Hi
A friend has asked me to fix a Paranormal Compressor which he bought on E-bay. The kit for this pedal was originally put out by Guitar Magazine but I can find a schematic for it any where on the net or in this forum.
If anybody has this schematic please could they let me know.
Kind regards
Axeman.
I think I'm right in saying that they never publish schematics for their projects, just paint by number instructions on how to assemble them.
In light of the fact it was designed as a DIY project, it would probably be a trivial matter to trace it. Might even be an idea comparing it with the most popular DIY compressors (Dyna/Ross/Orange) just in case it's a blatant copy.
Thanks Gez for the info.
Was just trying to avoid a long drawn out debug as I prefer building to mending !
Regards
Axeman.
QuoteI prefer building to mending
We all do, but in most cases those are just two phases of the same process.
Quote from: axeman010 on January 02, 2007, 08:45:56 AM
Was just trying to avoid a long drawn out debug as I prefer building to mending !
I know the feeling! The last time I had to trace a circuit was for a delay someone wanted modding. Thankfully, delays are pretty generic circuits so I was able to use the schematic for another pedal as a guide (there were more similarities than differences). You can usually tell pretty quickly if something's a clone/variant, so it is worth checking.
your searching skills can be improved:
Maybe you try this link:
www.guitarmagazine.co.uk/DIYguitarpedal_15_11_5.pdf (http://www.guitarmagazine.co.uk/DIYguitarpedal_15_11_5.pdf)
analogguru
Thanks Analogguru
I found this and there is no schematic on this page.
Axeman.
Maybe you can make some nice pictures - especially of the track side - and tell what is written on the transistors Q1 - Q6 and you will get a nice schematic.
As far as i can say now, it seems to be a Fet-based Compressor like the "orange squeezer" or the "soul-preacher".
analogguru
Of course, If you end up with a nice schematic, I could make a nice layout for said schematic and then build the thing!
I am a compressor junkie afterall! :icon_wink:
The problem with repairing a 'kit' is that you don't know whether it EVER worked!
could be wrong components, transistor wrong way round, anythng & everything!!
but, if the circuit were traced out, I suspect someone here would recognise it. :icon_wink:
so how is this one moving along has anyone actually got hold of the schematic for it. Looks like it wouldn't be a bad compressor. Has anyone built this from a a kit cause if so they could kindly scan the schematic in that came with it. Cheers
forum member Col worked out a schematic for this one. It's all discreet if I remember rightly, although I can't find my copy of the pencil scheme he'd drawn.
If you do a forum search for paranormal you'll find Cols schematic.
Just to refresh link to the magazine article: https://docdro.id/5wTjGIL (https://docdro.id/5wTjGIL). Currently out of time to trace this, but maybe after Christmas. :icon_biggrin:
I just thought: "Well, I have some free time right now why not trace this thing from the pictures to help the community?" - Fail.
From the input pad I can follow through the first filter cap (10n), but then I have no clue where the trace is going. Apart from that I would assume it goes to Q1, but I can't find a trace for that. They state Q1 is a FET. If it was a JFET the gate would likely be one of the outer lugs, but then it wouldn't be possible to substitute it with a BC549, so is it a MOSFET? Or another type of JFET I didn't come across yet?
The Input circuitry seems odd, so if anybody figures it out, please let me know. :D Unfortunately the pictures of the offboard wiring are just showing a spaghetti-mess, so not really helpful as well.
Is this better? I've transformed PCB bottom from the article and put it near PCB top which was photographed straight from above. However, it will be a little complicated to understand pot wiring :)
(https://i.postimg.cc/w7QP5D81/PCB.jpg) (https://postimg.cc/w7QP5D81)
QuoteIs this better?
That is helpful.
Does it look like the "input" wire goes to a 10n polybox and then.... nowhere? A broken track in the etch? Maybe a "bad" one was used to provide an assembly example. Should it really go to the middle pin of what looks like Q3?
I'm not familiar with many discrete FET comps, but we can see it has a full-wave bridge rectifier made with the 4 diodes, which might help the search for an original.
It's definitely a broken trace, but I believe it goes straight down to Q1 base.
Yep, it's probably supposed to go down to Q1B. Looks like they really wanted people to buy their kits. :D
OK, I took my time and traced this:
(https://i.postimg.cc/ZYWvZgXd/schematic-traced.jpg)
I just must ask someone to try to figure out potentiometer wiring. Also, there is 1 Ohm resistor (R14) going to ground, I believe it's a mistake.
great stuff, thanks!
I believe pots shall be wired like this:
(https://i.postimg.cc/9MfyHfj3/schematic-traced-v2.jpg)
The missing track definitely goes to the gate of Q1.
I think rankot's schematic is pretty close.
I also did a rough trace:
- I drew Q1 as a JFET but it's probably a MOSFET but in one of the pics I can see 2N ? ? ? ? so I thought maybe JFET.
- I got a few different values.
- My connections around Q4 and Q5 are different. When I checked it, mine looked correct.
You can see Q4 and Q5 have different bias networks on the bases.
[EDIT: OK I can see rankot's connection is correct. There's two bias networks (22k & 10k) but it's connected like rankot's. At the diodes 22k goes to +ve and the *10k* goes to ground.]
- As drawn (either rankot's or my schematic) the 1ohm across the input to Q2 just looks wrong.
I don't see how the circuit can ever put enough drive into the gate.
I have this feeling the resistor values in the pics are wrong. Maybe the guy that built it made
some mistakes! The rectifier looks weird to me.
- My guess is the Mix pot goes to the fixed side of the Squeeze pot. It make more sense
that the dry signal passes through without being affected by the Squeeze pot position.
A few pics in the PDF show the wiring.
Anyway I can't spend anymore time on it today.
(https://i.postimg.cc/PpQDfqh8/paranormal-compressor-V1-0.png) (https://postimg.cc/PpQDfqh8)
Rob, I believe both FETs are 2N7000, and it can be seen on one of the photos, indeed.
It would be nice if someone could pull out that schematic traced by Col as mentioned before in the thread.
There are two pads marked ground... I wonder if this was (incompletely, in the pictured form) adapted from a design for a bipolar supply.
I could be shooting above my pay-grade here (and it's definitely past my bedtime), but it doesn't seem like Q2 could do anything but conduct it's Idss with it's source grounded... unless Q4/5's tail were connected to a negative voltage.
If it's a MOSFET rather than a JFET... I haven't the slightest clue about Q2... but I still think this was a bad first attempt at a single-supply conversion.
I am pretty sure both FET transistors are 2N7000 because if you zoom page 3, picture 25, you can see the label. Also, AFAIK, only MOSFETs have gate in the middle, JFETs usually have gate as pin 1 (with excuse of Japanese JFETs which have gate in the middle too).
Rob, if you could share that ltSpice file, it would be of a great help :)
Hi Rankot,
Yep, both FETS are 2N7000.
Here is a pic of mine, I would have been following the instructions that came with the kit when I made it, and have done no modifications save for putting in a 9V dc jack.
It looks like I had to put in a jumper and R14 was not installed.
Mine was working but something is now causing Q1 (FET 2N7000) to fail, I've replaced it twice it works for a short while then no compression and the bypass tone gets the life sucked out of it.
(https://i.postimg.cc/9zh3Zmpx/Paranormal-01.jpg) (https://postimg.cc/9zh3Zmpx)
(https://i.postimg.cc/JstSMGrh/Paranormal-02.jpg) (https://postimg.cc/JstSMGrh)
Q1: 2N7000
Q2: 2N7000
Q3: C549C
Q4: C549C
Q5: C549C
Q6: looks like: BC56()429 The silkscreen says PNP
C1: 47uF
C4: 2.2uF
C11:47uf
Interesting thing is that diodes are connected reversed (cathode to + sign on silkscreen), but it is the same as in the article.
PNP is probably BC560.
Try to measure voltages on Q1 pins.
QuoteRob, I believe both FETs are 2N7000, and it can be seen on one of the photos, indeed.
Ah! of course. Thanks. I did that before I went to bed and I didn't even think of 2N7000 :icon_redface:
(When I posted my schem I noticed you had posted one also. For the thread your schematic can be the master copy.)
QuoteRob, if you could share that ltSpice file, it would be of a great help
It's not LT Spice it's a *really* old spice. If you want to try it I can send it.
QuotePNP is probably BC560.
IMHO, it is definitely PNP. It is marked on the PCB as "pnp" and the circuit doesn't makes more sense.
QuoteIt looks like I had to put in a jumper and R14 was not installed.
That makes a lot more sense. There's no way it would work with the 1ohm shown in the magazine!
I also noticed the 1k's in the magazine are 1k2 on your board.
QuoteMine was working but something is now causing Q1 (FET 2N700) to fail, I've replaced it twice it works for a short while then no compression and the bypass tone gets the life sucked out of it.
Maybe ESD (static electricity)? I normally don't blame ESD unless there's some evidence like known zaps in that area or the building or very low humidity.
QuoteInteresting thing is that diodes are connected reversed (cathode to + sign on silkscreen), but it is the same as in the article.
That's a correct thing in some circles. If it was a psu rectifier, the + supply would be coming out of the cathode end. It can cause a lot of confusion, especially as it could also be applied to silkscreen for LED's.
I will check diode orientation and whole that rectification part and compare with Rob's schematic in the morning, now I'm just too tired. Whole day of drafting, then driving, then drafting again... :(
Quote from: Rob Strand on December 06, 2018, 03:22:08 PM
It's not LT Spice it's a *really* old spice. If you want to try it I can send it.
Lets try!
QuoteThat makes a lot more sense. There's no way it would work with the 1ohm shown in the magazine!
I also noticed the 1k's in the magazine are 1k2 on your board.
Indeed, I've noticed that too!
Also some other resistor values, that I have read wrong (4k7 resistors on this board, while I thought they're 470 Ohms and few others). I will post corrections in the morning.
Quote from: Rob Strand on December 06, 2018, 05:41:00 AM
I also did a rough trace:
(https://i.postimg.cc/PpQDfqh8/paranormal-compressor-V1-0.png) (https://postimg.cc/PpQDfqh8)
I don't see this R24 of your schematic on PCB! Cathodes of those two diodes are connected to 100k+100n (their other leads are connected to anodes of other diode pair), 22k to 9V and 10k to ground. I definitely don't see 10k going to Q4 base from that point. Are you sure there is a resistor there?
QuoteLets try!
OK. There's nothing to lose. If it works it would be really cool. You will have to edit the transistor models names to suit your libraries (to be honest I only put any old junk in there to get the schematic done). I don't know how it will convert the symbols.
QuoteAlso some other resistor values, that I have read wrong (4k7 resistors on this board, while I thought they're 470 Ohms and few others). I will post corrections in the morning.
There was a few other places as well. Like the 100k to ground on the rectifier. 2k7 not 2k4 on the source of the MOSFET. I'm fairly certain the MIX pot should not connect to the wiper of the Squeeze pot.
QuoteI don't see this R24 of your schematic on PCB! Cathodes of those two diodes are connected to 100k+100n (their other leads are connected to anodes of other diode pair), 22k to 9V and 10k to ground. I definitely don't see 10k going to Q4 base from that point. Are you sure there is a resistor there?
R24 is R14 on my schematic. That divider is OK.
I reverse the values on the other divider, which doesn't help trying to find them:
Rob Rankot
R11 10k-wrong R20 22k-correct
R12 22k-wrong R21 100k-wrong should be 10k
My resistor designators do not match the PCB. I couldn't read them all from the pics.
I had in mind R24 on your schematic. :D
QuoteI had in mind R24 on your schematic
That will cause you some trouble :icon_mrgreen:.
QuoteThat's a correct thing in some circles. If it was a psu rectifier, the + supply would be coming out of the cathode end. It can cause a lot of confusion, especially as it could also be applied to silkscreen for LED's.
Best not to use the '+' at all. The diode *symbol* already has the polarity. The '+' causes confusion.
Quote from: rankot on December 06, 2018, 02:33:15 PM
Interesting thing is that diodes are connected reversed (cathode to + sign on silkscreen), but it is the same as in the article.
PNP is probably BC560.
Try to measure voltages on Q1 pins.
You've reminded me that I contacted the place I got the kit regarding the diodes, and got the following response:
Hi Chris
Fit the diodes as in the photo. Some confusion here as to what the anode and
the cathode look like on a diode, I expect. Anyway the photo orientation is
correct.I'll measure the voltages tomorrow, my multimeter isn't to hand at the moment.
I'm just fixing up my schem before I send you the file. I noticed these part errors on your schematic (my had some errors also):
R5 10k
R6 68k
R10 1k
As far as the sim goes it looks like it does work.
The bias points of Q1 and Q6 look reasonable.
With the MIX set to DRY: When the OUTPUT control set half way, I'm getting about -0.7dB gain which corresponds to about 5dB with the OUTPUT control set to full. The article mentions a 6dB gain.
With the MIX set to Compress: When OUTPUT control set half way the unity gain point is at about 50mV peak input. It compresses but it has some weird behaviour around 50mV pk input, like it is expanding not compressing.
The MOSFET output for large signals isn't clean. It is cleaner at 200Hz than 1kHz so I'm suspicious this is related to the Q2's high input capacitance combined with the larger 1M resistors feeding the gate.
Here's my revised schematic. I'm not going to post any more schematics as your schematic should be the master copy for the thread:
(https://i.postimg.cc/mzPqrT53/paranormal-compressor-V1-1.png) (https://postimg.cc/mzPqrT53)
It's definitely interesting, I've never seen MOSFET based compressor before.
QuoteIt's definitely interesting, I've never seen MOSFET based compressor before.
The problem with the 2N7000's and similar is they have high Drain-to-Gate capacitance. Also, the resistance is quite low compared to a JFET so the gate voltage needs to operate over a narrow range. IIRC they have more distortion because the on-window is small compare to a large VGS_off JFET.
Some time around March this year I'm sure I posted some tricks to increase RDS and to linearize the MOSFET. Here's the idea,
(https://i.postimg.cc/kDPkthpC/Series-MOSFET-w-linearization-VCA-Phaser.png) (https://postimg.cc/kDPkthpC)
BTW I worked out why the Paranormal Compressor goes a bit weird around 50mV peak input. That is when the MOSFET is fully turned on.
Quote from: rankot on December 06, 2018, 02:33:15 PM
Try to measure voltages on Q1 pins.
Voltages for the two FETs, but please bare in mind something keeps making Q1 stop working!
Q1
Pin 1 (Source) 9v
Pin 2 (Gate) 9v
Pin 3 (Drain) 9v
Q2
Pin 1 (Source) 9v
Pin 2 (Gate) 7.3
Pin 3 (Drain) 8.5v
All Pots are 100K, there is no A or B designation, so is it safe to conclude they are linear?
If it would be helpful I'll try and work out the pot wiring tonight?
Q2 source should be hardwired to ground 0v, so a connection to 0v is missing somewhere. If testing on battery, the negative might be via the ring of a TRS input socket and needs a jack plug inserted to switch the power negative on.
This is a "parallel" compressor. There is a mix between compressed and clean at the output. That means you can still have natural transient peaks coming through to keep thing interesting while the lower level "body" of the audio can have a more consistent average level due to compression. It's a trick commonly employed by record mastering engineers on final tracks, not usually on individual instruments. To some extent, if the compressor action was too snappy/obvious, it can be masked somewhat by having some clean signal present.
QuoteVoltages for the two FETs, but please bare in mind something keeps making Q1 stop working!
Q1
Pin 1 (Source) 9v
Pin 2 (Gate) 9v
Pin 3 (Drain) 9v
What the hell!
I'd be checking for shorts to 9V all around Q1. You might even have a badly etched PCB which is shorting everything. It's very weird to have all those voltages 9V!
Quote
Q2
Pin 1 (Source) 9v
Pin 2 (Gate) 7.3
Pin 3 (Drain) 8.5v
Those voltages also look weird.
Are you sure you have wrote Q1 and Q2 down correctly?
Maybe you have a wiring problem? Check your jack wiring.
FWIW, the voltages out of the simulator are:
Q1
D 5.8V
G 2.9V
S 0.83V
Q2
D 1.2V
G 1.9V
S 0V
The Q2 voltage could vary quite a bit and the meter loading could cause them to drop to 80% or 90%.
You *have* to have Q2 source at 0V if not there's a problem with the ground or jack wiring.
What you can do to bypass the whole jack wiring issue is to wire the battery directly to the power terminals on the PCB. They re-measure the voltages.
Quote from: rankot on December 07, 2018, 02:38:55 AM
It's definitely interesting, I've never seen MOSFET based compressor before.
I think midwayfair's (Jon) bearhug compressor uses a MOSFET in a very compact design.
QuoteI think midwayfair's (Jon) bearhug compressor uses a MOSFET in a very compact design.
It has a MOSFET but it's the amplifier. The voltage controlled resistance is done with a JFET.
Apologies regarding the obvious way out there voltages I measured, I'm still trying to figure where I went wrong, and an only assume I didn't connect to a ground, a problem of trying to measure something while having breakfast at the same time no doubt. Anyway in the mean time metal fatigue from my repeated turning the board over has resulted in three of the wires going to the pots breaking free from the PCB, two of which I do not know if I've reattached them the right way round!
For what it's worth here at the voltages I've just measured, the circuit is powered from a power supply set to 9v, however Q1 voltages still looks very questionable, but maybe this is indicating why my pedal stopped working.
Q1
Pin 1 (Source) 1.5v
Pin 2 (Gate) 2v
Pin 3 (Drain) 2.9v
Q2
Pin 1 (Source) 0v
Pin 2 (Gate) 1.5v
Pin 3 (Drain) 0.6v
This pedal has worked fine for years, well since 2005 when I made it, with nothing to compare it to I can't comment on how good it was, but I was able to dial in what I wanted, and nearly always used the mix knob to keep some of the original signal there which I thought made it sound natural. I would just like to get it going again, but am also preparing to build an Engineer's Thumb.
> 2N7000's and similar is they have high Drain-to-Gate capacitance.
5pFd. Plus 60pFd D to S. Max.
For the 10K+68K source, this gives nearly 200KHz bandwidth.
The large-signal response is typically limited by the body diode. For that source impedance you want to be under 0.4V peak. The paranormal output stage is gain of 20, so under 8V peak output; we run into the 9V supply before the MOSFET seriously hurts.
Voltage at Gate would be near 3V with a perfect meter. The observed 1.5V would fit if meter is 1Meg, a not atypical value for generic DMMs. Voltage at Drain is a Meg away so should be even lower, tho I figure 1V not the observed 0.7V.
Quote5pFd. Plus 60pFd D to S. Max.
For the 10K+68K source, this gives nearly 200KHz bandwidth.
The capacitance goes up quite a bit when the voltages across the device decrease There's a graph in the datasheet. I was thinking more the linearization gets stuffed up because the 2x1MEG are feeding that (larger) capacitance.
QuoteThe large-signal response is typically limited by the body diode. For that source impedance you want to be under 0.4V peak. The paranormal output stage is gain of 20, so under 8V peak output; we run into the 9V supply before the MOSFET seriously hurts.
It's quite possible. The body diode issue actually crossed my mind after I posted those series MOSFET configurations. I checked at 200Hz and 1kHz and there was no weird waveform at 200Hz. It looked like some sort of capacitive effect however it could very well be the cap in series with the MOSFET charging-up through the body diode. I'll have to have another look.
Another thing I've seen using those MOSFETs as VCR is the control ripple can cause an on-off effect when you get near the threshold. You can get some really weird waveforms. I don't think that's going on here though.
QuoteFor what it's worth here at the voltages I've just measured, the circuit is powered from a power supply set to 9v, however Q1 voltages still looks very questionable, but maybe this is indicating why my pedal stopped working.
Q1
Pin 1 (Source) 1.5v
Pin 2 (Gate) 2v
Pin 3 (Drain) 2.9v
Yes they look like something is wrong.
Initially I was thinking extra current could come back down from Q3 but I don't think that's what is happening.
If you calculate the drain current from the drain voltage,
Id = (9-2.9) / 10k = 0.61mA
Then the expected source voltage (roughly estimate 2.7k in parallel with the 10k etc as 2.55k),
Id *2.55k = 1.56V
Which agrees with your measurement.
What that is saying is Q3 isn't doing something funny and the source & drain circuits are operating as expected.
The voltage divider measurement on the gate is off but that' probably meter loading if your meter is 1Meg input impedance.
So that leaves the MOSFET. So it's either fried or the gate threshold voltage is way off what the circuit is designed for.
One test you can do is to short the gate of Q1 to the drain then measure the voltage between the drain and source. It should be around 2.1V.
Another test is to replace Q1, or swap Q1 and Q2, and re-measure.
There have been MOSFET compressors before, at least as DIY projects, however, the MOSFET's were in a CD4007 array chip, and sidesteps some of the issues of body diode and input protection.
It might be worth suspecting Q1 because there is the possibility of damage from an electrostatic discharge at the input. If it turns out it was damaged that way (hard to prove but easy to suspect), there is a simple add-on remedy...
http://www.muzique.com/schem/mosfet.htm
Quote from: anotherjim on December 08, 2018, 09:04:05 AM
There have been MOSFET compressors before, at least as DIY projects, however, the MOSFET's were in a CD4007 array chip, and sidesteps some of the issues of body diode and input protection.
Interesting, never seen one!
There was a Penfold project. IIRC only used 1 MOSFET from the 4007 as the control.
Not a compressor, but we did have a trem design here where the 4007 provided the pre-amp, the PSO oscillator and the control resistor.
There's also the ETI 446 Limiter (from Electronics Today International, Aug 1976)
https://www.diystompboxes.com/smfforum/index.php?topic=101953.0
Then there's some phasers like the ETI 447 Audio Phaser (Sep 76) and Electro-harmonix Bad Stone Phaser ( EH-5800).
Because MOSFETs have body diodes the designs usually try to limit the voltage across the MOSFET. You can see this more explicitly on the phasers as they will attenuate the signal, pass it through the circuit with the MOSFETs, then boost the signal back up. This process obviously isn't good for noise performance.
Those funny looking two MOSFET circuits I posted earlier try to get a bit more out of it, as well as increasing the resistance which make it more useable in audio circuits. The idea can't be used directly on CMOS devices.
I tried to import Pspice model into ltSpice, but it's a no go, so I drew schematic in ltSpice from the beginning. And the result is that I have "gain" of 50%. Tried with different MOSFET models, and the one I have for CD4007 performs the best, but still with not enough gain.
QuoteTried with different MOSFET models, and the one I have for CD4007 performs the best, but still with not enough gain.
There's many bad models for the 2N7000. They often don't work at low currents and all the stuff we use for effects pedals. If you search "Win Hill" 2N7000 or "Winfield Hill" 2N7000 you might find something.
The CD4007 is a *very* different device, much higher resistance.
These models are OK for small signal stuff.
It's a long while since I verified the ROB model.
* Win Hills version of this has M1 without L and W modified
* so Win's relies on default L and W.
.SUBCKT MZVN4106_ZTX 3 4 5
* Nodes D G S
M1 3 2 5 5 MOD1 L=1u W=1u
RG 4 2 343
RL 3 5 6E6
D1 5 3 DIODE1
.MODEL MOD1 NMOS VTO=2.474 RS=1.68 RD=0.0 IS=1E-15 KP=0.296
+CGSO=23.5u CGDO=4.5u CBD=53.5P PB=1 LAMBDA=267E-6
.MODEL DIODE1 D IS=1.254E-13 N=1.0207 RS=0.222
.ENDS MZVN4106_ZTX
*
* This is my best model so far for low currents (=M2N7000_AVGSS)
*
* Average 2N7000/BS170 device for small signal
* Based on some playing around.
* VTO is in the 1.8 to 2.0V region
* KP is in the 20e-3 to 30e-3 region.
* Originally Zetex Generic (N-channel DMOS, 2n7000, 2n7002 etc)
* CGDO increased from 4.5u to 12.5u to match measurements
.SUBCKT M2N7000_ROB 3 4 5
* Nodes D G S
M1 3 2 5 5 MOD1
RG 4 2 343
RL 3 5 6E6
D1 5 3 DIODE1
.MODEL MOD1 NMOS VTO=1.9 RS=1.68 RD=0.0 IS=1E-15 KP=26e-3
+CGSO=23.5u CGDO=12.5u CBD=53.5P PB=1 LAMBDA=267E-6
+L=1u W=1u
.MODEL DIODE1 D IS=1.254E-13 N=1.0207 RS=0.222
.ENDS M2N7000_ROB
*
Thanks Rob, you're great as always! Will try those models in the morning, now time to sleep :)
QuoteThanks Rob, you're great as always! Will try those models in the morning, now time to sleep
I wasn't clear about something:
MZVN4106_ZTX this one is good for higher bias currents
M2N7000_ROB this one is good for low bias currents like you get in effects.
If you build an amplifier with a low valued (or cap-bypassed) source resistor you will find the M2N7000_ROB model gives closer results. The MZVN4106_ZTX model will produce much higher predicted gains.
OK, I've tried it this morning and with Rob's 2N7000 model it works like with almost any other MOSFET I have in library - signal is actually very weak, some ±60uV at output, with ±100mV input:
(https://i.postimg.cc/grzrQPMt/simulation-2-N7000-ROB.jpg) (https://postimg.cc/grzrQPMt)
With CD4007 based transistors, I get much better results ±20mV at output, with ±100mV input:
(https://i.postimg.cc/Zv5RdrBz/simulation-CD4007.jpg) (https://postimg.cc/Zv5RdrBz)
Output is slightly bigger if I connect Compress pot CW to output, instead of the point marked with COMP_FEED.
So maybe I'm just missing something here?
QuoteSo maybe I'm just missing something here?
Your Drain resistor R3 is 100k it should be 10k.
I did simulate this and I got it to work before I sent the files to you.
It has some quirks but it more or less works.
If you can show the DC voltages on your schematic you should see the drain voltage of Q1 stuck at the same voltage as the source because R3 is too large. (And yes you will see that problem will all MOSFET models. The CMOS gate is closer to working because it is the weakest.)
Quote from: Rob Strand on December 09, 2018, 05:00:03 AM
Your Drain resistor R3 is 100k it should be 10k.
You're right, I've misread the value from photo :-[
It works now.