Gain stages - can someone explain this in non-technical term
I've been playing for 36 years. I still have my first real amp (among others), a solid state Kustom 150 watt with 4-10 inch speakers. It doesn't have a gain knob, just volume and tone (and reverb and tremolo.) It is a \"clean\" amp. For years I didn't know that there was such a thing as distortion that came from an amp. I thought you needed what we old timers called a Fuzz Box to get that sort of tone. I still have my 70's Big Muff Pi. I've read g3456's article about multiple gain stages, and Groovy's posts tearing into g3456's article, and I also met with a tube amp builder about two weeks ago, and he also got into this concept of gain stages. So, what are they? Why do I need to care about them? How are they manifested in solid state amps vs. tube amps? How do IC chips, like in the gNX4, emulate and deal with them. Please no technical engineering jargon, just tell me in terms that a musician can understand.
Comments
Terms of amplification of these preamps- when you hear 1st 2nd and 3rd stages the terms are defining cascading the amps. IOW, 1st feeds the second, second feeds the third etc. The gain of the amp stage can increase the signal within limits of the power stages. Each stage is defined by the circuit components and power sources (current). The number of stage is usually indicative of how much gain can accommodate the power stage. For instance, on a champ you may have 2-3 stages since it's a cleaner amp. On a Marshall, you could have 4-6 stages (producing more available saturation or distortion). Difference is, simply put, the champ needs a distortion box and the Marshall when pushed does not.
Interesting enough, the higher power amps do not always require a higher number of gain stages.. just enough for the signal but most often it's to further enhance the saturation at stage volumes. This is why a stack is not so pleasing at low volumes. They have to be pushed by design. I've modified some amps to work at less than 5W but it's easier to buy a 5W amp really. Another reason why the 18W amps have such popularity and favor. It's not a stack, but it sounds killer at 2 or even 10W. Take a rackmount amp.. it's design can yield 100 W rms. It has 2 preamps and a power stage so the fact the Champ has the same and is not as loud is not depending on the gain stages.. now it's the power stages that change what is available in watts.
Without getting into Class variables, the gain stages are merely there to bring the guitar signal level to a point to which the power stage (tube or SS) can amplifiy (power) the signal to the speakers.
The number of stages can produce both Clean and Distorted sounds. Some of the stages mix eq components along with that. Depends on the mfg. DrZ amps is a champion of do more with less parts. They use both filtering and amplification at the same time.
The GNX4, ada MP1, JMP1 etc etc are all preamps. The output gains of the GNX for instance can be equivalent to that of 2-3 stages of gain on an amplifier..if not more than that depending on the patch model etc. It is certainly enough to accommodate the power stage of most guitar amps and or directly feed a PA type amp, rack mount amp etc.
treat the GNX as a preamp. Imagine taking the preamp output of another head and driving your guitar amp's input. It won't take much to introduce or saturate the power stage of your amp. Will it add power to your existing amp?? Yes, but not really. It's only going to change the input source and you will have less GAIN requirements on your amp's controls to do the same job. It's like stompbox pedals and booster pedals that are simply preamps themselves. The more you add to the input of your guitar amp, the more Stages it sees looking in from the Power amps. Just like using stompboxes. At bedroom levels, you juiced the MXR.. at stage levels, you cut back the MXR gain or you get screechy overdrive and noise.
These are some of the reasons most people bypass the preamps of their guitar amps via the efx loop when using a modeler. It's untouched by the filters eq's (depending on the loop feed) and adds less color to the power output stage. On an amp without a loop, you have to accommodate all the variables that color the overall sound. When I played live with a big Efx rack rig, I had 2 stacks. One had the guitar only and the other head bypassed the front end for efx only. Mic and mix both cabs and you have your sound capable of being blended at the PA and FOH mix for the audience. One untouched, and the other jammed with EFX. Stage levels were based off where I selected the mix of the two. Often the EFX head was lower in Vol. Plenty enough to mix at the PA though.
Differences in amps whether SS or Tube is mainly harmonics and human ear perception. Both amps can be 50W, but the SS seems less than 50W since it has less of the harmonics that seem to envoke loudness. Go back to the days of lafayette and other HI FI tube amps. Recall the 10w tube systems of magnavox console stereos and compare that to a 10W boombox with equiv speakers. The 10W tube amp seems louder, cleaner.. so does the guitar amps tube vs SS. Tubes have a warm harmonic nature and SS are a little harsh (to most humans), but in some cases, are part of the Hybrid preamps in many top name amplifiers. IOW, just like adding a stompbox on the front end of the power stage for more effective GAIN. There are many SS amps that are much cleaner than tube amps, but using those kind of opamps (Ic's) can lead to costs higher than a 12ax7. So most mfg's settle on something reasonable.
What matters is knowing the GNX is a preamp. Set the gains on the amps as required to NOT defeat your amps ability to work with it. Less is more and a better starting point for mfx units, preamps, rocktrons, stompboxes, gainiacs, mp1's or triaxis' for that matter. Purity is defined by each ear and that is always different.
It is actually a function of the circuitry and the number of places in the circuit where the signal level is increased to before reaching the power side of the amp?
Want to see a cool example? These can drive a 412 ! and sound incredible!
http://zvexamps.com/
It's not just the stages, you can have less stages of better quality designs and get great performance. Most money on amps is based on the power stage. When we were co designing some amps the expense is not the preamps at all. It's the power stages, coupling components and power supply components that define the costs. Most circuitry for tube preamps is pretty cheap.. caps, resistors, etc and a decent pr of 12ax7's won't cost much. The transormer for the power supply on most 50W and above amps is more than the entire preamp assy components.
Yes you are correct.
Do you mean the factory models only ?
Or that irrespective of patch loaded, the GNX4 cannot model clipping characteristics of multiple stages while the GNX3000 can ?
Why do I think you are being sarcastic :roll:
There are no obvious bloopers, there is simple language. There are no wierd technical claims aimed at boosting product sales. Its just a clean and clear post that explains the situation very well.
Here it is explained that what a stage in an Amp does is important, rather than how many stages there are. The article at KEWL only stressed upon number of stages as the sole determiner of tone.
It deserves praise.
PS : G3456, maybe you can reword the KEWL article to incorporate the above post. That would make it much more complete and correct.
I will dig into my earlier posts about the other points I felt did not give exactly the right impression or could benefit from a slight rewording.
On other threads, where there are unsupportable technical claims, I discuss them equally factually.
gain = output/input
All stages have gain.
It can be a positive gain like 2x or 3x
or it can be a unity gain of 1x
or it can reduce the signal with a gain of 0.5x
So all stages are gain stages.
If you had many stages of different gain levels that were tonally flat and did not distort, and you assembled them in any random order and then tapped the same level of signal from them, you would get exactly the same output signal.
Lets call Tonally Flat, No Distortion as TFND and a gain of 2 as a TFND2
so TFND5->TFND2->TFND0.5-> TFND3 -> Volume control set to give 1 Volt signal
will sound the same as
TFND2->TFND6->TFND0.3-> TFND3 -> TFND5->TFND1->TFND0.8-> TFND8 -> Volume control set to give 1 volt signal
So we see ***FOR TFND STAGES*** that the amount of interstage gain does not matter. The number of stages also do not matter.
Now you can guess what I am leading to,
Real stages can be designed to be very close to ideal for small signals but are not Tonally Flat and they do distort on large signals.
However same tubes that are used in Guitar Amps are also used in old time Phono players and PA Amps.
In the PA Amp application, how come there is very little tonal changes and distortion as compared with a Guitar Amp, for the same number of stages built with the same tubes by the same manufacturer in the same year with the same price range ?
How come we can add two diodes to a tube amp and get totally different tone with same number of stages and same small signal gain ?
When studying tone, clearly there is a bit more to it than
number of stages
or type of tubes
or gain of each stage
or total gain of the system.
It is an oversimplification to lay all responsibility of tone at the feet of any one of these points. There has to be something else that generates tone.
G3456, care to take it from here ? You have more experience with tubes than me.
Just received back from repair two 20W McMartin MA-20 tube PA amps from The Ohio State University auction(sorry football fans in Texas and Michigan) that sound sweet for clean. In the Rockman line most run the 1/2 U modules on SS Pa amps but find the Ultimatum Distortion Pedal best with tube. The stereo now sounds better than mono into a Fender Princston Revervb(tube). These low volume tube amps compare to a governor on a racecar throttle to protect the ears. Now over winter I want to rerack some combos for future growth.
Maybe 2007 will allow broadband so I can enjoy more of this forum.
Worked on a Bogner Metrop 15 last week... total sweetness! Another amp that can go Fender to JTM, to Matchless by turning an schizo and volume knob!! Have another guy with the 30w version coming in next week.
The patch only the initial clipping stage. I know there's other clipping stages, that might be fixed, i.e. they might be fixed or could be that a flag in the patch indicates which clipping stages to load.
Another interesting tidbit, the AudioDNA2 claims 400% performance over the AudioDNA, which makes sense since the algorithm in the 3K is about 4x as complex.