Hi
this circuit is guaranteed good fun. Not a 1-trick pony at all IMO.
It uses three of the six inverting amplifiers in a CD4049UBE.
Although looking superficially like the tube-sound fuzz and its variants (Mark Hammer in particular is an expert concerning these), it is somewhat different. It starts with a JFET gain stage that generates just a tad of distortion.
One of the keys is that the 4049's supply voltage is reduced to about 6 V by the 220 ohm resistor (and polarity-protecting diode). This helps give a nice "compressed" feel and ensures that the onset of distortion is subtle and progressive, only getting severe when pushed hard. If you don't want the subtlety, the resistor should be changed to a low value (e.g. 10 ohms). Also note that the J201 JFET nominated here will give more gain than most other types, so try others if you want cleaner tones or lower gain.
The "drive" pot is shown as a linear type, but I actually use a LOG type that gives greater control over the "overdrive" end of the gain spectrum, but not much control over the "maxed out distortion " end (which happens as a mad rush between 3 and 5 o'clock).
The "drive" and "filter" pots interact in a similar way to those controls on a "Rat". At high gain, you'll probably want plenty of filtering to control excessive "sharpness".
Thanks to RG for the suggestion about unexplored magic in CD4049.
That's about it. Have fun. All feedback welcome. :icon_wink:
http://aronnelson.com/gallery/albums/BinOfBrett/Forty_niner.jpg (http://aronnelson.com/gallery/albums/BinOfBrett/Forty_niner.jpg)
Looks good, and I'll bet it sounds good too. We tend to look at those little triangular boxes and go "Ho hum" then get all excited about discrete FET or MOSFet-based units, all the while forgetting that inside those little triangular boxes on the schematic are MOSFets. :icon_exclaim:
The supply-line trick is worth thinking about. If you haven't already done so, take a look at the Charles Fischer project from EM that JD Sleep has posted over at GGG. Fischer used a current-control IC to vary power to the 4049 in his design in order to achieve variations in "splat".
If I can make one small suggestion. Consider altering the Filter control pot arrangement to the SWTC arrangement (http://hammer.ampage.org/files/SWTC.gif). This will give you the same control over tone, but without the interaction that normally occurs between filter setting and volume setting.
And just out of curiosity, I note that you use U1f essentially as an inverting buffer. It is not uncommon to find use of several paralleled invertor sections in other kinds of designs as a means of creating a higher-current output. Since you have 3 invertor sections just hanging around, I'm wondering if there is any tactical advantage to making use of them in that manner. Such a musing is directed at those with more electro-savvy. Is there something one could do more easily with several parallel invertor sections on the output? That could be as simple as being able to use a different value output pot or whatever.
very cool, Brett...ive been playing around with 4049's and 4069's over the past week, and theyre fun little chips....i'm woring on a combo boost / overdrive / distortion / tremolo off one 4069 currently.... :)
Nice Brett, there's mileage in those 4049's and 4069's, I have a couple that I messed with in a similar
way, Jfet front and the 220Ohm limiting resistor, I seem to have about 1 in 2 of my cmos builds "failing"
or at least not working quite as expected !
Perhaps I'm a bit full of "static" !!
Marty.
Quote from: MartyMart on July 10, 2007, 11:27:10 AM
Perhaps I'm a bit full of "static" !!
Marty.
You're full of "something", thats for sure ! :icon_lol:
Hi
thanks for the support and suggestions.
QuoteConsider altering the Filter control pot arrangement to the SWTC arrangement (http://hammer.ampage.org/files/SWTC.gif). This will give you the same control over tone, but without the interaction that normally occurs between filter setting and volume setting.
This is an interesting idea. I found the interaction OK. I guess that is because the filter pot is only 25k and the volume pot is 100k log. Given that the output is usually large (say 3V p-p), the volume pot will usually be set only a few k from ground. I *think* this minimises the interaction. For example, if the volume pot is set at 10k from ground, there's typically 90k of resistance "upstream", so changing the filter pot by 5k, and adding 5k to the 90k will have negligible effect on volume. (ie 10/90 is almost equal to 10/95) Is that right??
The limit to this approach of using a small filter pot and a large volume pot is that the output impedance of the previous stage must be much smaller than the filter pot.
QuoteAnd just out of curiosity, I note that you use U1f essentially as an inverting buffer. It is not uncommon to find use of several paralleled invertor sections in other kinds of designs as a means of creating a higher-current output. Since you have 3 invertor sections just hanging around, I'm wondering if there is any tactical advantage to making use of them in that manner.
I've used parallel buffers before (in a 4049-based sine-wave generator), and was thinking of using them here. However, it messed up my layout, and I couldn't see any advantages from extra current capacity. So I just used one inverter as both a buffer for the previous stage and driver for the filter.
If someone knows a cool use for a circuit like this that could push about 100mA, then 3 or 4 parallel buffers would certainly do the job.
thanks again for the feedback
PS thanks Marty for putting up that soundclip of the Hidrosis - really nice work
I have a 4049 circuit using 2 stages, 470k on the first with a 68pf, 150k on the second with a 120pf and
20k between, 22n caps ... does low to medium gain quite well and sounds good.
Front end is pretty much a fetzer valve.
Might be well to add a TC and then volume recovery using a third stage ?
How did it go with that transformer Brett ?
Hi Marty
still working on that valve project.... :icon_redface:
Here's an interesting thing about 4049 circuits... I think that many people have been smothing out the natural harmonics then adding artificial ones back in with more clipping in later stages.
Looking at Marty's resistance and capacitance in the first feedback stage (470k and 68 pF), the roll-off frequency is between 2 and 2.5 kHz. That's low. The reason why Marty's circuit sounds good is that the signal is clipped by a later stage with a rolloff at 8 to 10 kHz. This adds back a whole lot of top end. But only when the clipping is quite hard.
My circuit uses small caps relative to the resistors (22pF with a 1M resistor and 100pF with a 100k resistor) so that when clipping is slight or moderate, the natural highs of the guitar come through. Hence designs with large caps like the TSF are very "fuzzy" (ie synthetic sounding) and Marty's with intermediate sized caps will be "distortiony", but this one has small caps and is therefore capable of very mild overdrive. To make it work for distortion I needed the "filter" control to cut out the highs when the gain is turned up. It's a bit of a nuisance having to adjust both controls, but there is a good range of tones available.
Anyway, those are my 2c theories...
That's essentially why I ramble on constantly about how one needs to spool out highs in multi-stage clipping devices. One has to think about what it is that subsequent stages have available to clip. Keeping tight reins on which harmonics find their way through to a 2nd or third stage allows for an eventual output that I think many find more musical because it has more growl than rasp.
Of course, the notion that one should gradually loosen the reins on high end is entirely separate from how much to do it and at what frequencies. That's where trial and error and "taset-testing" comes into play.
Your comments about whether the filter/volume control interaction is problematic are quite cogent. There are plenty of circumstances/settings where no audible interaction should occur. I guess the reason I lean towards the SWTC is that it means you simply don't have to worry/think about interaction at all. You pick a tone-pot and volume pot value that don't impose too much default attenuation (e.g., you wouldn't want a 250k tone pot and 10k volume pot), pick a rolloff range and appropriate cap, and away you go.
Finally, I have found that sticking a bypass cap in the "Drive" pot (think "bright" switch) provides some nice bite to lower drive settings. Kind of "instant Rickenbacker". I leave it to you to figure out what suits your taste, but starting out with .01uf might be useful.
Thanks, Brett, cool roject. Thanks also, Mark, for the interesting comments and suggestions.
Uh, Brett, I don't mean to cause trouble, but I am sure you were not aware that Mark had 4049-based project called the "Forty-Niner," right?
http://hammer.ampage.org/files/FortyNiner-1.zip
Ben
sorry, folks,
but I don`t see an inverting buffer in U1f:
just a dead short between in & out;
I see two (shunting) FET-diodes going from the (center-biased) output of U1a to the respective rails. ("clipping"...)
:icon_question:
Ooops nevermind that...
Quote from: puretube on July 11, 2007, 12:34:31 PM
sorry, folks,
but I don`t see an inverting buffer in U1f:
just a dead short between in & out;
I see two (shunting) FET-diodes going from the (center-biased) output of U1a to the respective rails. ("clipping"...)
:icon_question:
He's right. What self-respecting electron would go through U1f when there is a perfectly good piece of wire to pass through?
Um, just how
DO you get something like a unity-gain inverting stage with a 4049?
2 equal (1series input-R & 1feedback-R) resistors...
Quote from: Mark Hammer on July 10, 2007, 09:06:14 AMIs there something one could do more easily with several parallel invertor sections on the output?
Drive heavier loads. A year or so ago I posted a schematic that parallels a few inverters to drive headphones. Not exactly low distortion (I don't meant fuzz here, I mean fidelity), but it works well enough. Downside is the current consumption (ridiculously high)
Quote from: puretube on July 11, 2007, 03:24:06 PM
2 equal (1series input-R & 1feedback-R) resistors...
...
excluding a zero-ohm input and feedback resistor, of course. :icon_biggrin:
Thanks.
Quote from: Mark Hammer on July 10, 2007, 09:06:14 AMIs there something one could do more easily with several parallel invertor sections on the output?
I posted this query because I remember discussing use of piggybacked op-amps with Mike Irwin, and he indicated that in some instances the behaviour of diodes might change with higher current drive feeding them. I didn't completely understand his point, but I figured that perhaps there might be some sort of context where extra current drive from paralleled invertors might conceivably be useful. If not, so be it. I figured that if they're just sitting there doing nothing anyways.....
Being mosfets, can inverters be used as clipers?
Mark: zero ohm input-R = OK;
zero ohm feedback-R: No.
Ben: see Brett`s schemo, 3rd inverter... (IMHO).
OK, Ton, that third inverter is being overdriven, right? What I meant was a clipper in the same sense as the way diodes are used in a TS or Dist+, to ground after gain or in the FB loop. Or does that make no sense for an inverter?
Also, w/re the question about paralleling inverters for better drive capability--would that not make sense ahead of the tone control? (Just based on the article that Aron linked to in another thread: http://www.diystompboxes.com/pedals/jo4049.html.)
TIA for your responses,
Ben
check John`s link, fig. 12a : (http://www.diystompboxes.com/smfforum/index.php?topic=59155.msg461678#msg461678)
in Brett`s circuit, Q1&Q2 are like antiparallelled diodes in a "clipper-to-ground" (after the gain of the previous inverters);
the fact that one goes to plus and the other to ground, doesn`t matter signal-(AC-)wise.
Thanks. I just printed out that article for my commuting-reading tonight.
Quote from: Ben N on July 11, 2007, 04:58:43 PMAlso, w/re the question about paralleling inverters for better drive capability--would that not make sense ahead of the tone control?
Never tried it, but it makes sense to me! Personally, I just DC connect a divider to earth and hook up its centre to the gate of a JFET follower. So long as you divide down enough, you won't get clipping in the JFET stage. Less current consumption this way (inverters are hogs in that respect)...
Hi again
yes, inverters are current hogs, and you don't really want to drive heavy loads with this circuit.
But when you DO want to produce lots of ampage, inverters are quite good (I presume that its the very low on-resistance of MOSFETs compared with JFETs that does the trick).
Re: the last inverter. 100 ohm input and feedback resistors would be good. ( :icon_redface:)
PS sorry about the name, Mark. Gees, I must have stored your "FortyNiner" name in my sub-conscious. I'll change it ASAP. Maybe to the "Inverter" or "Smooth-o-matic"?
Quote from: brett on July 11, 2007, 08:42:38 PM
Re: the last inverter. 100 ohm input and feedback resistors would be good. ( :icon_redface:)
A 100 om input resistor is no different than a 100 ohm load to ground for the previous inverter. Severe loading ensues. If you use equal resistors for U1f it doesn't necessarily act as a unity gain buffer as inverters have high output impedance, so the output of U1a (if U1f's input resistor value is low enough) could be loaded and its gain reduced (less than unity). That may, or may not, be desirable. Loads of, for example, 10k will reduce the gain of a stage. Sometimes that's good as it keeps overall gain throughout the circuit down and kills oscillation.
Quote from: brett on July 11, 2007, 08:42:38 PM
PS sorry about the name, Mark. Gees, I must have stored your "FortyNiner" name in my sub-conscious. I'll change it ASAP. Maybe to the "Inverter" or "Smooth-o-matic"?
No problem. I'm not offended and it's not trademarked. As for "Forty-Niner", you probably got it from the same place I did: the song "My Darling Clementine" ("Was a miner, forty-niner..."). And THAT would appear to have entered my own subconscious via the old Huckleberry Hound cartoon show.
The key thing is that every design that enters into the fray be identified in a unique way such that when person A refers to it by name, person B knows precisely what they're referring to, and when person C gets told to look for threads about it using the search function, that the search term work as planned.
Quote from: Mark Hammer on July 10, 2007, 09:06:14 AM
Is there something one could do more easily with several parallel invertor sections on the output? That could be as simple as being able to use a different value output pot or whatever.
I beleive the output impedance will drop, since they all will be in parallel.
This looks great! Has anyone started a pcb layout for it?
Quote from: Mark Hammer on July 12, 2007, 08:58:01 AMAs for "Forty-Niner", you probably got it from the same place I did: the song "My Darling Clementine" ("Was a miner, forty-niner...").
No offense, Mark, but there is no way that anyone from south of the border would have gotten it from that place. :icon_biggrin:
Ah, but that's where you'd be wrong. Remember, "My Darling Clementine" was Colonel Potter's favourite movie on "M.A.S.H."! :icon_biggrin:
How great is M.A.S.H by the way? Still sad, hysterical and interesting 30 years later
has anyone actually built this yet?
Hi
these might help simplify the building process for those interested.
I'm calling it the "Smooth-o-matic" because the "Forty Niner" was used by Mark Hammer. Ok, it's a weak name, but what do you want for nothing?
Here's a PCB layout:
http://aronnelson.com/gallery/albums/BinOfBrett/Smooth_o_matic_PCB.sized.jpg (http://aronnelson.com/gallery/albums/BinOfBrett/Smooth_o_matic_PCB.sized.jpg)
The overlay:
http://aronnelson.com/gallery/albums/BinOfBrett/Smooth_o_matic_overlay.sized.jpg (http://aronnelson.com/gallery/albums/BinOfBrett/Smooth_o_matic_overlay.sized.jpg)
And for completeness, the schematic. Although the last inverter isn't really used, I kept it in the schematic to be consistent with the layout above.
http://aronnelson.com/gallery/albums/BinOfBrett/Smooth_o_matic_schematic.jpg (http://aronnelson.com/gallery/albums/BinOfBrett/Smooth_o_matic_schematic.jpg)
Please note that these diagrams include a couple of last minute changes that I "jumpered" on my board, so I haven't tested this exact layout yet.
All feedback is greatly appreciated.
cheers
Quote from: puretube on July 11, 2007, 12:34:31 PM
sorry, folks,
but I don`t see an inverting buffer in U1f:
just a dead short between in & out;
I see two (shunting) FET-diodes going from the (center-biased) output of U1a to the respective rails. ("clipping"...)
:icon_question:
maybe not "diodes", but "resistive loads" ? "constant current"?, "biasing devices"?
in Fig.2, here (http://www.pat2pdf.org/patents/pat4071777.pdf) (N2/P2) an inverter is shown with in-/output shorted.
more theory, here... (http://www.nutsvolts.com/~downloads/fetjul.pdf)
Quote from: puretube on July 16, 2007, 09:35:07 AM
maybe not "diodes", but "resistive loads" ? "constant current"?, "biasing devices"?
in Fig.2, here (http://www.pat2pdf.org/patents/pat4071777.pdf) (N2/P2) an inverter is shown with in-/output shorted.
more theory, here... (http://www.nutsvolts.com/~downloads/fetjul.pdf)
I couldn't get that PDF to open, but I think you're on to something here Ton. If that last stage were non-inverting then yes, it would have no effect on the circuit. However, it's inverting: its input is still being pulled high/low and it's output will try to swing in the opposite direction. This probably has the effect of reducing the resistance seen at the output as the signal gets larger, in turn loading the previous stage. In other words, I think it might have the effect of compressing the signal coming out of that 2nd inverter.
Well, that's my guess... :icon_lol:
that 1st pdf is from: US patent #4071777
yes, what I meant: there is nothing happening "from in to out" (horizontally) in brett`s last inverter,
there`s rather something (clipping, squashing or loading) going on
from the previous` inverter (centered) output towards either rail (vertically)...
(and it sure looks a bit like the inverted "S" transfer-curve, that is so typical for these inverters) .
The acid test would be to simply A/B any CMOS fuzzer with that last stage tacked onto the output.
any fuzzer (or even just booster...) whose amplitude comes close to the CMOS`s rails. :icon_wink:
(currently don`t have breadboardable inverters at hand...) :icon_redface:
Quote from: puretube on July 16, 2007, 12:35:50 PM
(currently don`t have breadboardable inverters at hand...) :icon_redface:
I've got an 4049 sine LFO on the board and one output is square. Tomorrow, I'll feed it to a spare inverter wired up with a short from out to in and let you know what it does. :icon_wink:
1kHz sine driving a single stage:
(http://hometown.aol.co.uk/Gezpaton/Before.JPG)
Now with the addition of Brett's 'Compressortron':
(http://hometown.aol.co.uk/Gezpaton/After.JPG)
As predicted, there's limiting and further rounding (can't really see it here, but when I drove the first stage to the point of severe squaring, the 'buffer' rounded the corners out nicely).
Well done Brett!
Start breadboarding chaps (first one to Ebay wins a cream cake)!
Thanks for the pictures, Gez. Very interesting. They match my scope and auditory results. ie. clipping happens quite progressively.
At a low gain setting I found that I could throw a wide range of amplitudes of sine wave at it and get soft clipping (e.g. anything from a few to 1000mV). Only at high settings of the gain pot (past 3 and 4 o'clock on a log pot) did I see anything squarish with typical inputs (10 to 200 mV).
RE: ebay.
How do you describe it?
It's got multiple, stage-filtered, feedback-stabilised, push-pull CMOS amplifiers. Oh yeah, and parts LEFT OUT of the output buffer by some guy who was asleep at the design desk.
Quote from: brett on July 17, 2007, 08:16:48 AMOh yeah, and parts LEFT OUT of the output buffer by some guy who was asleep at the design desk.
From mistakes do great things occur! :icon_smile:
Can this be done with 2 discrete mosfets? I still don't understand how these things work by just biasing with a single resistor. I wonder if it would work with 2 jfets?
Quote from: jaytee on July 17, 2007, 09:37:00 AM
Can this be done with 2 discrete mosfets?
Yes, but personally I wouldn't (reasons given in a link in another active thread at the moment).
QuoteI still don't understand how these things work by just biasing with a single resistor.
Explanation given in said link (plus other links in other threads)
QuoteI wonder if it would work with 2 jfets?
No.
What thread is that in?
Quote from: jaytee on July 17, 2007, 10:33:41 AM
What thread is that in?
Here's a direct link to the info:
http://www.diystompboxes.com/smfforum/index.php?topic=17114.0
Apologies for not posting it earlier but I didn't have the time.
To understand the workings I'd recommend you take a look at the datasheet for the 4049 and hunt around in it for the schematic of an inverter, then read through the above.
If still not clear, think of the following: inverters invert. So, at switch on, if the output is high and the input is low, the output is going to pull the input up as there's a resistor attached between the two; this, in turn, pulls the output down (inverters invert remember). The input can't be pulled up higher than the output as the output, if it dips lower, would pull the input down with it...which causes the output to go high again (what do inverts do?). The end result of all this is that the output and input will sit at exactly the same voltage.
Next, think about RG's analogy of the p-channel and n-channel devices (often referred to as a 'totem pole' - and for obvious reasons when you see the schematic) as being like two voltage controlled resistors stacked on top of each other. If you bear in mind that the devices are matched (equal resistance) then it's easy to see that 'self-bias' results in the inputs and outputs sitting around half supply.
Thanks for explaining I get that. I guess it would be more difficult to bias if the fets wern't matched? Would it work to put a potential divider at the input to bias it?
My own experience of discrete inverters is that clipping isn't that soft.
(http://hometown.aol.co.uk/Gezpaton/Discrete+Inverter.gif)
Can't remember what values were used for the source resistors, or whether I bypassed them...lost in the mists of time!
Sir Paton: allow - now you got me completely puzzled with that schem (http://hometown.aol.co.uk/Gezpaton/Discrete+Inverter.gif)! ???
the way I see it, is
(assumed the wire-cross between the 100k max feedbackresistor/22µ cap/100k trimpot/1M drive-pot indeed is a node)
that DC-wise the 100kmax FB-resistor does indeed establish an exact "Ub/2" bias at in- & output, as is taught in the schoolbooks,
which might be able to be pulled away from half supply either way by the 100k trimpot,
BUT: any AC signal to be fed back from the out- to the input through that "100k max" /and hence limit the maximum gain (A= RFB/RIN) is being shunted to ground by that 22µ capacitor before it gets combined with the inputsignal,
such that the circuit will always be working at its maximum possible physical gain (let`s assume 50 - 70 times), independant of the value of that FB-resistor,
and the actual amplification factor of the circuit isn`t being defined by the RFB/RIN ratio,
but only by the attenuation of the inputsignal through the 1M pot.
(err: they say my posts are meaningless rubbish, lately, and ask why I do post here anyway, but this time I thought: what the heck - freedom of speech - let`s just try, write, and ask... :icon_wink:)
[(edit): hey: and congrats and welcome to the 5k+ club! :icon_biggrin:]
Quote from: puretube on July 17, 2007, 04:14:33 PM
[(edit): hey: and congrats and welcome to the 5k+ club! :icon_biggrin:]
Wow, I hadn't even noticed! Is that like the 5 mile high club??
Sir Toob ( :icon_razz:), your analysis is correct. AC feedback is decoupled by the 22u cap so the amp is run at full pelt and gain is controlled via the 1M drive control (which simply attenuates the signal).
The 100k trim does indeed bias unmatched MOSFETs (for symmetrical clipping). The 100k resistor is in parallel with the output resistance of the inverter and changing its value effectively controls gain by loading to a lesser or greater extent. However, it should be no bigger than 100k as the 22u cap will take too long to charge up and bias the (discrete) inverter...besides, any greater value will have little effect on gain.
I don't know why I typed all that, I just rewrote what you said in your post! :icon_lol:
Quote from: puretube on July 17, 2007, 04:14:33 PM
(err: they say my posts are meaningless rubbish, lately, and ask why I do post here anyway, but this time I thought: what the heck - freedom of speech - let`s just try, write, and ask... :icon_wink:)
I read you loud and clear. :icon_wink: Well, mostly! ( :icon_razz:)
Quote from: puretube on July 17, 2007, 04:14:33 PM
(err: they say my posts are meaningless rubbish
Meaningless? Perhaps. Rubbish? Never.
Or is that the other way round? ;D
I think the gain would be brought down by those source resistors. Bigger resistors, less gain. I was trying to get my head round why the transfer curve gets so bendy near the rails. I think its because the fets are kind of 'upside down'. The souce is at the rails and drains tied together. Biased half way theres 4.5v gate-source. An input signal would turn the fet OFF so you get to that bendy part of the transfer curve near where the fet turns on. Is that right?
Maybe I should start another thread on this one....
Quote from: jaytee on July 17, 2007, 06:57:59 PM
I think the gain would be brought down by those source resistors.
Yes, that's true. However, the transconductance of discrete MOSFETs is a lot higher, so reduction in gain is no bad thing. Having said that, I probably bypassed the source resistors (whatever value was used: note that there are queston marks by them) with large caps.
Unless you're after a booster (which is all that schematic is, as shown) then it's just a hell of a lot easier to use ICs...less components and it's well trodden territory (results are bound to be good).
PS I'm pretty sure I included the source resistors to reduce current.
Quote from: jaytee on July 17, 2007, 06:57:59 PMI was trying to get my head round why the transfer curve gets so bendy near the rails.
Transconductance of each device drops off when pushed into saturation, hence the compression.
Hi
QuoteThe 100k trim does indeed bias unmatched MOSFETs (for symmetrical clipping)
Or, for asymetric clipping with well-matched inverters like those packaged in a CD4049, you could bias *away* from half of Vsupply. Biasing to about 1/4 of supply might be interesting. Have I seen that done somewhere by using a large value resistor pulling the inverter input or output towards ground?
cheers
Quote from: brett on July 17, 2007, 08:31:39 PM
Have I seen that done somewhere by using a large value resistor pulling the inverter input or output towards ground?
cheers
There was a discussion a few years ago about using a trimpot, after which Tim Escobedo incorporated one into one of his designs. There are also a number of designs with large value resistors to ground to create offsets. The thing to bear in mind is that if you have offsets further down the line, then it's likely that large signals are going to be driving those stages so there's a danger that the protection diodes on the input will be brought into conduction (no soft clipping). This only applies if said stage(s) is/are AC coupled: with direct coupling, the output can't swing any lower/higher than the rails...though any offset in one stage creates further offsets in subsequent ones.
some factory-circuits play with resistors-to-ground intensively, too :icon_wink:.
Gez/Brett:
not to derail this thread, I posted the complete schemo (http://img.photobucket.com/albums/v437/latronax/sansvalve2138.jpg) about my interpretation of a discrete "CMOS Inverter Simulator" :
(http://img.photobucket.com/albums/v437/latronax/sansvalve2136.jpg)
in an extra thread...
(http://www.diystompboxes.com/smfforum/index.php?topic=59383.new#new)
to me, soundwise/curvewise it appears as an equivalent to a "Sixth Of Hex" :icon_smile:,
and is able to bring forth some soft clipping...
the dead-short link-trick from output to input doesn`t work on this one, however :icon_eek:
Hi
Has anyone else built this yet? I like it a lot, and would like to know whether anyone else likes it too. (IMO its as nice as my Tubescreamer).
Anyway, I took some photos of waveforms today. I used a fairly hefty input signal (250mV p-p), so the distortion is more than would be achieved with soft playing (and less than would be achieved if used with a booster):
(http://aronnelson.com/gallery/albums/BinOfBrett/Input_300mV.sized.jpg)
Here's the smooth-o-matic's output, on the same scale, with the gain at "noon":
(http://aronnelson.com/gallery/albums/BinOfBrett/Ouput_gain_low.sized.jpg)
And the output with the gain at "3 PM":
(http://aronnelson.com/gallery/albums/BinOfBrett/Ouput_gain_high.sized.jpg)
One thing interests me is that although it is self-biased, it isn't even-sided; the top is "fatter" or "flatter".
All comments and feedback welcome.
ooops:
sorry, Brett,
still haven`t built it yet...
but while pondering over a problem in another thread (http://www.diystompboxes.com/smfforum/index.php?topic=59383.msg485986#msg485986) and going through the usual literature,
I remembered (and found) what I was thinking about a few months ago
whith this "Grounded (or: shorted) Inverter Output" thing, and what it had reminded me of at that time:
Cmos OTA (http://www5b.biglobe.ne.jp/~houshu/synth/CmosOta.GIF),
where Osamu explains the working of a
CMOS VCA (http://www5b.biglobe.ne.jp/~houshu/synth/VcaMos0210.GIF)
(Mike Irwin-inspired too, I guess... :icon_wink:)
now I`m wondering, what an equivalent Jfet circuit would behave like, when artificially "saturated" (pageing GEZ... :icon_wink:)
...greetings btw., to all my stalkers, from the 6k+ club...
Quote from: puretube on October 13, 2007, 02:49:33 PM
now I`m wondering, what an equivalent Jfet circuit would behave like, when artificially "saturated" (pageing GEZ... :icon_wink:)
I haven't progressed to a 2 stage JFET circuit, yet, but I'll give Brett's idea a go when I do!
I just figured ou the drive control. Cool. :icon_cool:
That non-linear amplifier is sooooo cool (http://www5b.biglobe.ne.jp/~houshu/synth/VcaMos0210.GIF (http://www5b.biglobe.ne.jp/~houshu/synth/VcaMos0210.GIF)). It has the biasing control and everything.
The other link (to the OTA schematic) also has interesting piece of information in it, despite it looking so simple. Hmmm....the lower the supply voltage and Gm of the devices, the less linear the inversion. I didn't know that, but in hindsight it seems likely to be a reason why many people run their tube-sound fuzzes at low voltage. That sort of distortion seems analogous to what you get lots of in a class A tube amp. (?) My TSF-based circuit + shorted inverter is set to run at about 6V, but there's no reason why it wouldn't work ok at 4 to 5V, which might well make it less linear, and more compressed and tubey.
cheers
do we have a working layout for this? i'd love to give the build a shot and compare notes, but have no extra time to create a layout at the present.
As long as this thread is still around, can we get an update on the links for Brett's schematic and layout? They have gone 404 on me.
TIA,
Ben
Hi
the jpgs should be in the gallery.
My area is called something like "Brett's bin of bogus bits".
I'd be very pleased to hear anyone's thoughts.
cheers
Brett, Gez: Hsu (http://www.pat2pdf.org/patents/pat3946327.pdf), and g**gle: "Nauta" (Bram)... :icon_wink:
Interesting. So the extra stage with short from output to input makes transconductance independent of voltage supply. Or, to put it another way, it loads the preceding amp to such an extent that gain is pitiful across the whole voltage-supply range! :icon_razz:
Good work puretube.
And thanks for digesting that stuff Gez. My brain is a bit dead tonight.
I hadn't thought of what it looked like in terms of a load - "CMOS" and "low Zin" are stored in different parts of my brain.
So is the full-feedback inverter a "gain soak" for the previous stage because it is an active load (in the wrong direction) ?
thanks
Quote from: brett on June 03, 2008, 07:24:59 AM
So is the full-feedback inverter a "gain soak" for the previous stage because it is an active load (in the wrong direction) ?
thanks
That's my understanding, Brett. The author describes the preceding stage as the 'driver transistors' and the 'gain soak' stage as the "load transistors". Adding more driver stages increases transconductance, and adding more load stages decreases it. This is how he suggest controlling/setting gain. IMO, then, your term "gain soak" is an excellent description.
So, is the effect the same as reducing the size of the resistors in the feedback loops? I have noticed that it dropped the output some when connected. :icon_eek:
Quote from: WGTP on June 03, 2008, 09:52:40 AM
So, is the effect the same as reducing the size of the resistors in the feedback loops? I have noticed that it dropped the output some when connected. :icon_eek:
Not really, although if you don't include an input resistor and the feedback resistor is of low value, then you are going to load the previous stage as input impedance will be low. It will still invert, though, whereas an inverter with a connection from out to in won't (it just loads).
Quote from: gez on June 03, 2008, 12:00:09 PM
Quote from: WGTP on June 03, 2008, 09:52:40 AM
So, is the effect the same as reducing the size of the resistors in the feedback loops? I have noticed that it dropped the output some when connected. :icon_eek:
Not really, although if you don't include an input resistor and the feedback resistor is of low value, then you are going to load the previous stage as input impedance will be low. It will still invert, though, whereas an inverter with a connection from out to in won't (it just loads).
This still hurts my brain... ???
So what if the feedback resistor is super small like 2 ohms? Does it still invert? 1 ohm? 0.5 ohms? Clearly these would give gains of less than negative one, but what does the transition between inverting and non-inverting look like?
:icon_idea: Maybe I'll shed some light on it for myself by putting a small value variable resistor in the feedback loop, and then turn the resistor down to zero while watching the output on a scope or something. Yeah, I think that would do it. :)
Quote from: earthtonesaudio on June 03, 2008, 02:48:14 PM
So what if the feedback resistor is super small like 2 ohms? Does it still invert? 1 ohm? 0.5 ohms? Clearly these would give gains of less than negative one, but what does the transition between inverting and non-inverting look like?
With feedback resistance that small,
and if no input resistor is included, then I'm pretty sure it would act the same as if there was just a wire from output to input (non-inverting, 'active load' as Brett put it). With an input resistor, though, you'd have nothing/a minuscule signal at the output.
moretofollowsoon... :icon_wink:
Quote from: brett on October 18, 2007, 12:24:36 AM
Hi
the jpgs should be in the gallery.
My area is called something like "Brett's bin of bogus bits".
I'd be very pleased to hear anyone's thoughts.
cheers
I think it's great your stuff is online again. I don't see your Hall-effect wah or the Aussie compressor, though...
Quote from: puretube on July 16, 2007, 09:35:07 AM
Quote from: puretube on July 11, 2007, 12:34:31 PM
sorry, folks,
but I don`t see an inverting buffer in U1f:
just a dead short between in & out;
I see two (shunting) FET-diodes going from the (center-biased) output of U1a to the respective rails. ("clipping"...)
:icon_question:
maybe not "diodes", but "resistive loads" ? "constant current"?, "biasing devices"?
in Fig.2, here (http://www.pat2pdf.org/patents/pat4071777.pdf) (N2/P2) an inverter is shown with in-/output shorted.
more theory, here... (http://www.nutsvolts.com/~downloads/fetjul.pdf)
Make that
voltage dependant resistor workalikes, and you`re there where even the most ignorant
reworse-engineer (http://www.diystompboxes.com/smfforum/index.php?topic=69010.msg552890#msg552890) can understand it.