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What tube amp emulation circuit you are interested in?

Started by teemuk, June 30, 2007, 03:18:37 PM

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I'm pretty soon finished writing my book about SS guitar amplifiers and one of the final chapters I'm writing covers the various circuits that emulate tube amps. Included are some selected circuits under TransTube concept (Peavey), SansAmp (Tech21), Carvin's SX series Classic Tube, FlexWave (Crate), ValveState concept (Marshall) and Valve Reactor (Vox). DSP is out of the topic. Are there any other emulation circuits that interest you people?

...And no: I'm not going to cover Pritchard's circuits. They are far too extreme and IMO in all their complexity pretty much unusable learning material for common DIY:ers.  :)

LJ King

Well, please understand that first and foremost I don't believe in solid state circuits emulating tubes. That whole concept implies that new technology can only exist if it remains faithful to the old.

I'm not sure if it is true about all the examples you mentioned, but it seems like only op-amp based examples to me.

How about the first company to build a solid state amp intentionally meant to be overdriven like people were overdriving tube amps? 

That would be Sunn, and in particular the Coliseum 880 - issued around 1972 I believe.

But if you want to focus only on op-amp based circuits, then you can't ignore the "cmos" technology of the Sunn Beta series. These amps are still very popular and being used today.


I agree with you: Solid-state amplifiers can do much more than replicate tube technology. In fact, the peek at tube emulation topologies is just a small fraction of the book. The focus of the book mainly concentrates on perfecting the power amplifiers to linearity levels that cannot be matched by basic tube designs. Another large focus is on "preamplifier circuitry" like small signal stages, switching, tonestacks and limiters (harsh and soft). Third focus is on other important things like common circuits, practical design aspects (like component picking), speaker theory, cabinet design and thermal issues. So I assure you, the book is not about "how SS can sound like tubes" -hype.

Well, I hope that topic is clear now...

The "preamplifier" section has an inclusion about discrete preamp topologies (including FETs) and the portion describing various signal limiting circuits covers the use of CMOS gates that was - if I'm correct - first employed by Sunn in their beta lead series of amplifiers. And true as well; Sunn were the first company to experiment with overdriving FETs. However, I prefer to separate these circuits to same category as diode clippers etc. IMO they alone do not make a tube emulation topology as they can merely be just a part of one. I appreciate that you mentioned these circuits though.

It is an undeniable fact that tube emulation/simulation has become an important part of SS guitar amplifiers and eventhough the topic might not interest you it will interest some people. Truthfully, I'm not even a big fan of tube amplifier tone myself and my original intention was not to cover the topic because "tube tone" is so vague concept anyway. For example, there are tube HiFi and tube Hi-gain amps. Both sounding completely different. Personally I hate the muffled high end and compression associated with tube tone - and that tends to be the tone even for those "clean" tube amps. It's good for blues and sixties music but not for much else. Of course, that's just my opinion. Both clean and distorted tones I tend to prefer are created with SS amps. Anyway, to get back on topic, some of these tube emulators / simulators use pretty novel circuits so I'm having fun doing the research.

What comes to opamp based examples... Well, all I can say is that opamps are pretty clever devices that perform well and they are here to stay. Maybe that's why they tend to get used in most of the topologies. Some of the topologies I cover do use discrete circuitry. Do note that drawing the line between emulation and designs that just sound nice and "tube-like" is pretty hard. For example, SansAmp's design is very close to the limit of should I present it at all or not as it's basically just a collection of gain stages with selected equalizing - similarly to FET stuff found from runoffgroove.com My intention is not to belittle these circuits (as they sound pretty good) but in my opinion most of them are not novel enough to stand out from the pack of other similar circuits. Basically I think I will cover the SansAmop just as an example of this kind of "amplify-and-filter" approach.


Can't say I'm really interested in tube amp emulation, but I've always been a fan of actual hybrid amps where you use a tube in the preamp and ss poweramp or vise versa.

Are you actually going to have this book published btw?  And are you going to mention ssguitar.com  ;)

btw, I think it's awesome you are writing this book because it seems there isn't much out there about ss guitar amps...hence why I built this site with Chris.
Life is what you make it.
Still rockin' the Dean Markley K-20X

LJ King

I have a Peavey Special 130 I bought new in 1983, still works good.

It has "Saturation" which I think I remember was a tube emulation attempt. At any rate it is a pretty good sounding distortion, and better IMO than the "SuperSat" that came out afterwards.

I can see how the classification can get confusing.

I'd probably lump tube emulation under "fuzz boxes".   :lmao:


That "saturation" circuit is part of the TransTube concept I'm presenting. I guess they never called it TransTube back then but the idea is mentioned in the Peavey whitepapers concerning the TransTube concept. It was a pretty nice idea of introducing a gain stage that limits bandwidth in proportion to gain and was meant to simulate the bandwidth-limiting effect of saturating output transformers. Transformers saturate dynamically while Peavey circuit had a constant bandwidth limit throughout the signal amplitude range and therefore the dynamic properties were lacking. It was certainly a step into right direction though. "Supersaturation" or "Superdistortion" was another revision of the "Saturation" circuit with cascaded gain stages.

Joecool85: What comes to publishing the book is uncertain: This has been a side project I ventured into never expecting to get any profit out of it so I will likely release it in a .pdf form at first and see if there's any interest in printed copies (which are so much easier to read not to mention "eye-friendly"). You are right that the material concerning SS guitar amps is pretty much lacking. There's certainly plenty of solid-state theory material but few have composed it to concern only guitar amp design and all the information is pretty much scattered, thus I decided to start gathering it up.


Don't really know if it fits in here, but the way runoffgroove uses jfets insted of triodes is worth mentioning. A few of those preamps sound pretty good on higher voltages.

LJ King

Quote from: syndromet on July 01, 2007, 03:07:32 PM
Don't really know if it fits in here, but the way runoffgroove uses jfets insted of triodes is worth mentioning. A few of those preamps sound pretty good on higher voltages.

I don't dispute what you said.

But if he mentions this, he will have to dispute the myth that Jfets sound exactly like tube triodes, or that Jfets are the solid state equivalent of tubes. It's just not true.

But hey, maybe that kind of discussion is exactly is what needed.


FETs and tubes have similarities but, for example, the transfer curves of FETs follow Shockley's equation (exp 2) while transfer curves of tube triodes follow three-halves-power law (exp 1.5). This will create different harmonic spectrum. I think the main reason why FETs are considered sounding very similar to tubes is that they can be used in very similar circuits.


Agree that SS amps need to quit trying to sound 'just like' tubers.  But that will only change if some artist comes out with a 'new' sound that's made with a SS amp.  Until that happens, most musicians will think they haven't arrived until they have a 'real' (read tube) amp.  But I believe SS amps are capable of producing a sound all their own.  I just don't think any serious musician has gone after a new sound like that.  For a different sound most will just use a tube amp with some stompboxes or perhaps a different guitar configuration/tuning.  Jack White has a different tuning for some of his songs.  David Crowder has a REALLY odd tuning.  But a SS amp could have a sound all its own.  Be neat to hear someone who really knows how to make use of one get together with someone who knows how to build what the artist wants and come up with a unique sound.  If that happens, we could see a lot of interest in SS amps. 


I understand that this thread is a little old, but I becoming very interested in this topic as a guitar player.  The other day I played my Strat through a little solid-state Marshall MG15DFX.  I was amazed at the direct response and clear tone. (link below).  This is not an ad, but just a reflection:  I really heard the guitar in a way that I wanted to hear it: clear, direct, intact, and without intermediary.  This is something that I have *not* come to expect from my tube amp, especially as I navigate the black-art of tube upgrades and replacements.  Each tube makes my amp sound different and the experiment is leading me to want to find a solid-state amp that is fairly hi-fi and not necessarily only a reflection of a tube "sound".


BTW... what does "warm" mean anyway?


Check out the circuitry in a PEavey Musician Series 400, This old amp has a rich tone that is hard to beat , and approachs the tube tone. However , this was not a tube emulation , it is just the design of the amp.

                                         Rock On


In response to the guy who likes the MG series, The term Warm is referred to the tubes effect. The hotter/warmer they are the better they sound. SS amps can get warm, but more than likely not. They've got a 'cold' sound. It's just like the weather. Tubes have a looser more 'organic' sound like a natural plant would grow/adapt to it's environment, whereas SS amps have a direct sound and are tighter in response and sound closed up in a box and less free. You can get a good SS sound if you try hard, but if you like the tones of classic and modern rock, you're better off with Tubes. But all in all, the FDD switch the MG series has really does warm things up for the circuitry it has.

Another thing I noticed is SS amps have more 'room' to build in effects n such. Like the Line 6 Vetta sounds amazing and it's solid state, but mostly because it has the ability to program so much. It's got a computer inside of it, basically. So that's the advantage.

J M Fahey

I think that rather than "emulate tubes", the real challenge is "get good sound", which is often (but not always) found in tube amps, without using tubes themselves. I think Mr Pritchard is a genius, has *very* good sounding amps, but he misses the point, he often tries to emulate *everything* a tube does, which is not the real problem. Someday he´ll emulate a spirally wound 6.3V heated filament, a glass envelope, a 9 pin socket, the sound of high vacuum, and that´s not really necessary. I think Runoffgroove´s approach is basically flawed: Fets do not even approach triodes, (if any, they´re closer to pentodes); they copy (should I say mimic) classic circuits, horribly biased, horribly powered, that have ten times less gain than the originals, clip radically different, (just use a scope; I´me sure they don´t), harsh, dry, ugh!!  An example of good engineering (and audibly good taste) is found in the SansAmp guys, who do not use Fets , CMOS or even diodes but do get a very acceptable sound. I agree that Op Amps (universal gain blocks) with suitable components around them, skilfully used, are one of the safe ways to go.


Vox AD-VT series really attracts me. I'm selling a SS stack to get a AD50VT 1x12 combo. all it uses is a 12ax7 in the power amp[oddly enough] and I cranked this baby at the shop. Sounded superb, even when compared to all tube amps, it still holds it's place above your average SS amp.