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

[dschwartz]

Hi all:
The other day i tested a bogner alchemist on a guitar shop. Being used to my pedals distortion (which i love), i noticed that the bogner had a very nice compression and the notes kept ringing with a nice harmonically rich distortion that i liked very much, and felt very nice on the fingers. I tested it on low volume so i assume the compression was made from the cascaded preamp... so....

I simulated an ecstasy preamp on LT spice (assuming that is a similar circuit), and at the same time, i simulated cascaded gain stages with inverting opamp stages with a single clipping diode on feedback, as a crude tube simulation.

The simulation results were interesting, as tubes shown pretty asymetric clipping with some bias shift and pretty hard clipping. Opamp cascaded stages showed very similar asimetric clipping with bias shift, but much softer clipping. After i finish a couple of texas brownies, i´ll protoboard the thing to see how it goes..

Have anyone tried a similar approach so we can share some observations?

[dschwartz]

hmm no?
cool, i´ll be the first one!

[Jaicen_solo]

I'm not sure, but isn't that how the Crowther Hotcake works? That's supposed to sound really nice.

[dschwartz]

crowter hotcake?...i´ll search for schems, thanks!!

[dschwartz]

i checked the schem...nopes, not even close, is just 1 opamp stage and a lot of filtering...

[tommy.genes]

IIRC, the SansAmp is exactly what you describe - cascaded opamp stages with heavy EQ between stages, where variations in that EQ give the different amp "models".

-- T. G. --

[Paul Marossy]

Hi all:
The other day i tested a bogner alchemist on a guitar shop. Being used to my pedals distortion (which i love), i noticed that the bogner had a very nice compression and the notes kept ringing with a nice harmonically rich distortion that i liked very much, and felt very nice on the fingers. I tested it on low volume so i assume the compression was made from the cascaded preamp... so....

The only thing to keep in mind on these simulations and/or workalikes is that you can't really totally nail tube based stuff with solid state devices. I mean you can get very close, but solid state devices have mostly odd order harmonics and tubes have much more even order harmonics. Most important of those is a very strong 2nd order harmonic. Solid state decices typically have almost no even order harmonics at all. This is what makes tubes sound "warmer". And solid state devices don't compress like tubes will.

So what am I babbling on about? I'm just saying that for a standalone device, you're probably not going to get that jangly warm tube sound without real tubes being involved.

[caspercody]

Has anyone looked into the information on the another Jfet sensation from Russia thread? Just curious if there is anything there that may be different.

[Paul Marossy]

Has anyone looked into the information on the another Jfet sensation from Russia thread? Just curious if there is anything there that may be different.

Jfets seem to get the closest to an authentic tube sound. But they still sound "dry" to me. Probably because of the aforementioned even order harmonics thing I speak of above.

[dschwartz]

Hi all:
The other day i tested a bogner alchemist on a guitar shop. Being used to my pedals distortion (which i love), i noticed that the bogner had a very nice compression and the notes kept ringing with a nice harmonically rich distortion that i liked very much, and felt very nice on the fingers. I tested it on low volume so i assume the compression was made from the cascaded preamp... so....

The only thing to keep in mind on these simulations and/or workalikes is that you can't really totally nail tube based stuff with solid state devices. I mean you can get very close, but solid state devices have mostly odd order harmonics and tubes have much more even order harmonics. Most important of those is a very strong 2nd order harmonic. Solid state decices typically have almost no even order harmonics at all. This is what makes tubes sound "warmer". And solid state devices don't compress like tubes will.

So what am I babbling on about? I'm just saying that for a standalone device, you're probably not going to get that jangly warm tube sound without real tubes being involved.

I know i´ll never nail that exact sound, even using real tubes! there are far more other variables to consider when emulating an equipment. My goal here is to get closer to the "feel" and sustain of the amp, not to get "tube tone", let´s leave that to DSP.

I beg to differ about the differences in harmonic content since, in my opinion, it has more to do with wave clipping simmetry (look at SS octavers..thats all 2nd harmonic) and filtering than the device used.

My hypothesis here is that cascaded gain stages well calibrated can produce much better compression and touch sensitive qualities than single clipping stage like rat, DS1, dist+ and so on. And that you can even make the clipping more expressive by changing the clipping type on each stage, softer to harder, keeping a dynamic clipping, but a compressed signal amplitude. Also, asymetrical clipping on each stage should get closer to tube preamps (which are very asimetrical on each stage) harmonic content..

IIRC, the SansAmp is exactly what you describe - cascaded opamp stages with heavy EQ between stages, where variations in that EQ give the different amp "models".

-- T. G. --

Hmm, i´m not quite shure about that, i think the sans amp uses at most two clipping opamp stages, the rest are active filetring. I found the sans amp a little stiff on the fingers, it sounds to me more focused on frequency response simulation than on clipping.

i think the marshal sim LXH2 goes beyond the sans amp and does a better job simulating the clipping, altough is also very focused on frequency response more than clipping.

Has anyone looked into the information on the another Jfet sensation from Russia thread? Just curious if there is anything there that may be different.

Jfets seem to get the closest to an authentic tube sound. But they still sound "dry" to me. Probably because of the aforementioned even order harmonics thing I speak of above.

I´m not really fond of fets anymore, they sound great, but consistency, predictability and availability is an issue, and they dont have the flexibility that opamps have. As you say, i found them kind of dry also.

[Paul Marossy]

I know i´ll never nail that exact sound, even using real tubes! there are far more other variables to consider when emulating an equipment. My goal here is to get closer to the "feel" and sustain of the amp, not to get "tube tone", let´s leave that to DSP.

I beg to differ about the differences in harmonic content since, in my opinion, it has more to do with wave clipping simmetry (look at SS octavers..thats all 2nd harmonic) and filtering than the device used.

Yes, but if you look at a 1kHz sine wave into your whatever circuit on a scope, that doesn't tell you anything detailed about what is happening to the harmonics. To me, this is the key to how things sound - what is happening with all of the harmonics. When someone says something sounds "complex", they are hearing a lot of interaction in the harmonics, which you generally don't see on a scope. You need a spectrum analyzer to see that stuff, and they are very expensive. And it gets far more complex when you play a fat sounding open G chord.

Here's a couple of articles to read: http://www.milbert.com/TVTIEGA.pdf & http://www.dwfearn.com/tubes_vs_transistors.html
I read these pages several years ago and am convinced that they are dead on. If you ask me, it's all in the harmonic distortions. And this is the reason most guitar playing people prefer tube amps. Well, add to that "audiophiles".  

[Quackzed]

The simulation results were interesting, as tubes shown pretty asymetric clipping with some bias shift and pretty hard clipping. Opamp cascaded stages showed very similar asimetric clipping with bias shift, but much softer clipping. After i finish a couple of texas brownies, i´ll protoboard the thing to see how it goes..

I wonder if using the non inverting side of the opamp with some filtering would get you less 'soft clipping' and more hard clipping, and get you closer... or perhaps it will introduce more odd order harmonics... maybee introducing some of the odd order rich distortion back into the opamp to be cancelled would give you a bit more 2nd...or more assymetry... it just seems like if you can get an abundance of odd order harmonics, you should be able to block 'cancell' odd order harmonics as well...

[Paul Marossy]

The simulation results were interesting, as tubes shown pretty asymetric clipping with some bias shift and pretty hard clipping. Opamp cascaded stages showed very similar asimetric clipping with bias shift, but much softer clipping. After i finish a couple of texas brownies, i´ll protoboard the thing to see how it goes..

I wonder if using the non inverting side of the opamp with some filtering would get you less 'soft clipping' and more hard clipping, and get you closer... or perhaps it will introduce more odd order harmonics... maybee introducing some of the odd order rich distortion back into the opamp to be cancelled would give you a bit more 2nd...or more assymetry... it just seems like if you can get an abundance of odd order harmonics, you should be able to block 'cancell' odd order harmonics as well...

Interesting idea. But my point is that solid state devices by their very nature don't produce hardly any even order harmonic distortions. So you don't really have any to start with. And they are way too small in comparison to try and emphasize.

[DougH]

My hypothesis here is that cascaded gain stages well calibrated can produce much better compression and touch sensitive qualities than single clipping stage like rat, DS1, dist+ and so on. And that you can even make the clipping more expressive by changing the clipping type on each stage, softer to harder, keeping a dynamic clipping, but a compressed signal amplitude. Also, asymetrical clipping on each stage should get closer to tube preamps (which are very asimetrical on each stage) harmonic content..

I suspect this will be easier to do with a higher voltage supply. 9v doesn't leave a lot of headroom for "subtleties".

[aron]

Did you play the Alchemist without effects? FWIW, I love Bogner amps. There's something about the sound I like.

[aron]

Paul,

I understand what you are saying and in fact, I have read those documents that you linked to as well. So I ask these questions now:

If tubes are so great by themselves as overdrive/harmonic generators, why isn't the majority using tube-based pedals?
If tubes alone produce that wonderful sound, then why are there so many bad sounding amps and preamps that only use tubes?
Why are there so many guitarists out there using stompboxes for distortion and sustain?
Why is modeling not the ultimate generator since it should be easy to add harmonics to the base signal?

For an op amp based design that sounds good to me, I will say that the JD-10 sounds very good - probably because of the filtering and it is enhanced even more with a compressor.
I have not utilized multiple op amps enough in my testing. I think that they might sound good with the right filtering.
I have noticed the "dry/stiff" feeling with certain FET designs, but later designs do not exhibit this problem. Anyway, a little reverb or compression goes a long way.
For me, I have yet to play a pedal that is more responsive than my Shaka Pedals for my setup. I keep trying other pedals, but feel is not correct for me.

Finally, I guess I will say that the sound - which most people focus on, might be secondary to the way the circuit reacts for me. A lot of circuits sound pretty darn good or fun, but the feel is incorrect. I can believe that I might have it backwards - since I guess I value feel maybe more than the final sound.

[aron]

There is a thread in the lounge that started somewhat about this.... anyway, referring to this pic:

http://www.milbert.com/Files/articles/tstxtfig5.gif

As I said:
Well, I was looking at this waveform and it seems to me the way to do this (crudely) with clipping diodes is to use maybe 4 Ge diodes in one side of the anti-parallel diodes and the other side 1 Si diode. It looks like the "rounded" bottom side is roughly twice the level of the top sharply cut side. Then maybe even a smoothing capacitor or resistor

I guess I noticed it has a DC bias on it too.

[aron]

Daniel,

How many stages are you thinking??? 4? I like the idea about softer to harder clipping.

[dschwartz]

Hi aron!
I´m thinking 4 stages, with moderate gain each step (around 5-10X each), first stage, no clipping, just boost and gain control, 2nd stage, mild assymetric OD with 1 Ge diode on feedback path, the signal becomes pretty asimetric and softly clipped on one side, so some dynamics are retained.. 3rd stage is the same, but since it is inverting, it will clip the other side of the wave softly, last stage has similar amout of gain, but one diode at feedback, and a LED to vref at the output, giving an asimetric hard-bottom, soft top, bias shifted output.. gently touches will not clip, or only clip 2nd stage...medium picking should clip 2&3rd stages, so its compressed and transparent, harder picking or more gain will clip the last stage and crunch up the thing...

note that back to back diode is not the same as clip each side by separate, since first stage of asymetrical clipping will generate harmonics that will be amplified by the second clipping stage, generating more harmonics, mostly even. and so on...interesting isnt it?

Paul..solid state devices can create even harmonics as well as tubes, and tubes can create nasty odd harmonics, it´s much more a topology thing that a device thing.. that "tubes Vs SS" paper is so old, biased, and it doesnt consider topology and filtering. Did you know that an AB tube power amp stage produces ONLY ODD harmonics? and it CANCELS even harmonics? and hey, it´s 100% tubes!!! and 90% of guitar amps are built with that topology!
Russel hamm paper is beloved by many, but to me is full of....manure...

[dschwartz]

Did you play the Alchemist without effects? FWIW, I love Bogner amps. There's something about the sound I like.

i played the alchemist with & without its internal effects.. it was lovely, and the effects are not bad at all! i just missed a hi end "sparkle" like marshalls, but really sweet mids were there instead..