Dist+ or DOD 250 or Ross Distortion?

[amptramp]

A late teaching colleague used to get load-out gigs at various concerts around town.  He was surprised to find out that many cabs in the mountain of Marshalls that Kiss had on stage were actually empty, and many of the amp heads were just parked, unpowered, atop those cabs.

Suspicions confirmed:

[zbt]

I always think about this, when I was little I went to an exhibition, and entered a small room with 4 little speakers
The sound was very big, I was confused in my heart and said how could that be?

It looks exactly like this


At that time I only saw the 4 small monitor speakers, the big one
which is like an invisible subwoofer, after I read in a magazine article about how it works. If I'm not mistaken, it's like an organ pipe, resonating at 45Hz and 90Hz. maybe for resonance too,
that's why I wondered if it wasn't like a small lizard that looked big.
but I think it seems strange, so we might as well just ask them what it's for 

Frankly, I don't know, the lesson for me is that I should ask directly

before I forget, (many circuit so short time)



For LM308 there transistor set like diode clamp for 0.7V



And OP07 would be 1.4V maybe different from LM308 cause it sound a bit bright



so for LM741 is it possible to make slew it like this?
anyone know how to calculate the value for the capacitor?





while NE5534 same as LM308, it could be the secret of Uncle Jimi Pink Clipper
or Pink Triple Clipper 

reminds me of



Black Repper, Yellow Humper, Green Ringer, Pink Clipper, Blue Clipper, Red Ranger
lets make two other hero Purple Peaker and Orange Squeezer   
Introducing Dan Armstrong Eight Rangers

We should build it for kids today, hopefully they can learn guitar while they young.

does anyone know the schematic for the black one

[Mark Hammer]

A quick addition, if I haven't posted it already.

When an op-amp-based overdrive uses diodes in the feedback loop, we tend to refer to it as "soft" clipping, as opposed to "hard" clipping, when the diodes go from the output to ground.

As I'm fond of noting, with a 9V power supply, a typical guitar signal can really only be amplified maybe 20-30x by an op-amp before encountering serious headroom limitations and clipping.  Most op-amps can really only swing +/-3.5V with a 9V supply.  And even the most demure of overdrives will amplify the input signal several hundred times.  The Dist+, DOD250, and Ross provide for up to 214x gain.  So, before the signal ever gets to the diode pair, it is clipping hard, due to headroom limitations.

In contrast, with diodes in the feedback loop, the voltage swing, independent of the gain, is going to max out at around +/-650mv, which is well below the maximum voltage swing of the op-amp.  The diodes will clip the signal, but that's as clipped as it gets.  In contrast, circuits like the Dist+ and 250 clip the signal twice, once within the op-amp and again when the clipped signal hits the diodes to ground.  Small wonder the result can sound harsher, and earn the title of "hard" clipping.

But this leads to something worth considering, and that is the manner in which the particular op-amp used clips, when it runs out of headroom.  In the case of the Dist+, the majority of layouts assume a single op-amp, likely a 741.  Others may assume use of one half of a dual op-amp, like a 4558 or TL072, et al.  Sonic differences between pedals that have ostensibly the same circuit diagram will depend on how the op-amp clips at maximum voltage swing, and what the diode pair to ground is.

[zbt]

What I caught, seems to be that the hard clip happens first, then the opamp, so the soft clip doesn't seem to have much of an effect.

Vpeak   A 200   A 100   A 10   A 5
0.700   0.003   0.007   0.070   0.140
1.400   0.007   0.014   0.140   0.280
2.100   0.011   0.021   0.210   0.420
3.500   0.018   0.035   0.350   0.700
4.500   0.023   0.045   0.450   0.900

maybe for a humbucker or given a boost like the DS1.

[Mark Hammer]

Not quite sure what you mean here.  Do you mean that, since the forward voltage of a diode pair to ground is smaller/lower than any clipping resulting from bumping up against the maximum voltage swing of the op-amp, then I guess you're right.  Of course, those diodes would only conduct "first", and uniquely, when the gain is low enough that the op-amp is not being asked to swing terribly wide.  So, for example, a gain of 10x might yield some diode clipping in the absence of any op-amp clipping, and primarily on pick attack, without much effect after that.  Under real world circumstances, however, most end users would have the gain up higher than that.

My sense is that the original purpose of both the Dist+ and DOD250 was to serve as clean boosters for part of their range, and then clipping drives above that.  Remember that it took several years before separate clean boosters, like the Micro Amp, appeared on the market (although the EHX LPB-1 had been around for several before that).  What led me to this view was the use of C-taper 500k gain pots.  C-taper proceeds through the highest resistance values of a pot "quickly", and offers a more gradual progression through smaller values in more clockwise settings.  That is why they are generally used for setting LFO speed in modulation pedals.  If one is interested solely in achieving grit and grind, then why not use a 100k or even 50k gain pot?  Why use 500k?  My inference is that the circuit was intended to provide relatively clean boost between, say, the 7:00 and 9:00 gain settings, and grind above that.  The DOD circuit improved that by employing silicon clipping diodes with a higher forward voltage.  That not only permitted fairly clean boost at lower gain, but also more "clean" output volume with such diodes in place.  On top of this, by using the ground leg of a non-inverting op-amp to set the gain, at lower gains bandwidth was at its widest, with lots more bass in the output.

Now, I don't have ANY proof of this.  It's just an inference on my part.  But even if it was just a happy accident in circuits designed with other goals in mind, I would think the makers were content with the result.

[zbt]

I use a value of 100K for the volume on the MXR D+ circuit, for 10K the sound is strange.


I am trying to calculate what input value is needed for the clip output value on the diode.
If use 100K with a diode output of 0.6V then get a value of 1.1 x 0.6 = 0.66V
with gain 213.76 (A=1M/4K7+1) Calculator

I got an estimated value of around 3mV
for clip opamps 3.5V around 16-17mV for 4.5V around 21mV

Input   Output 
 3 mV   0.66V   Diode clip
17 mV   3.5V    Diode clip + Opamp clip
21 mV   4.5V    Diode clip + Opamp clip

with this data I conclude that the diode clip will take effect first compared to the opamp

so when if clip on input happens in NE5334 (0.7V)
May be Humbuckers would help cause range is 0.5V - 2V Guitar Voltage

If I calculate using 0.7V the Vo value is 149.63V, this is impossible because the supply voltage is 9V with a peak of 4.5V

For input 0.7V with
RF      Gain    Vo
4.7K    2       1.4V    diode input clip + diode output clip
20K     5.25    3.67V   diode input clip + diode output clip + opamp clip
27K     6.74    4.72V   diode input clip + diode output clip + opamp clip

A=1000/1004.7=1.99      MXR D+
A=1000/504.7=2.98       DOD 250

So if use the NE5334 it looks like the gain has to be very low, as your sense Sir for clean boosters. 
As for the difference in sound, whether it will be felt, I don't know yet, considering that my ears are not very good.

for capacitor "Input lag compensation is provided by C3, limiting the slew rate of the amplifier to reduce high frequency intermodulation".

[amptramp]

If you are using a 5534, you might want to control the tendency to oscillate by adding a small capacitor from the output to the inverting input of about 47 pF.  You will also need decoupling right at the power pins of the op amp.  The 5534 is a wideband amplifier and it needs to have decoupling on the supply voltage whereas the 741 is an op amp from the age of steam and usually works without it but the treble gain really falls off for gains of more than five.

[antonis]

As for the difference in sound, whether it will be felt, I don't know yet, considering that my ears are not very good.

Same here..

But in case of your eyes are in much better state than your ears, you can trace output waveform for input signal of 300 mV ('cause your op-amp gain can't go lower than 1.995) both for gain set to min and to max..
(the former is a sine wave clipped at top and bottom where the later is an almost squared one - both of the same amplitude..)

[marcelomd]

Just some thoughts.

When you clip at the opamp (either with diodes in the feedback loop or when hitting the rails) and then clip with shunt diodes to ground, the effect is a composition of the clipping characteristics of both methods. It's not a world of difference, but enough, to me, to give that sense of touch sensibility if you "space" the onset of clippings right.

Also, if you want to clip the opamp, to my ears, NE553x is not the best clipper. TL07x, TL06x sound nicer to me (or TLC226x, which the Sansamps use).

You can also use a combination of feedback and shunt diodes. That way you can tailor the onset of clipping at the opamp, make it (a)symmetrical, etc.