Discrete TubeLess...

[puretube]

The 2 "OverCrosser" pots described for the "CSPWMB" work as follows:

P1 controls the amount (percentage) of crossover-distortion, and can vary the waveform horizontally, when rotated,
while
P2 controls the position of the crossover point in the waveform vertically, when rotated.

And I answer with Blade.

But now that I bring that up I got some new ideas.

Andrew

that`s what this thread is for... 
(bringing up new ideas)

BTW: the "OverCrosser"-mod does it crackle-free. 

[gez]

Had a little time this morning to do some more testing.  By biasing both gates slightly off-centre, I was able to reduce/control current in the inverter and remove the source resistors.  However, transconductance was too high and clipping was harsh (no subtle compression as the output nears the rails).  Pity, as the source resistors definitely contribute towards distortion of the wave form and, after a little testing, I think I know what's going on.

Due to negative feedback, neither the n or p device acts as a follower.  Instead, each source resistor forms a divider with the channel of its respective device.  The effective resistance of each device's channel changes with the voltage on the gates.  Considering (for convenience) the n-channel's source only, the source will drop as the output drops.  However, with negative swings on the gates (positive output swings) the n-channel narrows, its effective resistance increases and it pushes the (comparatively small) source resistor down.  End result is full-wave rectification, albeit around a shifting DC centre-point.  The latter is partly due to inverters making poor amplifiers.  The virtual-earth effect isn't perfect so a tiny voltage is seen at each source (it acts as a slight follower).  When either the p or n device are pushed into saturation, negative feedback is lost and a slight voltage builds up on the gates, in turn increasing the slight 'follower signal' seen at the source.

Unfortunately, all of the above causes slight distortion to the peaks of the signals.  Perhaps this accounts for the slight 'rattle' I mentioned?  Bypassing the source resistors cures the problem but creates another: transconductance is too high and clipping is hard (again, there is no soft compression as the output approaches the rails).

Looks like drain resistors might be the way to go (for me)...

[puretube]

I like!

Andrew

I wonder, whether the MO or the PM-Club is the better place to disclose the schematic for the Waveply,
or if I just ought to wait to submit it for the monthly contest (being a neg-FB-circuit)...

Well, on second and third thought, it not neccessarily being a neg. FB circuit, but rather some kind of to-and-fro-feed
of those tiny signal-dirt remnants that Gez mentioned above on the "southern" sources,
why not show the block-schemo here:



and the full one there... 

(clips in reply#21).


BTW., Gez: aren`t you now heading towards the "normal" class AB complimentary pushpull amp?


(my intentions in this circuitry are purely distortional, so I`m not that puzzled about "sidenoises"  )

[gez]

BTW., Gez: aren`t you now heading towards the "normal" class AB complimentary pushpull amp?


(my intentions in this circuitry are purely distortional, so I`m not that puzzled about "sidenoises"  )

Hmm, possibly (though the drains are still doing all the work)...

[nordine]

wow, how has this thing evolved...
design is rad and samples sound great!

now, the only mosfets i know (and have) are BS270 and 2n7000, both N-channel ..which are common or good replaces for BS250's (none of the near stores have it)?

edit: by stores i mean 'local stores', smallbear-futurlec-mouser are 'international stores' for me

[puretube]

sorry, nordine,
I don`t have any experience with other types
since that 170/250 combination is the most common one here
(a.o. propagated by "Elektor" over the years...)

BTW.: our local store has closed forever, 2 weeks ago 



and: yes, with bass it can sound very cool - depending on what you expect from a bass-effect, however... 
(I`m very Bootsystic in this matter.)!

[nordine]

mmm.. looks i'll have to look harder for these P channel thingyes, overtones are always welcome on bass guitar.. it the secret weapon for presence (when mids give you only honk)

in the meantime, i had to experiment with this concept, so throwed in some starved tubes (hey keep reading ), which is weird at least -being it a tubeless design-, and got a real ugly-ass and mean bass distorter 

[WGTP]

Any new info on this?  I'm going to have to try it this weekend.  I'm wondering if 2 of these would work in a dual Mu-Amp set up like the BSIAB, or driven by an op amp like the Shaka or a Mosfet Boost.   

[gez]

Sine wave through a 1 stage discrete JFET version:



Softer clipping characteristics than the MOSFET version due to lower transconductance.  Also very low current consumption - less than 1mA, and could probably get it lower (will see).

Have only scoped the circuit so no idea how it sounds, but if any good will enter it in this month's competition.

[gaussmarkov]

Softer clipping characteristics than the MOSFET version due to lower transconductance.  Also very low current consumption - less than 1mA, and could probably get it lower (will see).

Have only scoped the circuit so no idea how it sounds, but if any good will enter it in this month's competition.

[gez]

Plugged in the JFET circuit today and it sounds amazing!  Didn't have to change a single component value of the circuit I sketched out (love it when that happens)!

At the moment I'm only driving a single stage with an op-amp, but it has a wonderful, natural sound: amp on the edge of breaking up sort of thing.  Initially, I was going to sort out a tone control, but it doesn't seem to need it.  The reason seems to be the softer clipping: even when driving the JFETs (one n-channel, one p-channel) hard so that the sides square up, the corners are always rounded so there's less hi-end fizz than CMOS circuits.

I expected this to be one of those 'quirk' circuits that I just breadboard, have a little fun with, then move on; but, I think I may end up building a variant of this little beast!

Will post a schematic at the end of the month as a part of The Tone God's competition.  Stay tooned...

[gez]

PS  The biasing is different, so don't go subbing JFETs into any of the above MOSFET schematics, they won't work.

[gaussmarkov]

PS  The biasing is different, so don't go subbing JFETs into any of the above MOSFET schematics, they won't work.

mind reader!!!   for quite some time, i've been planning a discrete version of the red llama.

[gez]

I think we should call the 'new' technology CFET, or possibly CJET (complementary JFET).  Unless anyone has a better name? 

[Steben]

I think we should call the 'new' technology CFET, or possibly CJET (complementary JFET).  Unless anyone has a better name? 

It's push-pull no matter what. JFET push-pull overdrive.

I have an idea what your circuit may be (a bit like the circuits where RG discusses mu-amps, right? - but a tad different)
But what JFET's did you use? I don't know complementary JFET's as close as in 2N3904 and 2N3906.

[gez]

I think we should call the 'new' technology CFET, or possibly CJET (complementary JFET).  Unless anyone has a better name? 

It's push-pull no matter what. JFET push-pull overdrive.

I have an idea what your circuit may be (a bit like the circuits where RG discusses mu-amps, right? - but a tad different)
But what JFET's did you use? I don't know complementary JFET's as close as in 2N3904 and 2N3906.

Well, perhaps the 'C' should have been left out as the JFETs aren't necessarily complementary: I didn't match them, I just used whatever was to hand and incorporated a trimmer for bias.  Your name/description is more acurate, I suppose, but a little lengthy.  I'll have to have a rethink.

The bare bones of the circuit is exactly the same as an individual CMOS inverter, in that a p-channel device is stacked on top of a n-channel device to form a 'totem-pole'.  Both joined at the drain, and the output is taken from the drain.  It works on exactly the same principal as a MOSFET inverter, only the biasing for the circuit is a little more complicated (source resistors need to be included for one thing, plus separate feedback networks for each transistor).

I'm still experimenting with it, so don't want to post anything yet, but will definitely enter a version in this month's competition.

[puretube]

Well, perhaps the 'C' should have been left out as the JFETs aren't necessarily complementary: I didn't match them

maybe not complementary (complimentary?) but maybe oppositely "polarized":

OPFET ?

[WGTP]

Well, I got the Sansvalve working biased at 4.85v with 9v battery.  Removed the feedback loop, it's running open loop I guess.  BS170/BS250. (stupid pin outs)  Reduced input cap to .001uf.  Pretty dark, but smooth distortion. 

Driven by a Distortion + type op amp, minus the diodes, back to 100n input cap, feedback loop of 1M resistor with 100pf cap parallel for fizz reduction (probably the op amp distortion contributes to this).  Tweaks continue.  Thanks for the very cool new "stage"

[johngreene]

I think we should call the 'new' technology CFET, or possibly CJET (complementary JFET).  Unless anyone has a better name? 

'new'?
http://www.geofex.com/Article_Folders/foolwfets/foolwfets.htm

[soulsonic]

Some really cool looking JFET circuits that are similar to the concepts discussed here can be found on this page:
http://www.rusblues.ru/articles/tech/tech04.shtml

Pa Ruski, but its totally worth playing with Babelfish to get it figured out. Viktor Kempf has some cool ideas!
Очень интересно!