How do multi channels amps work?
- Thread starter Pierre
- Start date
Jeff_H
Dean Hardtail Fanologist
Re: How do multi channels amps work?
That's a very basic idea of how they work. The clean channel is assigned one tube (or one side of a tube depending on the design) and the drive channel is assigned another. Then there may be a 3rd gain stage, reverb driver ect...then a phase inverter and then power tubes.
The pre-amp is active on both the clean channel and the drive channel. You can dial in how much effect (or gain) the pre-amp has by controling the pre-amp gain.
There are a bunch of folks who say they offer Fender cleans and Marshall OD in one package...but only a few that actually deliver the goods. I have one, but I had it custom wired by Jeff Seal. It is Fender sparkley clean and pure Marshall crunch all in the same package.
That's a very basic idea of how they work. The clean channel is assigned one tube (or one side of a tube depending on the design) and the drive channel is assigned another. Then there may be a 3rd gain stage, reverb driver ect...then a phase inverter and then power tubes.
The pre-amp is active on both the clean channel and the drive channel. You can dial in how much effect (or gain) the pre-amp has by controling the pre-amp gain.
There are a bunch of folks who say they offer Fender cleans and Marshall OD in one package...but only a few that actually deliver the goods. I have one, but I had it custom wired by Jeff Seal. It is Fender sparkley clean and pure Marshall crunch all in the same package.
Pierre
Stratologist
Re: How do multi channels amps work?
The design I had in mind would use both cathodes of a 12AX7 for the clean channel, with its assigneable gain knob, and the other would use 3 or 4 triodes. The last triode could be the reverb driver simply enough. So it's entirely possible I take it eh?
The design I had in mind would use both cathodes of a 12AX7 for the clean channel, with its assigneable gain knob, and the other would use 3 or 4 triodes. The last triode could be the reverb driver simply enough. So it's entirely possible I take it eh?
shredaholic
New member
Re: How do multi channels amps work?
You mean both sides/triodes of a 12AX7? A cathode is one of 3 pins that each side has, and then there's the three heater pins. There's not really much to designing multi channel circuits, theres loads of easy ways to do it; but the really hard part is spending a long time swapping out different values to maintain a good balance and getting the right sound.
Pierre said:
You mean both sides/triodes of a 12AX7? A cathode is one of 3 pins that each side has, and then there's the three heater pins. There's not really much to designing multi channel circuits, theres loads of easy ways to do it; but the really hard part is spending a long time swapping out different values to maintain a good balance and getting the right sound.
Marcel
New member
Re: How do multi channels amps work?
Just go read some shematics...
IIRC on a SLO for example the first gain stage is shared than it's divided in the two channels (with opto-copplers) and put together after the master volumes (with optos again)...
You can learn very much about amps by reading those diagramms
Just go read some shematics...
IIRC on a SLO for example the first gain stage is shared than it's divided in the two channels (with opto-copplers) and put together after the master volumes (with optos again)...
You can learn very much about amps by reading those diagramms
Pierre
Stratologist
Re: How do multi channels amps work?
I thought so too, but most modern amps' clean channels sound NOTHING like old Fenders. Even with European components and small differences, they should still be able to make them sound in the ballpark no? Maybe I'm not familiar enough with dual channel tube amps though, but in my experience that's how it is.
I thought so too, but most modern amps' clean channels sound NOTHING like old Fenders. Even with European components and small differences, they should still be able to make them sound in the ballpark no? Maybe I'm not familiar enough with dual channel tube amps though, but in my experience that's how it is.
mind_transplant
New member
Re: How do multi channels amps work?
The problem with putting both a Deluxe and JCM 800 in one amp is that those amps are different in almost every conceivable way. Even if you forget the two completely different preamp circuits (and subsequently different B+ voltages) you still have to contend with several other factors. We're talking amps with very different transformers, power tubes, rectifiers, speakers and enclosures/cabinets, which all put together means very different sounding amps. Some boutique builders do a great job, but no matter how much you tweak it a 100 watt amp with EL-34s and a 4x12 will never really be able to compete with a nice Blackface Deluxe.
Pierre said:
The problem with putting both a Deluxe and JCM 800 in one amp is that those amps are different in almost every conceivable way. Even if you forget the two completely different preamp circuits (and subsequently different B+ voltages) you still have to contend with several other factors. We're talking amps with very different transformers, power tubes, rectifiers, speakers and enclosures/cabinets, which all put together means very different sounding amps. Some boutique builders do a great job, but no matter how much you tweak it a 100 watt amp with EL-34s and a 4x12 will never really be able to compete with a nice Blackface Deluxe.
Last edited:
Pierre
Stratologist
Re: How do multi channels amps work?
Well I was talking about the circuits, but of course then the speakers and powertubes change it all.
My design would be 4 12AX7s and 2 6V6s, in a 212 combo. Switchable SS or tube rectifier maybe. Just a random idea, I didn't work on it at all, just one of them 'eh it'd be cool' things.
And yeah I was affraid of that... basically, both preamps would have to be at the exact same voltage/current when they hit the poweramp and yeah... can't be easy I guess.
Well I was talking about the circuits, but of course then the speakers and powertubes change it all.
My design would be 4 12AX7s and 2 6V6s, in a 212 combo. Switchable SS or tube rectifier maybe. Just a random idea, I didn't work on it at all, just one of them 'eh it'd be cool' things.
And yeah I was affraid of that... basically, both preamps would have to be at the exact same voltage/current when they hit the poweramp and yeah... can't be easy I guess.
Lake Placid Blues
New member
Re: How do multi channels amps work?
It would be good to have a basic understanding of the signal chain of the Tweed/Plexi preamp as a starting point. On these amps, there are two low gain channels; a bright channel and bass channel. Since each preamp tube is two mini tubes in one bottle, the first preamp tube in line handles both channels. The signal for each ch then passes through their independant volume controls, then through what are refered to as the mix resistors, the signals are mixed together, and then go through the second preamp tube triodes, and finally through the shared tone stack, or EQ controls. From the there it's on to the power amp, the phase inverter being part of the power amp. The preamp ch's are both low gain, having passed through only 3 preamp triodes each. Distortion is created mostly by the power amp tubes at extremely high volume on these amps.
A Master volume amp (ofton called a JCM800 these days) only has minor variations on this basic design. On a MV amp, the high sensitivilty ch uses both of the first tube's triodes in series, passing through V1A and then through V1B. The Volume control right after V1A becomes a gian control, and if it is cranked up, V1B is overdriven creating distortion. This is a buzzy type of distortion compared to power tube distortion. Another volume control is inserted between the tone stack and the poweramp to control the overall volume of the amp. The total number of preamp triodes the signal passes through is one more than before, one of them overdriven.
To create a high gain amp, another preamp tube (or two additional overdriven triodes) can be added between the plexi V1 and plexi V2. This is essentially what a SLX is. A diode clip can also be used here instead to reduce buzziness. You could also add a bypass from V1A to the voltage amp (plexi V2) section. This creates a clean Ch when the high gain signal path is blocked. This is essentially what a Soldano SLO100 preamp is.
A Black Face Fender is a bit diffrent. Here the two low gain ch's each have their own V1 tubes, with their independant tone stacks, each inserted between V1 triodes. The signals are then mixed into a single signal path, post Eq, instead of pre EQ.
A high gain channel can be created using the Black Face design as a foundation, by inserting additional gain stages between V1a and V1B on one of the channels. You could create a trimodal amp by putting a by pass on the new high gain ch. Getting quiet switching between the hi gain ch and the other low gain ch may be problematic though.....
It would be good to have a basic understanding of the signal chain of the Tweed/Plexi preamp as a starting point. On these amps, there are two low gain channels; a bright channel and bass channel. Since each preamp tube is two mini tubes in one bottle, the first preamp tube in line handles both channels. The signal for each ch then passes through their independant volume controls, then through what are refered to as the mix resistors, the signals are mixed together, and then go through the second preamp tube triodes, and finally through the shared tone stack, or EQ controls. From the there it's on to the power amp, the phase inverter being part of the power amp. The preamp ch's are both low gain, having passed through only 3 preamp triodes each. Distortion is created mostly by the power amp tubes at extremely high volume on these amps.
A Master volume amp (ofton called a JCM800 these days) only has minor variations on this basic design. On a MV amp, the high sensitivilty ch uses both of the first tube's triodes in series, passing through V1A and then through V1B. The Volume control right after V1A becomes a gian control, and if it is cranked up, V1B is overdriven creating distortion. This is a buzzy type of distortion compared to power tube distortion. Another volume control is inserted between the tone stack and the poweramp to control the overall volume of the amp. The total number of preamp triodes the signal passes through is one more than before, one of them overdriven.
To create a high gain amp, another preamp tube (or two additional overdriven triodes) can be added between the plexi V1 and plexi V2. This is essentially what a SLX is. A diode clip can also be used here instead to reduce buzziness. You could also add a bypass from V1A to the voltage amp (plexi V2) section. This creates a clean Ch when the high gain signal path is blocked. This is essentially what a Soldano SLO100 preamp is.
A Black Face Fender is a bit diffrent. Here the two low gain ch's each have their own V1 tubes, with their independant tone stacks, each inserted between V1 triodes. The signals are then mixed into a single signal path, post Eq, instead of pre EQ.
A high gain channel can be created using the Black Face design as a foundation, by inserting additional gain stages between V1a and V1B on one of the channels. You could create a trimodal amp by putting a by pass on the new high gain ch. Getting quiet switching between the hi gain ch and the other low gain ch may be problematic though.....
Last edited:
Lake Placid Blues
New member
Re: How do multi channels amps work?
Another factor in the rack era was adding stereo effects post distortion. You want most of your stereo time delay effects and reverbs to come after distortion. Power amp distortion just garbles these effects. On a regular tube amp with an effects loop, it may be possible to have reverbs ect.. after a buzzy preamp distortion ....in mono. However, if you want the effects in stereo, and you want the sound of switchable muliple whole tube amps before reverb, chorus, and flange effects, then a complicated rack system is needed.Zerberus said:Side note: This is one reason why racks became so popular, multiple but wholly independent preamps through the same power section
mind_transplant
New member
Re: How do multi channels amps work?
The one problem that inevitably seems to occur with these types of designs is that they don't sound very good as high-gain amps, partly due to the location of the tone stack. Practically all high-gain master volume amps (Marshall, Boogie, Bogner, Soldano, etc.) have the tone stack as a cathode follower at the end of the preamp, wheras the Deluxe has it coupled to the plate right after V1. Adding several gain stages and a master after the classic Blackface tone stack tends to sound pretty sour, so most builders stick with the cathode follower design (originally from the Tweed Bassman) or have completely independent channels.
Lake Placid Blues said:
The one problem that inevitably seems to occur with these types of designs is that they don't sound very good as high-gain amps, partly due to the location of the tone stack. Practically all high-gain master volume amps (Marshall, Boogie, Bogner, Soldano, etc.) have the tone stack as a cathode follower at the end of the preamp, wheras the Deluxe has it coupled to the plate right after V1. Adding several gain stages and a master after the classic Blackface tone stack tends to sound pretty sour, so most builders stick with the cathode follower design (originally from the Tweed Bassman) or have completely independent channels.
