"diode-less" overdrive ???

[tubelectron]

Hi All,

Any of you experimented a "diode-less" overdrive (lo or hi gain) ?

I mean there is no diode clipper inside, it relies on the clipping of the OP Amp(s) (or transistors)...

I was thinking about something with 2 LM308N, for example.

I have no time to breadboard anything these times, so I ask...

Thanks & A+!

[Mark Hammer]

The Black Cat overdrive relies on op-amp clipping.  The MXR Distortion+ continues to clip even without diodes.  Just about any Fuzz Face variant clips in the absence of diodes.

[joegagan]

there are hundreds of designs - cascading gainstage ODs that rely on overdriving stages rather than diodes. runoffgroove, joe davisson and many commercial pedals do this.

[Earthscum]

I've actually got an LM358 distortion I was designing before I got sidetracked by a 386. That resulted in the ChipDrive. Was gonna jump back to the 358 tonight hopefully. It is just based on misbiasing. Simple but very effective.

[tubelectron]

@Earthscum : I had a look to your LM386 one-knob overdrive - I record it, even if the previous trials I have made with LM386 were deceptive.
@Mark : I'll search about the black cat ovd - I have a MXR MC402, good tone, but it has an awful decay...
@joegagan : runoffgroove, joe davisson - yes ! I'll browse there also.

Thanks for your suggestions, guys - I was also thinking about MusicMan opamp hybrid preamps found on their RD-65 and Co : I found them sounding quite well, and there's no diode clipper inside.

And of course, I can try classic designs, remove the clipper and add an extra input opamp gain preamp stage to push on clipping, or do it multi-stage at lo to moderate gain each...

In fact, I would try to duplicate the tone character of my MKIIA Boogie : soft bluesy to smooth long sustain overdrive, singing tone... While avoiding to build the tube preamp section of my MKIIA in a stompbox !

A+!

[PRR]

Guitar signals are part-Volt.

Amplifier overloads are typically many-Volts.

Diode overloads are part-Volt.

Using diodes avoids boosting the signal way up to many-Volt and then dropping it down to part-Volt again.

[Minion]

I"m pretty sure a true overdrive pedal should have as much clean gain as possible without clipping (as opposed to a distortion pedal) cuz overdrive is there to overdrive the input of your amp not to be a distortion effect in it"s self ........

[nexekho]

I wonder what kind of distortion a class D amplifier with an intentionally misshapen control wave would sound like... high/low pass filtering it could in theory delinearise the amp and produce a diodeless overdrive.  Had a quick look around, can't see any class D-based distortions/overdrives.  I imagine it's been done at some point right?  Or is the high frequency stuff a little unreliable outside of SMD?  (don't know)

[tubelectron]

nexekho,

I do not have advice about that, nor knowledge - but I remember a friend who tried to overdrive a small Hi-Fi audio power class D amp (10W if I recall well) and it sounded bad, with an harsh and unstable clipping. But obviously it wasn't designed for that...

My ideas are to stay analogic, say :

1 - to use a 1st OpAmp as an input amp, providing enough gain to overdrive a 2nd OpAmp to clip, this second one having the gain control, or the first one (?).

2 - to have a dual gang variable gain pot on the 2 OpAmp, in order to distribute the clipping operation on both, for a "cascaded clipping".

"Soft Bluesy" to "Smooth Long Sustain Overdrive, singing tone" is the target, while feeding a clean amp (Silverface Fender Twin Reverb, for example).

A+!

[DavenPaget]

Well you definitely don't want to distort a Class D .
But that is definitely a old design for it to sound harsh .
New designs don't do that and i know that .

[nexekho]

If you overdrive a Class D merely by overloading it, it will sound harsh because it should in theory be a near perfect square clip.  However, I'm talking about replacing the precision triangle wave generator used as the second input to the comparator with something intentionally imprecise that spends more time in the middle to squash the signal up against the upper and lower bounds creating a soft clip.

Example idea using a high pass filtered square wave

I'm just thinking if this kind of thing could work it could offer a LOT of flexibility in how it overdrives because all kinds of filters could be pushed between the osc. and the comparator.  I think digital logic (AND gate) could be used to modulate signals together too.

[Jazznoise]

Might seem a little redundant but why go to the bother of distorting an op amp at all? Just build a boost and overdrive the input of your amplifier! I was recording some guitar tracks for a freind today and I'd the Fuzz section of my Graphic Fuzz totaly bypassed, I was just EQ'ing and driving the input of the amp for different tones.

[tubelectron]

Might seem a little redundant but why go to the bother of distorting an op amp at all? Just build a boost and overdrive the input of your amplifier! I was recording some guitar tracks for a freind today and I'd the Fuzz section of my Graphic Fuzz totaly bypassed, I was just EQ'ing and driving the input of the amp for different tones.

my specs are :

"Soft Bluesy" to "Smooth Long Sustain Overdrive, singing tone" is the target, while feeding a clean amp (Silverface Fender Twin Reverb, for example).

The amp would be another kind of type, found on extra-reharsal or impromptu sessions, when I don't have one of my amps. Let's say a Fender Mustang III or any other solidstate amp able to give a reasonable good clean sound (the Mustang III, preset 93 "basic twin" with reverb at 5 sounds very decent, for example).

Just build a boost and overdrive the input of your amplifier

IMHO, it would be useless with a SS amp, and I don't need one with my amps (DIY models not shown) :





A+!

[PRR]

> is the high frequency stuff a little unreliable outside of SMD?

That's been possible since vacuum-tubes.

> class D amplifier with an intentionally misshapen control wave

Anything you do to the "control wave", you could just as easily do directly to the signal.

And maybe this idea is worthy of its own thread, instead of drifting Bruno's question?

[oh7hhi]

Hi!

Maybe OP should try the Blackstone Appliances Mosfet Overdrive.
I build one for a friend two years ago and it's still in his board .

Very bluesy and singing tone, someone could say "Dumble-like"...

[tubelectron]

Hi!

Maybe OP should try the Blackstone Appliances Mosfet Overdrive.
I build one for a friend two years ago and it's still in his board .

Very bluesy and singing tone, someone could say "Dumble-like"...

Oh, yes ! I forgot this one... I missed one on eBay last year and only have pictures of the device, so if you are willing to post the schematic ( or send it to me through pm, if you prefer), I would be very interested, indeed (Thanks !).

A+!

[DougH]

The implied premise of the original post that "all/most/typical overdrives use diodes to clip" is false.


Just thought I'd mention that.

[tubelectron]

Hi!

Maybe OP should try the Blackstone Appliances Mosfet Overdrive.
I build one for a friend two years ago and it's still in his board .

Very bluesy and singing tone, someone could say "Dumble-like"...

OK - I see (thanks !) - it's more or less an improved Hot Tubes / Tube Sound Fuzz design. Circa 20 years ago, I have been given a mint Hot Tubes from EH (that I sold stupidly for peanuts) and I remember that it worked better on organ than on guitar...

I do not have in favor the mos-fets, finding that they sound inexplicably somewhat harsh and uneven harmonically on the trials I have made, the last one being a clone of a traced-from-an-original MG "Sexy Drive" pedal (which uses cascading J201 and 2N5457 fets). But it would be time for me to start new trials on that field...

A+!

[bhill]

On the other forum,  look up the SeaMoon Fresh Fuzz. That is the 70's pedal that the Black Cat copied, and it is a fuzz, not an overdrive in spite of the name. Looking at your pictured amp collection, you would do better with a simple mosfet boost.

[WGTP]

http://diystompboxes.com/analogalchemy/

Some Great overdrive/distortions without "clipping" diodes.