How does the Master Volume work on a PRS amp?
- Thread starter EL34lover
- Start date
No - it does nothing to the preamp stage.
The MV is a LarMar Post Phase Inverter, named after the guys who came up with it. All it does is reduce the level of signal going to the power tubes.
The reason it sounds like gain is being added as the MV comes down (and this gets a bit technical), is that as the level of signal sent to the power tubes goes down, so too does the negative feedback, which by design is intended to reduce certain types of distortion. So if you "remove negative feedback", you are actually letting more of the original pre-amp and phase inverter distortion get through.
There are ways to modify this type of MV so that as the MV lowers, you keep the negative feedback the same. It would require and extra knob somewhere.
Mesa MV's control the level of signal being sent to the output stage. But they do so BEFORE the phase inverters.
You can't really compare the 2 types of amps. They are fundamentally different architectures. A non-master volume Marshall is really about a complete end-to-end circuit that collectively gets louder and louder. A Mesa, and most other high-gain amps, can really be thought of as a Pre-amp and a power amp that are bolted together, and designed to work independently. The fact that Marshall-plexi style amps have master volumes is something that wasn't even thought of until much later, when guys started to create high levels of distortion. So hacks modified the amps to figure out how to do it.
The MV is a LarMar Post Phase Inverter, named after the guys who came up with it. All it does is reduce the level of signal going to the power tubes.
The reason it sounds like gain is being added as the MV comes down (and this gets a bit technical), is that as the level of signal sent to the power tubes goes down, so too does the negative feedback, which by design is intended to reduce certain types of distortion. So if you "remove negative feedback", you are actually letting more of the original pre-amp and phase inverter distortion get through.
There are ways to modify this type of MV so that as the MV lowers, you keep the negative feedback the same. It would require and extra knob somewhere.
Mesa MV's control the level of signal being sent to the output stage. But they do so BEFORE the phase inverters.
You can't really compare the 2 types of amps. They are fundamentally different architectures. A non-master volume Marshall is really about a complete end-to-end circuit that collectively gets louder and louder. A Mesa, and most other high-gain amps, can really be thought of as a Pre-amp and a power amp that are bolted together, and designed to work independently. The fact that Marshall-plexi style amps have master volumes is something that wasn't even thought of until much later, when guys started to create high levels of distortion. So hacks modified the amps to figure out how to do it.
I guess this explains it. Thanks for pointing me in the right direction:
http://www.thegearpage.net/board/archive/index.php/t-1017133.html
http://www.thegearpage.net/board/archive/index.php/t-1017133.html
In both cases, the MV "lets" more of the pre-amp signal reach the power tube section. The difference is that on a Mesa, that is done BEFORE the PhaseInverter, and in the PRS, it's done AFTER the PhaseInverter. PhaseInverter distortion is a part of the Marshall crunch sound, while on a Mesa, it is not.
The gain (on a Mesa) and the Volume (on a PRS) determine how loud the pre-amp gets before it hits the MV.
I didn't like the Lead channel on the SE50 amp so I put it on Ebay. I set the volume to some amount of distortion and used the MV to control how "loud" the amp sounded. The distortion sounded fizzy to me. Now I take the amp, turn the MV all the way up and use the volume dial to control how loud it gets. WOW: what a difference in tone. So now I love the amp and it's probably the best value in an EL34, 50 watt combo amp I know of. Probably gonna pull the listing. Wondering if I will consider the HXDA I just ordered worth the difference in $...
I was VERY interested in a 2 CH, until I realised the great sound I was hearing in PRS demos were done with the MV maxed - too loud for a studio setting. What is great about some Mesa circuits (I currently own 3) is the global output knob, which gives me the flexibility to go from studio loud to earthquake loud without messing with gain / master / EQ settings
The HXDA really does get my GAS going though ..
Chester, the good news is that the HXDA sounds great with the master set for low volume. It's also a much quieter amp with significantly less noise than any Mesa I've owned, which is altogether around ten Mesas, including a Mark V. The sound is rich, buttery and not fizzy when the master is set low, as happens with some Mesas.
I've posted clips on the forum that were generally recorded with the master set around ten o'clock, which is a reasonably low volume. If you check my thread about the McCarty Singlecut "Hammer of the Gods" guitar, you should find a link to a clip recorded with that guitar straight into the amp, no pedals, master low, etc.
I would never say that one amp is somehow "better" than another amp, but the HXDA works better for me than any Mesa (or any other amp, and it's a long list) I've owned.
CatStrangler
PRS Enthusiast
Thanks for the explanation. I though I heard more gain as I turned down the MV, now I know why.
Thanks Les - appreciate the input from someone who has direct experience of the amps in question, AND makes a living from producing good tone! If I could find one in the UK, I could be tempted
How is the Grissom at low master volume? Or the MDT?
I haven't tried an MDT, though Aristotle has one and prefers it to his HXDA. Based no clips I've heard, I think the HXDA leans more in my direction - we're all a bit different.
The Grissom is very good at low master volume, but the master is inherently different for a couple of reasons. First, it's a pre-phase inverter design. Thus, the setting of the Master affects what happens with the volume (gain) control. So if you dial in a great gain setting, and then turn down the master, you have to readjust the gain control, and in addition, the tone controls sometimes need a little tweaking.
PRS and Grissom both say that he sets his amp up with the Master wide open, and uses the gain control as a true volume control. So the amp is designed to sound its best that way, and that is pretty darn loud if you want preamp tube grit with your playing.
However, I set the amp up with the gain about 12:02 o'clock, where I get a little top-end crunch with the guitar's volume controls up full, and this seems to work very nicely with the Master anywhere between 10 o'clock and 3 o'clock. Fair warning, it's a loud 30 watt amp, and even 10 o'clock is a pretty loud setting on the Master.
If I want more grit than "edge of breakup" I use pedals, and the DG is a great pedal platform.
I'm getting quite used to the DG, and it does an awful lot of things. For me the HXDA is still my favorite for "guitar>>cable>>amp" tone, but the DG is the amp I record with most because it's such a great pedal platform and I can do all kinds of things that way.
