Since I am a huge fan of Tony Iommi, DoesItDoom and their Walpurgis pedal, but also want to get into PCB designing myself, I recently put together a Laney in a box style schematic in EasyEDA. I used an article on tagboardeffects for the two separate channels, and an article from effectslayouts for the presence circuit. I would have went for only the effectslayouts schematic if it were complete with the channel selector. Essentially, the pedal is supposed to do what the DoesItDoom Walpurgis Vol. 2 does, but without the Rangemaster and with added separate Gain controls for both channels. This keeps the amount of knobs on the pedal down and justifies me having 3 different Rangemasters in front of it for 'testing' (we all know i just can't decide). It was quite hard for me to turn the tagboard thing into a schematic thing, but i hope it worked. I drew everything on paper, tidied it up several times and then manually copied it into EasyEDA. I want to turn this into an Aion Style PCB, so footswitch with LED and DC stabilization on one PCB, pedal itself on the other PCB. I have always found wiring on Aion boards the cleanest, with one designated connection point for everything. Anyways, I do not know much about electronics and just wanted to ask some of the smarter people about what they think of my schematic. Especially how I numbered the parts is probably weird, I hope you can forgive me on my first schematic ever. Do you think my idea is ready to be turned into a pedal or do you see any problems? If so, please tell me. Thanks in advance!
Double check where the pins are connected on your pots. Your mids and presence pots for example seem to be reversed, so they're going to function backwards.
C107/C106/D2 aren't connected to ground, so they won't do anything.
Q4 is not going to work as intended. This is a source follower stage, not a common source amplifier. The trimpot is only going to decrease headroom as the resistance increases because of the voltage drop across it. The large source resistor could potentially also lead to limited headroom because it forces the FET to run on very low current. So, remove TR102, connect the drain directly to V+ and decrease R3 to 10K for J201 if it sounds too distorted at 100K.
I wasn't certain whether the output section after the tone stack is going to work, so I simulated it in LTSpice. It does kind of work, but you're losing a lot of volume here. Unfortunately my understanding of this whole section is too limited to offer any advice. Maybe someone else can chime in.
Very cool for your first-ever schematic, from a self-professed electronics neophyte.
Extremely ambitious, and I mean that as a complement — that's how things get done!
Nonetheless, I'll tell the cautionary tale of my very first pedal, a combination of several circuits on different boards in one box (the PCBs pre-fabbed by a DIY-supplier, not by me) — everything worked individually. Learned to solder doing this pedal, about 5 different boards and only lifted one pad which my Sifu showed me how to jumper it and make it work. However, jamming everything in the box, the pedal did not work. Circuits all worked fine individually out of the box, but not together in the box.
So maybe build a few Iommi-related circuits on PCBs that are already available? Sometimes the great leap forward takes a few steps before running for it.
Your mids and presence pots for example seem to be reversed, so they're going to function backwards.
C107/C106/D2 aren't connected to ground, so they won't do anything.
Fixed that! Don't know how I missed that grounding thing, was probably messing with the 3PDT switch wiring for too long!
Pots were a stupid mistake. I tried to keep the schematic clean by not crossing too many wires, ended in that stupid mistake.
Q4 is not going to work as intended. This is a source follower stage, not a common source amplifier. The trimpot is only going to decrease headroom as the resistance increases because of the voltage drop across it.
I added TR102 as the last part i think. It is more of an experiment kind of thing than something well thought out. Every Transistor had a Trimpot so I figured 'why not add one there?'. There was no reasoning behind that. I will check it out that way and bridge it if I don't happen to like it.
Also, R3 is exactly as in the 2 schematics I took as an inspiration. I may experiment with a Trimpot in its spot first to see whether 10K or 100K will fit the bill. Until then, it will remain as 100K in the schematic.
I wasn't certain whether the output section after the tone stack is going to work, so I simulated it in LTSpice. It does kind of work, but you're losing almost 30dB with the trimmers maxed at 100K.
I guess the output section is the stuff driven by TR100/101, right? Those were also in the original schematic from effectslayouts. I think I will keep them in. However, I will remember your words and set them very low first during testing.
But I also have one question: I am currently running my Sabbath Distortion (Catalinbread Sabbra Cadabra Clone) on 18V and it sounds much better than on 9V. (it felt kind of 'squishy' on 9V and always sagged when I hit the strings) How I currently have it spec'd out, this pedal should work mighty fine at up to 40 Volts (Transistor rating). I intend to run it at 18 Volts, would that affect the LEDR value in any way? In my Sabbath Distortion, which also uses 4.7K as LEDR (R100 in the documentation) the LED has not been killed yet. Am I currently frying my LED or is it fine?
So maybe build a few Iommi-related circuits on PCBs that are already available? Sometimes the great leap forward takes a few steps before running for it.
Thanks for your concern! However, I have already built 16 pedal kits in the last 2 years if I am not miscounting. I gifted my guitar teacher a Naga Viper clone 2 years ago, it has since never left his board and is still working. My soldering work from back then is definitely 10 times worse than what I can do today, so I think I can now trust myself with bigger projects. I do not (yet) know much more about electronics than what I learned in school, but this is why I still go to school and learn stuff everyday. Putting together this schematic was not as difficult as you might think. I just had to turn this tagboard thing into a schematic, stole the presence control off of the effectslayouts.com schematic and connected both. That connection was super easy to make. The most annoying thing was actually getting the schematic neat and tidy and not just have it be a lump of resistors and caps. Every part below 100 is from the tagboard schematic, and everything above from the other one. There is no magic to that, just system. Soldering kits has really sparked my interest in electronics, so much in fact, that I am about to hand in two application to study electronics or mechatronics (is that even a word in english) at my local university. I know I have a lot to learn, but I see this as an opportunity. The pedal community is very supportive and teaches you about stuff that actually is useful and interesting. Designing a PCB and reading some electronics books will hopefully get me closer to where I want to be. After all that, I have one final question: Does the way I numbered stuff make sense? I feel like I needed to disconnect the two parts of which I created this thing just for me to understand stuff better, but off of what system do you guys usually decide which cap is C1 and which is C5? When I was numbering the components, I was just counting through them numbering them in the order in which I got to them. But the choice seems haphazardly at junctions such as transistors and potentiometers. How do you go about that stuff?
Hm... I strongly suggest breadbording the circuit before ordering/making a PCB.
Up to C100 it seems to be OK. Well, except for the aforementioned TR102. But the next part... let's assume that you set the bias for Q5 and Q6 using TR100 and TR101. Let it be 5V. As soon as you use the Presence potentiometer, what will happen? Presence is in the source circuit of Q5 and Q6, so its value also determines the drain voltage. The presence value is very high, so a small turn is enough for the drain voltage to go from 5V to almost max.
Big oof on my side. TrebleGain1 should be 1M, Presence should be 5K, Master should be 100K. Don't know how I missed that, but it is correct in my parts list, only false in the digital schematic. The stuff I drew up on paper is correct. I thought I was smart for only searching one component for type (resistor, film cap, ceramic cap) of component with the correct footprint and then copying it and changing its value. Copying worked, but changing values didn't. Checked my paper back with the original schematics and then the paper with what I drew digitally. All values seem to be correct now. Thanks for noticing that mistake!
Right on Lefty. I figured with a schematic that intense you had more chops than you were letting on.
As for numbering... I've never found/seen a method that made complete sense; I've just been working from left to right and top to bottom, for the most part.
Q5-Q6 simulate the phase inverter of the amp. As it is, I am not sure it will work, since both sides are hard-connected via the output capacitors. I'd be inclined to use a couple of mixing resistors (say, 33k for example) between the caps and the master volume. As stated above, presence will throw your bias all over the place.
If I were you, I'd just steal the post-tonestack section of the EAE Model Fet to replace that one. It is a tried and tested, good sounding one. Otherwise, look for the Dinosaural Tone Bender, or Any Gallien-Krueger guitar amp schematic from 1980-1984 for differential amplifier ideas
Presence control can be implemented in a myriad ways by means of low-pass filters. Almost any passive, non-BMP tone control will do the job.
Adding to Temol and Blackboardcult, I have succesfully adapted the post-tonestack section of the EAE Model Fet for 9V single supply and it sounds quite good
On a side note, I remembered EffectsLayouts used to offer a preamp like the one you want. It was called the Super Trouper (you could build it to Supergroup of Model T specs) and you can still find the build docs for it (link here). No idea how it sounded, though. It is not very far from a Model Fet, so I suppose you could adapt a Mofeta to sound Laneyish
On a side note, I remembered EffectsLayouts used to offer a preamp like the one you want. It was called the Super Trouper (you could build it to Supergroup of Model T specs) and you can still find the build docs for it (link here). No idea how it sounded, though. It is not very far from a Model Fet, so I suppose you could adapt a Mofeta to sound Laneyish
The Presence/phase inverter section of the SuperTrouper seems to be exactly what I chose for my adaptation, so I don't understand how that could not work, if it has been tested already. Honestly though, I don't yet understand much about electronics anyways. Maybe I could go with the Presence section from the Sabbath Distortion PedalPCB project, but I need to understand the differences. Like, how does sending a tiny DC voltage to the signal path help the sound? Does it open up the transistor a little bit or something, so that the actual signal gets through better? I really don't get it. It looks kind of different to the effectslayout adaptation but also similar to it, i don't know how to put my train of thought into words here. I have not yet understood the bias issue in the presence section that @temol tried to explain, I assume replacing the 1M pot with a 5K should have fixed the issue he had with the design.(?) Also, I don't want to mess with op-amps too much. This is due to firstly, me not knowing exactly what I am doing, and secondly, me wanting to keep the circuit original. Again, the way I am going to be running the pedal will mainly be at 18V as a preamp directly into the power amp, skipping my actual amp's preamp. This is what the Sabbra Cadabra does really well, and I want that exact thing but with upgrades and more variables, so I can dial in a broader variety of Iommi tones and combine it with a variety of Treble Boosters. Thanks for all your replies and thoughts, even though they are confusing the heck out of me. I like how this community seems to understand what they are doing.
Edit: added in part of the Sabbath Distortion schematic to illustrate my ideas.
The original Laney presence control relies on modifying the frequency response around the feedback loop between the phase inverter and the power amp stage (essentially allowing more/less high frequencies to feedback). In your schem, and the EffectsLayouts project, the phase inverter is replicated almost to a T, except there is no feedback taking place, because there is no power output stage to take it from. As such, it will not behave in the same way as the original Laney. I haven't breadboarded or spiced it, but the fact that it passes signal/distorts pleasantly does not necessarily mean it's designed in a way that ensures consistency
We are sometimes guilty of following the "doctrine of signatures" when designing circuits, meaning that if it has the same topology, it has to sound the same, but when aping tubes with SS, more similar does not necessarily more faithful to the tone. What I'd essentially aim at, if I were to mimic a full Laney Supergroup, is a soft clipper (phase inverter, by means of the EAE circuit that Temol posted) followed by a hard clipper (power amp stage, including crossover distortion if I was feeling like adding some flimflam). The ROG Thunderbird circuit posted above achieves that remarkably well with very few components, and is mimicking a power section that is almost identical to the Laney one.
As for the presence circuit from the Sabbra: exactly that! Since we have no feedback to tinker with, a high cut that dumps frequencies to ground is what is needed, especially in a circuit that barely has any tone shaping or taming of nasty, harsh overtones.
Okay. I don't yet feel ready to use op amps, so I might just go with the Sabbra Cadabra style circuit. However, I have just asked a guy who built the effectslayouts SuperTrouper and am waiting on his response. Thanks for all the replies! Will report back when I have some answers!
I cant't force you to follow our suggestions. Think about one thing - why designers of effects that emulate tube amplifiers don't copy tube schematics 1:1. I mean commercial pedals. Why do they simplify certain issues, or use equivalent circuits that do not resemble the original at all from the schematic viewpoint. One of the reasons is that not everything that works on tubes and high voltages can be obtained on 9V or 18V and transistors.
I know that. Did that in my own schematic. I have that attached in post #6. My whole intent was to 'unlock' the separate channels and a working tonestack. Only thing I still have problems with is, as previously mentioned, the presence control.
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. Did that in my own schematic. I have that attached in post #6. My whole intent was to 'unlock' the separate channels and a working tonestack. Only thing I still have problems with is, as previously mentioned, the presence control.