In response to the Little Jim MOSFET distortion circuit https://www.diystompboxes.com/smfforum/index.php?topic=125174.msg1190435#msg1190435 (https://www.diystompboxes.com/smfforum/index.php?topic=125174.msg1190435#msg1190435), I was asked if I could maybe use the LND150 depletion mode MOSFET in a distortion pedal design, as it might be less hissy. The Moon LNDer is what I managed to come up with. It comprises 3 common source gain stages in series, with a James style EQ at the end of the chain. It has less gain than the Little Jim, and is more from clean to mid gain than heavy distortion, but it responds nicely to playing dynamics. The two band James EQ is more flexible than a simple tone control and lets you match it to the input of your amp more easily. There's noticeably less hiss than when using BS170 MOSFETs which is nice. The LND150 has much lower input capacitance than the BS170 so I was able to get away without a unity gain source follower on the input, instead just connecting to the first gain stage directly, without too much tone suck.
(https://i.postimg.cc/pm06jXKV/moonlander-schematic.png) (https://postimg.cc/pm06jXKV)
(https://i.postimg.cc/GBWzPBtR/PXL-20201107-231305370-PORTRAIT-01-COVER.jpg) (https://postimg.cc/GBWzPBtR)
(https://i.postimg.cc/HrKFKknZ/PXL-20201107-231314836-PORTRAIT-01-COVER.jpg) (https://postimg.cc/HrKFKknZ)
(https://i.postimg.cc/1gqbZ1N9/PXL-20201107-231322597-PORTRAIT-01-COVER.jpg) (https://postimg.cc/1gqbZ1N9)
(https://i.postimg.cc/jDCGZ7xn/PXL-20201107-231334583-PORTRAIT-01-COVER.jpg) (https://postimg.cc/jDCGZ7xn)
(https://i.postimg.cc/MMJN63y1/PXL-20201107-231340446-PORTRAIT-01-COVER.jpg) (https://postimg.cc/MMJN63y1)
Here is a video demo of the Moon LNDer in action:
The signal chain is guitar -> moon LNDer -> Two notes Torpedo CAB M (loaded with Celestion G12M impulse response) -> Strymon reverb -> PC.
SOUNDS GREAT!!!
wouldn't you place the bass control before the distortion/clipping instead of after? i always wondered why no one seems to do that, especially with lower gain overdrive circuits, to give it more versatility in the character of the drive.
cheers, Iain
edit: what range would i need to expect the source voltages to be? 0,8-ish volt?
i wonder what diode bias would sound like on a MOSFET circuit, i really like the sound on JFET circuits, a certain growl that resistive bias doesn't do.
Quote from: iainpunk on November 08, 2020, 09:52:44 AM
SOUNDS GREAT!!!
wouldn't you place the bass control before the distortion/clipping instead of after? i always wondered why no one seems to do that, especially with lower gain overdrive circuits, to give it more versatility in the character of the drive.
cheers, Iain
edit: what range would i need to expect the source voltages to be? 0,8-ish volt?
i wonder what diode bias would sound like on a MOSFET circuit, i really like the sound on JFET circuits, a certain growl that resistive bias doesn't do.
I would not say no one does that thing with bass control before clipping. I always do that, if I have a bass control at all.
Care to share a design with diode source bias?
@Johnny
Great design! I've been meaning to track down some useful DMOS devices for use as variable resistors. Seems like these may be useable for my purpose, although I whish the on-resistance was a bit lower but I can probably design around that. Maybe.
Andy
this is a SRPP gain stage which is really cool, it has high gain and soft clipping, great as a starting point for most of my designs. the biggest downside is the relatively high quensient current and the need for somewhat matched-ish jfets. if you put 2 after each other, you get a nice gainey distortion. i have only tried it with BF245's since i have a bunch of those (near 50) and no other Jfet's, but i believe that if they are somewhat close in Beta, they should work.
(https://i.postimg.cc/BPHkvr8W/gainstage.png) (https://postimg.cc/BPHkvr8W)
cheers, Iain
Quote from: jonny.reckless on November 07, 2020, 09:13:57 PM
In response to the Little Jim MOSFET distortion circuit https://www.diystompboxes.com/smfforum/index.php?topic=125174.msg1190435#msg1190435 (https://www.diystompboxes.com/smfforum/index.php?topic=125174.msg1190435#msg1190435), I was asked if I could maybe use the LND150 depletion mode MOSFET in a distortion pedal design, as it might be less hissy. The Moon LNDer is what I managed to come up with. It comprises 3 common source gain stages in series, with a James style EQ at the end of the chain. It has less gain than the Little Jim, and is more from clean to mid gain than heavy distortion, but it responds nicely to playing dynamics. The two band James EQ is more flexible than a simple tone control and lets you match it to the input of your amp more easily. There's noticeably less hiss than when using BS170 MOSFETs which is nice. The LND150 has much lower input capacitance than the BS170 so I was able to get away without a unity gain source follower on the input, instead just connecting to the first gain stage directly, without too much tone suck.
I'm amazed how quickly you managed to make a prototype of this! :o
I bought a bag of 50 LND150 from mouser. They were very closely matched, all within 50mV of each other for VGSoff. Much closer matching than you normally get with JFETs. In this circuit I'm running around -0.8V on the gate for a current of approx 200uA. This seemed to be the sweet spot for these devices in terms of getting a nice looking waveform with lots of second harmonic. The lack of gate current means you don't need to worry about blocking distortion.
I noticed the audio is a bit out of sync with the video, no big deal for a pedal demo of course, but a small tip is to clap at the beginning of the video and use that distinctive point to sync the A/V (and then remove the beginning of the video, to just before the actual video starts) ;)
Nice demo!
Have you tried to run it at 18V, for example?
Sounds great! Plenty of gain to my ear, and really nice as an MIAB. Time to order some of those LNDs.
Quote from: rankot on November 09, 2020, 04:06:05 AM
Nice demo!
Have you tried to run it at 18V, for example?
I did briefly, it didn't sound as good as with 9V, I presume I would need to readjust the bias points for 18V operation.
By increasing R7 to 100k and R6 to 47k, I was able to get a bit higher gain out of the circuit without having to add an extra gain stage. Here's a quick demo, recorded with my phone camera and mic, into a Blackstar HT20 set to clean.
Quote from: jonny.reckless on November 09, 2020, 09:06:16 PM
By increasing R7 to 100k and R6 to 47k, I was able to get a bit higher gain out of the circuit without having to add an extra gain stage.
Did you have to rebias? If not, double-pole switch, Rock/Metal.
Quote from: willienillie on November 09, 2020, 11:35:06 PM
Quote from: jonny.reckless on November 09, 2020, 09:06:16 PM
By increasing R7 to 100k and R6 to 47k, I was able to get a bit higher gain out of the circuit without having to add an extra gain stage.
Did you have to rebias? If not, double-pole switch, Rock/Metal.
Just those two resistor changes, so it could be done with a DPDT switch. It gives about another 6dB or so of gain; just enough to take it into classic lead territory.
Quote from: jonny.reckless on November 10, 2020, 12:29:15 AMBy increasing R7 to 100k and R6 to 47k, I was able to get a bit higher gain out of the circuit without having to add an extra gain stage..... another 6dB or so of gain....
In JFETs, voltage gain goes about as inverse of square-root of current. For similar voltage bias, R7 from 10k to 100k implies 1/10th the current and 3.16 times the gain, 10dB. R8 will shave that some, and this is not a JFET, but yeah "6dB or so" is expectable. And a clever place to find free gain.
The "drawback" is less extended treble. But the LND150 has 12AX7-like capacitances (it's not one of those monster MOSFETs), and 100k will support well beyond the guitar band.
Quote from: PRR on November 10, 2020, 12:41:42 AM
In JFETs, voltage gain goes about as inverse of square-root of current. For similar voltage bias, R7 from 10k to 100k implies 1/10th the current and 3.16 times the gain, 10dB. R8 will shave that some, and this is not a JFET, but yeah "6dB or so" is expectable. And a clever place to find free gain.
The "drawback" is less extended treble. But the LND150 has 12AX7-like capacitances (it's not one of those monster MOSFETs), and 100k will support well beyond the guitar band.
Thanks. I didn't really notice any more treble roll off, the output stage rolls off pretty early anyway to tame the fizz. I actually like the LND150 - it's kind of JFET like in its behavior and tone, low capacitance (at least compared with the BS170) so you can couple the guitar straight into a common source gain stage and not get killed by Miller capacitance. Also you don't have to worry about blocking distortion or weird bias shifts due to the gate current as you would in a JFET or BJT design. And from my limited experience, they do seem pretty quiet too - certainly much less hissy than the BS170 / 2N7000, and comparable to J113s which have been my go to FET for guitar preamp circuits for about 25 years. I might start developing a few preamp ideas around the LND150 :)
Readily sold as thru-hole for a half-buck. Worth putting on the idiots palette. My idiot is old so needs syntax tweaks.
*LND150 MODEL, from MicroChip, edited for Cadence/ORcad Pspice 9.1, (C)1999
*
.MODEL LND150 NMOS (
LEVEL=3
RS=150.00
NSUB=5.0E13
DELTA=0.1
KAPPA=1.O
TPG=1
CGDO=2.1716E-12
RD=40.0
VTO=-2.0
VMAX=1.0E8
ETA=0.1
NFS=6.6E10
TOX=1.0E-7
LD=1.698E-9
UO=862.425
XJ=6.4666E-7
THETA=1.0E-5
CGSO=5.09E-10
L=10.0E-6
W=600E-6)
* .ENDS
*
There IS a well-known MOS model quirk right at VTO: a kink in what should be a monotonic curve. But it is at 1 micro-Amp so should be moot for audio. (The model takes VTO too literally while the crystal is more gradual.)
(https://i.postimg.cc/0Kyfxhmk/LND150-kink-42.gif) (https://postimg.cc/0Kyfxhmk)
Quote from: jonny.reckless on November 10, 2020, 01:41:01 AM...I didn't really notice any more treble roll off...
You wouldn't. Because you follow Leo's feetsteps.
High-Mu triode, plate resistor 470k gives AM-radio treble (we don't like static). 270k gives a little less gain and more treble, Often seen on Gibson. After some fluttering, Leo Fender tended to use the 100k plate resistors. Taking 220k and 100pFd load this runs about -3dB @ 40KC (kHz), or 1dB at 20kHz, for one stage. "Too good" except a g-amp is multiple stages. Apparently Leo or his cohort could hear the difference 100k or something higher. Probably by a rising response not rising through cascaded -1dB@5KC stages.
Was googling about replacing tubes with bjts (you know, I try to make everything not BJT into BJT... due to availability ::)) and found this comment by merlin...
https://www.diystompboxes.com/smfforum/index.php?topic=108690.20
Check out reply 28...
Sorry not as related to topic, but wanted to share... :icon_mrgreen:
I know this is out of topic, but I can't find the answer myself, and I need your help - I plan to use LND150 as a source follower in my build of Alembic F2b, so I can have lower output impedance. Will it be OK to put it there, no hi freq loss? I tried to simulate this, and it seems to be fine.
hi Jonny Tell us about your impressions and experiences. I see the advantages of the LND150 over the Jfet in that there is no need to adjust the offset, apparently the minimum variation in parameters. How is the LND150 doing with the usual MOSFet problems? I noticed that you used a zener for static protection, is this transistor protected? I did not see the input capacitor in the first stage, usually such transistors do not work without a capacitor at the gate. What can you say about the difference in sound compared to regular Jfet? I was disappointed with the sound of the BS170 / 2N7000 due to their capacity.
Quote from: POTL on April 12, 2021, 07:46:09 AM
hi Jonny Tell us about your impressions and experiences. I see the advantages of the LND150 over the Jfet in that there is no need to adjust the offset, apparently the minimum variation in parameters. How is the LND150 doing with the usual MOSFet problems? I noticed that you used a zener for static protection, is this transistor protected? I did not see the input capacitor in the first stage, usually such transistors do not work without a capacitor at the gate. What can you say about the difference in sound compared to regular Jfet? I was disappointed with the sound of the BS170 / 2N7000 due to their capacity.
The datasheet is your friend:
https://www.microchip.com/wwwproducts/en/LND150
The LND150 has an internal gate ESD protection diode, so no need for that extra Zener you'd use on BS170s. Input capacity is 10pF max. The LND150 is a depletion MOSFET and therefore needs to be biased like a JFET, not like a enhancement MOSFET (e.g. BS170). Depletion devices in self bias configuration are biased to ground like triodes and therefore do not need a DC blocking cap at the input.
Andy
thanks Andy it remains to understand if there are any advantages in sound (frequency and dynamic range). I know the LND150 has been successfully used in tube amplifiers, but is there any benefit from it at 18-27 volts, will it give better results than regular Jfets?
For most pedal purposes, you can probably treat the LND150 as if it was a JFET. It can take very high voltages but that is not really relevant for us, is it? It has tighter specs than many JFETs, which is good for consistent design. But some high quality JFETs have tighter groupings still, although these are getting harder to find. Noise may or may not be on par with JFETs. I think availability is a factor, the LND150 seems to be in active production and is quite cheap. Apart from that, it's mostly taste. Do you like the sound better than that of a certain JFET?
Andy
I'm not sure if I can tell one jfet from another by sound. however, I remember when I collected clean preps or tweed, they sounded cleaner and better on the 2N7000, the sound was warmer (thanks to the Miller capacity, I did not know about its existence then) and more spacious. Jfet (I tried several different ones and did not notice much difference) sounded more toned and flat, the clean sound was cold, but the medium and high gain (preamps with 3-4 amplification stages) were definitely more readable and had a pleasant Chug, in contrast to the loose sound and coarse grain 2N7000. I just wondered if the LND150 would be somewhere in the middle, sounding good in a clean and distorted sound, since it's used in real tube amps?
Hey Johnny,
If I wanted to graft the moon LNDer onto the Rosie, do you think that scaling parts to hold similar quiescent current as the 9V is the right choice?
Any idea of where the gate bias should end up in that circumstance?
Thanks in advance,
Quote from: phasetrans on April 14, 2021, 04:06:29 PM
If I wanted to graft the moon LNDer onto the Rosie, do you think that scaling parts to hold similar quiescent current as the 9V is the right choice?
Any idea of where the gate bias should end up in that circumstance?
It would be pretty easy to do. I'd raise the drain resistors to 10k, and adjust the source resistor so that the drain sits around 2/3 of the supply.
Quote from: POTL on April 12, 2021, 07:46:09 AM
hi Jonny Tell us about your impressions and experiences. I see the advantages of the LND150 over the Jfet in that there is no need to adjust the offset, apparently the minimum variation in parameters. How is the LND150 doing with the usual MOSFet problems? I noticed that you used a zener for static protection, is this transistor protected? I did not see the input capacitor in the first stage, usually such transistors do not work without a capacitor at the gate. What can you say about the difference in sound compared to regular Jfet? I was disappointed with the sound of the BS170 / 2N7000 due to their capacity.
Here are some general observations:
JFETs (J112 / J113) - tricky to bias due to variations in VGSoff. Low noise. Good sound - quite tube like especially if you bypass the source with a capacitor. Great for light crunch all the way to heavy distortion. Typically you'll need 3 or 4 cascaded gain stages to get decent modern distortion. I really like the sound of JFET preamps for guitar. I think you'd be hard pressed to tell a well designed JFET preamp from a tube preamp in a double blind test. I used JFETs for the Boba FET and Rosie amps (both available on this site).
MOSFET (2N7000 / BS170) - high input capacitance (especially high Miller cap in a bypassed common source gain stage), so you need a buffer on the input to avoid treble loss. Lots of hiss! High gain, and an aggressive, crunchy / grainy sound. Can be brittle unless you carefully control treble response. Can work well for aggressive high gain distortion sounds. You don't need more than 3 cascaded to get high gain, but you'll end up with about 12dB more hiss than with a JFET equivalent. I used BS170s for the Little Jim distortion pedal.
LND150 (depletion MOSFET) - these are quite interesting. They have low input capacitance and (in my experience) low noise like a JFET. They are internally protected against gate ESD. You bias them using self bias, and they seem to be more consistent VGSoff unit to unit than JFETs. They work great at 9V, and also at tube HT voltages so they complement preamp tubes nicely. The tone is pretty smooth and "tube like". They're pretty cheap and readily available in TO92. Because they are a MOSFET, there is no gate current when forward biased, so you don't have to design for blocking distortion. I was able to come up with the Moon LNDer circuit quite quickly after playing with them for a couple of days. I still think I have a marginal preference for the tone of a JFET preamp, especially under break up / mild overdrive conditions, but I definitely think there is scope for more people to come up with good sounding designs with these. I'm surprised they are not more widely used in guitar circuits given their numerous advantages. I'm planning a preamp "amp in a box" using these, I just need to find the time to finish the PCB, and most of my free time is currently being spent on the firmware for my upcoming reverb module (which I will post on this site if I ever get it finished :) ).
Hi, Johnny, got my LND150s in and i'm going to have to give this a go on perf.
What did you use for all those 10uf caps? The schematic doesn't indicate polarity. The bypass caps are obvious enough, but there is also a 10uf coupling cap into the tone stack, and IIRC you like MMCCs as an alternative to electrolytics or too-big films.
Quote from: Ben N on April 20, 2021, 05:21:10 PM
What did you use for all those 10uf caps?
He used MLCC AFAIK (see previous posts).
Quote from: jonny.reckless on April 19, 2021, 04:42:51 PM
Quote from: phasetrans on April 14, 2021, 04:06:29 PM
If I wanted to graft the moon LNDer onto the Rosie, do you think that scaling parts to hold similar quiescent current as the 9V is the right choice?
Any idea of where the gate bias should end up in that circumstance?
It would be pretty easy to do. I'd raise the drain resistors to 10k, and adjust the source resistor so that the drain sits around 2/3 of the supply.
Thanks Jonny. A question, the schematic as it exists in this thread already has 10K on the drains? Did you mean some other value?
Also you try bypassing the source(s) while doing your tinkering?
Quote from: jonny.reckless on April 19, 2021, 04:52:15 PM
MOSFET (2N7000 / BS170) - high input capacitance (especially high Miller cap in a bypassed common source gain stage), so you need a buffer on the input to avoid treble loss. Lots of hiss! High gain, and an aggressive, crunchy / grainy sound. Can be brittle unless you carefully control treble response. Can work well for aggressive high gain distortion sounds. You don't need more than 3 cascaded to get high gain, but you'll end up with about 12dB more hiss than with a JFET equivalent. I used BS170s for the Little Jim distortion pedal.
Why didn't you use input buffer for this? Too much treble?
I am very much thinking about building this wonderful pedal!
A question though. It has the potential to be a very versatile pedal, it is incredibly even and smooth.
Would it be possible to add "grit" to it? Excuse the term I did not find a better word... What I mean is like a switch or knob that would make it break up in a nasty raw way. Preferably in the mids.
I was thinking a switch or knob so that it could go back easily to the clean smooth distortion/overdrive it has.
If that is possible it would make it the ultimate pedal for my needs.
I will try to find good examples of what I mean and post it here.
Quote from: Dreadneck on April 23, 2021, 04:56:30 AM
I am very much thinking about building this wonderful pedal!
A question though. It has the potential to be a very versatile pedal, it is incredibly even and smooth.
Would it be possible to add "grit" to it? Excuse the term I did not find a better word... What I mean is like a switch or knob that would make it break up in a nasty raw way. Preferably in the mids.
I was thinking a switch or knob so that it could go back easily to the clean smooth distortion/overdrive it has.
If that is possible it would make it the ultimate pedal for my needs.
I will try to find good examples of what I mean and post it here.
you could experiment with crossover diodes, a clipping pair in line with the signal (instead of going to ground), i would put this in between the 1st and 2nd stage, but experimenting with the placing would be a good idea.
crossover gives a certain growl which i personally really love, but it also creates a gate-effect, which threshold is determined by the diodes Vf
cheers
Has anyone seen depletion-mode MOSFETs used as voltage controlled resistors, like in the Orange Squeezer? It looks like it should be possible, but the behavior in the ohmic region looks a bit different to that of JFETs.
Quote from: bowanderror on April 23, 2021, 06:13:53 PM
Has anyone seen depletion-mode MOSFETs used as voltage controlled resistors, like in the Orange Squeezer? It looks like it should be possible, but the behavior in the ohmic region looks a bit different to that of JFETs.
Mind the body diode, though.
Andy
Quote from: rankot on April 22, 2021, 03:27:40 PM
Quote from: jonny.reckless on April 19, 2021, 04:52:15 PM
MOSFET (2N7000 / BS170) - high input capacitance (especially high Miller cap in a bypassed common source gain stage), so you need a buffer on the input to avoid treble loss. Lots of hiss! High gain, and an aggressive, crunchy / grainy sound. Can be brittle unless you carefully control treble response. Can work well for aggressive high gain distortion sounds. You don't need more than 3 cascaded to get high gain, but you'll end up with about 12dB more hiss than with a JFET equivalent. I used BS170s for the Little Jim distortion pedal.
Why didn't you use input buffer for this? Too much treble?
I did. The Little Jim uses BS170s for the gain stages and J112 as a source follower input buffer. I found you don't need one with the LND150s as their capacitance is much smaller than the BS170.
Quote from: iainpunk on April 23, 2021, 03:49:28 PM
Quote from: Dreadneck on April 23, 2021, 04:56:30 AM
I am very much thinking about building this wonderful pedal!
A question though. It has the potential to be a very versatile pedal, it is incredibly even and smooth.
Would it be possible to add "grit" to it? Excuse the term I did not find a better word... What I mean is like a switch or knob that would make it break up in a nasty raw way. Preferably in the mids.
I was thinking a switch or knob so that it could go back easily to the clean smooth distortion/overdrive it has.
If that is possible it would make it the ultimate pedal for my needs.
I will try to find good examples of what I mean and post it here.
you could experiment with crossover diodes, a clipping pair in line with the signal (instead of going to ground), i would put this in between the 1st and 2nd stage, but experimenting with the placing would be a good idea.
crossover gives a certain growl which i personally really love, but it also creates a gate-effect, which threshold is determined by the diodes Vf
cheers
An other way get some "grit" is to experiment with the DC bias voltage of the final gain stage, you get a much fuzzier sound when the bias is closer to ground that the typical 2/3 of VDD.
Hi All,
my suggestion of small modifications of the circuit.Sorry for the hand drawing :icon_smile:
Regards,
box
(https://i.postimg.cc/fkbfJPwB/Moon-LNDer.jpg) (https://postimg.cc/fkbfJPwB)
Hi,
I'm sorry but I need to update some small changes to the drawing.
Regards,
box
(https://i.postimg.cc/hJGpGmvn/Moon-LNDer.jpg) (https://postimg.cc/hJGpGmvn)
Jonny, thank you for your answer. I do not quite understand what you mean about mixing J113, the problem is in the wide spread of VGSoff and it is necessary to select transistors (or just use a trimpot)? Or is the problem in a wide range of parameters and we have a big difference in gain from transistor to transistor? Some transistors have a low gain, some are large?
Are the LND150s so consistent that I don't need to pick them up and change the drain resistor value? I understand correctly that the drain resistor will work in a wide range of values, like in BJT, and not in a narrow one, like in Jfet?