Hi new learner her, would like to know how does the tone change inf you where to say use a smaller cathod cap with a lower wattage reistor ,does this affect the bias of the tube? and also the tonal changes with using different compositions of resistors and caps , what are the best for a trainwreck express i have a ciera tone clone and the highs seem a bit bitting and a tad to much bass would like to smooth it out a bit and warm it up
Thanks
EXPRESS CATHODE CHANGES
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Re: EXPRESS CATHODE CHANGES
reducing cathode cap can help on marshall, but I haven't tried it on my express. have anyone else tried it? did it result in tighter bass?
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LeftyStrat
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Re: EXPRESS CATHODE CHANGES
The first gain stage cathode cap can be adjusted to roll off bass. Though I'm not sure I've ever heard of an Express with too much bass. You can experiment with something like 1 uf or .68 uf in that cap position.
Harshness in the highs can sometimes be the result of layout. You can play with the high pass filter between the second and third stage, that is composed of the 150k resistor to ground and the cap there. Reducing the resistor will allow more bass through.
Another place to tweak is the cap across the output of the phase inverter. In fact you can put a 250k pot in series with a .0047 cap and you have a high cut control.
But first I would play with lead dress and see if that affected things. I would also try different tubes, especially V1.
Harshness in the highs can sometimes be the result of layout. You can play with the high pass filter between the second and third stage, that is composed of the 150k resistor to ground and the cap there. Reducing the resistor will allow more bass through.
Another place to tweak is the cap across the output of the phase inverter. In fact you can put a 250k pot in series with a .0047 cap and you have a high cut control.
But first I would play with lead dress and see if that affected things. I would also try different tubes, especially V1.
Re: EXPRESS CATHODE CHANGES
Hi Lefty,
just a typo: reducing the 150k resistor will allow less bass through the amp.
just a typo: reducing the 150k resistor will allow less bass through the amp.
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LeftyStrat
- Posts: 3114
- Joined: Fri Jan 14, 2005 6:58 pm
- Location: Marietta, SC, but my heart and two of my kids are in Seattle, WA
Re: EXPRESS CATHODE CHANGES
Oops, thanks.
f = 1 / (2 * pi * R * C)
f = 1 / (2 * pi * R * C)
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Re: EXPRESS CATHODE CHANGES
dunno about the wattage of the resistor ... 1.5K resistor with about 1.2 volts across it will even work with a tiny 1/8W resistor... the 1/2W typical in tube amps does the trick just fine.
Anyway ...
the resistor sets the bias point for the tube, and the capacitor keeps that bias point stable. Reducing the capacitor will allow the bias point to be changed or modulated with respect to the input signal, although I would think pretty much anything over about 2.2uF is probably enough to bypass all guitar range audio frequencies. It ends up having an effect similar to a high pass filter.
If you reduce the resistor value, you are biasing the tube hotter. Increase it, you bias it colder.
FWIW I use .1uF caps often times in amps where I want tighter bass and a focused, lead guitar response. Most of the bottom end roll off in the TW circuit is that .001 or .002 uF coupling cap on the way to the "clipping stage", and then of course that super cold biased tube with no cathode bypass cap helps too.
Anyway ...
the resistor sets the bias point for the tube, and the capacitor keeps that bias point stable. Reducing the capacitor will allow the bias point to be changed or modulated with respect to the input signal, although I would think pretty much anything over about 2.2uF is probably enough to bypass all guitar range audio frequencies. It ends up having an effect similar to a high pass filter.
If you reduce the resistor value, you are biasing the tube hotter. Increase it, you bias it colder.
FWIW I use .1uF caps often times in amps where I want tighter bass and a focused, lead guitar response. Most of the bottom end roll off in the TW circuit is that .001 or .002 uF coupling cap on the way to the "clipping stage", and then of course that super cold biased tube with no cathode bypass cap helps too.