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Topic: Tube amps, pickups, resistors, impedance. |
Marc Jenkins
From:
Victoria, British Columbia, Canada
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Posted 22 Nov 2008 11:24 am |
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So. I'm learning about tube amps currently, looking towards doing some kit building and mods etc. I'm in the extremely early (read: lots of reading!) stages.
Last night I played a Neil Young tribute, and finally bothered to bring separate amps for guitar and steel. What a great improvement! At soundcheck, I tried going into my Garnet (50/60 watts EL34 w/2x12" Webers) either straight in or with a Matchbox. I definitely preferred a certain 'woodiness' in tone while going straight in, and I really felt the steel and amp responding as one all night, especially as things got a bit loud... I barely needed to use the VP at all, the sustain was already HUGE. The tone with the Matchbox was a bit bigger and bolder, but less awesome.
What I'm wondering about; the straight in setup (Shobud w/Truetone) required turning the treble down from 4 to ZERO to have a similar brightness to using the Matchbox (tone at center). Honestly, I could have dropped it a little more... Would it be better to change the treble cap value, or change the input resistor to better 'meet' the 18k pickup?? |
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Paul Arntson
From:
Washington, USA
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Posted 22 Nov 2008 10:48 pm
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Interesting question. When you say "better" do you mean nicer tone or better electronically? Electronically, I would think it matters just how permanent you want to make the change and how easy it is to do.
You could always take some alligator clips and try each approach to see if there were a tone difference overall once you got the treble where you wanted.
The resistor method is using the inherent inductance in the pickup windings and so it might have a different rolloff. Both the cap and the input impedance will be "single pole" but the curves or the frequencies might sound different to you.
Maybe the best would be something reversible, like a push pull pot on the amp, if you are going to mod the amp.Then you could switch it in or out. |
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Jim Sliff
From:
Lawndale California, USA
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Posted 23 Nov 2008 8:52 am
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| Quote: |
| What I'm wondering about; the straight in setup (Shobud w/Truetone) required turning the treble down from 4 to ZERO to have a similar brightness to using the Matchbox (tone at center). |
This is typical of high-impedance, high-output (high impedance does NOT necessarily mean a hotter pickup - there's much more to it than that) steel pickups plugged straight into guitar amps. Treble is often over-the-top, and if you plug effects in between many of the classic ones distort like crazy (almost all MXR pedals dislike any high-impedance, high-output pickup). Rather than modify the amp I'd take a small project box and build a passive Fender-style volume/tone control circuit, using the Esquire-like 3-position switch; using 1 meg pots would be best - then using the switch to provide a route just through the tone/volume pots with a .1uf or .047uf tone cap (.1 will give you a huge swing; the smaller the value, the less treble is rolled off - Fender's standard was .047/.5uf but normally is now .022uf).then in the other two positions switch in two different caps for instant mellowing of the treble. A capacitor substitution box is an invaluable tool if you do this stuff very often (all techs I know have them - I do and don't know how I'd get along without it) as you just hook up wires and flip a switch to change values. The volume/tone/switch box would plug straight in to the output jack of the guitar - you'd find rolling off a little volume AND tone would work wonders.
This is one real disadvantage to "modern" pedal steel construction methods; more and more players are opting for new or vintage tube amps in lieu of the cheaper SS Peaveys for tonal reasons, and pedal steel makers have not caught up - not enough players ask for controls, so they don't install them. I've seen stacked pots intalled in a GFI underneath and may do that on mine, although I prefer controls on top - on my Fenders I am constantly adjusting things to "massage" tone for various songs or even fills or solos.
The box described above would not require power and would not be an impedance matcher; but having tried it, it DOES work much better than "straight in" with a tube amp - plus you will likely find yourself able to create your OWN sound rather than the one sound the guitar manufacturer provides.
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No chops, but great tone
1930's/40's Rickenbacher/Rickenbacker 6&8 string lap steels
1921 Weissenborn Style 2; Hilo&Schireson hollownecks
Appalachian, Regal & Dobro squarenecks
1959 Fender 400 9+2 B6;1960's Fender 800 3+3+2; 1948 Fender Dual-8 Professional |
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Marc Jenkins
From:
Victoria, British Columbia, Canada
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Posted 23 Nov 2008 11:01 am
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Thanks guys. Jim, that sounds like a pretty good idea all around.
I did once compare my Sho-Bud to an older push-pull I helped forumite Bob Blair score. The Emmons had a MUCH lower output pickup, and actually sounded TERRIBLE through the Matchbox. Straight in, it was incredible. |
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