I know i´m beating a dead horse, but, have anyone tried this?

[Paul Marossy]

> Lab Series L5 ... I thought it sounded pretty good. I was surprised to find out that it wasn't a tube amp.

It is very dated, unsophisticated, except the A110 distortion stage. Hi-pass signal is fed to the control port of a VCA. This gives rising-with-frequency 2nd harmonic; to around 7% at/above 2KHz. Moog had good ears and simple taste in design.

Very interesting. When I heard my first King's X album, I was really curious what amp he was using. I assumed all along that it was some sort of tube amp and was very, very surprised to find out it was a solid state amp. Even if it's a very dated design, it certainly sounds very good in the context in which Ty Tabor used it.

I think it's pretty established that something like a Fetzer Valve jfet or a rangemaster with a bipolar transistor can create plenty of even harmonics. Same thing with opamps and diodes. If you create assymetrical clipping you get even harmonics added to the odd harmonics. What I think tubes do better than transistors is they go into and out of clipping better. That gives the nice feel and pick sensitivity. Opamps particularly, to my ear, just don't transition well. And the note decay crackles and fizzles. If you play super distorted so you never let it clean up the distortion character can sound great. But if you want to play between blues and crunch it's just not the same. I think that's why a compressor helps SS.
When I read about tubes, the jist I get is that they are actually a more linear amplifier in raw form than SS. SS needs loads of negative feedback to be clean. Think op amps. So a tube can transition smoothly into clipping and back out better because it isn't fighting so much negative feedback.

You might be onto something. I kind of feel the same way about most of what you say. It is said by many people that the tube overloads more gracefully, perhaps for the reasons you state. For me, nothing has the kind of touch sensitivity as a tube amp with a tube rectifier combined with a good sensitive speaker. You can feed the amp whatever distortion pedal you want into the input and it still has that tube character in the end result. That's where it's at for me. But I don't like running thru an FX loop on an amp, it has a different sound than when you have everything going thru the input and thru the whole preamp section.

[Caferacernoc]

"You can feed the amp whatever distortion pedal you want into the input and it still has that tube character in the end result."

I agree. Even when the tube amp is set "clean" it is distorting a little. And that bit of soft clipping and compression AFTER a solid state dirt box smooths it out because a tube amp can't pass a square wave without rounding off the corners.

Back to the original question about opamps with assymetrical clipping cascaded. See the carvin style for a similar idea. All about the shifting duty cycle:

http://www.trueaudio.com/at_eetjlm.htm

[dschwartz]

wow! pretty interesting article..looks like murphy has done it before, i´m going to try my own approach anyway..
thanks!

[Paul Marossy]

Yeah, that's an interesting article.

Those harmonic differences account for the "raspy and obnoxious" sound of the solid-state amp in clipping, compared with the much-more-mellow sound of the tube-amp clipping. A second, more-subtle difference is that solid-state amps tend to have a fixed 50-percent duty cycle as they clip, whereas most class A tube amps clip with a duty cycle that varies as a function of the drive level.

This suggests to me that there is also a little bit of intermodulation distortion present in a tube circuit. Maybe that is what makes it a little more interesting sounding than a solid state amp?

"Push-pull, class AB tube power amps tend to clip much like solid-state amps, but they sound different because of their high output impedance. In particular, tube power amps exhibit a peak in their frequency response by as much as 10 dB or more at the resonance frequency of the speaker they are driving."

This is an interesting statement.

[dschwartz]

ok.. time for my observations:
i breadboarded the circuit i described:
1st stage: 10X gain inverting opamp, no clipping (it clipped anyway, or my amp did)
gain control: 100k pot as volume with 1n bypass cap. ..pin 1 to vref
2nd stage: 4x inverting with 1n4148 at feedback path. 1n cap in feedback path
3rd stage: 10x inverting with 1n4148 at feedback path. 470p cap in feedback path
4th stage: 5x inverting with 1n4148 at feedback path and red led from out to vref. 470p cap in feedback path
volume control
output

results:
rightaway it sounded as a very high gain, mesa-style distortion, felt really good on the fingers, but kinda noisy, and worst, gated..it gated out when not playing, and was impossible to get relatively clean tones when turning down the guitar volume and/or the gain pot. I discovered that stage 4 didnt have an input resistor.. put one there and the gating improved greatly, but it sounded strange..i couldn´t get "warm" bluesy tones out of it, which for me is the first thing a good distortion does

definetly it´s something there..i have to try more combinations..maybe too much gain somewhere or too much assymetry..

[DougH]

The bottom line FOR ME is that I like my distortion/OD pedals into my tube amp(s), but I don't like them as a standalone unit for recording direct, they simply don't sound good.

The speaker has more effect on the overall sound than the amp, electronics in the amp, the pedals, etc, etc...

[aron]

To add a bit more:

http://www.diystompboxes.com/smfforum/index.php?topic=9267.0

and (which I still have not built!!!!)

http://www.sugardas.lt/~igoramps/article68/article.htm

crate distortion:

http://www.muzique.com/schem/louis.gif

[caspercody]

Aaron,
You posted about the Peavey patent schematic out there, has anyone used this design? Does it have a different sound? Or now this Crate schematic you have posted?

I also am curious of the sound of the Russian design (I also mentioned earlier about another Russian Jfet design), has anyone tried these? I was bored and entered them into Eagle, if anyone wants them?

I have read most of this tread, and get some of what you are trying to do. Still new to this world, and mostly just interested in the distortion/OD side. I am curious, I know some have used Jfets in place of tubes (to create distorion pedals based on amp schematics), is there a way to replace the tube with a op amp? I am sure I know the answer, but wanted to ask. Or even some way to use Joe Davissons diode op amp?

Is the LXH2 projects somewhat close to what you are trying to accomplish here? I just found that web link, and to me looks interesting, but curious if it is much different than the many distortion pedals, amp emu pedals, I have already made?

Thanks
Rob

[Quackzed]

this thread got me thinking that some sort of dc offset control could be useful for dialing in some even order harmonics...
i wonder if you could somehow allow more  dc with a larger input signal and less with a small input signal, to mimick the behavior of tubes...maybe split to a led/ldr and use the ldr from 9v to base, with an appropriate resistor from  base to ground of a transistor stage to get a variable bias point...
theres probably a better way to get a dynamic dc offset shift happening, but i bet it would add some magic if it could be set up right...

[caspercody]

Daniel,
Just curious if you have made any more progress on this?

[dschwartz]

hi, well, i moved on and started playing with cmos inverters..

[caspercody]

I am also looking at them to. I do not know much about them though. I have made the Blackstone appliance mosfet distortion, and is a really nice low to medium distortion. But I want more. So looking at all I have found (MXR Hot Tubes, Fallout, 49er, Tube Sound Fuzz, and the Blackstone) all use op amps pushing only two or three stages of inverters. But the Double D, and Hot Harmonics are using Jfet stages to push three stages of inverters. These last ones sound (to me) the higher gain ones. Curious to see if anyone can get more stages without as much noise?

[caspercody]

I wonder what this what do:

A mosfet stage (like a SHO) pushing some stages of a cmos. Than a baxandell tonestack (maybe the one with mid control). And if needed a recoery stage.

[dschwartz]

I am also looking at them to. I do not know much about them though. I have made the Blackstone appliance mosfet distortion, and is a really nice low to medium distortion. But I want more. So looking at all I have found (MXR Hot Tubes, Fallout, 49er, Tube Sound Fuzz, and the Blackstone) all use op amps pushing only two or three stages of inverters. But the Double D, and Hot Harmonics are using Jfet stages to push three stages of inverters. These last ones sound (to me) the higher gain ones. Curious to see if anyone can get more stages without as much noise?

cmos inverters are not great in terms of impedance, you need a low impendance source to drive them to get reasonable frequency response.
Last night i played with inverters, put 2 in series and played around. i got some decents overdrives but most of them were kinda dull.. no sparkle/twang there. I think it is because i didn´t use an input stage with low output impedance..an opamp/fet/mosfet/darlington or whatever input stage would isolate the guitar impedance for the first inverter.

[aron]

Daniel,

Reminds me of the time I was fooling around with the Hot Harmonics, I was changing parameters etc... and people were listening. At one point someone says "what happened? It was sounding incredible". Uh, when? I couldn't get the magic back. It exists though in the Hot Harmonics.

[dschwartz]

i think cmos inverter designs are great..
as you aron, i was playing with a single inverter stage, and took away the feedback path and  wow, it sounded amazing!!, but i couldn´t reproduce it after!

[Ed G.]

I'm surprised I've never played around with CMOS inverters. Every sound clip I've heard of circuits using them sound like they have this really nice, organic sounding distortion. Not harsh like a DS-1, and not "dry" sounding like JFETs can sound.

[caspercody]

Is there anywhere one can go to to find out about how these work for distortion pedal applications? Someone mentioned (somewhere) that the 74HCU04 is a better audio chip than the 4049?

[zambo]

I just cascaded actual tubes together and it worked pretty good and easy to build. Three valvecasters together. Here is a clip if you are interested I can try to work up a schematic.
http://www.youtube.com/watch?v=qbDJYMAp6Mo   

hope this helps...

[teemuk]

It's seems people are still struggling with the "Ghost of Hamm's Paper".

You know, the harmonic theory and blah blah blah. I think everyone is familiar with the results and conclusions of that paper but less familiar with the several rebuttals it got. One of them, titled "Transistors Can Sound Better Than Tubes" (written by Monteith and Flowers) actually went as far as to describe a SS preamplifier, which had much more impressive harmonics specs than a tube preamp - judged by Hamm's standards that is. (You know, plenty of even order harmonics, especially 2nd). I think it sound like a crappy broken radio but it must be great because Hamm wrote so and clearly his harmonic theory proves it.  

Or not.

People got way too caught with that paper. And yes, solid-state amps can easily create even order harmonics: Just clip the signal asymmetrically and you create plenty. Couple that with DC bias shifts and you nail the asymmetric duty cycle -thing as well. Those tube waveforms aren't unique to tubes - except when compared to ideal solid-state devices like OpAmps designed from entirely different principles than circuit deliberately designed to mangle and distort the signal in a pleasing way. Personally, I don't see much value in such a skewed comparison.

--

By the way OP, I think you basically invented what Carvin's head designer John Murphy invented in the late 1980's.  
http://www.trueaudio.com/at_eetjlm.htm