Steel guitar tube input preamp

Swampertech

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Hello all! I posted this over on Doug's site, and would like your thoughts. Are there any specific parameters for the design of a tube input preamp/power amp for use with a pedal steel guitar. I understand the frequency response needs to be wider than a guitars' (more bass response), and the input impedance needs to accommodate the guitar depending on the pickup used. I read on a steel guitar forum that the first preamp doesn't need a cathode bypass capacitor. Do any of you play pedal steel guitar, and if so what is your favorite amp? Thanks!
 

Wally

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There is more to it than the input, but yes….one needs to deal with the input of the steels big low strings.
Amp??? Imho, ideally, a UL Dual Showman 135 watt head is the ticket. If not that, a 100 watt Dual Showman Reverb. The UL’s use a large capacitance in the first stage….110mfds compared to the 50 mfds in the 100 waters. This larger capacitance tightens up the amp…especially the low end..and increases articulation.
in the preamp, you can decrease the input signal…or simply plug into the #2 input of a Fender reverb amp….and many other amps…to access that 6db cut in signal strength. Or…you can manipulate the gain in that first stage…remove the bypass is one way.
I once set up a 1954 5D6 Bassman…first 4x10 Bassman…for pedal steel. The owner had bought it new. When he picked the amp up, he brought his steel. He had been playing for a bit when I asked him what he thought. He put the bar on the low string on the C neck..up high. He hit the note and then slid the bar down the neck and pulled it off…letting that big open string ring. He looked up at me with a big grin and said:
“I have never been able to do that!”
 

Jon Snell

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A standard valve pre amp is all that is required. Nothing special about it.
The speaker size however matters. There is a lot of air to push on the lower strings.
A decent electric organ amplifier (Hammond design) would be beneficial.
Most older Fenders will do the job but not the Blues Junior range!
 

mistersparkle

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I just finished building what amounts to a Fender Vibroverb specifically for use with my Fender double-eight Stringmaster non-pedal steel. The amp uses 2 6L6GC power tubes and produces about 40 watts. I put a sturdy 15" Eminence speaker in the cabinet as I know many steel players prefer the sound of a single 15" amp like the trusty, old Peavey Session 500. My Stringmaster never sounded better!
 

Swampertech

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I just finished building what amounts to a Fender Vibroverb specifically for use with my Fender double-eight Stringmaster non-pedal steel. The amp uses 2 6L6GC power tubes and produces about 40 watts. I put a sturdy 15" Eminence speaker in the cabinet as I know many steel players prefer the sound of a single 15" amp like the trusty, old Peavey Session 500. My Stringmaster never sounded better!
From all I've read, it seems that a 15" speaker is a must for steel guitars. Is your Vibroverb the standard Fender input preamp, eq, PI, output? What is the low frequency response of your speaker?
 

mistersparkle

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From all I've read, it seems that a 15" speaker is a must for steel guitars. Is your Vibroverb the standard Fender input preamp, eq, PI, output? What is the low frequency response of your speaker?
The circuit is a basic AB763 configuration with mostly standard Fender component values in the preamp, EQ, PI and output section. I messed a bit with the bright cap values on the two channels and ended up with 250pF on the normal channel and 47pF on the "vibrato" channel. I used a Mercury Magnetics FDP-20 power transformer and FBFVO-40-M output transformer. The Eminence EPS-15C speaker is rated at 42Hz - 2.9kHz usable frequency range with a resonance of 42Hz.
 

OldManAP

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Off topic, but maybe some of you guys can help me understand something. When I started building my most recent pedalboard, which does double duty as a guitar board and a pedal steel board, I was studying pedalboard buffers and got the advice that for large boards one should put a buffer at the beginning and the end of the chain with a 1M ohm input impedance and a 100 ohm output impedance, based on the fact that the input impedance of most guitar amps is 1M. But looking at the specs of all the popular Peavey steel amps (Nashville 112, Session 400, etc.) I see input impedances in the tens to hundreds of ohms. Just about every other popular (guitar) amp I’ve looked up has the 1M. What I’m trying to figure out is WHY did Peavey design their steel amps like this? Is there an advantage? Is it because traditionally pedal steel players ran straight from the guitar (with no volume knob) through a passive pot volume pedal to the amp? Makes sense in my mind, but presents a potential mismatch with modern (possibly non-country) steel rigs with sometimes lots of effects in the signal path. Just trying to understand the rationale, and the best approach to dealing with it. Thanks, and sorry for derailing the topic!
 




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