Another New Design.. i present you the "DUI distortion"

[~arph]

Very nice, you might want to add pot values too btw

EDIT:    oops.. disregard my comment

[dschwartz]

  It has no trimpots, 2 mu amps and an Opamp.
  That means if you wire it right you don't have to fiddle with other Jfets [though they will alter the sound], and trimpots, and working to get ungatey sounds jibing with the bias arrangements.
  I would ground the inputs on the unused side though, or use a single OA.
  The biasing setup is like what I've chosen for later Mu's.
  Am I not seeing a gain pot value ?
  Looks good from here, TIA for any Sounclips ! !

yes, a 741/071/081 opamp would be better..
Tl072 was there cause i was experimenting, and probably for further evolutions i will need that extra opamp, maybe for tonestack driving or a clean channel, who knows..

[dschwartz]

Very nice, you might want to add pot values too btw

the pot values are at the shem picture low left....

[~arph]

yes.. somehow, I totally missed that and was wearing my glasses too..
Thanks, nice design, how is the low end? it sounds a bit trebly to me.
(looking at the caps, it looks trebly too  )

[dschwartz]

yes.. somehow, I totally missed that and was wearing my glasses too..
Thanks, nice design, how is the low end? it sounds a bit trebly to me.
(looking at the caps, it looks trebly too  )

is not trebly at all, and the tone control gives plenty of low end.. i used my hi fi stereo through the multicab sim, and sounded just right..it has a lot of sparkle and bite..i agree the second clip is kinda trebly, but the rest are ok..if you find it trebly, just adjust the tone control, is pretty effective

[zencafe]

Hola Daniel!

I've tried this baby on sunday, (btw thanks Daniel for the help with the hum debugging on my Ampeg Preamp ) It sounds amazing!
Very nice crunchie overdrive, and very harmonically rich!
Nice to play, specially chords...
Congratulation,s good work again,
And thanks for sharing!

D.

[DougH]

Looks and sounds nice, Daniel!

Reminds me of the old days of the forum when we were experimenting with op amps and miniboosters. Good stuff.

[dschwartz]

i´ve heard some comments that the sound is too trebly.. i used big hi fi speakers, so maybe iot doesnt sopud trebly to me..i´ll try to post new demos showing the tone control range..

[DougH]

It sounds trebly to me but I didn't bring my good earphones today and am listening through computer speakers. Still, the basic elements are there AFAIC- gain, harmonics, touch-sensitivity, headroom. Sounds like it does a wide variety of good sounds. Excessive treble is easily dealt with and people will tweak it for their own rigs anyway.

[jacobyjd]

It almost sounds like you're parallel processing two distortions in the sound clip--one that's just barely clipping, and another that's all-out. It gives it a nice element of transparency--lots of distortion if you want it, but I can still hear when you hit the strings.

Nice

I've been itching to mess around with combining various gain stages with clipping to achieve something similar to this--mostly as a learning experience, but it'd be great to find something really usable

Good show.

[dschwartz]

It almost sounds like you're parallel processing two distortions in the sound clip--one that's just barely clipping, and another that's all-out. It gives it a nice element of transparency--lots of distortion if you want it, but I can still hear when you hit the strings.

Nice

I've been itching to mess around with combining various gain stages with clipping to achieve something similar to this--mostly as a learning experience, but it'd be great to find something really usable

Good show.

it was quite interesting how i get to the sound..most of the distortion comes from the opamp diodes..by itself gives a really nice bluesy crunch. I instinctively put the u-amps with lots of gain at first, which sounded good, but only on full distortion settings, on mid gain settings they started to fart and fuzz (which i just hate), then, i lowered the gain of the u-amps stages and let them be at the point they just start to clip, that way we get nice u-amp compression and harmonic content. I was looking for more metal sounds, but it blew me away with the tone on that configuration..

i have to try a boosted setting..i´m not sure if i give more gain to the opamp or to the uamps.. feel free to try more or less gain..

i think the sound approximates a tube amp boosted with a distortion or a TS..

[arawn]

It is most definitely not too trebley, It sounds great nice nice Vanhalen Sounds and some pretty good metal sounds too at the end of the one clip, but it is very very Brown sounding I love it

[suprleed]

You always have good stuff senor dS!  The max gain clip was impressive.  I also liked the low gain blues, I could definitely hear the SRV influence there.  Great work!   

[Joe Hart]

There is another thread about JFETs being widely variable. How much will that impact this circuit?
-Joe Hart

[Joe Hart]

it was quite interesting how i get to the sound..most of the distortion comes from the op-amp diodes..by itself gives a really nice bluesy crunch.

Earlier, you mentioned that the diodes don't make much difference. I know that in a TS or DOD250 I hear a HUGE difference between diode types (ignoring Si and Ge -- even between green and red LEDs and certainly between 3mm and 5mm). And I don't mean this to be a wise guy. I think the circuit sounds amazing!! And I am totally going to build it, I just want to get the facts straight so I know what's going on with the circuit (with my incredibly limited knowledge!).

Thank you!!
-Joe Hart

[dschwartz]

i havent tried different fets on the prototyupe, but theory say that you don´t need matched fets, or set the bias, i will auto bias...nevertheless, different fets can give different gain..

about the leds, i tried germanium and leds, liked leds more than germaniums in there, and yes they make a big difference (but i tried Ge and Leds, so big difference is expected)

[alanlan]

..you can change the upper fets, since they only work as current sources, and they dont amplify..

Not quite - you may want to check out some of R.G.'s articles on JFETs at geofex.

If you remove the caps to the upper JFETs gates THEN you have current sources...

Regards,

Jay Doyle

hmm...from RG keen´s "fooli´n with fets", about the u-amp configuration

Connected this way, the upper N-channel JFET is still helping move the load, but is not contributing any gain itself. Also, since its input has to be driven from the drain of the lower JFET, the lower JFET is now driving the bias resistors of the top JFET, but more importantly it's also driving the JFET source impedance. This loading keeps the max gain down to about 90 even with 10M biasing resistors for the upper JFET.

A couple of points:
a) JFETs are modelled as current sources i.e. id = gm.vgs. so it's a bit of a mute point.
b) in the mu amp, the load JFET (or MOSFET) is acting as a very low value constant current source (ideally zero current).  Why is this?  Because the capacitor across the gate and source ensures that there is very little AC signal across vgs and hence very little AC change in id.  Effectively, the FET looks like a very large value resistor at AC and a smaller value at DC (which allows it to bias without dragging the drain of the main JFET too low).  It is this which contributes to the overall gain of the circuit.

[dschwartz]

..you can change the upper fets, since they only work as current sources, and they dont amplify..

Not quite - you may want to check out some of R.G.'s articles on JFETs at geofex.

If you remove the caps to the upper JFETs gates THEN you have current sources...

Regards,

Jay Doyle

hmm...from RG keen´s "fooli´n with fets", about the u-amp configuration

Connected this way, the upper N-channel JFET is still helping move the load, but is not contributing any gain itself. Also, since its input has to be driven from the drain of the lower JFET, the lower JFET is now driving the bias resistors of the top JFET, but more importantly it's also driving the JFET source impedance. This loading keeps the max gain down to about 90 even with 10M biasing resistors for the upper JFET.

A couple of points:
a) JFETs are modelled as current sources i.e. id = gm.vgs. so it's a bit of a mute point.
b) in the mu amp, the load JFET (or MOSFET) is acting as a very low value constant current source (ideally zero current).  Why is this?  Because the capacitor across the gate and source ensures that there is very little AC signal across vgs and hence very little AC change in id.  Effectively, the FET looks like a very large value resistor at AC and a smaller value at DC (which allows it to bias without dragging the drain of the main JFET too low).  It is this which contributes to the overall gain of the circuit.

thanks for clearing that up!!
(although when "Vgs off", "gm.vgs", "cutoff", "beta" and other words are in a sentence, i get kind of lost...give me a year to digest those terms)

[JDoyle]

A couple of points:
a) JFETs are modelled as current sources i.e. id = gm.vgs. so it's a bit of a mute point.
b) in the mu amp, the load JFET (or MOSFET) is acting as a very low value constant current source (ideally zero current).  Why is this?  Because the capacitor across the gate and source ensures that there is very little AC signal across vgs and hence very little AC change in id.  Effectively, the FET looks like a very large value resistor at AC and a smaller value at DC (which allows it to bias without dragging the drain of the main JFET too low).  It is this which contributes to the overall gain of the circuit.

A couple of points -

- It's not a 'moot' point - A JFET may be modeled as a current source, like every other transistor, but we don't care about Id - we care about Is as that is the terminal feeding the lower JFET.
- How can a constant current of zero be a current source? Electrically speaking, it's nothing. And if that is the ideal situation, how would the output voltage not also be zero? In fact, your ideal situation means that there is no battery/power source either because even leakage currents can't get through - and they always do.
- The output impedence at the source of a JFET is low, which according to Ohm's Law, and not a model, means that it is closer to a voltage source - the opposite of a current source. To make a JFET into a current source is simple - but the terminal one HAS TO use for it to have a high Zin, and thus be a current source, is the drain NOT the source.
- There is also very little change in Vgs in a source follower - are you saying then that the output impedence at the source of a source follower is very large as well? If so, why is the Zout of a source follower LESS than Rs - if its Zout is high, as you say, wouldn't Rs then dominate as Rd does in the case of a common source stage?

The upper JFET is a source follower that is also being driven by the signal on it's source - which, as R.G. said in the quote, doesn't contribute any (voltage) gain, but DOES help to move the load.

The top JFET is not a current source. At all. It provides current to the bottom JFET, but that doesn't make it a current source. The best way to think of it is that it 'bootstraps' the gm of the lower JFET. 

Regards,

Jay Doyle

[Xavier]

Very interesting circuit design , I will build it right away. On paper it looks like BSIAB on steroids .

I will try to post a perf layout later today.

Tiene muy buena pinta , Daniel , gracias !!!