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Old 1st April 2011, 04:50 PM   #1
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Default Roland keyboard thru audio tube amp?

Hi, I have a Roland FP5 keyboard with yamaha speakers with some sort of preamp / amp deal in them. I was wondering what's the feasibility of using a tube amp and loading some cabinets with speakers and using that as my system? Would a keyboard be able to go thru the same type of tube amp as hifi audio? Are different types of tube amp more suited for different things in this way?
And would I hear an appreciable difference considering that the signal is totally digital to begin with?

Any help would be appreciated, I need direction in terms of types of amps and speaker combinations that would be suitable for this application, and also FWIW i would probably have a boutique pro build it rather than myself since i want it to be reliable for gigs.

Thanks,
Pat
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Old 1st April 2011, 05:20 PM   #2
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The keyboard has a line-out connection, and that's an analog signal. I don't know if its controlled by a volume control (you need one somewhere) but it should drive a hi-fi amp just fine. With good speakers it should be better than the small ones that are built in.

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Old 1st April 2011, 07:36 PM   #3
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What are you expecting of a valve amp?, generally keyboards want quality clean sound, not the distortion of valve amps.
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Old 1st April 2011, 09:10 PM   #4
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For keyboards, you want a good, balanced speaker system, like a small PA. What role do the keyboards play in your music? Do they handle bass frequencies, or are they essentially pads and lead? If the latter, buying an existing vocal system would probably me more economic than getting someone to build it for you, and it will already be designed for transport (the people who know how to make something tough for the road, and the ones who make things that sound good don't always inhabit the same skin). What is more, you can listen to it in advance, to be sure it's what you need.

Generally, keyboards get Hi Fi style amplification. Yes, of course I've run a Hammond organ cranked up until the Leslie spits and growls, or a Fender Rhodes through a guitar combo so it distorts, but most electronic keyboards want the sound to go through clean; if you want amp effects, you add them with an effects unit. Now, valve amps (tube) can do this very nicely, but A) they're a whole lot more expensive than their solid state equivalents, B) they're relatively physically fragile, C) they are difficult to find in power ratings suitable for matching up with a drummer, and D) they are, watt for watt, excessively heavy. If you really think the valve sound is going to be important, consider getting a rack mount valve preamplifier, and feeding it either into active speakers or a rackmount transistor power amp. Add an effects unit with reverbs, delays and amp simulations, and leave space for an equaliser, and shock mount the rack in a flight case.

If the keyboard is doing bass lines, and the system is handling the public rather than just on-stage monitoring, I definitely wouldn't be looking at valve amps. In fact, I'd be considering adding a simple rack mixer in there, so it can be used as a small club PA on your days off. You could take the outputs into a bass guitar style amp, but your other instruments will be mangled. Crossing over onto a subwoofer system could help some, but you've still got to stay undistorted; intermodulation of multiple sources is not something to aim for.

Where a guitar is one instrument, one amplification system, a keyboard is potentially many more sources; and, unless you have a pretty sophisticated one, no way of separating them.
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Old 2nd April 2011, 03:14 AM   #5
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I agree with Chris. The point of tubes in a guitar amp is to add a certain tube-ness to the sound, in the area of overdriven distortion, and power supply sag adding "sustain." But as a rule, keyboard amplification is really just a small PA system. A clean strong amplifier that faithfully reproduces the input signal. Most keyboardists wouldn't want their stage amp messing with their signal other than for specific effect.

There is a tremendous range of existing keyboard amps, and I am not sold on your comment that a boutique builder will make one more reliable. I own and operate a pro audio service shop, and I work with most major brands over ehre. I can;t say any commercial brand has a reliability "problem." If someone sells a million of some model, yes you will see them at repair shops. But if your Peavey KB100 amp fails, chances are REAL good there is a Peavey repair shop in the area you find yourself. If Joe the Amp Man makes you a tremendous amp in Boston, and it fails in San Francisco, where do you take it?

And if you are like most keyboardists, I see expanding signal sources in your future. A couple MIDI sound boxes adding in for example. A commercial keyboard amp will have three or four input channels. And another option would be a small powered mixer - a small PA system. They come in any number of channels, powered mixers probably start at around 5 pr 6 channels and go up to 24 or more.
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Old 3rd April 2011, 09:33 PM   #6
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I had a Christmas cantata saved by the tube ST70 when the transistor ST120 went up in flames again. Neither will your tube amp blow up your expensive speaker if it faults, which could happen if you bought a transistor amp with inadequate protection circuits. Lots of PA amps have little protection besides the input fuse. (Some do, they tend to cost more and most musicians don't care until their show goes up in smoke). If you do go with a tube amp, make sure it has a 600V capacitor on the input to protect your expensive keyboard from a grid shorted to plate due to too hard a hit moving it around. The ST70 has no such capacitor, and sounds fine without it, but my input device is a $35 op amp disco mixer, not a $1500 keyboard. If it blows, I can replace every semiconductor in the mixer for about the price of 2 600v 0.1 uf input capacitors. Not so with your keyboard.
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Old 27th April 2011, 12:41 AM   #7
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Quote:
Originally Posted by Nigel Goodwin View Post
What are you expecting of a valve amp?, generally keyboards want quality clean sound, not the distortion of valve amps.
Given the date of this post, I assume you're kidding, right?

To the OP: When selecting speakers make sure they can handle the keyboard's output as far as excursion and cone breakup goes. A musical instrument speaker tends to have a bit stiffer suspension and cone due to the fact that it is handling a high level of sound, and a sound that is coming straight off the source. In other words, not through a microphone/mixer/mastering process/CD burner/playback system. The speaker will be handling far fewer frequencies, timbres, and other audio information that home speakers normally deal with, which means the cone will need to be more piston-like, and less prone to bottom out.

However, the tube amp should be just fine for this purpose.
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Old 27th April 2011, 03:42 PM   #8
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Quote:
Originally Posted by BrassTeacher View Post
Given the date of this post, I assume you're kidding, right?
Nope - and it was posted after 12:00

Valve distortion and poor frequency response is fine for guitars, why would you want it for piano?. All it's going to do is lower the sound quality he already has from his powered speakers.
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Old 28th April 2011, 02:47 AM   #9
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I'm at a loss as to where people get the notion that valve amps distort? Perhaps some badly made ones, and decent ones when they are driven to clipping. But distortion is rare in a well designed and well built home audio tube (valve) amp, even if they were not considered top of the line. And as far as musical instrument amps are concerned, you have to DELIBERATELY build them to distort if that's what you want, or build them where they are easily overdriven. I recently completed a rebuild of an early '60's Fender Champ, and that little beast was extremely clean, until you turned the volume up past 2/3rds. Poor frequency response would be a function of an inadequate output transformer and/or an inadequate speaker, not the fact that the signal was carried by a valve...
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Old 28th April 2011, 04:31 AM   #10
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I agree with BrassTeacher. There is no reason why you can't use valve amps with keyboards. Depending on the design, valve amps will reproduce the clean sound required by your keyboard.

But (!) --- you need to ensure the following: first, you need to keep your signals low enough not to get within the distortion/clipping range of the tube to avoid dis-coloration of the sound patch; and second, you need to use hi fi speakers to get the full spectrum sound.

The first one is extremely difficult to achieve when playing keyboards and synths due to the high dynamic sound range they produce. Imagine the sound generation of from lowest note going to highest note, and then adding the touch response.

With that said, it is still ideal to run your keyboard under the clean sound of solid state amps. And there's a lot more reasons that go against the use tube as other have previously stated (e.g. cost, fragility of tubes, matching speaker loads, etc).

But it is your style that drives your choice. So if you required a warm tube sound, then by all means use a valve amp. If you need it as an added effect only, you may consider a switchable tube pre-amp, then a final solid state amp (similar to the Traynor K4 keyboard amp).

But if you simply need a practice amp, I would suggest you use a stereo LM3886 amp to drive a couple of 8" to 10" stage monitor speakers. That setup is more than enough for small gigs.
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