This is the Little Jim distortion pedal. It's inspired by and named after Jim Marshall, and attempts to capture that bright, crunchy, raucous sound of a cranked Marshall amp, which is also deceptively complex and rich with harmonics and timbral movement.
Most of my guitar preamp designs for the last 30 years have used JFETs for the gain stages. I experimented with using MOSFETs for this one. They sound quite similar, but are a bit more aggressive and crunchy, although they do produce more hiss than their JFET counterparts. They are not subtle, but work quite well in this high gain application. The pedal is a bit noisy (hiss) as a result.
The circuit is pretty simple. It's 3 cascaded BS170 MOSFET common source gain stages. The input stage uses a J112 as a buffer, because the input capacitance of the BS170 is quite high and will suck the tone of a guitar if connected directly without some form of buffering. The tone control is basically a variable frequency treble roll off but boosts the bass which compensates for the bass cut in the first gain stage to avoid flubbiness and farting out.
I found that the bag of BS170s I bought from Tayda were all very closely matched for Vth so I didn't have to do any special MOSFET threshold matching, you may need to check before soldering your MOSFETs that they have a similar spec, as the tolerance on the datasheet is quite wide, but in practice, mine were all within about 150mV of each other.
(https://i.postimg.cc/nM7fR9VF/Capture.png) (https://postimg.cc/nM7fR9VF)
(https://i.postimg.cc/LJxcYzDT/01.jpg) (https://postimg.cc/LJxcYzDT)
(https://i.postimg.cc/gwwTx1nz/02.jpg) (https://postimg.cc/gwwTx1nz)
(https://i.postimg.cc/VJkT8Jwb/03.jpg) (https://postimg.cc/VJkT8Jwb)
(https://i.postimg.cc/LhjGBdvh/04.jpg) (https://postimg.cc/LhjGBdvh)
(https://i.postimg.cc/qNDFMpBD/05.jpg) (https://postimg.cc/qNDFMpBD)
(https://i.postimg.cc/LnT7wzcp/06.jpg) (https://postimg.cc/LnT7wzcp)
(https://i.postimg.cc/Lq7Gv2rg/PCB.png) (https://postimg.cc/Lq7Gv2rg)
Listen to it here:
killer sound.
(But I can't help to note once more the use of a jFET correctly followed by quite a lower impedance pot than usually)
I have to compliment you on not showing something until it is really complete. Not just a drawing of an idea, but a finished product, including pics of a build. Nicely done. Like the name, too. Hommage, but not outrageous. Kudos.
Quote from: Mark Hammer on August 16, 2020, 08:47:16 AM
I have to compliment you on not showing something until it is really complete. Not just a drawing of an idea, but a finished product, including pics of a build. Nicely done. Like the name, too. Hommage, but not outrageous. Kudos.
And each build comes with a pcb, layout, and a great video! :icon_biggrin: :icon_biggrin: :icon_biggrin:
Jonny, what software do you use?
Sounds great.
A couple of questions:
In the schematic C4 and C7 are labeled as NF with no values. In the photo C4 is 4.7n and C7 seems to be missing?
C1, C3, C5, C13 (10u) looks like tantalums in the photo. Is that correct?
I had some time tonight and did a quick vero layout. Do you mind me posting it?
Quote from: cab42 on August 16, 2020, 05:18:28 PM
Sounds great.
A couple of questions:
In the schematic C4 and C7 are labeled as NF with no values. In the photo C4 is 4.7n and C7 seems to be missing?
C1, C3, C5, C13 (10u) looks like tantalums in the photo. Is that correct?
I had some time tonight and did a quick vero layout. Do you mind me posting it?
NF means "not fitted" - I removed C4 during testing as I preferred the more aggressive sound without it. You could put it back and it softens the high frequency a bit and reduces the hiss very slightly. The 10uF caps are 5mm pitch multilayer ceramic. I generally don't use tantalum caps for anything any more. You could probably use tantalums or even radial electrolytics in there if you like, I doubt it will affect the tone very much.
Happy for you to share your vero layout, thanks for doing that. My vero prototypes are always a total mess (and tend to oscillate at high gain settings) so I don't generally share layout until I have a working PCB :)
Quote from: Steben on August 16, 2020, 10:08:47 AM
Jonny, what software do you use?
Lots :)
For EDA, I've used Protel (now Altium) since the mid 90s when it was on Windows NT. It's too expensive to buy for hobbyist use but I have an old license tied to a (now defunct) startup I used to work for a few years ago. I use OBS Studio to capture the videos, and Vegas Movie Studio to edit them. I use LT spice for simulation, Daqarta and ARTA for various audio testing. I don't work as an EE these days - my day job is software engineering - so I can't afford expensive test equipment or CAD software any more 8)
love it..great sound man right up my street...nice work. 8) 8) 8)
Not knowing about the ins and outs of circuit design, curiosity question, where does the hiss originate in this mosfet design?
> where does the hiss originate in this mosfet design?
http://lamp.tu-graz.ac.at/~hadley/psd/problems/fetnoise/s.pdf
http://web.mit.edu/klund/www/papers/UNP_noise.pdf
https://www.nikhef.nl/~jds/vlsi/noise/sansen.pdf
Quote from: PRR on August 17, 2020, 12:19:07 PM
> where does the hiss originate in this mosfet design?
http://lamp.tu-graz.ac.at/~hadley/psd/problems/fetnoise/s.pdf
http://web.mit.edu/klund/www/papers/UNP_noise.pdf
https://www.nikhef.nl/~jds/vlsi/noise/sansen.pdf
I'm going to be
noise silent or some will call me OCD
Great work, and what an awesome demo as well. A rockin' sound (though always difficult to judge in the context of other factors determining the sounds (e.g. microphone type and position, cabinet type, power amp)).
I'd like to try Little Jim on a breadboard, but was wondering about other types of Mosfets. How critical is it to use a BS170? I remember having BSS138 and 2N2007 mosfet in my parts collection, but would have to order BS170.
Rutger
Looking at the datasheet, 2n7002 seems to have a comparable Rds On, but a much lower drain current rating (which I assume you're not needing here).
Quote from: rutgerv on August 18, 2020, 11:04:23 AM
Looking at the datasheet, 2n7002 seems to have a comparable Rds On, but a much lower drain current rating (which I assume you're not needing here).
I only had BS170 and 2N7000 in my parts bin. I found they sound pretty similar, although the 2N7000 was slightly worse for hiss. Any small signal N channel MOSFET with a Vth less than 3V should work OK, you just might need to adjust the VBIAS to get the drains to sit around 2/3 to 3/4 of VDD. If you look at the drain signal on a scope, you should see asymmetrical clipping with the top half cycle rounded and fat, and the bottom half cycle clipped pretty hard.
You do need 3 MOSFETs with similar Vth, ideally around 2V or so. I found the bag I bought from Tayda were all closely matched. I guess you could just test them in a component tester to select for similar threshold to keep the bias points consistent. Maybe even different MOSFETs in each position might sound cool.
Quote from: rutgerv on August 18, 2020, 11:01:11 AM
A rockin' sound (though always difficult to judge in the context of other factors determining the sounds (e.g. microphone type and position, cabinet type, power amp)).
Rutger
Signal chain for the demo video was Guitar -> Little Jim -> Hall of fame 2 reverb -> Marshall JCM800 50W head set to completely clean -> Marshall 1960A 4x12 -> pair of large diaphragm condensers mics in XY capturing the room sound. It's a fairly accurate representation of how it sounded in my shed :)
Hi Jonny,
thanks for the elaborate answers! Will let you know how my experiments work out with other MOSFET types.
One other thing I was wondering about: the 100 ohm resistor (R15) in the PSU input stage, does it serve any purpose for the dynamic response (sagging) of the rest of the circuit? Or is it purely for keeping out the PSU noise?
Rutger
BS170 transistors frequently have a suffix eg -D27Z. What is its significance and does it matter in your circuit?
> BS170 and 2N7000 .......... slightly worse for hiss.
I *suspect* (you may know better) that between MOSFETs of similar scale (die size, active area), the difference in hiss may be more about when and where they were made, not what they are marked as.
Hiss in most MOS applications is not a "problem" except it indirectly indicates contamination ("dirty Silicon") and leakage. The industrial buyers won't pay the price for "perfectly clean". (You and I and all of us don't buy enough to matter.) So, like fish-fry oil, one day it is fresh and clean, next week not-so-clean, and maybe clean again the day after the manager says "Ugh..."
Quote from: tonyharker on August 19, 2020, 03:01:55 PM
BS170 transistors frequently have a suffix eg -D27Z. What is its significance and does it matter in your circuit?
I believe it is just to describe the packing style and pin spacing - ammo, reel, 0.08 vs 0.1 pin spacing?
Threshold voltage is the most important property in getting the circuit to bias correctly. I have one of those cheap component testers you see on eBay and measure threshold voltage of MOSFETs and JFETs before I install them into a circuit. They are amazing value for money, it's worth having one:
https://www.ebay.com/itm/12864-Mega328-ESR-Transistor-Resistor-Diode-Capacitor-Mosfet-Inductance-Tester/322883932945?_trkparms=aid%3D1110006%26algo%3DHOMESPLICE.SIM%26ao%3D1%26asc%3D20131231084308%26meid%3Dd7f8392b48ee408797cf2f6f659dedca%26pid%3D100010%26rk%3D1%26rkt%3D12%26sd%3D262474886090%26itm%3D322883932945%26pmt%3D1%26noa%3D1%26pg%3D2047675%26algv%3DDefaultOrganic&_trksid=p2047675.c100010.m2109 (https://www.ebay.com/itm/12864-Mega328-ESR-Transistor-Resistor-Diode-Capacitor-Mosfet-Inductance-Tester/322883932945?_trkparms=aid%3D1110006%26algo%3DHOMESPLICE.SIM%26ao%3D1%26asc%3D20131231084308%26meid%3Dd7f8392b48ee408797cf2f6f659dedca%26pid%3D100010%26rk%3D1%26rkt%3D12%26sd%3D262474886090%26itm%3D322883932945%26pmt%3D1%26noa%3D1%26pg%3D2047675%26algv%3DDefaultOrganic&_trksid=p2047675.c100010.m2109)
(https://i.postimg.cc/qtbJYPv9/Capture.png) (https://postimg.cc/qtbJYPv9)
Quote from: rutgerv on August 19, 2020, 01:23:06 PM
One other thing I was wondering about: the 100 ohm resistor (R15) in the PSU input stage, does it serve any purpose for the dynamic response (sagging) of the rest of the circuit? Or is it purely for keeping out the PSU noise?
I put it there to get rid of a little bit of hum I was getting. I have no idea if the sag affects the sound or not :)
Call me ET101, I have searched for this answer, I believe I know, Here are my questions:
On the Little Jim circuit drawing I recon that on the main circuit:
1) VDD shown in 4 places indicates 9v supply (D for drain).
2) VBIAS shown in 3 places indicates ground.
3) The 2 smaller circuits are for 9v dc supply (if used) and an LED indicator (if used).
4) The last is the switch wiring for true bypass.
5) So for battery operation, connect pos to VDD and gnd to gnd, use the main circuit and switch
circuit and you are good to distort ?
Thanks for any comments , Regards
Paul
Hi Paul,
Quote from: Phend on August 20, 2020, 09:58:05 AM
1) VDD shown in 4 places indicates 9v supply (D for drain).
Yes, you could see it that way, though it's not entirely correct. As you can see in the left bottom of the schematic, VDD is in fact the 9V supply *after* it went through some filtering (R15 + C12). As a consequence of the current required by the circuit, and the presence of R15 in this filter causes a slight voltage drop on Vdd, making it 8.56V as indicated in the schematic. The real 9V would only be found on the socket (input) to the right of R15 and gets filtered and then is called 'VDD' for the rest of the schematic.
Quote from: Phend on August 20, 2020, 09:58:05 AM2) VBIAS shown in 3 places indicates ground.
No!.... the ground is labeled 0V in the schematic and occurs many more times. VBIAS is a voltage that sits between Vdd and 0V (ground), and is created by two resistors (left bottom) R7 and R8 forming a voltage-divider. Capacitor C5 filters the VBIAS supply line.
Quote from: Phend on August 20, 2020, 09:58:05 AM3) The 2 smaller circuits are for 9v dc supply (if used) and an LED indicator (if used).
Yup! Also take note of a nice example of engineering experience: the LED is fed from 9V rather than from Vdd. If you understood what I tried to describe with respect to current draw and voltage drop, and you know how much current a LED draws, this is a smart thing. Also... switching LEDs induces noise in supply lines, so supplying the LED with a voltage from the 'other side' of the supply filter (R15 and C12) is a clever thing to do.
Quote from: Phend on August 20, 2020, 09:58:05 AM4) The last is the switch wiring for true bypass.
Correct!
Quote from: Phend on August 20, 2020, 09:58:05 AM5) So for battery operation, connect pos to VDD and gnd to gnd, use the main circuit and switch circuit and you are good to distort ?
To be exact: for battery, connect - of your battery to 0V and + of your battery to 9V, but leave out R15. In battery operation R15 is less important as a filter, and getting rid of it avoids the voltage drop you'd otherwise get from this resistor. With batteries running empty the voltage will already be on the low side, and you can't afford to lose more voltage. R7 and R8 are crucial to keep! C12 might also be beneficial (I don't know how well batteries deal with load variations).
And then indeed... rock and roll!
Rutger
Paul, don't be afraid to ask any kind of question. Nobody is a born know-it-all. Some things that may seems basic-ish were questions everybody had when we all started, and we got the answer either by asking (smart way) or by doing mistakes the finally asking (hard way).
Way back then, I built some circuits that had a "Vref" indication but no drawing of a voltage divider (because it was assumed it's a basic knowledge), I tied all the "Vref" points together and as expected the circuit didn't worked. Now I know the reason, but back then I didn't.
A few tips:
- gnd is usually labeled gnd (written), gnd (the gnd symbol), 0V or an arrow pointing downwards. This schematic uses 0V and the arrow pointing downwards. But be careful on symetrical power supplies (+9V and -9V, for example), the arrow may mean the negative voltage instead of gnd.
- the 9V power supply is usually labeled V+ (or +V), 9V, +9V, 9VDC or by an arrow pointing upwards. In this schematic, you can see both 9V and 9VDC. But take a look at this schematic (https://www.diystompboxes.com/analogalchemy/sch/shocktave.html), you see +9V by an arrow pointing upwards, and all arrows pointing upwards are also connected to +9V even they're not labeled.
- Vref, VA, VB, V1, V2, Vbias or "V something", or BA, B1, B+1 or "B something) are usually voltages based on some reference that's not the full power supply. In this case, you have two voltage references: VDD and VBIAS, which are both below the full voltage (+9V). If you check the schematic for a tube amp (like those ones http://revolutiondeux.blogspot.com/2013/04/trainwreck-amplifiers-express-liverpool.html), you can see at the power supply a B+1 voltage, then a resistor that drops the voltage a bit, then a B+2 voltage which is lower than B+1. This is pretty common for tube amps. For pedals, usually you'll see the full voltage and a "Vref" or "Vr" voltages (http://www.runoffgroove.com/tubereamer.html for example)
Thanks much rutgerv and marcos, I missed the 9v in the left circuit. It being a 8.79v battery.
So using the entire circuitry, sans 9v dc plug, one would connect all VDD as together, all VBIAS 3.88 together and of course all v0 together.
But as marcos mentions this might be a mistake, should I connect all VDD together except for VDD 8.56 (2) which would be connected separately .
(Being from the mechanical world, this circuit method reminds me of assemblies and Sub-assemblies.)
Quote from: Phend on August 20, 2020, 08:28:23 PM
But as marcos mentions this might be a mistake, should I connect all VDD together except for VDD 8.56 (2) which would be connected separately .
No, all VDD points are the same and should be connected together. the 8.56 is just to indicate the voltage reading Jonny got at that point, to help on possible troubleshootings. So let's say your build doesn't work, if you measure the voltage between ground and VDD you know you're expecting a reading around 8.56V.
This is not a so common but not so unusual practice. In fact, it should be done more times, so we all have more info on what to exactly look for on a non working build. But yeah, it indeed can be confusing when you look at it for the first time.
Btw, I should add something I didn't said yet. The circuit sounds amazing! I made a 1590A layout for it yesterday, and if things goes well it should be tested some time next week.
As mention earlier I did a quick vero layout. Currently, it is not verified and I maybe should have waited until I have built and verified it. However, the BOM and my parts collection seems to be completely out of phase, so I need to make a parts order first.
Please let me know if you see something that should/could be changed!
(https://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=53866&g2_serialNumber=1)
BTW, there are some really good and helpful answers in this thread, thanks to all of you!
Quote from: jonny.reckless on August 20, 2020, 01:36:26 AM
Quote from: rutgerv on August 19, 2020, 01:23:06 PM
One other thing I was wondering about: the 100 ohm resistor (R15) in the PSU input stage, does it serve any purpose for the dynamic response (sagging) of the rest of the circuit? Or is it purely for keeping out the PSU noise?
I put it there to get rid of a little bit of hum I was getting. I have no idea if the sag affects the sound or not :)
Class A stages. No dynamic current draw.
^ This. I would expect no significant "sag", given moderately low current draw (preamps merely need to amplify voltage), constant current draw of class-A stages in average, low filtering resistance (100 ohms) and large-ish filtering capacitance (470 uF).
For example, to generate any worthwhile current draw to generate sag for FET preamp's power supply rails Roland Blues Cube amps had to feature a whole "mini" push-pull power amp driving a dummy load. Most preamp-based "sag" schemes feature somekind of envelope follower that modulates reference voltage for clipping.
While no considerable sag is produced using a power supply RC filter is a good idea for decoupling purposes so that signal does not couple from one gain stage to another via supply rail modulation. This circuit design does not decouple any of its four gain stages but does, however, isolate them from the variable impedance of the power supply. (Without the RC filter the increased source impedance of a dying battery might cause stages to couple through the supply rail).
I'm simultaneously working on some Amt jfet preamps and see they have a habit of adding a generic RC supply filter for the pedal, and (!) an extra RC supply filter for the first stage (perhaps it requires the highest clean gain?).
Quote from: teemuk on August 21, 2020, 09:24:21 AM
^ This. I would expect no significant "sag", given moderately low current draw (preamps merely need to amplify voltage), constant current draw of class-A stages in average, low filtering resistance (100 ohms) and large-ish filtering capacitance (470 uF).
For example, to generate any worthwhile current draw to generate sag for FET preamp's power supply rails Roland Blues Cube amps had to feature a whole "mini" push-pull power amp driving a dummy load. Most preamp-based "sag" schemes feature somekind of envelope follower that modulates reference voltage for clipping.
A loaded opamp can do this as well I guess.... I thought about those things before. Problem is: what do we
want with sag? 5 a 10 % rail supply fall? Or induced crossover? Mostly the latter and that can be achieved easier. Recently I suddenly appreciated the fact VOX AC amps hardly have power sag given the rather low amount of average current rise. It's all about cathode bias shift there. And no one calls AC amp "not tubey"
So as to not interfere with jonny.reckless s circuit I made a simple connect the dots diagram.
Connected VDD and VBias and 9v added battery removed 9vdc plug connected input and output. These are just for Reference. The image is light, you need to zoom and squint. So, as a check, are the connections correct ? Thanks in advance...Paul
(https://i.postimg.cc/QKZ45TzK/Untitled-Scanned-04.jpg) (https://postimg.cc/QKZ45TzK)
Almost correct. Since you're using a battery, you don't need R15, so you can skip it and connect the battery directly to VDD. The other parts are all correct.
Thank you very much marcos and rutgerv.....got it, drawing my own circuit to work from sans R15. Monday plan on ordering the few parts I need. Will make Little Jim....special thanks to jonny.reckless for sharing advanced circuit and you all for some circuit design education. Also will post results or the need for HELP. LOL. (I will fill those hiss making holes in the mosfets with some silicone cement, that should fix that)
Happy to report I have a working version of this circuit on my breadboard as of today!
I'm not quite sure yet if it sounds exactly as intended though. Probably because I made some part substitutions (I didn't have all the original parts, but was still eager to try). I used 2N7000 MOSFETs and was able to find 3 with roughly matching Vth of 2.6V. I didn't have sufficient 4K7 resistors, but approximated them with parallelled 10K resistors (resulting in 5K), and didn't have 22nF capacitors, but substituted with two times 47nF in series (coming to 23.5nF). I noticed a couple of things in the sound:
- the overall Marshall tone is there and rocks! Especially with AC/DC-like riffs. I play it into a NUX Solid Studio IR loader (1960 cabinet) with Power Amp sim (EL34) enabled.
- when playing rather dynamically with neck strat pickups the sound goes rather suddenly from clean to distorted. It doesn't feel very natural.
- There's quite some noise, and turning the gain knob makes the noise change 'colour' as well. As if there's additional filtering happening
- the low end behaves a bit odd in terms of dynamics... Somehow I struggled to get a nice "chug chug" out of palm muted lower E-string riffs. It's worse for pick-ups with a lot of low-end, and becomes better when the sound is high-pass-filtered before entering the Little Jim.
I suspect a lot of the above has to do with my suboptimal choice of parts, and I'm intending to look at the individual gain stages with a scope tomorrow to see if it needs a change in bias.
@Jonny: can you provide some guidelines on what to aim for, when adjusting the bias on scope? How "asymmetric" should things be, to make it sound as intended?
Rutger
ps. In the configuration going straight into my NUX CabSim the tone control of the Little Jim is much needed, as it can be extremely bright! I also noticed quite a shift in the mid-range EQ curve when turning the tone control to maximum bright... is that intended?
Quote from: rutgerv on August 23, 2020, 03:44:33 PM
@Jonny: can you provide some guidelines on what to aim for, when adjusting the bias on scope? How "asymmetric" should things be, to make it sound as intended?
Rutger
ps. In the configuration going straight into my NUX CabSim the tone control of the Little Jim is much needed, as it can be extremely bright! I also noticed quite a shift in the mid-range EQ curve when turning the tone control to maximum bright... is that intended?
The MOSFET drains should sit around 2/3 to 3/4 of VDD, i.e. somewhere between 6 and 7.5 volts is ideal. Looking at the signal on a scope with a 440Hz sinewave, the top half should be rounded and fat, and the bottom half should be hard clipped. Adjust R8 (VBIAS) to get the drains where you want with the MOSFETs you have. Also make sure the source of TR3 is sitting at at least 2VDC so you don't get unwanted hard clipping on the input stage.
Voicing the circuit is a highly personal thing and depends on the MOSFETs you used, your guitar, pickups, playing style, the EQ and voicing of your amp's clean channel, and choice of speakers. Here are some ideas to play with.
- Reducing C8 will reduce the bass before the gain stages. This will make the distortion more crunchy and bright, and less fuzzy.
- Make sure you use an audio taper pot for RV1 to get a reasonable gain response. As I said in the video, it's not subtle, and doesn't do the tube screamer thing, it's a full bore high gain distortion!
- You can play around with the output filter comprising C10, R14 and C11. These are all interactive, you can simulate the response with LT spice if you like. Reduce C10 to get less bass. Reduce C11 to change the roll off turnover frequency.
Add C4 back in to soften the high end a bit, start with 4n7 and experiment.
rutgerv , have you tried it with humbuckers?
The problems with palm muting and chugging suggest the bias voltage is not quite right. My prototype chugs nicely. Once you have got the bias voltages set up correctly, you can also reduce the pre gain bass further by reducing the value of C6. Both C6 and C8 affect the low end response of the first gain stage, they behave slightly differently under clipping so it might be worth experimenting, maybe start by halving the value of one or both of them and see how it behaves in your circuit.
The output tone control starts to roll off at 70Hz and varies the point it stops rolling off, so you get a nice bass boost with the tone control in the middle. You can change this by reducing the value of C11 to 10n, this will start the roll off around 700Hz which is more what you get with a tube screamer tone control. Note that by doing this you will lose a lot of low end, but there's plenty of opportunity for tweaking!
This is actually an interesting idea.
At the moment, this is certainly not a marshall, but a good platform to start with, I have seen a similar one with Catalinbread RAH and Jack Orman Mosfet Booster.
Connecting gate resistors to bias is a good idea to get away from Zvex style BOR / BOM / SHO etc. biasing.
We have no feedback and no Miller effect, which means our high frequencies are safe.
MOSFETs have a number of advantages over the classic AIMP Jfet choice.
1) We can change the drain resistor and affect the gain, just like in the anode resistor of a lamp (JFET either works or not).
2) We can assemble a circuit without trimming resistors, which means we can simplify our work.
3) There is no need to select transistors
4) These transistors are not obsolete and can be easily found on the market, Jfets are gradually becoming a rarity, as are germanium transistors.
But there is nothing perfect in life and we have a number of disadvantages.
1) Transistors are afraid of static voltage (although some newer models have built-in protection)
2) Noise and this is the main problem, JFETs hiss and noise can be reduced or eliminated altogether, MOSfets make noise like a transformer booth and I don't know a real way to remove noise, they are just noisy.
3) Several years ago I made breadboards, but I could not make a really pleasant sound with high gain, it was loose and fuzzy, maybe this is a lack of knowledge in those years or the MOSFet is really unsuitable for high gain. But the clear sound is much better than the JFET.
4) I tested only ZVEX style circuits and Miller effect got bored pretty quickly, maybe your CB RAH / Jack Orman style circuit will be much better.
Now let's get back to your circuit.
We know that the sound of the preamp is formed in many parts of the circuit, you have not conveyed much
1) Tone Stack forms most of the sound, you don't have it, which means there is no mid cut
2) There is no follower, although the follower forms the sound, adds compression. Yes, you can also hear it on transistors, I checked.
3) Where is the proprietary filtering Marshall 470k // 470p? This is part of their sound.
Wow, just spent a nice hour of playing several guitars and pick-ups through the Little Jim into my IR loader + poweramp sim! Very inspiring! With the tips of Jonny I was able to figure out that all something strange was going on in the last gain stage, probably a bad connection on my breadboard. It's fixed now, and suddenly it has "the sound" I was expecting. It really rocks!
So please forget my negative comment made earlier. This was really a case of "user error". Palm muted chugging is nice now, though not "heavy metal" in any way, but more classic rock (a la Led Zeppelin's Communication Breakdown). I also love how easy harmonics come out on upper strings, and how much detail/movement can be heard on 3-note chords played somewhere in the middle register. As mentioned, this pedal isn't for subtle gain, and not for 'dynamic' playing. It's indeed amp-on-11 style, though I discovered there's an interesting sweet spot in the gain knob travel. First, the Little Jim starts distorting in a fairly 'normal' way, but beyond a certain point a second type of distortion comes in on top of the first, and that really adds 'richness'. Very soon after this point, distortion becomes uncontrollable for rhythm/chords and only still serves a purpose on leads, but it's that spot just before that I think is very much unique to this circuit!
Anyway, thumbs up Jonny! I think I', going to try and put this circuit on a proper PCB, instead of the breadboard. I noticed that near maximum gain the circuit was on the brink of internally oscillating, and a better circuit board/layout might prevent that.
Rutger
I'm so pleased you got it sounding great. There's plenty of opportunity for further improvement.
Let me know if you would like one of my spare PCBs, or if you'd like me to share the Gerbers and NC drill files for the board I built.
So, it took me more time than I initially tought, but I finally built it yesterday.
(https://i.postimg.cc/KkdQSjgN/littlejim.jpg) (https://postimg.cc/KkdQSjgN)
I used 2N7000 for the mosfets and a J201 (legit) for the jfet. Imo there was no noise because of the 2N7000. I mean, it's a high gain circuit with no sshielded wires and outside of a metal enclosure (for now), so it isn't really quiet, but nothing different than any distortion circuit under the same conditions.
This one surely rocks! Good for palm muting, good for chords, good for harmonics and good for classic rock riffs. The tone pot offers a good range of usable sounds. To be honest, it have the exact drive sound I have using just my guitar and my AX84 Hi Octane amp, and I was looking for a pedal which gives me this exact sound, so building this one was a big win. Imo, it have a bit less gain than I was thinking it have (and also almost the same gain as my HO, maybe a bit more), but not a big deal, a simple booster/od can solve it. I'm kinda afraid on showing this one to my friends, because I know one or two of them that'll want to "borrow it to test it for a while but will probably never return it to me" :icon_lol:. I'll surely box it and will add it to my pedalboard, just have to decide on the artwork, which is the hard part since I don't have good artwork ideas :icon_lol:.
Edited: I don't have a place to host the layout files, but if Jonny or anybody else want the files, just let me know and I'll gadly share them. I should make a google drive folder or something like that to share my layouts, but I end up being too lazy to create a kinda decent looking pdf file :icon_lol:.
Hi,
Quote from: Marcos - Munky on September 17, 2020, 12:23:02 PM
just have to decide on the artwork, which is the hard part since I don't have good artwork ideas :icon_lol:.
I have ideas but lack the skills to make them real :icon_lol:
Quote from: Marcos - Munky on September 17, 2020, 12:23:02 PM
I don't have a place to host the layout files.
You can create a Gitlab [1] account. Gitlab is a free git projects repository [2].
You can then benefit from versioning, issues tracking, releases, branching, tags, wiki, etc. People can then fork, contribute, etc.
If you don't want to share some of your repositories, you can make them private (it's free as well)
And you have looots of space (10GB per project.) You only pay if you require more computing time than what is in the free plan (you need it to compile, test code, which would not be the case in your situation)
I prefer to use it from command line [3,4], but there are lots of GUI clients to use with git [5]
Cheers,
[1] https://gitlab.com/
[2] https://git-scm.com/
[3] https://files.jrebel.com/pdf/zt_git_cheat_sheet.pdf
[4] https://git-scm.com/docs
[5] https://git-scm.com/downloads/guis/
https://github.com (https://github.com) also has free private repositories.
If it's just for sharing, a free Google Drive, Dropbox, One Drive (the one from MS) will do.
Quote from: marcelomd on September 17, 2020, 02:18:31 PM
https://github.com (https://github.com) also has free private repositories.
I didn't mention Github on purpose (after having used it for years). Without going into details useless in this context, from my experience:
Gitlab: 10GB, way to weight issues, roles based access, better documentation
Github: 500MB, no way to weight issues, unacceptable ways of handling customers (it's my own experience)
I do not recommend the other tools in your list as they are not SCMs. If it's for sharing and working with a community, one should use tools made for sharing and for working together, don't you think (fork, release, tag) ?
Best regards
Keep it up! I have like 1000+ BS170 that I need to get rid off! hahaha
Quote from: kraal on September 17, 2020, 03:20:36 PM
Quote from: marcelomd on September 17, 2020, 02:18:31 PM
https://github.com (https://github.com) also has free private repositories.
I didn't mention Github on purpose (after having used it for years). Without going into details useless in this context, from my experience:
Gitlab: 10GB, way to weight issues, roles based access, better documentation
Github: 500MB, no way to weight issues, unacceptable ways of handling customers (it's my own experience)
I do not recommend the other tools in your list as they are not SCMs. If it's for sharing and working with a community, one should use tools made for sharing and for working together, don't you think (fork, release, tag) ?
Best regards
I agree with you in general. I've worked with most of the "public" SCM providers and all of them leave something to be desired in one way or another. Github is just the most famous and so it's easier to find help/tutorials/tools =)
Full featured version control for our projects would be nice (if a bit overkill), even if not everybody gets over the learning curve.
Quote from: kraal on September 17, 2020, 01:25:46 PM
I have ideas but lack the skills to make them real :icon_lol:
Well, I also don't have skills, but what are your ideas? :icon_lol:
For the "where to host", I didn't used anything before, so I don't know how Gitlab and Github words. My Google account have a Drive I didn't used even once so far, so space won't be a problem, and pdfs takes so little space anyways. It's the "I don't know how to create a half decent pdf file to share and I do some things on Eagle that I can easily understand but it'll looks like a mess for other users" that kept me from uploading the files on Drive. I have to take some time and make a template of a half decent pdf file then the rest should be easy enough, but there are so many things to do and I keep forgeting on doing that.
Here's a link to my Google drive folder with the schematic, bill of materials, assembly photos, PCB Gerbers and NC drill files:
https://drive.google.com/drive/folders/1nzRh_Ax2i9DMiyzEAqyzJoUVYRm6h0ny?usp=sharing (https://drive.google.com/drive/folders/1nzRh_Ax2i9DMiyzEAqyzJoUVYRm6h0ny?usp=sharing)
Marcos I can grant you write access if you email me with your Google account info.
With the Little Jim circuit still on my breadboard I've recently started experimenting a little bit with some variations, such as a full tone-stack behind it. Also, I've been wondering if there would be a way to make it more touch-sensitive and/or clean-up more gradually than the original circuit.
I started looking at some other Mosfet-based overdrive, mainly the Box of Rock (ZVex) and its near-copy-with-extra's: Bogner La Grange. Besides both of these pedals having an extra RC-network between gain-stage 1 and 2, I also noticed they differ in two other ways
1) gain/filter structure. Little Jim uses rather high source resistors and bypasses these for high frequencies with a 10u (or 220n) capacitor. The other two circuits use a much lower (100 to 330 ohm) source resistor without HF bypass.
2) Mosfet biasing. Little Jim uses a special part of the power supply that connects through 100K resistors to the gates of the Mosfets. The other two circuits use resistors to ground and to drain (both 1M).
With my limited knowledge of Mosfet circuit, it seems the Zvex-approach to Mosfet biasing has some advantages. First of all, the dual resistor approach seems to be more forgiving to different supply voltages, and the resistors being an factor of 10 larger also means the gate-source capacitance of the mosfets will act up less easily (in some Spice simulations with 2N7000s and the original Little Jim circuit I can actually see it creates a resonance hump right around 2K, though not sure if GS-capacitance in this spice model is realistic).
I'm wondering if the current bias configuration in Little Jim was a deliberate choice, and weather it has effects sound-wise. I'm wondering similarly about the gain-structure and filtering decisions. Was there a specific reason to do it this way? (Or framing it differently...would Zvex have a specific reason for their topology?)
Hoping to learn from you!
Rutger
Quote from: rutgerv on September 20, 2020, 02:13:42 PM
would Zvex have a specific reason for their topology?
Basically, Zvex "created" the SHO, and then just stacked a few stages and it sounded good. That's it.
@Jonny, I'll try to create a half decent pdf file, then I'll send it to you. Then, if you want, I can send you the eagle files (and gerbers, which can be gotten from eagle). Give me some time, I have to put my mind back to where it should be, then I'll do the file. Good news is I'm almost set on the artwork, so it'll be boxed sooner than I was thinking.
nice work as always, sir! salute!
you can still get real Jfets from mouser but they will run you around 4-5 dollars per unit
Quote from: rutgerv on September 20, 2020, 02:13:42 PM
I'm wondering if the current bias configuration in Little Jim was a deliberate choice, and weather it has effects sound-wise. I'm wondering similarly about the gain-structure and filtering decisions. Was there a specific reason to do it this way? (Or framing it differently...would Zvex have a specific reason for their topology?)
I'd never seen the box of rock before, it's quite a different design (apart from obviously using BS170 MOSFETs for the gain). How does it sound in comparison to Little Jim? My guess is it is quite a lot darker, with more low end distortion. Higher impedance gate circuits would mean that the Miller effect becomes even more of a problem, killing pretty much all of the treble in the first gain stage, and possibly introducing high Q resonant peaks, so it becomes quite fussy with what you drive it with. I try to drive the MOSFET gates from low impedance sources to minimize this so as to preserve high frequency gain, and get that tasty bright Marshall crunch. All the MOSFET gain pedal designs I have seen just connect the input to a MOSFET common source gain stage, and it really sucks the tone of a passive pickup, especially a high inductance pickup like a Seymour Duncan JB bridge. This is why I used a JFET source follower on the input, and couple each gate from the previous drain directly with a cap and no series resistance. Putting a passive guitar pickup into a MOSFET common gain stage like this will likely roll off from 500 - 800 Hz, and present an effective Miller input capacitance in the nanofarad range. Perhaps that is what the designer intended, but it wasn't my intention here. I chose the 220n source decoupling capacitor on the first gain stage to provide a suitable treble boost to avoid fuzziness and farting out. I did briefly try a Marshall style treble lift between the second and third gain stages. I typically like this with JFET preamps, but with this pedal, I preferred it without.
My suggestion is just to experiment on your own. If you like the sound, then go for it! It's all a matter of personal taste; there's no "correct" way to do things. I voiced Little Jim to my taste, with my guitars, amps and cabs. I didn't try to model any specific amp or pedal, rather just get that bright, crunchy, swirling sound of a classic Marshall cranked. There's lot of ways you could improve it! If you come up with something you're happy with, please post a demo video and a schematic and I'll make one :)
Quote from: LightSoundGeometry on September 20, 2020, 11:40:17 PM
you can still get real Jfets from mouser but they will run you around 4-5 dollars per unit
J113s (my favorite JFET for audio preamps) are $0.129 each for 100 off at Mouser. If somebody wanted $5 a JFET I'd be looking to get into the FET supply chain business 8)
The Crazy Tubes Ziggy is similar to both Little Jim and Box of Rock in architecture:
(http://guitar-fx-layouts.42897.x6.nabble.com/file/n30185/Zod_nocentelli_schem_corrected.png)
I like it.
I also like how easy is to get good sounds out of simple MOSFET gain stages. Mix and match.
smd j201 , 33p each.... 8)
just add converter pcb n legs... :)
https://www.mouser.co.uk/ProductDetail/ON-Semiconductor-Fairchild/MMBFJ201?qs=ljbEvF4DwONpFpdsobl6fQ==&vip=1&gclid=EAIaIQobChMI24_YssP66wIVyentCh2UzwUGEAQYAiABEgJmvfD_BwE
Quote from: jonny.reckless on September 21, 2020, 03:35:07 AM
Quote from: LightSoundGeometry on September 20, 2020, 11:40:17 PM
you can still get real Jfets from mouser but they will run you around 4-5 dollars per unit
J113s (my favorite JFET for audio preamps) are $0.129 each for 100 off at Mouser. If somebody wanted $5 a JFET I'd be looking to get into the FET supply chain business 8)
you got me lol , I wasnt specific. the j201's and 2n5457 are around 5 dollars a piece. I have not compared specs between the j201 and j112. I have never messed with a j113 but guess who is adding to mouser cart some fets lol
https://www.mouser.com/datasheet/2/308/MMBFJ113-D-1811481.pdf
Quote from: deadastronaut on September 21, 2020, 11:11:44 AM
smd j201 , 33p each.... 8)
just add converter pcb n legs... :)
https://www.mouser.co.uk/ProductDetail/ON-Semiconductor-Fairchild/MMBFJ201?qs=ljbEvF4DwONpFpdsobl6fQ==&vip=1&gclid=EAIaIQobChMI24_YssP66wIVyentCh2UzwUGEAQYAiABEgJmvfD_BwE
I totally forgot about doing this . I just got back to work a few weeks ago, forgot a lot of the tricks of the trade. I was really sick due to fiberglass poisoning and am in a lawsuit right now. my house is unoccupied and has 30k worth of damages. im alive though and glad to be back on forums and in the shop.
It took me some time, but here's my verified 1590A layout: https://drive.google.com/file/d/1M03EY3GVBd35o7Lodkq3S2jJQcjmUzut/view?usp=sharing
Still didn't boxed it yet, but I'm planning to do it as soon as possible. Let me know if the link works. Also Jonny, if you want me to send you the eagle files/gerbers let me know, or if you want to upload the layout on your google drive account feel free to do it.
Quote from: rutgerv on August 19, 2020, 01:23:06 PM
One other thing I was wondering about: the 100 ohm resistor (R15) in the PSU input stage, does it serve any purpose for the dynamic response (sagging) of the rest of the circuit? Or is it purely for keeping out the PSU noise?
Rutger
I think simple answer is No, not for sag
It appears that the word "Sag" has two meanings
A) Like an Amp with an overload on its power supply. Hence initial part of note is higher volume and cleaner, but as voltage drops, the note gets compressed, more distorted. After a very short time, the voltage recovers and than we can have same story for the next notes
B) Like a permanent drop of voltage normally seen in a fuzz circuit, leading to the circuit operating at a different point. There is no "recovery" since the voltage does not go back to normal.
Hence here the resistor is only for hum and ripple rejection by increasing the time constant of the filtering capacitor.
But maybe different sounds are possible by changing this resistor to higher values (Idea B)
Quote from: jonny.reckless on August 15, 2020, 06:11:38 PM
This is the Little Jim distortion pedal. It's inspired by and named after Jim Marshall, and attempts to capture that bright, crunchy, raucous sound of a cranked Marshall amp, which is also deceptively complex and rich with harmonics and timbral movement.
Thank you for posting your project, Sir Jonny !!!
A) I am interested in studying inter-stage frequency response and transfer functions to be able to achieve a particular sound.
I request you to post these graphs if possible
Alternatively, if your files are compatible with LT SPICE, maybe I know enough to be able to make these graphs.
B) Did you try to aim for particular inter-stage frequency response and transfer function while designing this circuit ? Please help me to understand how the various capacitors were calculated.
Thank you !!!
I've built a few with JFET's like this, but without the buffer. I have to hand it to you Jonny, really nice job; other attempts I've made weren't quite so smooth and responsive :) This thing wails! Must be...Mosfet booster power! ;)
I can't say yet if overdriving my amp is contributing, tho I've tried it on very low levels to avoid this, with great results. Modded some stuff...2N5457 for buffer with a 100k to bias, and since not selecting the BS170s by hand, dialing them in at the drain w/4.7k source R's. All the same, nice little Marshall-emulating project! I look forward to boxing it and running it thru my Astro Sim. Thanks for sharing!
I just tossed a bottle of etchant away thinking I was going to ltspice a fabbed board ;D now I want to do this ! but this is the crazy sheeite that you can do shrinking stuff down
modified to say I miss radio shack ..there is a void where I am for electronics ...would a brick and mortar work or people just buy online? considering SAFB is right next to me there would be a lot of hobbyist ( those air force guys like them rc planes and drones) , radio guys , there is some bloke in waterloo, a few towns over, who builds amps etc ..seems like a good idea to open a store lol. if radio shack was open still, I would be in there in the morning to get etching and a copper clad ..if I print the file will the layout be sized automatically?
Hi everyone,
The more I play with this circuit, the more I like it! For my own learning process, I experimented with the original Little Jim circuit and tried a couple of modifications. Here are my findings (and some new questions raised, that perhaps someone knows the answer to already):
1) tried the alternative biasing method with a 1M from gate to ground and 1M from gate to drain (like in the Box of Rock and La Grange circuits previously mentioned). Can confirm what Jonny said before: certainly no improvement. Overall brightness didn't suffer too much, but the sound became more lifeless and less immediate. I suspect it influences the dynamics of the circuit somehow.
2) I tried running the circuit at a higher (and lower) voltage and learnt that it has a dramatic effect on brightness. At 12V the circuit is much brighter (too much for my taste). I was hoping to incorporate the circuit in a preamp that I was planning to run on 12V. If anyone knows a way to bring the circuit back to it's original 9V while running it from 12V, I'd be happy to hear! Otherwise I apply some filtering
3) Again, trying to learn from the alternative (not necessarily better) approach in the Box of Rock and La Strange, I tried some alternative gain structures. Instead of connecting C3 to ground, I connected it to a 330 ohm resistor. This made a big change. Overall gain of the circuit drops (but for my taste it has plenty left), the low-end becomes a bit more lively and there's more audible compression on peaks. Actually I very much liked this tweak! The only down-side (on my breadboard) was a higher amount of hum/noise. I struggle to understand why, because I was expecting the exact opposite from lowering the gain in the last stage. Perhaps it's just my breadboard layout? Or is there a more fundamental reason (increased influence of a dirty PSU?). I also tried a similar modification with a 100 ohm resistor in the stage before the final gain stage, but that didn't make such a dramatic difference.
4) I see many MOSFET pedals carry protection zener's near the MOSFET's, and was wondering it would be wise to include any in the Little Jim if I put it to its final board, but can't think of any reason why a boxed pedal could suffer from voltage spikes beyond 60V on the MOSFET gates.
Rutger
QuoteI was hoping to incorporate the circuit in a preamp that I was planning to run on 12V. If anyone knows a way to bring the circuit back to it's original 9V while running it from 12V, I'd be happy to hear!
LM7809 voltage regulator?
Quote from: rutgerv on October 03, 2020, 06:12:27 AM
Hi everyone,
2) I tried running the circuit at a higher (and lower) voltage and learnt that it has a dramatic effect on brightness. At 12V the circuit is much brighter (too much for my taste). I was hoping to incorporate the circuit in a preamp that I was planning to run on 12V. If anyone knows a way to bring the circuit back to it's original 9V while running it from 12V, I'd be happy to hear! Otherwise I apply some filtering
Rutger
I can understand how harmonics can change in a circuit with a change in supply voltages, due to different bias operating points leading to different clipping.
Do you feel that the brighter sound at 12V was due to change in clipping due to difference in bias operating points ?
Finally boxed mine. The etching didn't came out too good because I tried a different paper for the tone transfer. But I liked the result anyway.
(https://i.postimg.cc/PpsMkXVn/little-jim.jpg) (https://postimg.cc/PpsMkXVn)
What if you use LND150? They are lateral MOSFET, maybe they have less noise than BS170?
Quote from: rankot on October 19, 2020, 09:32:07 AM
What if you use LND150? They are lateral MOSFET, maybe they have less noise than BS170?
They're depletion mode MOSFETs so you'd have to bias them with a negative gate voltage, or use source biasing like you would for a JFET, so the circuit would have to be different. They have a much lower input capacitance and a much higher channel resistance than the BS170. It might be worth trying to substitute them in a few JFET based preamp circuits and seeing how they sound, but my guess is you'd have to specifically design a circuit around them. Depletion mode MOSFETs with high channel resistance are quite unusual.
I'll buy some and see if I can come up with a circuit to use them. Watch this space 8)
This guy built JCM800 emulation using LND150. https://www.ssguitar.com/index.php?topic=2006.msg15734#msg15734 (https://www.ssguitar.com/index.php?topic=2006.msg15734#msg15734)
Quote from: rankot on October 25, 2020, 05:01:42 AM
This guy built JCM800 emulation using LND150. https://www.ssguitar.com/index.php?topic=2006.msg15734#msg15734 (https://www.ssguitar.com/index.php?topic=2006.msg15734#msg15734)
I listened to those clips, it's a great sounding preamp but neither of them sound remotely like my JCM800 2x12 4211 combo. Everybody quotes, copies or models the JCM800 series, and just about everybody gets the gain structure and voicing wrong. Most of the distortion tone of those amps comes from two things: asymmetric clipping in the DC coupled cathode follower driving the tone stack, and cutoff clipping in the phase inverter stage. There's some transformer compression with the output stage too and power amp harmonics which relies on the EL34 screen grid kinks. I actually built a direct copy of a JCM800 master volume head once, with the exact same component values, tube types, and Dagnall electronics UK wound transformers, and people who heard it said it lacked gain and definition 8) The truth is that the JCM800 is quite a primitive, low gain, inflexible amp, that sounds magic for blues and vintage rock, but needs a stomp box or two to make it really sing, and only comes alive when you overdrive the 100 watt power stage at ear splitting volume. I've owned several of them (original Bletchley manufactured from the 80s) and to get a decent tone out of them I always had to put a drive pedal in the front, and use quite a bit of EQ in the mix.
I was never trying to build a clone, that's more runoffgroove's thing. The Little Jim is far too simple and primitive for that. I was just going for a saturated tone with some harmonic motion and a nice bright cutting distortion tone. That guy's preamp sounds great but has about 10x the component count! It looks like he's using 2SK216 not LND150?
Quote from: jonny.reckless on October 26, 2020, 04:45:49 AM
the gain structure and voicing wrong.
a saturated tone with some harmonic motion and a nice bright cutting distortion tone.
I am trying to learn a bit about emulating Amps by copying the gain structure, voicing, harmonic motion of each stage.
Please help me to understand your target of gain structure, voicing, harmonic motion of the stages of Little Jim and how you achieved it.
Thank you !!!!
Quote from: Vivek on October 26, 2020, 05:07:52 AM
Quote from: jonny.reckless on October 26, 2020, 04:45:49 AM
the gain structure and voicing wrong.
a saturated tone with some harmonic motion and a nice bright cutting distortion tone.
I am trying to learn a bit about emulating Amps by copying the gain structure, voicing, harmonic motion of each stage.
Please help me to understand your target of gain structure, voicing, harmonic motion of the stages of Little Jim and how you achieved it.
Thank you !!!!
The circuit design of Little Jim is very simple.
The input stage is a unity gain buffer designed to present high impedance and low capacitance to the guitar pickup.
The first gain stage is partially bypassed, so that its frequency response has a pole around 160Hz and a zero around 3kHz. This allows for a bright crunchy sound due to accentuating the higher harmonics of the guitar frequency range.
The second and third gain stages are fully bypassed for maximum gain.
The drains are biased at DC to around 2/3 VDD to provide asymmetric clipping with a fat rounded top half wave and a heavily clipped bottom half wave. This exploits the quadratic nature of the field effect transistor for plenty of even and odd harmonics.
The filter stage rolls off the sharp high frequencies introduced by the clipping stages for a more rounded tone.
All amps and distortion circuits follow these general principles to some degree: filter the bass, overdrive, clip, then filter the treble and / or boost the bass.
Thanks !!!!
Is it necessary to design the circuit so that goes into symmetrical clipping for larger signals ?
Please help me understand the "Harmonic Motion". Is that something that needs to be especially designed in, or is a natural byproduct of having multiple clipping stages ?
Quote from: jonny.reckless on October 26, 2020, 04:45:49 AM
Quote from: rankot on October 25, 2020, 05:01:42 AM
This guy built JCM800 emulation using LND150. https://www.ssguitar.com/index.php?topic=2006.msg15734#msg15734 (https://www.ssguitar.com/index.php?topic=2006.msg15734#msg15734)
I listened to those clips, it's a great sounding preamp but neither of them sound remotely like my JCM800 2x12 4211 combo. Everybody quotes, copies or models the JCM800 series, and just about everybody gets the gain structure and voicing wrong. Most of the distortion tone of those amps comes from two things: asymmetric clipping in the DC coupled cathode follower driving the tone stack, and cutoff clipping in the phase inverter stage. There's some transformer compression with the output stage too and power amp harmonics which relies on the EL34 screen grid kinks. I actually built a direct copy of a JCM800 master volume head once, with the exact same component values, tube types, and Dagnall electronics UK wound transformers, and people who heard it said it lacked gain and definition 8) The truth is that the JCM800 is quite a primitive, low gain, inflexible amp, that sounds magic for blues and vintage rock, but needs a stomp box or two to make it really sing, and only comes alive when you overdrive the 100 watt power stage at ear splitting volume. I've owned several of them (original Bletchley manufactured from the 80s) and to get a decent tone out of them I always had to put a drive pedal in the front, and use quite a bit of EQ in the mix.
I was never trying to build a clone, that's more runoffgroove's thing. The Little Jim is far too simple and primitive for that. I was just going for a saturated tone with some harmonic motion and a nice bright cutting distortion tone. That guy's preamp sounds great but has about 10x the component count! It looks like he's using 2SK216 not LND150?
He actually has two designs, the one I linked to is using LND150s. http://milas.spb.ru/~kmg/files/projects/jcm800mv/fet/lnd150/jcm800mvfSch.pdf (http://milas.spb.ru/~kmg/files/projects/jcm800mv/fet/lnd150/jcm800mvfSch.pdf)
I posted it just as a reference to you, if you decide to try those depletion mode lateral MOSFET.
Quote from: rankot on October 26, 2020, 10:05:04 AM
He actually has two designs, the one I linked to is using LND150s. http://milas.spb.ru/~kmg/files/projects/jcm800mv/fet/lnd150/jcm800mvfSch.pdf (http://milas.spb.ru/~kmg/files/projects/jcm800mv/fet/lnd150/jcm800mvfSch.pdf)
Wow, look at these voltages! :). Might as well use tubes then!
I'm guessing the diodes in the gate circuit are to simulate grid current when the grid is positive biased. Interesting idea, but needing the high voltage makes it unsuited to a simple (or cheap) pedal design - generating 300V from 9V is not practical with a simple boost converter, you need a coupled inductor with multiple windings to get that kind of voltage ratio (or multiple stages of boost conversion). Personally if I was going to all that trouble I'd just use ECC83s and be done with it :)
Back in the 90s at Trace Elliot we made a hybrid guitar power amp using a tube topology, with a pair of push pull high voltage MOSFETs, driven by a MOSFET phase splitter, driving an output transformer which coupled to the speaker. I think it ran on around 400VDC. I can't remember the name of it now, it was one of Clive Button's designs, but it responded surprisingly like a traditional push pull tube power amplifier when overdriven.
I've been using JFETs in tube like guitar circuits since the mid 90s, and it works pretty well. You don't need to copy the schematic exactly, just generally get a similar circuit topology and then voice it to suit FETs. The same rules apply: reduce the bass (or boost the mids / treble) early in the signal path, progressive clipping, moving DC bias points, some form of asymmetry to give even order harmonics, and a lowpass filter at the end to remove unpleasant high order harmonics. I like the sound and feel of multi stage clipping circuits, you get more "swirl" and "harmonic motion" than with a single diode-op-amp type clipper, due to the fact the interstage DC bias points are modulated by the signals as they go into and out of saturation. Provided you don't get blocking distortion, it sounds rich, complex and more "amp like". I've posted a couple of similar amp designs on here before, the Boba FET and the Rosie amp, which use this approach with JFETs.
https://www.diystompboxes.com/smfforum/index.php?topic=118627.0 (https://www.diystompboxes.com/smfforum/index.php?topic=118627.0)
https://www.diystompboxes.com/smfforum/index.php?topic=123572.0 (https://www.diystompboxes.com/smfforum/index.php?topic=123572.0)
@Ranko, I got some LND150s today from Mouser and started to play around with them. They are interesting. Much lower saturation current and higher drain resistance than even most JFETs. I've got some basic ideas for a distortion pedal using them, the common source gain stage looks quite usable on the scope when correctly biased. When I've pulled a complete design together I'll post again here, probably in a couple of weeks. It's going to be quite similar to Little Jim, but I'd like to add separate bass and treble controls.
Quote from: jonny.reckless on October 27, 2020, 01:34:04 AMBack in the 90s at Trace Elliot we made a hybrid guitar power amp using a tube topology, with a pair of push pull high voltage MOSFETs, driven by a MOSFET phase splitter, driving an output transformer which coupled to the speaker. I think it ran on around 400VDC. I can't remember the name of it now, it was one of Clive Button's designs, but it responded surprisingly like a traditional push pull tube power amplifier when overdriven.
"Reactor" it was called. IIRC, the phase inverter was actually opamp based and quite similar to that in Music Man hybrid amps, with the exception of featuring zener diodes in the feedback loop that clipped the signal. (Could have been the primary clipping mechanism, IIRC).
Didn't have high supply voltage either, it was pretty much in the range of generic SS power amps with similar output power rating (e.g. 80V rail-to-rail). No need for high supply voltage because the output MOSFETs had low impedance and there was no need for similar current-voltage transform as in tube amps with high plate output impedance.
Speaking of which, IIRC the amp also featured the typical current feedback scheme in order to increase the output impedance artificially.
There was also a 30W Reactor amp with just two high power opamps running bridged and no OT.
Gallien-Krueger made several transformer-coupled SS amps in the early 1970's (with current-starved PI for clipping and "power scaling") and Fender had a patent for one as well (although I don't know if they ever employed the idea in practice). I recall Trace Elliot had an European patent as well. Most importantly, these designs were similar to tube amps by topology, not just OT in output of a follower output like in 70V line systems and such.
Great thread. I would love to see the Trace schematics, but Google searches only come back with Vox Reactor.
Any further ideas?
Many tahnks
Peter
Try "TVT9 schematics". ;)
Thanks!
Quote from: jonny.reckless on October 27, 2020, 01:34:04 AM
I'm guessing the diodes in the gate circuit are to simulate grid current when the grid is positive biased.
This. The diodes basically allow more asymmetry to clipping (similarly to generic triode gain stages, and I think due to having lower clipping threshold than just forward biasing the gate-source diode). Peavey "TransTube" patent describes this in better detail and even suggest minimum percentage of asymmetry to emphasize that aforementioned DC bias point shifting in enough of "tube-like" fashion.
One can do that with ordinary BJT's as well, no specific need to use FETs.
Is this the correct patent ?
https://patents.google.com/patent/US5647004A/en
That's one of them. There's also a patent where FETs are replaced with discrete bipolar transistors in darlington configuration (results to high-ish gain and input impedance and so the stage behaves more in "voltage drive" -fashion similarly to tubes and FETs). That is also the circuit version Peavey employs in their "TransTube" circuits. AFAIK, Peavey prefers predictability of BJT's over wide variance of FETs and regards overall clipping asymmetry to be more important characteristic in triode emulation than any subtle differences of FET vs. BJT distortion.
BTW, Peavey's "TransTube" guitar preamps are also damn nice examples of straightforward tube-to-SS conversion because they largely replicate the exact circuit architecture of Peavey's typical tube-based guitar amp preamps (excluding 5150). You know, the ones with that "Ultra" gain channel and alike. Some impedance levels, gains and clipping thresholds are just tweaked accordingly to match the solid-state circuitry. It's not paint-by-numbers -conversion but real close, which is impressive feat given how well these things actually mimick the original circuit.
Enough of OT from me, but yes, one could use the very same ideas to convert, say, some classic Marshall tube preamp, like 2204.
Ranko, here's the link to the LND150 distortion pedal I managed to come up with:
https://www.diystompboxes.com/smfforum/index.php?topic=125775.msg1199458#msg1199458 (https://www.diystompboxes.com/smfforum/index.php?topic=125775.msg1199458#msg1199458)
I finally got the parts I was missing and have had the Little Jim on the breadboard for a couple of days and it sounds great.
I had some problems making it work, though. I do not have a transistor tester so I just plugged in some BS170's, but had very low drain voltages (app. 4.5 v) compared to the schematic voltages and no or bad sound. After fiddling with drain resistors and VBias, I found out that my bag of 10 BS170's varied a lot and I found that four of them gave drain voltages near the ones in the schematic. Using three of those made it sound comparable to Jonny's sound sample.
I posted a vero layout on page 2. Looking a bit closer I found out that I had the pinout of the J112 wrong. I have fixed the layout and reuploaded so the image on page two is correct. Now I just need to build it and verify.
BTW: Is there any simple method to measure the threshold voltage? The ones I found looked pretty complicated.
Quote from: cab42 on November 15, 2020, 05:53:30 PM
I finally got the parts I was missing and have had the Little Jim on the breadboard for a couple of days and it sounds great.
I had some problems making it work, though. I do not have a transistor tester so I just plugged in some BS170's, but had very low drain voltages (app. 4.5 v) compared to the schematic voltages and no or bad sound. After fiddling with drain resistors and VBias, I found out that my bag of 10 BS170's varied a lot and I found that four of them gave drain voltages near the ones in the schematic. Using three of those made it sound comparable to Jonny's sound sample.
I posted a vero layout on page 2. Looking a bit closer I found out that I had the pinout of the J112 wrong. I have fixed the layout and reuploaded so the image on page two is correct. Now I just need to build it and verify.
BTW: Is there any simple method to measure the threshold voltage? The ones I found looked pretty complicated.
I just use one of those cheap component testers: https://www.amazon.com/Mega328-Digital-Transistor-Resistance-Capacitance/dp/B07WT9VVZB/ref=sr_1_3?dchild=1&keywords=component+tester&qid=1605596118&sr=8-3 (https://www.amazon.com/Mega328-Digital-Transistor-Resistance-Capacitance/dp/B07WT9VVZB/ref=sr_1_3?dchild=1&keywords=component+tester&qid=1605596118&sr=8-3)
I bought a bag of 50 BS170s and the whole bag had threshold voltages matched to about 100mV or so, I was pleasantly surprised. As long as you get them reasonably matched, the absolute threshold value is not important, you can tweak the value of R8 to get the drains to sit between 6 and 7 volts. The exact drain voltage doesn't appear to be critical to the sound. I played around with a preset in R8 and I couldn't really hear much of a difference until the drains got to 5.5 and 7.5 volts. Of course at 4.5 volts you've got no voltage left across the FET so it won't work.
^ The tester:
Measures Transistors, Diodes, Resistors, Caps, Mosfet, Jfet, everything except for your weight.
Fast and east to use, I am not promoting this device, nor will vouch for its accuracy.
One problem is I had to get 3 of them, the first 2 had a broken corner on the glass screen.
Returned one, unopened. I modified the plastic box so the battery can be easily replaced.
Paid around $14.00 us. Kind of inexpensive.
(https://i.postimg.cc/5XzZ1MX9/IMG-7217.jpg) (https://postimg.cc/5XzZ1MX9)
Took awhile but I finally got Little Jim on the board. Sounds great, definitely worth boxing it up.
Biggest change is to replace R8 (drain adjust) with a 10K pot. On the board I am using trims, in the box I will use pots.
Think I will call R8 "Vibas", which can be adjusted to eliminate almost any hiss.
(It can be tweaked but not adjusted to far off. Maybe leave it as a trim, need to experiment)
9.27 v Battery
7.98 v at drains
Matched BS170 at 2.5 Vth
R8 pot set 5.9 k
Per rutgerv suggestion will add a (switched) 330 ohm at C3, it does work.
The 4n7 cap at TR2 did not seem to do any thing nor the 100 ohm R15.
(Maybe those work with other setups)
(https://i.postimg.cc/w1hdhyDd/IMG-7219.jpg) (https://postimg.cc/w1hdhyDd)
Done !! See pictures in BYOS pictures folder.
Thanks to all.........
Now to the secret R & D project for the next build (if it works)...no wood ...lol
(https://i.postimg.cc/SnCyCL0n/IMG-7230.jpg) (https://postimg.cc/SnCyCL0n)
^ cool, is that text inlay?.
^ I engrave (raster) a pocket into the wood slide cover. Then clean up the edges in vector mode.
The vector trace takes about 8 seconds to do. Then using the same file I cut out the letters. On Little Jim I used .005 inch (.127 mm) thick self adhesive acrylic and cut it out. I have also used abalone on some other boxes. If I were using metal box I would probably use Cermark, a substance that is either painted or sprayed on then using the laser fused to the metal. Can do very detailed designs using that and once it on fused it is there for good, least you get the grinder out. I have applied numbers to stainless steel for the Navy, those parts are used under the sea. Google Cermark if interested.
Did you try to make this with PMOS transistors, BS250 for example? Andy published Zazen Booster (https://www.diystompboxes.com/smfforum/index.php?topic=119198.msg1157967#msg1157967 (https://www.diystompboxes.com/smfforum/index.php?topic=119198.msg1157967#msg1157967)) using that approach, he claims it has less noise than NMOS. I tried to simulate, and this is the working version, but I don't have time to test it in a real world right now:
Version 4
SHEET 1 3204 680
WIRE -160 -208 -160 -240
WIRE -112 -208 -160 -208
WIRE 0 -208 -32 -208
WIRE 96 -208 0 -208
WIRE 128 -208 96 -208
WIRE 0 -160 0 -208
WIRE 96 -144 96 -208
WIRE 560 -144 560 -176
WIRE 656 -144 560 -144
WIRE 960 -144 960 -176
WIRE 1056 -144 960 -144
WIRE 1312 -144 1312 -176
WIRE 1408 -144 1312 -144
WIRE -160 -128 -160 -208
WIRE 560 -112 560 -144
WIRE 960 -112 960 -144
WIRE 1312 -112 1312 -144
WIRE 656 -96 656 -144
WIRE 1056 -96 1056 -144
WIRE 1408 -96 1408 -144
WIRE -160 -16 -160 -48
WIRE 0 -16 0 -80
WIRE 0 -16 -160 -16
WIRE 96 -16 96 -80
WIRE 96 -16 0 -16
WIRE -160 0 -160 -16
WIRE 560 48 560 -32
WIRE 656 48 656 -32
WIRE 656 48 560 48
WIRE 960 48 960 -32
WIRE 1056 48 1056 -32
WIRE 1056 48 960 48
WIRE 1312 48 1312 -32
WIRE 1408 48 1408 -32
WIRE 1408 48 1312 48
WIRE 1712 48 1712 32
WIRE 560 64 560 48
WIRE 960 64 960 48
WIRE 1312 64 1312 48
WIRE -480 96 -560 96
WIRE -288 96 -480 96
WIRE -160 96 -224 96
WIRE -112 96 -160 96
WIRE 16 96 -32 96
WIRE 64 96 16 96
WIRE -160 128 -160 96
WIRE 656 128 656 48
WIRE 1056 128 1056 48
WIRE 1408 128 1408 48
WIRE 1712 128 1712 112
WIRE -480 144 -480 96
WIRE 16 144 16 96
WIRE 112 144 112 128
WIRE 176 144 112 144
WIRE 288 144 240 144
WIRE 416 144 368 144
WIRE 560 144 560 128
WIRE 560 144 416 144
WIRE 608 144 560 144
WIRE 960 144 960 128
WIRE 960 144 848 144
WIRE 1008 144 960 144
WIRE 1312 144 1312 128
WIRE 1312 144 1200 144
WIRE 1360 144 1312 144
WIRE 112 176 112 144
WIRE 416 176 416 144
WIRE 656 256 656 224
WIRE 704 256 656 256
WIRE 848 256 848 144
WIRE 848 256 768 256
WIRE 1056 256 1056 224
WIRE 1104 256 1056 256
WIRE 1200 256 1200 144
WIRE 1200 256 1168 256
WIRE 1408 256 1408 224
WIRE 1408 256 1328 256
WIRE 1456 256 1408 256
WIRE 1552 256 1520 256
WIRE 1712 256 1712 208
WIRE 1712 256 1632 256
WIRE 1776 256 1712 256
WIRE -480 272 -480 224
WIRE -160 272 -160 208
WIRE -160 272 -480 272
WIRE 16 272 16 208
WIRE 16 272 -160 272
WIRE 112 272 112 256
WIRE 112 272 16 272
WIRE -480 288 -480 272
WIRE 416 288 416 256
WIRE 848 288 848 256
WIRE 1200 288 1200 256
WIRE 1712 288 1712 256
WIRE 656 304 656 256
WIRE 1056 304 1056 256
WIRE 1408 304 1408 256
WIRE 848 384 848 368
WIRE 1200 384 1200 368
WIRE 656 400 656 384
WIRE 1056 400 1056 384
WIRE 1408 400 1408 384
WIRE 1712 400 1712 368
FLAG -480 288 0
FLAG -160 0 0
FLAG 656 400 0
FLAG 1776 256 Out
IOPIN 1776 256 Out
FLAG -160 -240 V+
FLAG 112 32 V+
FLAG 128 -208 Vr
FLAG 416 288 Vr
FLAG 560 -176 V+
FLAG 1056 400 0
FLAG 960 -176 V+
FLAG 848 384 Vr
FLAG 1408 400 0
FLAG 1312 -176 V+
FLAG 1200 384 Vr
FLAG 1712 400 0
FLAG 1712 32 0
FLAG -560 96 IN
IOPIN -560 96 In
SYMBOL voltage -160 -144 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V1
SYMATTR Value 9
SYMBOL voltage -480 128 M0
WINDOW 123 24 124 Left 2
WINDOW 39 24 152 Left 2
SYMATTR Value2 AC ac 1
SYMATTR SpiceLine Rser=11k
SYMATTR InstName V2
SYMATTR Value SINE(0 .07 440)
SYMBOL cap 0 144 R0
SYMATTR InstName C1
SYMATTR Value 150p
SYMBOL res -144 224 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R2
SYMATTR Value 1Meg
SYMBOL res 672 400 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R4
SYMATTR Value 4k7
SYMBOL diode 576 128 R180
WINDOW 0 24 64 Left 2
WINDOW 3 24 0 Left 2
SYMATTR InstName D1
SYMATTR Value 1N4148
SYMBOL res 576 -16 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R9
SYMATTR Value 4k7
SYMBOL pmos 608 224 M180
SYMATTR InstName M1
SYMATTR Value BS250P
SYMBOL res -16 80 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R11
SYMATTR Value 10k
SYMBOL cap -288 112 R270
WINDOW 0 32 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR InstName C3
SYMATTR Value 100n
SYMBOL njf 64 32 R0
SYMATTR InstName J1
SYMBOL res 96 272 M180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R1
SYMATTR Value 4k7
SYMBOL cap 240 128 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C2
SYMATTR Value 220n
SYMBOL res -128 -192 R270
WINDOW 0 32 56 VTop 2
WINDOW 3 0 56 VBottom 2
SYMATTR InstName R5
SYMATTR Value 10k
SYMBOL res -16 -176 R0
SYMATTR InstName R7
SYMATTR Value 9k1
SYMBOL cap 80 -80 M180
WINDOW 0 24 56 Left 2
WINDOW 3 24 8 Left 2
SYMATTR InstName C7
SYMATTR Value 10µ
SYMBOL res 400 160 R0
SYMATTR InstName Gain
SYMATTR Value 10k
SYMBOL cap 768 240 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C4
SYMATTR Value 22n
SYMBOL cap 672 -32 R180
WINDOW 0 24 56 Left 2
WINDOW 3 24 8 Left 2
SYMATTR InstName C5
SYMATTR Value 220n
SYMBOL res 1072 400 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R3
SYMATTR Value 4k7
SYMBOL diode 976 128 R180
WINDOW 0 24 64 Left 2
WINDOW 3 24 0 Left 2
SYMATTR InstName D2
SYMATTR Value 1N4148
SYMBOL res 976 -16 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R6
SYMATTR Value 4k7
SYMBOL pmos 1008 224 M180
SYMATTR InstName M2
SYMATTR Value BS250P
SYMBOL cap 1168 240 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C6
SYMATTR Value 22n
SYMBOL cap 1072 -32 R180
WINDOW 0 24 56 Left 2
WINDOW 3 24 8 Left 2
SYMATTR InstName C8
SYMATTR Value 10µ
SYMBOL res 864 384 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R13
SYMATTR Value 100k
SYMBOL res 1424 400 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R8
SYMATTR Value 4k7
SYMBOL diode 1328 128 R180
WINDOW 0 24 64 Left 2
WINDOW 3 24 0 Left 2
SYMATTR InstName D3
SYMATTR Value 1N4148
SYMBOL res 1328 -16 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R10
SYMATTR Value 4k7
SYMBOL cap 1520 240 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C9
SYMATTR Value 220n
SYMBOL cap 1424 -32 R180
WINDOW 0 24 56 Left 2
WINDOW 3 24 8 Left 2
SYMATTR InstName C10
SYMATTR Value 10µ
SYMBOL res 1216 384 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R15
SYMATTR Value 100k
SYMBOL pmos 1360 224 M180
SYMATTR InstName M3
SYMATTR Value BS250P
SYMBOL res 1728 384 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R12
SYMATTR Value 100k
SYMBOL res 1648 240 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R14
SYMATTR Value 22k
SYMBOL res 384 128 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName Gain1
SYMATTR Value 1
SYMBOL res 1728 224 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName Tone
SYMATTR Value 10k
SYMBOL cap 1728 112 R180
WINDOW 0 24 56 Left 2
WINDOW 3 24 8 Left 2
SYMATTR InstName C12
SYMATTR Value 100n
TEXT -472 -56 Left 2 !.tran 0 .1 .08
TEXT -472 -24 Left 2 !;.ac oct 16 10 50k
TEXT -472 -88 Left 2 !.param dr=500
(https://i.postimg.cc/xXzX3H86/PMOS-Jim.png) (https://postimg.cc/xXzX3H86)
^ I haven't, plus keep us posted
You can try it, since you have it on breadboard already! :icon_cool:
Quotecool, is that text inlay?
deadastronaut's website and effects are exceptional.
Even some vintage space puppet clips (I believe that is what they are).
I remember watching the Thunderbirds and Fireball XL5 back in the 60's.
Looking for BS250P to try as rankot suggests, Mouser will have them in April.
Newark has them in the UK, Amazon has them for $3.80 each, will wait.....
Maybe you can try with ZVP2106A? They're similar and cheaper. There are even more SMD parts, if you are willing to use them.
What puzzles me is the fact why are PMOS devices less noisy than NMOS (if they really are). The most part of the noise shall be generated by Rds(on), and that one is already low for NMOS parts (approx. 1.2 Ohm), while, one the other hand, for BS250P only maximum value of 14 Ohm is given in datasheet. I have few of AO3407A PMOS transistors with Rds(on) of only 50mOhm, so they should have unnoticeable noise figure, but I will have to find some time to test them.
How important is Vth in this case?
I can't answer the threshold question, maybe one of the others can...
Next to the LED....
Looking at the circuit on page one, what is the purpose of C13 (10u) ?
Is it in essence in parallel with C12 ?
If C13 was not there what might the effect be...
Of course I can try it, and will, but technically what does it do ?
C13 (i think) is an anti-LED-pop capacitor, which, as its name says, stops the LED, when triggered, from potentially making a pop.
R15, R7 and R8 are configured in a voltage divider to provide the mosfets with VDD (around 8.56v, as per schematic. R15 and C12 form a lowpass filter to filter PSU noise from 9v to VDD... or something along the lines of that... :icon_lol:
So no, C12 and C13 are not parallel with each other...
Thanks 11 90 an , your help is much appreciated.
Just finished: Little Jim MOSFET overdrive with P-MOS BS250 transistors, Vth is 3.1V. I made this PCB so it can be made with both N-MOS or P-MOS devices. Now I have to make N-MOS one so I can compare noise levels :)
Thanks Jonny, this one will be labeled as Little Jonny once I make a box for it!
(https://i.postimg.cc/v1XcJVwn/Little-Jim.jpg) (https://postimg.cc/v1XcJVwn)
It's the same one as in my schematic on previous page, but I have omitted D1 and D2. In case I decide to put some static electricity protection, which diodes do you guys suggest and where should I put 'em?
Jonny, how to choose the right bias? I have tried with trim pot there, and it sound reasonably good from approx 2.5 to 4.3V, but it also seems that bias affects low end - higher bias, more lows and lower bias, more highs. Is it normal (or I'm just trippin)?
Why not use three low noise BJTs after a higher input resistance follower. It can be SF or is can be another follower design.
Some thing from the past
https://www.diystompboxes.com/analogalchemy/sch/vulcan.html (https://www.diystompboxes.com/analogalchemy/sch/vulcan.html)
Also look at the Bee Baa and BMP, with BMP biasing think about how the gain is set you don't need the C to B to be 100k
Also an emitter degeneration BJT circuit without the emitter resistor bypass cap can be triode like
Quote from: rankot on March 07, 2021, 03:24:43 PM
Jonny, how to choose the right bias? I have tried with trim pot there, and it sound reasonably good from approx 2.5 to 4.3V, but it also seems that bias affects low end - higher bias, more lows and lower bias, more highs. Is it normal (or I'm just trippin)?
Yes I've noticed that too, the DC bias point seems to affect the perceived amount of bass in the signal. Generally with N channel devices I try to get the drain voltage between 2/3 and 3/4 of VDD. This gives the best looking signal on a scope with the top half of the waveform fat and rounded, and the bottom half cycle clipped pretty hard. From there, it's just a matter of personal taste. The audible difference is quite subtle until you get towards the extremes, both of which sound bad to my ears.
Quote from: Gus on March 07, 2021, 03:53:47 PM
Why not use three low noise BJTs after a higher input resistance follower. It can be SF or is can be another follower design.
Some thing from the past
https://www.diystompboxes.com/analogalchemy/sch/vulcan.html (https://www.diystompboxes.com/analogalchemy/sch/vulcan.html)
Also look at the Bee Baa and BMP, with BMP biasing think about how the gain is set you don't need the C to B to be 100k
Also an emitter degeneration BJT circuit without the emitter resistor bypass cap can be triode like
Yes, I've done guitar preamp designs with BJTs and more often JFETs. The Little Jim was specifically an attempt to see if I could make something simple work with MOSFETs, since I wasn't aware anybody had done that at the time (I subsequently found out about the box of rock which is a similar idea but voiced differently). You get a more aggressive, crunchy sound with MOSFETs compared with JFETs which works well but it's not subtle.
For using BJTs the Peavey Transtube style circuit works really nicely in my opinion. The Vulcan is a nice circuit but again, it's a bit noisy, and the bias is tricky to get just right.
My "go to" approach will always be NJFETs. I love the sound of them.
https://www.diystompboxes.com/smfforum/index.php?topic=123572 (https://www.diystompboxes.com/smfforum/index.php?topic=123572)
https://www.diystompboxes.com/smfforum/index.php?topic=118627 (https://www.diystompboxes.com/smfforum/index.php?topic=118627)
Quote from: jonny.reckless on March 09, 2021, 02:09:05 AM
Yes I've noticed that too, the DC bias point seems to affect the perceived amount of bass in the signal. Generally with N channel devices I try to get the drain voltage between 2/3 and 3/4 of VDD. This gives the best looking signal on a scope with the top half of the waveform fat and rounded, and the bottom half cycle clipped pretty hard. From there, it's just a matter of personal taste. The audible difference is quite subtle until you get towards the extremes, both of which sound bad to my ears.
OK, I will try to check this on scope, this description is quite useful! What is position of Gain pot for that? I tried to match simulated waveform of NMOS circuit, but it is more like symmetrical clipped signal with gain at max. Like this:
(https://i.postimg.cc/McfBD156/LJNMOS.jpg) (https://postimg.cc/McfBD156)
Hello Ranko,
I was going to input Little Jim into LTSPICE
is it possible that you share your file with BS170s
Thanks.
NMOS version:
Version 4
SHEET 1 3204 680
WIRE -160 -208 -160 -240
WIRE -112 -208 -160 -208
WIRE 0 -208 -32 -208
WIRE 96 -208 0 -208
WIRE 128 -208 96 -208
WIRE 0 -160 0 -208
WIRE 96 -144 96 -208
WIRE 560 -144 560 -176
WIRE 656 -144 560 -144
WIRE 960 -144 960 -176
WIRE 1056 -144 960 -144
WIRE 1312 -144 1312 -176
WIRE 1408 -144 1312 -144
WIRE -160 -128 -160 -208
WIRE 560 -96 560 -144
WIRE 656 -96 656 -144
WIRE 960 -96 960 -144
WIRE 1056 -96 1056 -144
WIRE 1312 -96 1312 -144
WIRE 1408 -96 1408 -144
WIRE -160 -16 -160 -48
WIRE 0 -16 0 -80
WIRE 0 -16 -160 -16
WIRE 96 -16 96 -80
WIRE 96 -16 0 -16
WIRE -160 0 -160 -16
WIRE 560 48 560 -16
WIRE 656 48 656 -32
WIRE 656 48 560 48
WIRE 720 48 656 48
WIRE 848 48 784 48
WIRE 960 48 960 -16
WIRE 1056 48 1056 -32
WIRE 1056 48 960 48
WIRE 1088 48 1056 48
WIRE 1200 48 1152 48
WIRE 1312 48 1312 -16
WIRE 1408 48 1408 -32
WIRE 1408 48 1312 48
WIRE 1456 48 1408 48
WIRE 1712 48 1712 32
WIRE 656 64 656 48
WIRE 1056 64 1056 48
WIRE 1408 64 1408 48
WIRE -480 96 -560 96
WIRE -288 96 -480 96
WIRE -160 96 -224 96
WIRE -112 96 -160 96
WIRE 16 96 -32 96
WIRE 64 96 16 96
WIRE -160 128 -160 96
WIRE 1712 128 1712 112
WIRE -480 144 -480 96
WIRE 16 144 16 96
WIRE 112 144 112 128
WIRE 176 144 112 144
WIRE 288 144 240 144
WIRE 400 144 368 144
WIRE 608 144 400 144
WIRE 848 144 848 48
WIRE 1008 144 848 144
WIRE 1200 144 1200 48
WIRE 1360 144 1200 144
WIRE 112 176 112 144
WIRE 400 176 400 144
WIRE 1408 224 1408 160
WIRE 1408 224 1328 224
WIRE 576 240 576 224
WIRE 656 240 656 160
WIRE 656 240 576 240
WIRE 976 240 976 224
WIRE 1056 240 1056 160
WIRE 1056 240 976 240
WIRE 1456 256 1456 48
WIRE 1552 256 1520 256
WIRE 1712 256 1712 208
WIRE 1712 256 1632 256
WIRE 1776 256 1712 256
WIRE -480 272 -480 224
WIRE -160 272 -160 208
WIRE -160 272 -480 272
WIRE 16 272 16 208
WIRE 16 272 -160 272
WIRE 112 272 112 256
WIRE 112 272 16 272
WIRE 576 272 576 240
WIRE 656 272 656 240
WIRE 848 272 848 144
WIRE 1056 272 1056 240
WIRE 1200 272 1200 144
WIRE 1408 272 1408 224
WIRE -480 288 -480 272
WIRE 400 288 400 256
WIRE 1328 288 1328 224
WIRE 1712 288 1712 256
WIRE 976 304 976 240
WIRE 576 384 576 336
WIRE 656 384 656 352
WIRE 656 384 576 384
WIRE 848 384 848 352
WIRE 976 384 976 368
WIRE 1056 384 1056 352
WIRE 1056 384 976 384
WIRE 1200 384 1200 352
WIRE 1328 384 1328 352
WIRE 1408 384 1408 352
WIRE 1408 384 1328 384
WIRE 656 400 656 384
WIRE 1056 400 1056 384
WIRE 1408 400 1408 384
WIRE 1712 400 1712 368
FLAG -480 288 0
FLAG -160 0 0
FLAG 656 400 0
FLAG 1776 256 Out
IOPIN 1776 256 Out
FLAG -160 -240 V+
FLAG 112 32 V+
FLAG 128 -208 Vr
FLAG 400 288 Vr
FLAG 560 -176 V+
FLAG 1056 400 0
FLAG 960 -176 V+
FLAG 848 384 Vr
FLAG 1408 400 0
FLAG 1312 -176 V+
FLAG 1200 384 Vr
FLAG 1712 400 0
FLAG 1712 32 0
FLAG -560 96 IN
IOPIN -560 96 In
SYMBOL voltage -160 -144 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V1
SYMATTR Value 9
SYMBOL voltage -480 128 M0
WINDOW 123 24 124 Left 2
WINDOW 39 24 152 Left 2
SYMATTR Value2 AC ac 1
SYMATTR SpiceLine Rser=11k
SYMATTR InstName V2
SYMATTR Value SINE(0 .07 440)
SYMBOL cap 0 144 R0
SYMATTR InstName C1
SYMATTR Value 150p
SYMBOL res -144 224 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R2
SYMATTR Value 1Meg
SYMBOL res 672 368 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R4
SYMATTR Value 4k7
SYMBOL res 576 0 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R9
SYMATTR Value 4k7
SYMBOL res -16 80 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R11
SYMATTR Value 10k
SYMBOL cap -288 112 R270
WINDOW 0 32 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR InstName C3
SYMATTR Value 100n
SYMBOL njf 64 32 R0
SYMATTR InstName J1
SYMATTR Value J112
SYMBOL res 96 272 M180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R1
SYMATTR Value 4k7
SYMBOL cap 240 128 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C2
SYMATTR Value 220n
SYMBOL res -128 -192 R270
WINDOW 0 32 56 VTop 2
WINDOW 3 0 56 VBottom 2
SYMATTR InstName R5
SYMATTR Value 10k
SYMBOL res -16 -176 R0
SYMATTR InstName R7
SYMATTR Value 8k2
SYMBOL cap 80 -80 M180
WINDOW 0 24 56 Left 2
WINDOW 3 24 8 Left 2
SYMATTR InstName C7
SYMATTR Value 10µ
SYMBOL res 384 160 R0
SYMATTR InstName Gain
SYMATTR Value 10k
SYMBOL cap 784 32 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C4
SYMATTR Value 22n
SYMBOL cap 592 336 R180
WINDOW 0 24 56 Left 2
WINDOW 3 24 8 Left 2
SYMATTR InstName C5
SYMATTR Value 220n
SYMBOL res 1072 368 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R3
SYMATTR Value 4k7
SYMBOL res 976 0 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R6
SYMATTR Value 4k7
SYMBOL cap 1152 32 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C6
SYMATTR Value 22n
SYMBOL cap 992 368 R180
WINDOW 0 24 56 Left 2
WINDOW 3 24 8 Left 2
SYMATTR InstName C8
SYMATTR Value 10µ
SYMBOL res 864 368 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R13
SYMATTR Value 100k
SYMBOL res 1424 368 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R8
SYMATTR Value 4k7
SYMBOL res 1328 0 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R10
SYMATTR Value 4k7
SYMBOL cap 1520 240 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C9
SYMATTR Value 220n
SYMBOL cap 1344 352 R180
WINDOW 0 24 56 Left 2
WINDOW 3 24 8 Left 2
SYMATTR InstName C10
SYMATTR Value 10µ
SYMBOL res 1216 368 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R15
SYMATTR Value 100k
SYMBOL res 1728 384 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R12
SYMATTR Value 100k
SYMBOL res 1648 240 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R14
SYMATTR Value 22k
SYMBOL res 384 128 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName Gain1
SYMATTR Value 1
SYMBOL res 1728 224 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName Tone
SYMATTR Value 10k
SYMBOL cap 1728 112 R180
WINDOW 0 24 56 Left 2
WINDOW 3 24 8 Left 2
SYMATTR InstName C12
SYMATTR Value 100n
SYMBOL nmos 608 64 R0
SYMATTR InstName M1
SYMATTR Value BS170
SYMBOL nmos 1008 64 R0
SYMATTR InstName M2
SYMATTR Value BS170
SYMBOL nmos 1360 64 R0
SYMATTR InstName M3
SYMATTR Value BS170
SYMBOL zener 592 224 R180
WINDOW 0 24 64 Left 2
WINDOW 3 24 0 Left 0
SYMATTR InstName D1
SYMATTR Value BZX84C15L
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL zener 992 224 R180
WINDOW 0 24 64 Left 2
WINDOW 3 24 0 Left 0
SYMATTR InstName D2
SYMATTR Value BZX84C15L
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL zener 1344 224 R180
WINDOW 0 24 64 Left 2
WINDOW 3 24 0 Left 0
SYMATTR InstName D3
SYMATTR Value BZX84C15L
SYMATTR Description Diode
SYMATTR Type diode
TEXT -472 -56 Left 2 !.tran 0 .1 .08
TEXT -472 -24 Left 2 !;.ac oct 16 10 50k
TEXT -472 -88 Left 2 !.param dr=500
TEXT -488 352 Left 2 ;ALOG
TEXT -408 352 Left 2 !;.step param Rx list 1 180k 360k 540k 720k 900k 920k 940k 965k 999k
TEXT 1544 -96 Left 2 !;.noise Out In oct 32 10 20k
PMOS version:
Version 4
SHEET 1 3204 680
WIRE -160 -208 -160 -240
WIRE -112 -208 -160 -208
WIRE 0 -208 -32 -208
WIRE 96 -208 0 -208
WIRE 128 -208 96 -208
WIRE 0 -160 0 -208
WIRE 96 -144 96 -208
WIRE 560 -144 560 -176
WIRE 656 -144 560 -144
WIRE 960 -144 960 -176
WIRE 1056 -144 960 -144
WIRE 1312 -144 1312 -176
WIRE 1408 -144 1312 -144
WIRE -160 -128 -160 -208
WIRE 560 -112 560 -144
WIRE 960 -112 960 -144
WIRE 1312 -112 1312 -144
WIRE 656 -96 656 -144
WIRE 1056 -96 1056 -144
WIRE 1408 -96 1408 -144
WIRE -160 -16 -160 -48
WIRE 0 -16 0 -80
WIRE 0 -16 -160 -16
WIRE 96 -16 96 -80
WIRE 96 -16 0 -16
WIRE -160 0 -160 -16
WIRE 560 48 560 -32
WIRE 656 48 656 -32
WIRE 656 48 560 48
WIRE 960 48 960 -32
WIRE 1056 48 1056 -32
WIRE 1056 48 960 48
WIRE 1312 48 1312 -32
WIRE 1408 48 1408 -32
WIRE 1408 48 1312 48
WIRE 1712 48 1712 32
WIRE 1312 64 1312 48
WIRE -480 96 -560 96
WIRE -288 96 -480 96
WIRE -160 96 -224 96
WIRE -112 96 -160 96
WIRE 16 96 -32 96
WIRE 64 96 16 96
WIRE -160 128 -160 96
WIRE 656 128 656 48
WIRE 1056 128 1056 48
WIRE 1408 128 1408 48
WIRE 1712 128 1712 112
WIRE -480 144 -480 96
WIRE 16 144 16 96
WIRE 112 144 112 128
WIRE 176 144 112 144
WIRE 288 144 240 144
WIRE 416 144 368 144
WIRE 560 144 560 128
WIRE 560 144 416 144
WIRE 608 144 560 144
WIRE 960 144 960 128
WIRE 960 144 848 144
WIRE 1008 144 960 144
WIRE 1312 144 1312 128
WIRE 1312 144 1200 144
WIRE 1360 144 1312 144
WIRE 112 176 112 144
WIRE 416 176 416 144
WIRE 656 256 656 224
WIRE 704 256 656 256
WIRE 848 256 848 144
WIRE 848 256 768 256
WIRE 1056 256 1056 224
WIRE 1104 256 1056 256
WIRE 1200 256 1200 144
WIRE 1200 256 1168 256
WIRE 1408 256 1408 224
WIRE 1408 256 1328 256
WIRE 1456 256 1408 256
WIRE 1552 256 1520 256
WIRE 1712 256 1712 208
WIRE 1712 256 1632 256
WIRE 1776 256 1712 256
WIRE -480 272 -480 224
WIRE -160 272 -160 208
WIRE -160 272 -480 272
WIRE 16 272 16 208
WIRE 16 272 -160 272
WIRE 112 272 112 256
WIRE 112 272 16 272
WIRE -480 288 -480 272
WIRE 416 288 416 256
WIRE 848 288 848 256
WIRE 1200 288 1200 256
WIRE 1712 288 1712 256
WIRE 656 304 656 256
WIRE 1056 304 1056 256
WIRE 1328 304 1328 256
WIRE 1408 304 1408 256
WIRE 848 384 848 368
WIRE 1200 384 1200 368
WIRE 656 400 656 384
WIRE 1056 400 1056 384
WIRE 1328 400 1328 368
WIRE 1408 400 1408 384
WIRE 1712 400 1712 368
FLAG -480 288 0
FLAG -160 0 0
FLAG 656 400 0
FLAG 1776 256 Out
IOPIN 1776 256 Out
FLAG -160 -240 V+
FLAG 112 32 V+
FLAG 128 -208 Vr
FLAG 416 288 Vr
FLAG 560 -176 V+
FLAG 1056 400 0
FLAG 960 -176 V+
FLAG 848 384 Vr
FLAG 1408 400 0
FLAG 1312 -176 V+
FLAG 1200 384 Vr
FLAG 1712 400 0
FLAG 1712 32 0
FLAG -560 96 IN
IOPIN -560 96 In
FLAG 1328 400 0
SYMBOL voltage -160 -144 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V1
SYMATTR Value 9
SYMBOL voltage -480 128 M0
WINDOW 123 24 124 Left 2
WINDOW 39 24 152 Left 2
SYMATTR Value2 AC ac 1
SYMATTR SpiceLine Rser=11k
SYMATTR InstName V2
SYMATTR Value SINE(0 .07 440)
SYMBOL cap 0 144 R0
SYMATTR InstName C1
SYMATTR Value 150p
SYMBOL res -144 224 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R2
SYMATTR Value 1Meg
SYMBOL res 672 400 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R4
SYMATTR Value 4k7
SYMBOL diode 576 128 R180
WINDOW 0 24 64 Left 2
WINDOW 3 24 0 Left 2
SYMATTR InstName D1
SYMATTR Value 1N4148
SYMBOL res 576 -16 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R9
SYMATTR Value 4k7
SYMBOL pmos 608 224 M180
SYMATTR InstName M1
SYMATTR Value BS250P
SYMBOL res -16 80 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R11
SYMATTR Value 10k
SYMBOL cap -288 112 R270
WINDOW 0 32 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR InstName C3
SYMATTR Value 100n
SYMBOL njf 64 32 R0
WINDOW 3 60 3 Left 2
SYMATTR Value J112
SYMATTR InstName J1
SYMBOL res 96 272 M180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R1
SYMATTR Value 4k7
SYMBOL cap 240 128 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C2
SYMATTR Value 220n
SYMBOL res -128 -192 R270
WINDOW 0 32 56 VTop 2
WINDOW 3 0 56 VBottom 2
SYMATTR InstName R5
SYMATTR Value 9k1
SYMBOL res -16 -176 R0
SYMATTR InstName R7
SYMATTR Value 10k
SYMBOL cap 80 -80 M180
WINDOW 0 24 56 Left 2
WINDOW 3 24 8 Left 2
SYMATTR InstName C7
SYMATTR Value 10µ
SYMBOL res 400 160 R0
SYMATTR InstName Gain
SYMATTR Value 10k
SYMBOL cap 768 240 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C4
SYMATTR Value 22n
SYMBOL cap 672 -32 R180
WINDOW 0 24 56 Left 2
WINDOW 3 24 8 Left 2
SYMATTR InstName C5
SYMATTR Value 220n
SYMBOL res 1072 400 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R3
SYMATTR Value 4k7
SYMBOL diode 976 128 R180
WINDOW 0 24 64 Left 2
WINDOW 3 24 0 Left 2
SYMATTR InstName D2
SYMATTR Value 1N4148
SYMBOL res 976 -16 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R6
SYMATTR Value 4k7
SYMBOL pmos 1008 224 M180
SYMATTR InstName M2
SYMATTR Value BS250P
SYMBOL cap 1168 240 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C6
SYMATTR Value 22n
SYMBOL cap 1072 -32 R180
WINDOW 0 24 56 Left 2
WINDOW 3 24 8 Left 2
SYMATTR InstName C8
SYMATTR Value 10µ
SYMBOL res 864 384 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R13
SYMATTR Value 100k
SYMBOL res 1424 400 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R8
SYMATTR Value 4k7
SYMBOL diode 1328 128 R180
WINDOW 0 24 64 Left 2
WINDOW 3 24 0 Left 2
SYMATTR InstName D3
SYMATTR Value 1N4148
SYMBOL res 1328 -16 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R10
SYMATTR Value 4k7
SYMBOL cap 1520 240 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C9
SYMATTR Value 220n
SYMBOL cap 1424 -32 R180
WINDOW 0 24 56 Left 2
WINDOW 3 24 8 Left 2
SYMATTR InstName C10
SYMATTR Value 10µ
SYMBOL res 1216 384 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R15
SYMATTR Value 100k
SYMBOL pmos 1360 224 M180
SYMATTR InstName M3
SYMATTR Value BS250P
SYMBOL res 1728 384 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R12
SYMATTR Value 100k
SYMBOL res 1648 240 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R14
SYMATTR Value 22k
SYMBOL res 384 128 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName Gain1
SYMATTR Value 1
SYMBOL res 1728 224 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName Tone
SYMATTR Value 10k
SYMBOL cap 1728 112 R180
WINDOW 0 24 56 Left 2
WINDOW 3 24 8 Left 2
SYMATTR InstName C12
SYMATTR Value 100n
SYMBOL cap 1344 368 R180
WINDOW 0 24 56 Left 2
WINDOW 3 24 8 Left 2
SYMATTR InstName C11
SYMATTR Value 10n
TEXT -472 -56 Left 2 !.tran 0 .1 .08
TEXT -472 -24 Left 2 !;.ac oct 16 10 50k
TEXT -472 -88 Left 2 !.param dr=500
Sorry for the late response, I was on a summer holiday! :icon_mrgreen:
Thanks for the LTSPICE files
I can now see the same schematic that you posted
(https://i.postimg.cc/McfBD156/LJNMOS.jpg) (https://postimg.cc/McfBD156)
A) When I ran it, it said BS170 model not found, so I added this directive:
.model BS170 VDMOS VTO=1.824 RG=270 RS=1.572 RD=1.436 RB=.768 KP=.1233 Cgdmax=20p Cgdmin=3p CGS=28p Cjo=35p Rds=1.2E8 IS=5p Bv=60 Ibv=10u Tt=161.6n
Does this match the model you used ?
B) I see that there is place near R9, R6 and R10. Is that for you to try out capacitors ? What works best ?
C) I see that the Zeners are not connected. Is that correct ?
D) Please teach me about the noise analysis you did. Thanks
E) I get the "Mid Hump" at around 20Khz !! Do my results match yours ?
Just out of curiosity - how does one take the list that Rankot posted and import it to LT Spice? I've never had the need to do this, but now I am interested :) Thx
Copy it from here
make a new text file
call it "NMOS Little Jim.asc"
Paste the text into it
Open with LTSPICE
find that some models are missing
Find that some characters are not in the correct character set and cause peoblems
fix the problems
Thank the person who posted the Net List
Sorry, I thougth those MOSFET models are part of the standard library. I have them there like this:
.model BS170 VDMOS (VTO=1.824 RG=270 RS=1.572 RD=1.436 RB=.768 KP=.1233 Cgdmax=20p Cgdmin=3p CGS=28p Cjo=35p Rds=1.2E8 IS=5p Bv=60 Ibv=10u Tt=161.6n mfg=Fairchild Vds=60 Ron=1.5)
.model BS250P VDMOS (pchan Rg=160 VTO=-3.193 RS=2.041 RD=0.697 IS=2E-13 KP=0.277 Cjo=105p LAMBDA=1.2E-2 RB=0.309 Rds=1.2E8 Cgdmax=57p Cgdmin=5p CGS=47p TT=86.56n BV=45 IBV=10u mfg=Fairchild Vds=-45 Ron=14 Qg=1.8n)
Zenners are there to protect MOSFET in real life, I just wanted to see if that kind of protection affects the tone.
Empty space around those resistors in NMOS version are simply there because I was too lazy to erase lines. If you compare N/PMOS versions, you will see those capacitors are on their places.
I copied that noise analysis line from somebody other's file, but didn't run it yet. :-[
I don't get a hump, and at 20kHz it certainly can't be mids :)
(https://i.postimg.cc/V0fsZBrG/n-pmos.jpg) (https://postimg.cc/V0fsZBrG)
I will try again, using your models
Quote from: jonny.reckless on March 09, 2021, 02:11:19 AM
Quote from: Gus on March 07, 2021, 03:53:47 PM
Why not use three low noise BJTs after a higher input resistance follower. It can be SF or is can be another follower design.
Some thing from the past
https://www.diystompboxes.com/analogalchemy/sch/vulcan.html (https://www.diystompboxes.com/analogalchemy/sch/vulcan.html)
Also look at the Bee Baa and BMP, with BMP biasing think about how the gain is set you don't need the C to B to be 100k
Also an emitter degeneration BJT circuit without the emitter resistor bypass cap can be triode like
Yes, I've done guitar preamp designs with BJTs and more often JFETs. The Little Jim was specifically an attempt to see if I could make something simple work with MOSFETs, since I wasn't aware anybody had done that at the time (I subsequently found out about the box of rock which is a similar idea but voiced differently). You get a more aggressive, crunchy sound with MOSFETs compared with JFETs which works well but it's not subtle.
For using BJTs the Peavey Transtube style circuit works really nicely in my opinion. The Vulcan is a nice circuit but again, it's a bit noisy, and the bias is tricky to get just right.
My "go to" approach will always be NJFETs. I love the sound of them.
https://www.diystompboxes.com/smfforum/index.php?topic=123572 (https://www.diystompboxes.com/smfforum/index.php?topic=123572)
https://www.diystompboxes.com/smfforum/index.php?topic=118627 (https://www.diystompboxes.com/smfforum/index.php?topic=118627)
I'vr recently made a DIY version of an AMT soldano clone with JFETs. AMT has An interesting way to simulate tubes with JFETs and I've been wondering if the same technology could be used to create a circuit with the sound of little Jim but less noise. One things in which the AMT circuit excels is low noise at high gain, but I love the tone of the little Jim. What do you think?
Please post link to the AMT Soldano schematic.
Thanks
Quote from: Vivek on September 23, 2021, 07:29:56 AM
Please post link to the AMT Soldano schematic.
Thanks
https://tinyurl.com/yutwzm8x
transistors: 2SK208-R
Better have a look at this link https://guitar-gear.ru/forum/index.php?app=core&module=attach§ion=attach&attach_id=39108
The S2 is the Soldano and slightly updated version of what was posted earlier. jFETs are indeed 2SK208-R.
I believe it is mainly the J177 paired with the SK208R (OR equivalent 2sk30) that allows to achieve a more specific type of asymmetry in the saturation curve.
Thank you Temol and Rutgerv !
I am on a quest to analyse as many AIAB as possible.
Phew this schematic is big, it might take me a week to enter into spice.
One thing we discovered on an earlier thread,
If later stages are too hard symmetrical clipping, they wipe out all effects of earlier asymmetric clipping.
Don't bother putting everything into Spice, the first page contains the buffering, switching and clean amp that is the same throughout the whole Legend series. The part that counts for Tone is the S2 section of the schematic. I've also been able to reverse engineer the Vt2 from the same series and while very close to the S2 it has a bit more body in the mid range. Also here the lack of noise at high gain is impressive.