Members Mr Songwriter Posted May 17, 2011 Members Share Posted May 17, 2011 I know a lot of people prefer power tube breakup to preamp breakup, that's a given, but realistically, you're not going to be able to crank your amp to 11 all the time, so preamp drive circuits are a useful thing to have...so anyway, I've been looking at the gain staging in a few amps that I've owned and/or tried recently and I noticed that I prefer the drive tone on the amps that have the greatest number of stages in the drive circuit, my favourite being one that had four stages (both stages of two 12AX7's...obviously)...so I was wondering, if more appears to be better, why stop at just four? why not 5, or even 6? I doubt it would add much to the cost of the amp, or would it create other problems? (more noise etc) Any thoughts? Link to comment Share on other sites More sharing options...
Members guitarbilly74 Posted May 17, 2011 Members Share Posted May 17, 2011 Preamp and power amp distortion are 2 very distinct things, they don't sound alike at all. Adding more preamp gain won't make up for the lack of power amp distortion due to low volume. Also after a certain point, it just becomes a distorted mess and the amp starts to lose tightness and focus. Having said that, there are many amps out there with more than 4 gain stages. The 5150 for example, goes through 6 gain stages. Link to comment Share on other sites More sharing options...
Members Mr Songwriter Posted May 17, 2011 Author Members Share Posted May 17, 2011 Having said that, there are many amps out there with more than 4 gain stages. The 5150 for example, goes through 6 gain stages. Right, I'm not sure if I'm using the terminology correctly here, the amp I was talking about had four gain stages *in the drive circuit* plus one preamp stage before it (common to both channels) and a poweramp stage afterwards. Also after a certain point, it just becomes a distorted mess and the amp starts to lose tightness and focus I'd also strongly agree with that statement. Link to comment Share on other sites More sharing options...
Members Mr Songwriter Posted May 17, 2011 Author Members Share Posted May 17, 2011 I've just had a look at the schematic for the 5150 and there are six preamp stages (including the very first one) Link to comment Share on other sites More sharing options...
Members Zozobra Posted May 17, 2011 Members Share Posted May 17, 2011 Adding stages isnt straight forward and considerable tone shaping needs to be done between the stages or you end up with a {censored}ty mess.Firstly more stages usually means less bass and more fizz due to the nature of AC coupling and harmonic distortion. Having lots of bass in the preamp usually ends up in blocking distortion somewhere in the preamp and that sounds like ass so the bass is usually cut in the preamp by using smaller coupling caps and not fully bypassing cathodes - to compensate for this some bass is added back in the power amp by adding a depth control to the negative feedback loop. This sounds quite different to a lower gain amp with a bassier preamp. Harmonic distortion increases high frequency content dramatically. Each stage to an approximation adds an amount of overtones of the input frequency. These overtones then get feed into the next stage creating further overtones of the overtones so more stages moves the frequency balance higher and higher. These are usually snubbed in someway in modern designs by using anode bypass caps or by dumping some of the high frequencies to ground in between stages. 4 is the usual magic number of stages for good gain and moderate versatility. You can squeeze a lot of gain from that. Anymore stages means thinking about the shaping a lot more which makes the preamp more of a one trick pony. This is ignoring parallel stages and cathode followers from the equation which can be used to good effect depending on what our aim is. Link to comment Share on other sites More sharing options...
Members ruppert240 Posted May 17, 2011 Members Share Posted May 17, 2011 I would say 90% of people on this forum don't/wouldn't like "power tube breakup". Metal guys generally want clean power amps. Link to comment Share on other sites More sharing options...
Members Cougar Hunter Posted May 17, 2011 Members Share Posted May 17, 2011 I would say 90% of people on this forum don't/wouldn't like "power tube breakup". Metal guys generally want clean power amps. {censored}in A. I was going to say 99% of the people here LIKE preamp drive more than power amp drive, including myself. Link to comment Share on other sites More sharing options...
Members teemuk Posted May 17, 2011 Members Share Posted May 17, 2011 Why is it that newbs always count the numbers of stages instead of focusing on things such as arrangement of the said number of stages, voltage gain within the stages, voltage attenuation in between the stages, and so on. For example: - Three gain stages with volume control following the first stage may not provide nearly any preamp overdrive. Three gain stages with volume control following the third stage may provide tons of preamp overdrive. - stages after things like volume controls or passive tone controls may not really contribute anything to actually overdriving the amp, they merely recover signal losses taking place in earlier circuits - A triode stage can have a voltage gain ranging from 1 to 100 depending on its architecture. The 5150 is a great example of utilizing a triode stage with voltage gain of 1 but that is overdriven with high enough signal resulting into harsh hard clipping, the characteristic of the 5150. Soldano's SLO100 is another good example of throwing in gain stages with very low voltage gain.. and I don't even mean that attenuator and the recovery stage for the FX loop. - Some Carvin amps featured 8 - 12 gain stages in cascade - and attenuation in between. All in all they do not sound too different from more typical high gain amps with less gain stages. You do not need a gigantic amount of stages to acquire similar effects. Some Marshall's did the entire preamp overdrive with just two tube stages and bunch of diodes. - The stage architecture itself can result into different overdrive characteristics like harder or softer clipping, symmetric and asymmetric clipping, etc. All making much more importance in the overall picture than the number of gain stages. Link to comment Share on other sites More sharing options...
Members mrtweeker Posted May 17, 2011 Members Share Posted May 17, 2011 Guitarbilly is right on the money, preamp tube and power tube overdrive tones are very different from each other. Amps that use many preamp stages will never sound like amps that are overdriving the power tubes. If you take the Marshall Jcm800 2203 or 2204, the reason they sound so good is that the amp when cranked is overdriving the preamp, the phase inverter, and the power tubes. Each section is not being overdriven alot but the sum of all three sections creates a very pleasing powerfull tone which works for alot of different styles of music. The only problem is that in order to achieve this the amp will be playing at volumes that can kill small animals. So some form of attenuation should be used if you value your hearing. Master volume controls and 4 plus preamp stages are used to try to copy this tone but it always falls short IMO. Link to comment Share on other sites More sharing options...
Members knope Posted May 17, 2011 Members Share Posted May 17, 2011 1% here The best crunch tone my amp has is the clean channel on full volume but I also have 4 preamp tube which delivers a decent amout of preamp gain on the dirty channel. I need to get in a band to see how this little baby performs with pre and power distortion... Link to comment Share on other sites More sharing options...
Members Mr Songwriter Posted May 17, 2011 Author Members Share Posted May 17, 2011 Thanks to everyone for the informed replies, you've given me plenty to think about. Link to comment Share on other sites More sharing options...
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