Author Topic: Possible dumb question: transistors instead of op-amp for Rat (slow loris)?  (Read 585 times)

greysun

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Re: Possible dumb question: transistors instead of op-amp for Rat (slow loris)?
« Reply #15 on: February 23, 2023, 08:34:40 AM »
Here's a thread that works towards a transistor based approach towards a Rat.

https://www.diystompboxes.com/smfforum/index.php?topic=129355.40

Ha! It seems like they got something working, but are still trying to figure out some volume issues... I'll have to keep an eye on that. Again, the whole thing was just thinking of the transistor vs. op-amp muff and whether something like that would work for a RAT to get a little different flavor.

I like Jimilee's notion of creating something with a lot of clipping options. I was able to make a 1590B-sized single-sided PCB with board-mounted pot/switch placements. I based it on the Brian's schematic compared with the original schematic with the added (toggled) FatRat mods. Vol, Filter, Distortion, Fat (toggle), Clipping (1P8T rotary, 7 clipping + 1 no clipping. I did away with the Ruetz mod, I just don't use it and think the clipping options would be more flexible for me)... still need to get some of the more obscure parts, breadboard it, test it and etch it, but working toward solutions! hehe...

I also have to remember that the Slow Loris I have is 10+ years old now, and was the FIRST pedal I'd ever made. It has a lifted pad on the top layer (I guess the bottom pad is the one needed? lol) and isn't for the faint of heart when it comes to solder beauty. I looked at the schematic differences between Brian's now and the one I have, and there's a few parts he's taken out through the years that might explain some of the volume issues (an added 10k resistor, a pull down cap with the LED clipping diodes). When I look at Brian's schematic now compared to the original circuit, outside of the clipping options, it's effectively identical (a couple of power/biasing mods aside).

At any rate, I'll post the progress as I go along... As always, the madbean board proves it's the best for knowledge on this stuff! Thank you, all, once again!

greysun

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Re: Possible dumb question: transistors instead of op-amp for Rat (slow loris)?
« Reply #16 on: February 24, 2023, 08:36:50 AM »
Actually, I have one last question, pertaining to diodes...

In setting up a board for a switchable clipping diode option, I'm not sure the sizing needed for a few of them... e.g. a 4001 uses the same spacing as a resistor (I call it 4 hole spacing), while a 914 uses less (3 hole spacing).

While the following seem like they use 3-hole spacing based on internet photos, I don't want these standing up on the board... Anyone know the relative sizes for the following diodes:

- D9E
- 1N34A
- BAT41

As well, it seems like 914 and 4148 diodes have the same forward voltage and are used interchangeably at times... Does anyone know if there's an audible difference in sound for these?

jessenator

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Re: Possible dumb question: transistors instead of op-amp for Rat (slow loris)?
« Reply #17 on: February 24, 2023, 09:03:08 AM »
I'm rather new to all the standards, but these are they, apparently: https://en.wikipedia.org/wiki/DO-204 however, there are variations amongst manufacturers. I 3D printed a component lead bender just to make sure I'm being nice to the component itself: you fold it wrong and they break very easily (ask me how I know).

I measured a D9E and the glass casing measures 7.5mm, around the size of the "max" value on that wikipedia article for DO-7.
My ITT 1N34As measure around 7mm, in the mean.

This is where I bend them with that bending tool where the body fits most comfortably:


so whichever is closest to 12mm is what I'd do. Smaller diode leads can be bent to fit. Better for spacing to be too big than too small.

Also, some unsolicited advice: I would socket your germanium diodes (as much as I've bashed the single-strip machined socket headers).

greysun

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Re: Possible dumb question: transistors instead of op-amp for Rat (slow loris)?
« Reply #18 on: February 24, 2023, 09:07:11 AM »
I'm rather new to all the standards, but these are they, apparently: https://en.wikipedia.org/wiki/DO-204 however, there are variations amongst manufacturers. I 3D printed a component lead bender just to make sure I'm being nice to the component itself: you fold it wrong and they break very easily (ask me how I know).

I measured a D9E and the glass casing measures 7.5mm, around the size of the "max" value on that wikipedia article for DO-7.
My ITT 1N34As measure around 7mm, in the mean.

This is where I bend them with that bending tool where the body fits most comfortably:


so whichever is closest to 12mm is what I'd do. Smaller diode leads can be bent to fit. Better for spacing to be too big than too small.

Also, some unsolicited advice: I would socket your germanium diodes (as much as I've bashed the single-strip machined socket headers).

GREAT stuff! and I tend to socket anything that I think might need changing over time - diodes especially, so good call.

thank you! :-)

jessenator

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Re: Possible dumb question: transistors instead of op-amp for Rat (slow loris)?
« Reply #19 on: February 24, 2023, 09:10:56 AM »
No prob!

greysun

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Re: Possible dumb question: transistors instead of op-amp for Rat (slow loris)?
« Reply #20 on: February 24, 2023, 09:16:58 AM »
No prob!

AND if you feel like 3D printing another one of those lead-benders and shipping it to Chicago, I mean... I'd take one. ;-)

I have little to offer in return other than gratitude and some dollars for the trouble and shipping. hehe...

greysun

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Just throwing out an update on this project... I got everything breadboarded to test out the different clipping options. (Similar to Jimilee, I'm making a version with an 8-way rotary - 7 options for clipping and 1 op-amp). Once I have the boards together, I can more easily record a video, but for now these were my findings... If there's an option floating around out there (and the parts are still available, hehe), Let me know... I'm open!

1. Silicone symmetrical options: I actually tried Schottkeys first... 5817s and BAT41s. 5817s was too quiet - BAT41s sounded better, but ultimately very similar to 4148/914s with a HAIR less volume, so I think I'll save the BAT41 for asymmetrical option. 4148 is a classic for the clippers, so why not? a little drop in volume, but a fuzzier and smoother sound than the straight op-amp.

2.  Germanium symmetrical options: 1n34a and D9V. D9Es are impossible to find, and I'm not sure why I couldn't get 1n60p, but I tried out D9V - cool sound, but definitely the quietest of the bunch, and 1n34a sounded similar with better volume, so it wins the germanium slot. The sound was unique - a little more gritty and dark, less fuzz-like - probably good for overdrive if you pull back the distortion level. Probably the most quiet of the bunch still...

3. LED symmetrical: Red, Yellow and Green were ones I liked (in that order), but Red ultimately wins out (though yellow was a close second - might socket this one). It's the perfect mix of all the best parts of the RAT sound - fuzzy tone (but not too fuzzy), great volume, good clarity but retaining the grit that makes it a RAT. (Of note, orange sounded the same as yellow to my ear and blue didn't change the sound at all, and since the forward voltages go red (1.7), orange (2.0), yellow (2.1), green (2.2), THEN blue (3.2) and upward for the other colors, I didn't even try others).

4. Asymmetrical option - silicone/schottkey mix: a 4001/bat41/bat41 combo sounded pretty good here - it's a little similar to the LED clipping, honestly, but it definitely has its own flavor, and I notice more of a difference with leads, which had more grit.

5. Silicone symmetrical #2: 4001s surprised me - I don't know why, but the sound was smooth and had decent volume. Definitely went more into fuzz territory, but felt more controlled and clear.

6. FET symmetrical option #1: I got some BS170s because they were in some of the original RATs - I combined it with 4148 and it produced something unique, so I'm into it. Hard to describe

7. FET symmetrical option #2: 2n7000s sounded pretty good. So did the BS170s, but the 2n7000s had a hair more volume and a bit more grit. Since the BS170s were already used with the 4148s, the 2n7000s win

8. op-amp clipping (e.g. no diodes or FETs): I was surprised by how different this sounded - more raw for sure... almost feels "incomplete" and I definitely prefer the clipping options, but it might be the most distinct of all the options, so it has earned its place. Perhaps great with the distortion rolled off and in overdrive territory.

Another interesting thing - I A/B'd with the Slow Loris from roughly 2012/2013 (clipping options were LED, none, 914, I think) - There are some circuit differences since then and the new version sounds clearer and louder - my testing was done with an OP07cp, but I'll throw a 308 in there for the final. In LED clipping mode, almost no difference in sound, but in op-amp or 914 mode, it was definitely different. Excited to get it going and boxed up!

I tested using the FAT RAT toggle, as well. I found that on neck pickups (single coil or humbuckers), the fat setting muffled things a bit more than I liked, but on bridge single coils it added just the right amount of thicker tone without changing the character of the pedal. This is more useful to me than the Ruetz mod, so I'm forgoing that altogether.

I initially asked about a transistor version of the RAT, but having FAT and clipping options (or knowing what options are out there) has done given me choices to customize the sound for me, so thank you madbean board for leading me that direction! More to follow on this and I'll hopefully do a video soon... and if you have other suggestions, please send them my way!

jimilee

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1.2v zeners have a great sound, too. I was really surprised. I need to build another multi rat, I have mine to Dan. I still think the road kill rat was an awesome option, too. Itís ideal for the opamp only selection.


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