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Topic: Impedance matching for amps and pedal steel guitars? |
James Holland
From:
Alabama, USA
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Posted 5 May 2012 6:59 am |
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I tried a search, but couldn't find a discussion about impedance matching amps for pedal steel guitars - I know its important for acoustic amps, and bass amps.
Since the pickups on PSGs are 3-4 times higher than typical solid body guitars, shouldn't the amplifier have a different impedance to better match a pedal steel guitar? Or is that part of the design of an amp for pedal steels? |
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Brad Sarno
From:
St. Louis, MO USA
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Posted 5 May 2012 7:22 am
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Most steel guitar pickups are developed for the typical 500k loading that is seen when using a pot type pedal. But that doesn't mean 500k is ideal for every pickup and every setting.
The Telonics volume pedal, the Steel Guitar Black Box, and the FreeLoader offer variable input impedances to best match your pickup and get the desired treble peak response out of that pickup. Many people find that once their amp's tone is dialed in, the most useful tone control of all during a gig is the variable impedance. The amplifier's input impedance doesn't matter that much. It's the first device that the pickup sees that's most critical as that's what determines the pickup's tonal response. For steel players, the first device the pickup sees is typically a buffer or a volume pedal.
http://www.sarnomusicsolutions.com/products/fl.html
Brad |
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Howard Steinberg
From:
St. Petersburg, Florida , USA
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Posted 5 May 2012 10:00 am
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For what it's worth I've never quite "got" the issue of impedance matching with respect to pickups on a steel.
First of all I've used pot pedals with guitar for many years. I played on an MSA Classic for about 7 years. This guitar had volume and tone pots. I ran this into a passive pot pedal and it sounded fine. I replaced that guitar in 1985. I believe the pickups on the new (back then) guitar were Lawrence 805's. The guitar sounded absolutely awful with a sound that I can only describe as lacking highs, mids and lows. I added a Goodrich Matchbox 2 into the mix and all was well. What am I missing. Not trying to hijack the thread but it seems like the same issue as the original post.
_________________
Justice Pro Lite (4-5), Justice D-10 (8-5)x2 , Quilter Steelaire, Hilton Pedal, BJ's bar. |
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Lee Baucum
From:
McAllen, Texas (Extreme South) The Final Frontier
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Posted 5 May 2012 11:00 am
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I've used several different brands of impedance matching devices over the years. At times, I have just placed a little digital delay unit between the guitar and the pot-pedal.
My favorite box has been the Sarno FreeLoader. Brad has put some sort of voodoo magic in those boxes. Not only does it serve as a matching device, it has a knob for adjusting the voodoo magic. You can back that knob off from ten and it starts taming the highs. If you have some offending high frequencies, it finds them and gets rid of them. It does that without affecting the the crispness on the lower, wound strings. It seems to bring out all the best frequencies and bring out all the best tones of your guitar. |
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Joseph Meditz
From:
Sierra Vista, AZ
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Posted 5 May 2012 4:34 pm
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| Howard Steinberg wrote: |
| For what it's worth I've never quite "got" the issue of impedance matching with respect to pickups on a steel. |
Neither have I because I don't think that this is matching as in matching the impedance of an antenna to an amp for maximum power transfer.
The diagram below was taken from
http://www.guitar-repairs.co.uk/how_guitar_pickups_work.htm
The L and the C determine the frequency location of the resonant peak. The R shown is the DC resistance of the pickup. But, to complete the circuit there is an additional resistor in series with it, namely the input resistance of the device it is connected to, i.e., the load. Let's call the combination of those two resistors Rt for "total." The pickup resistance is fixed, but Rt varies depending on the device the pickup is connected to.
While L and C determine the location of the resonant peak, Rt determines the width of that peak. If Rt were big, like 1M Ohm, the peak will be narrower than if Rt were smaller, like 100k Ohm. The narrowness of the peak is expressed as the Q of the circuit. The higher the Q the narrower the peak.
So, when you use a pot pedal, like a Goodrich with a 500k pot, when the pedal is floored (loudest) the resistance is maximum and the peak will be narrower than when the pedal is close to off. Pedals that have 250k pots will not sound as sharp as one with a 500k pot. And a pot pedal, having the lower resistance, will not be as bright as an electronic pedal.
Also, the amp has an input resistance and a blocking capacitor that has some effect on tone must be taken into account as well.
In summary, I think these so-called matching devices are really shaping the peak by modifying the Q. If they do more than that by inserting a capacitor, then they would be more like a tone control and move the peak as well.
This is my SWAG at this question. Let's see what others say.
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James Holland
From:
Alabama, USA
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Posted 6 May 2012 9:15 pm
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Thanks for the responses and keep them coming.
I just checked, and the two input impedances on a Nashville 112 are 68k and 220k ohms (low and high gain inputs). The two inputs on an Express 112 are 69k and 200k ohms respectively. Basically no difference!
I'll have to experiment with my Goodrich 500k pedal as suggested. My current amp is a Crate 15w with a 1.5M ohm input impedance - I selected it years ago for its high input impedance. |
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Dave Grafe
From:
Hudson River Valley NY
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Posted 7 May 2012 8:19 am
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| How are you measuring the "impedances" on your guitars and amps? If you are simply sticking a VOM across them you are measuring DC resistance which is not at all the same thing as AC impedance! |
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James Holland
From:
Alabama, USA
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Posted 8 May 2012 9:21 am
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No measurements - impedances were published values from owners manuals.
I'm overdriving my Crate acoustic amp. Can't turn it past 2 without soft distortion, with or without headphones. Sounds kinda cool, but.....I'll try a DI box tonite, and I'll drag out an old bass combo. The problem will go away when my MCI sells and I get a proper amp. Till then, I'm in homework mode trying to select an amp for a PSG. Good thing I like research and shopping... |
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Bobby Snell
From:
Austin, Texas
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Posted 8 May 2012 4:36 pm
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| Crate acoustic amp? Is the input designed to amplify an acoustic guitar pickup? |
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James Holland
From:
Alabama, USA
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Posted 9 May 2012 4:22 pm
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| Bobby Snell wrote: |
| Crate acoustic amp? Is the input designed to amplify an acoustic guitar pickup? |
Yep, so I tried a decent bass amp last night, same input impedance as Peavey's Nashville 112. Same sound as the Crate. At this point, I'm not sure there's a problem, except with my perception. At anyrate, my questions have been answered as far as impedance expectations for suitable amps, and I did learn a lot from Sarno's and other's inputs. |
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Olli Haavisto
From:
Jarvenpaa,Finland
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Posted 9 May 2012 5:02 pm
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More gain at the amp,less output from the pedal will get you less distortion.
You never floor the pedal except at the end of sustaining a note.
Put the amp on 5 and regulate the volume with the pedal.
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Olli Haavisto
Finland |
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Lane Gray
From:
Topeka, KS
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Posted 9 May 2012 5:55 pm
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I've found that really sharp attack can sometimes overwhelm an amp, even when subdued by a volume pedal.
Do you strike with an explosive right hand?
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2 pedal steels, a lapStrat, and an 8-string Dobro (and 3 ukes)
More amps than guitars, and not many effects |
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James Holland
From:
Alabama, USA
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Posted 9 May 2012 7:31 pm
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| yes and yes - I'll back off the pedal, and my picking hand is pretty aggressive right now. Thanks! |
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Chris Lucker
From:
Los Angeles, California USA
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Posted 10 May 2012 12:17 am
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I am not the best player by any means, but I disagree with playing with the volume pedal backed off very much. Playing with the pedal backed off sucks out tone to my ears.
Practice without a volume pedal and you will learn how to use your right hand and learn to get sustain from your bar hand.
But remember, this is coming from a terrible player.
_________________
Chris Lucker
Red Bellies, Bigsbys and a lot of other guitars. |
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