so helpful and educational that they just straight up went to heaven. They're just up there chilling, playing songs with John Prine.

[@redpillcommando]

@@theandromedacorporation Is that a joke or are you telling me the Electrosmash guy is dead?

[@theandromedacorporation]

@@redpillcommando I don't know who runs that site. I hope they live a long time.

[@wayahedia9989]

Dude.. the diode isn't a 'Fuse'. That is a perfect use of a diode and it is what they were designed for. Hard to take the rest of this seriously when you fail miserably within the first minute. Why don't you explain a better way to do this? And it has to be as cheap as a single diode.