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Post by skydog958 on Feb 25, 2007 13:44:15 GMT -7
So I know that the Gain knob controls preamp gain, and the Master controls volume/output tube distortion, but my question is is there a relationship between the EQ settings and the amount of output tube distortion? Does cranking the eq knobs drive the tubes harder? I heard Myles say that it was an old Marshall trick to get the presence and treble pots as high as possible--does this add to it too? I'm trying to get good output tube breakup without using too much preamp gain.
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Post by skydog958 on Feb 28, 2007 12:16:24 GMT -7
It's been several days but no response yet...hmmmmmm.
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Post by Don on Mar 1, 2007 10:26:17 GMT -7
It's been several days but no response yet...hmmmmmm. Oldster - "How come you're not in school!"
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Post by skydog958 on Mar 1, 2007 13:54:19 GMT -7
'Cause we get out at 2:00! ;D
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Post by haitone on Mar 15, 2007 10:30:02 GMT -7
I'll give you an answer. This is my opinion. Yes, signal gain can be increased by setting the tone controls to 10. And signal gain drive output tubes, sort of. Tone controls in a traditional tone stack are frequency filters that dump signal to ground. So having them maxed will dump less signal to ground, especially the mid as it’s tied directly to ground. But since they come before the master volume, they will have a limited influence on driving the power tubes. Given the exact same master volume settings, turning up the bass, mid, or treble will raise the gain level but probably not in a pleasing way and not very much. On the other hand the presence control is tied to the power section via the feedback loop. It also dumps to ground, filtering just the highs, but is not affected by the master volume voltage divider between the preamp and the phase inverter. The “old” Marshall your referring to I will assume is the non-master models 1959 or 1986, 1987, etc. Those models had the treble wiper (output) feeding the phase inverter directly. By having the treble and the presence up fully you dump less signal to ground, and cut through the band mix and probably at least the first twenty rows of the audience because it’s so bright and shrill because at that point the 500pF treble cap is acting like a coupling cap and the bass and mid controls are rendered ineffectual. The treble control should be between 3 and 7 to be most useful (toneful). To get brown power tube distortion the amp must be designed with that goal in mind paying no heed to clean headroom. The filter caps would be small in value and the plate voltages lower (the basic premise of power scaling). I like 32mF and 375 VDC on hot running EL34’s myself.
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Post by sonicgator on Mar 15, 2007 20:22:21 GMT -7
I'll give you an answer. This is my opinion. Yes, signal gain can be increased by setting the tone controls to 10. And signal gain drive output tubes, sort of. Tone controls in a traditional tone stack are frequency filters that dump signal to ground. So having them maxed will dump less signal to ground, especially the mid as it’s tied directly to ground. But since they come before the master volume, they will have a limited influence on driving the power tubes. Given the exact same master volume settings, turning up the bass, mid, or treble will raise the gain level but probably not in a pleasing way and not very much. On the other hand the presence control is tied to the power section via the feedback loop. It also dumps to ground, filtering just the highs, but is not affected by the master volume voltage divider between the preamp and the phase inverter. The “old” Marshall your referring to I will assume is the non-master models 1959 or 1986, 1987, etc. Those models had the treble wiper (output) feeding the phase inverter directly. By having the treble and the presence up fully you dump less signal to ground, and cut through the band mix and probably at least the first twenty rows of the audience because it’s so bright and shrill because at that point the 500pF treble cap is acting like a coupling cap and the bass and mid controls are rendered ineffectual. The treble control should be between 3 and 7 to be most useful (toneful). To get brown power tube distortion the amp must be designed with that goal in mind paying no heed to clean headroom. The filter caps would be small in value and the plate voltages lower (the basic premise of power scaling). I like 32mF and 375 VDC on hot running EL34’s myself. Eddie, is that you?
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Post by skydog958 on Mar 19, 2007 18:07:53 GMT -7
Thanks for the insight.
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