Charlie: I have read quite a bit lately about the Fender Tweed versus the Fender Blackface tonality. Can you comment on the different circuits used to achieve these different sounds?
As I understand it, the Tweed breaks up sooner than the Blackface which in turn breaks up sooner than the Silverface. Are the differences associated in these differing tonalities mostly in the preamp?
Fender Tweed Versus Fender Blackface Sound
Moderator: jingle_jangle
Fender Tweed Versus Fender Blackface Sound
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As a follow-up while I await your reply and for anyone else, in modifying a Twin Reverb does it make sense that simply by changing the tone stack values that different meaningful sounds can be achieved in different channels.
For example, could you have an early 1960s Tweed sound in one channel and a later 1960s blackface sound in the other or would each channel have to have a different preamp in order to accomplish this?
For example, could you have an early 1960s Tweed sound in one channel and a later 1960s blackface sound in the other or would each channel have to have a different preamp in order to accomplish this?
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I change the tone stack in my Blues Jr. This made a significant difference. The Jr. comes with a stack similar to the tweed 4X10" Bassman. The change put it more in line with a Princeton 1X12". This was an improvement to my ears, but it also may have had something to do with having a similar speaker.
I thought the differences as far as "breakup" and the "tweed" or "brown sound" had to do with the rectifier section and the output transformer size. I think the various speakers used would also have a big effect.
I thought the differences as far as "breakup" and the "tweed" or "brown sound" had to do with the rectifier section and the output transformer size. I think the various speakers used would also have a big effect.
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Thanks Ken, interesting. I appreciate your comments.
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Peter, the nice thing about having a 2 ch. amp is it is easy to do A-B comparisons as long as you don't use the effects. If you are interested in the mod I made I can get you the info when I get home this afternoon. It's on my home computer. Maybe some of the other tweed amps had stacks close to the Bassman.
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soundmasterg
- RRF Consultant
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Peter, the Fender blackface/Silverface and the Fender Tweeds are two different animals, and within each family, there are quite a lot of different sounds too. The main differences are in the arrangement of the stages, and in the votlages used.
If you run a preamp stage at a higher voltage like a Blackface amp does (Silverface is even higher), you get more gain, and more headroom in that stage. Keep in mind that gain and distortion/overdrive are not the same thing. The larger blackface amps like the twin reverb are running around 220v on the preamp tubes, which gives them more headroom, allows them to accept a larger input signal without distorting, and gives them more gain so they amplify the signal more. The tweeds are more like 150-170v, which takes the gain down a bit from each stage, causes them to overdrive sooner, and the can't take as large of an input signal, so they will distort easier if one stage is overloading the next.
The other important thing is the arrangement of the stages. Most of the tweeds are what is considered a 2 + 0 setup, and most of the blackface amps are a 1 + 1 or a 1 + 2(bassman heads) This refers to the arrangement of the gain stages in relation to the tone stack. The tweeds have two gain stages before the tone stack, and the blackface silverface stuff has 1 before the stone stack, and either 1 or two after it. The tone stack sucks a lot of gain away and in the tweeds a cathode follower circuit is used just before the tone stack to keep as much gain from getting lost as possible. The output of a cathode follower is low impedance, which allows the tone stack to work better, and allows more gain out of it. In the blackface amps, they take the signal off the plate of the tube, so it is high impedance and the tone stack sucks a lot of the gain away and doesn't work as well either. BUT, since the tone stack in the blackface comes after only one stage, it works better than the tweed setup because there is less overdrive at that point in the circuit arrangement. Also, the settings of the controls on the blackface determines how much signal gets to the following stages and gets amplified a lot more than is the case on the tweed stuff.
You could change the tone stacks around, but you wouldn't get the full effect unless you changed the arrangment of the stages, and reduced voltages to a given channel's preamp tubes. This is a lot of work as currently the preamp channels share power supply nodes, so you would have to seperate them by adding several caps and resistors with their values chosen so they get you the correct tweed voltages. You would also have to change the existing ones on your blackface/silverface channel because now that the load is different on these since you've removed some tube stages from them, the voltages will rise and get them even more clean than they are now. You can leave all that as it is now and just change the values in the tone stack and it will just change the frequency response of the tone stack and shift it one way or the other. Check out the tone stack simulator on this site...its pretty useful for amp work and you can see how the tone stack works. Its a free download.
http://www.duncanamps.com/tsc/index.html
While you can mess with the amp and channels to get the character different, if your main goal is to get it to break up sooner, I would do two things.
1) disconnect the negative feedback loop
2) change the dropping resistor values for the preamps to a higher value so that the preamp voltages will be lower. This change more than anything will brown the amp up and get it to overdrive sooner.
If you run a preamp stage at a higher voltage like a Blackface amp does (Silverface is even higher), you get more gain, and more headroom in that stage. Keep in mind that gain and distortion/overdrive are not the same thing. The larger blackface amps like the twin reverb are running around 220v on the preamp tubes, which gives them more headroom, allows them to accept a larger input signal without distorting, and gives them more gain so they amplify the signal more. The tweeds are more like 150-170v, which takes the gain down a bit from each stage, causes them to overdrive sooner, and the can't take as large of an input signal, so they will distort easier if one stage is overloading the next.
The other important thing is the arrangement of the stages. Most of the tweeds are what is considered a 2 + 0 setup, and most of the blackface amps are a 1 + 1 or a 1 + 2(bassman heads) This refers to the arrangement of the gain stages in relation to the tone stack. The tweeds have two gain stages before the tone stack, and the blackface silverface stuff has 1 before the stone stack, and either 1 or two after it. The tone stack sucks a lot of gain away and in the tweeds a cathode follower circuit is used just before the tone stack to keep as much gain from getting lost as possible. The output of a cathode follower is low impedance, which allows the tone stack to work better, and allows more gain out of it. In the blackface amps, they take the signal off the plate of the tube, so it is high impedance and the tone stack sucks a lot of the gain away and doesn't work as well either. BUT, since the tone stack in the blackface comes after only one stage, it works better than the tweed setup because there is less overdrive at that point in the circuit arrangement. Also, the settings of the controls on the blackface determines how much signal gets to the following stages and gets amplified a lot more than is the case on the tweed stuff.
You could change the tone stacks around, but you wouldn't get the full effect unless you changed the arrangment of the stages, and reduced voltages to a given channel's preamp tubes. This is a lot of work as currently the preamp channels share power supply nodes, so you would have to seperate them by adding several caps and resistors with their values chosen so they get you the correct tweed voltages. You would also have to change the existing ones on your blackface/silverface channel because now that the load is different on these since you've removed some tube stages from them, the voltages will rise and get them even more clean than they are now. You can leave all that as it is now and just change the values in the tone stack and it will just change the frequency response of the tone stack and shift it one way or the other. Check out the tone stack simulator on this site...its pretty useful for amp work and you can see how the tone stack works. Its a free download.
http://www.duncanamps.com/tsc/index.html
While you can mess with the amp and channels to get the character different, if your main goal is to get it to break up sooner, I would do two things.
1) disconnect the negative feedback loop
2) change the dropping resistor values for the preamps to a higher value so that the preamp voltages will be lower. This change more than anything will brown the amp up and get it to overdrive sooner.