Guitar signal path?

[alex1fly]

Can someone explain the path that the guitar signal takes when going through an amp, with regards to the controls? That is, guitar to preamp, the gain controls ________, then the signal goes to ______, master controls _____, and so on. I'm trying to better understand what my amp's controls do.
Thanks!

 

[AdmiralB]

Depends on the amp. Until the Rectifiers came out, Mesa amps were based upon blackface Fender topology...input>gain>tone controls>volume>gain....then reverb, if equipped, then power section.

The Mark I added an extra gain stage at the front of the chain. The Mark II copied the Dumble concept of adding two gain stages at the end. The Marks III and IV follow the Mark II concept.

The Rectifiers stack all the gain stages in front, the tone controls are at the end of the chain (before reverb or loop, if equipped). AFAIK all the current Mesa amps except for the Mark IV and Lone Star follow this chain (don't know about the Express, though).

Mesa's implementation of master volumes has always come after the last gain stage, before the loop (if one is present). Then they typically add a 'master master' after the loop. This design ensures that all the distortion comes from the preamp until you're into SERIOUS volume.

Some amps place the master inside the power amp, after the phase inverter but before the power tubes. This allows the phase inverter to distort at low volume, but still keeps the power tubes clean.

The number of gain stages, and the way they're configured (pre- or post-tone controls) have a tremendous effect on the tone and feel.

 

[alex1fly]

Cool, thanks for the info! My particular amp is a Roadster. How do multiple gain stages affect the tone as opposed to just one gain stage? I'm coming from a Fender Hot Rod, so I understand the single gain stage.

Since Mesas have a "master master," does that mean that on a Roadster if you crank the Master volumes and keep the Output control low you aren't actually driving the power tubes?

 

[TP Parter]

Since Mesas have a "master master," does that mean that on a Roadster if you crank the Master volumes and keep the Output control low you aren't actually driving the power tubes?

Exactly

 

[AdmiralB]

How do multiple gain stages affect the tone

Depends on lots of things but IMO, in general, all else equal (that is, controls set for similar amounts of distortion, the more gain stages you have, the smoother the tone. It's tougher to get raw sounds, like a nonmaster Marshall or tweed Fender, with an amp that has lots of gain stages like a DR, SLO, 5150, etc.

Of course, all else is rarely equal!

 

[alex1fly]

Since Mesas have a "master master," does that mean that on a Roadster if you crank the Master volumes and keep the Output control low you aren't actually driving the power tubes?

Exactly

****... so this whole time I was thinking that preamp distortion wasn't as good, striving for power tube saturation with my cranked Master levels, but it turns out that the rocking tones that I'm growing to love actually IS preamp distortion. Ah, the path of amplifier enlightenment.

So then it goes back to "if you want power tube distortion at lower volumes you need an attenuator or speaker isolation cab or any of the other various methods." That is good to know.

Here is a question though - about how loud does the amp need to be to start overdriving the power tubes? Right now, like I said, my channel 4 Master is around 12, I use a boost pedal, and my gain is around 10.... using drums as a comparison volume level, if I'm using the Output control to bring the volume down to a drummer's volume level or a little louder - is this sufficient volume for power tube distortion? I can definitely tell the difference in tone quality when the amp is a little quieter than a drummer than when its a little louder (it is much better and clearer when its slightly louder than the drummer).

 

[alex1fly]

OK, I played around with the amp yesterday and experimented with volume levels... its pretty **** loud, but I found the difference between Tube rectifier and the diode as far as volume levels go - the diode keeps getting louder whereas the tube rectifier loses out on the volume increase. That is helpful to know, as far as balancing between channels goes. I was able to get very close to overdriving the tubes with SPONGY, 50 watt, diode, and playing at drummer/practice volumes. I also tried using a Hot Plate on 4 and 8 db to help me drive the amp extra hard, and I don't think I like the tone when I push the power tubes REALLY hard, but I like when I make them work a little. It just doesn't sound as good when the tubes are overdriven completely - driven sounds great, but overdriven becomes a bit of a muddy mess in my opinion. The tone just seemed to suffer once I started really cranking it - though I'm not sure how much of that was due to the Hot Plate, because I was using it to help control the volume level. But I found the sweet spot, where the compression kicks in and playing becomes almost effortless - I'll probably be using SPONGY more now in order to get closer to the sweet spot at practice levels. I was having so much fun jamming that I was 25 minutes late to my lab

 

[TP Parter]

OK, I played around with the amp yesterday and experimented with volume levels... its pretty **** loud, but I found the difference between Tube rectifier and the diode as far as volume levels go - the diode keeps getting louder whereas the tube rectifier loses out on the volume increase. That is helpful to know, as far as balancing between channels goes. I was able to get very close to overdriving the tubes with SPONGY, 50 watt, diode, and playing at drummer/practice volumes. I also tried using a Hot Plate on 4 and 8 db to help me drive the amp extra hard, and I don't think I like the tone when I push the power tubes REALLY hard, but I like when I make them work a little. It just doesn't sound as good when the tubes are overdriven completely - driven sounds great, but overdriven becomes a bit of a muddy mess in my opinion. The tone just seemed to suffer once I started really cranking it - though I'm not sure how much of that was due to the Hot Plate, because I was using it to help control the volume level. But I found the sweet spot, where the compression kicks in and playing becomes almost effortless - I'll probably be using SPONGY more now in order to get closer to the sweet spot at practice levels. I was having so much fun jamming that I was 25 minutes late to my lab

I find that for the high-gain tones I like (clear and punchy) it works much better to set the master high, like 2:00 +, and keep the gain around 12:30-1:00, and then hit that with a boost when I want a little extra oomph.

 

[MusicManJP6]

So, you are setting the channels' masters down quite a bit to be able to crank the amp's main master to 2:00? Or you are cranking channel 4's master to 2:00 and keeping the main master turned down? Sorry for the confusion. I'm stuck in the master volumes battle as well...