Sequence of signal stages in Mark V

[Induktionator]

I spent some time going through the schematic to work out the major signal stages of this amp. I didn't find someone else had posted this, so here it is. I hope this information is helpful to someone.

This information is pretty raw, I haven't messed around with formatting it nice. Maybe it would be easier to understand in a more graphical (Block diagram) form, but I'm an engineer, not a graphic designer. Maybe some frequent questions are helped by knowing the sequence your signal goes through between the guitar and the speakers, and which controls affect the others further down the line. It's interesting that the gain and treble/mid/bass and master volume controls aren't in the same order in the 3 channels.

The channel choice and the FX loop settings affect the main signal flow. The channel modes (clean, fat, etc) mostly just switch different combinations of components in/out of the circuit but without affecting the overall flow. I didn't say anything about the power section, it's pretty cool how it gets reconfigured.



Common:
Input
V1A
From here on it is different depending on Ch1/2/3:

Ch1:
V1A
TMB
GAIN
V1B
(Reverb: V4A,springs, V5B, level)
V3A
MASTER
V3B
EQ
From here on it is common (Further below)

Ch2:
V1A
GAIN
V2A
TMB
V1B
(Reverb: V4A,springs, V5B, level)
V3A
MASTER
EQ
From here on it is common (Further below)

Ch3:
V1A
TMB
V1B
GAIN
V5A
V4B
V3A
(Reverb: V4A,springs, V5B, level)
V6A
MASTER
EQ
From here on it is common

Common part:
EQ
* Tuner out jack
* Send level,
* FX send/return jacks (Just the jacks are bypassed if the FX footswitch button pressed),
* V6B
* Output, Solo
* The above (*) bypassed in case of True Bypass
Mute
PI (“Presence” NFB here)
Power tubes
OT
8, 4ohm jacks (each pair wired in parallel)
Slave level
Slave out jack

 

[giorikas81]

Excellent info thanks for the post. The second channel reminds me of the lonestar signal path on the lead channel.

 

[Anonymous]

Wow!!! nice work...... it is nice to see the channel stages in your format!!!!!

great info :wink:

 

[bird_droppings]

For those of us who are not amplifier engineers, would you give us a key to what some of those acronyms mean?

This seems like incredibly useful info and I'd love to understand it better.

Thanks...

 

[Induktionator]

For those of us who are not amplifier engineers, would you give us a key to what some of those acronyms mean?.

V1A, V2B, etc. are the preamp tubes. Each preamp tube has 2 circuit elements inside, each can, for example, add gain or boost the signal.

Most of the other abbreviations are the controls:
TMB are the Treble Mid Bass controls
MASTER, GAIN are the Master and Gain controls
EQ is the Equalizer
Send Level, Reverb Level, Slave Level, Presence, Output and Solo are some more controls
The various jacks are named, too.

Just a few are real engineer geekiness:
PI is the Phase Inverter (V7A+V7B), this is a circuit that makes a pair of positive and negative signals that drive the power tubes.
OT is the Output transformer.
NFB is Negative Feedback. This is a signal from the output that is fed back to the input again, but opposite polarity. The way it works is real engineer geekiness, but basically it's the presence control and affects just the power amplifier part.

 

[phyrexia]

I thought that mark I mode changed the order of tubes compared to the rest of ch2. doesn't the manual say that?

 

[>Photi G<]

Where did you find the schematic? Send it to me please! From one engineer to another :wink:

 

[bird_droppings]

One of many things I don't fully understand is that for each channel, there are 4 separate volume knobs: Gain, Master, Output, Solo.

Output and Solo are clearly related and they come late in the signal path.

It's Gain and Master I don't fully understand. One theory is that Gain sets the basic loudness of the amp. As you start to crank it, at some point your signal starts to distort. All of the other volume knobs would then attenuate this basic signal.

If that's true you might leave the Master wide open and control the final loudness with the Output knob. Is this true?

My Mark V is coming on Monday, so I have nothing to experiment on until then.

 

[bird_droppings]

Another way of putting this is I don't understand how I would balance those four knobs to get various effects.

For example, to get the cleanest sound the amp will create, do I keep the gain low and boost the Master?

Once I've used the gain knob to get the distortion I want, which of the Volume knobs should I use to quiet the amp for bedroom levels?

 

[Induktionator]

Schematic found here: http://music-electronics-forum.com/t15431/


About the Mark I mode, I didn't describe all the changes that the different modes make. It's pretty complicated, and mostly involves changing various resistors and capacitors in the circuit., but there's some tricky clever details that the schematic is more useful to show the details than trying to describe it all.

About how the different knobs effect the sound, the TMB are pretty clear, but where they are in the circuit affects the character of the sound. Early in the signal chain, and all the valves after it are amplifying a signal that already has the frequencies cut by the tone controls. Late in the signal chain, and most of the valves are amplifying the signal from the guitar without the tone settings applied.

The same goes for the Gain, Master and Output controls. the earlier in the circuit the Gain is, the more stages there are that are amplifying a stronger signal, and each valve distorts more depending on the strength of the signal. The master is later in the circuit, and most of the stages after it are pretty clean, but if you turn the master up enough, it is possible to to get distortion from the few later stages, like the effect loop driver, and eventually the PI and output tubes. Practical considerations about how loud you can play pretty much limit how much you can play with distortion in the later stages of the amp. This is why Non-master volume amps have a special sound, but are incredibly loud.

 

[MrMarkIII]

One of many things I don't fully understand is that for each channel, there are 4 separate volume knobs: Gain, Master, Output, Solo.

Output and Solo are clearly related and they come late in the signal path.

It's Gain and Master I don't fully understand. One theory is that Gain sets the basic loudness of the amp. As you start to crank it, at some point your signal starts to distort. All of the other volume knobs would then attenuate this basic signal.

If that's true you might leave the Master wide open and control the final loudness with the Output knob. Is this true?

My Mark V is coming on Monday, so I have nothing to experiment on until then.

Gain sets the amount of pre-amp distortion. So, yes, for the cleanest sound, run the Gain low and the Master high.
The Masters are like channel faders on a mixer. The idea is to use the Masters to balance the loudness of the three channels, then use the Output to turn everything up or down while maintaining the balance between the channels.

 

[bird_droppings]

Gain sets the amount of pre-amp distortion. So, yes, for the cleanest sound, run the Gain low and the Master high.
The Masters are like channel faders on a mixer. The idea is to use the Masters to balance the loudness of the three channels, then use the Output to turn everything up or down while maintaining the balance between the channels.

This makes a lot of sense.

I'm still wondering a little about gain. As I dial gain up, the sound should stay clean until he amp runs out of headroom and distortion starts happening. Up until that point does it matter whether I increase volume from the gain or from the master?

 

[MrMarkIII]

The Gain really adjusts distortion rather than loudness. That's the (Channel) Master's job.
Like a mixer, you can pump the gain so that even the cheapest microphone overloads the input, but it can still be loud or soft, depending on the (Channel) fader.

 

[bird_droppings]

The Gain really adjusts distortion rather than loudness. That's the (Channel) Master's job.
Like a mixer, you can pump the gain so that even the cheapest microphone overloads the input, but it can still be loud or soft, depending on the (Channel) fader.

Can I set the Gain to zero, turn up the Master and still hear signal? Or do I always have to have a little gain?

This will be easier to figure out once mine comes on Tuesday. In the meantime, I'm reading all things Mark V on the web.

Thanks for the help!

 

[domct203]

Gain adjusts how much signal is fed into the preamp, channel master adjusts how much preamp signal goes to the poweramp.

Yes, if the gain is on zero, no signal is fed to the preamp so you always have to have a little gain setting.

Dom

 

[SteveO]

Channel one stays relatively clean through quite a bit of range of the gain control in clean and fat mode, tweed breaks up earlier. I can maintain a clean tone with no hair up to about 12:00 on the gain control on those two settings. Also, the treble and to some extent the midrange controls also affect the gain structure.

You'll have to play around with it when you receive it to get a decent feel for how it works, but that's half of the fun.

 

[bird_droppings]

Channel one stays relatively clean through quite a bit of range of the gain control in clean and fat mode, tweed breaks up earlier. I can maintain a clean tone with no hair up to about 12:00 on the gain control on those two settings. Also, the treble and to some extent the midrange controls also affect the gain structure.

You'll have to play around with it when you receive it to get a decent feel for how it works, but that's half of the fun.

Interesting. My guitar teacher was showing me one of his amps and pointed out that as he increased the gain, it kept getting louder, but only until it started distorting. Then, of course, it couldn't get any louder, instead it just got more and more distorted. I'm assuming the Mark V will work the same way.

But I think it's interesting that as long as you keep the gain below the point where the sound starts breaking up, you have two different dials to control loudness. I imagine the effect of each is just slightly different. I further imagine that you want to be careful with turning the gain too low, since you want a signal coming from the pre-amp that is well above the noise floor.