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Topic: Profex input impedance too low for steel |
Jim Pitman
From:
Waterbury Ctr. VT 05677 USA
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Posted 4 Sep 2002 5:05 pm |
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Perhaps this old news but........has anyone else experienced a loss of high frequency tone when plugged directly into the Profex and volume pedal at full?
I believe we solved this mystery at the Fessenden booth in st Louis with the help of the great(est) steel guitar player whose name I won't mention.
With pedal at full the pickup is overloaded with the Profex input impedance - max load. Back off and the fidelity returns, which makes sense as the impedance of the pedal is gradually inserted in series with the Profex impedance reducing the load the pickup sees as you back of on the volume pedal.
Lesson - Put the Profex in the effects loop if you can. Its' input Z is too low. Let your amp's preamp do its job. We did this - problem gone!
Jim Pitman
Jaspit Electronics |
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Donny Hinson
From:
Glen Burnie, Md. U.S.A.
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Posted 4 Sep 2002 5:57 pm
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Are you saying they designed this thing without the thought that someone might plug a guitar into it? 
That sure doesn't sound like Peavey!
(I'm sure Mike Brown will comment on this.) |
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Jim Pitman
From:
Waterbury Ctr. VT 05677 USA
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Posted 4 Sep 2002 6:47 pm
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Got one? Try it.
I suppose it's possible the pedal in use had a marginally low Z. Place another marginally low Z load in parallel and together they make the pickup's series inductance quite significant. |
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Jim Smith
From:
Midlothian, TX, USA
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Posted 4 Sep 2002 6:56 pm
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I was there, and saw and heard the results. I believe I heard that the ProFex series was originally designed for six string guitar, whose pickups have much lower impedance than pedal steel pickups. Maybe that's the reason.
In my Stereo Steel rig with a Boss GX-700, I keep the input volume of the GX almost off to keep from overdriving the unit. |
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DJ Sillito
From:
Lethbrige, Alberta, Canada
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Posted 4 Sep 2002 9:40 pm
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Just curious Jim if you would know if using a product like the goodrich matchbox or the Hilton pedal etc. would help. If there is an impedence difference these should help? I admit I am a little lost in the electronics department but I do find it interesting. BTW I tried the effects loop way with the profex and if I remember correctly I had to add the Effects loop setting to the presets, it seemed alittle tedious at the time maybe I didn't do it right?!,
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Darren James
Carter D-10 8P 5K
Nashville 400, ProfexII |
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Keith Hilton
From:
248 Laurel Road Ozark, Missouri 65721
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Posted 5 Sep 2002 4:39 am
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How many times have you heard the following?
"My tone with the band sounded great when we first started. As the night went along the band got loud and my tone started sounding terrible". There is a "simple" reason for this. You set tone at low volume, not loud playing volume. A pot is nothing more than a voltage divider. When you divide voltage you change impedance. When you change impedance the tone of a music instrument changes. The person who's tone started sounding terrible
made one error. He set tone at low volume as he was tuning and getting ready to play. He did not set tone at the louder volume. As the night wore on, and the band's volume increased, this person go more "into" his volume pedal. When he did this, the pot was no longer where he set tone. The problem is not in the input of a Peavey ProFex II. The problem is not in the guitar pickup. The problem is in the pot. What causes the problem? Really 3 things: #1 A pot is a voltage divider. #2 A pot has capacitance even when wide open and this cuts highs. #3 There is some resistance in a pot even when wide open. Sometimes there is a lot of resistance because the string never seems to pull the pot all the way open. The solution to this problem is very simple: For those of you who don't want to spend a penny, use the Peavey 3 cord hookup method. For those of you who want some extra features in solving this problem buy a Goodrich Pre-Amp or Hilton Pre-amp product, and put it between the pickup and the pedal. I need to mention that my infrared pedal does not contain a pot. For those of you with good hearing, try this test: Use a pot pedal and play something with the pedal wide open. Un-hook the pedal and run a straight guitar cord to your amp from the guitar without a pedal even hooked up. Unless you have hearing problems you will hear the following: The volume will be slightly less with the pot
wide open than with a straight guitar cord. The sound will be slightly duller with the pot pedal than it is with a straight guitar cord run from the guitar to the amp. It is difficult for some to hear good if they are real close to big amps. To hear what I am talking about, have someone play your guitar and get back 20 feet and listen. Unless you have hearing problems you can clearly hear what is going on. Many musicians have hearing loss so don't feel bad if you can't hear the difference.[This message was edited by Keith Hilton on 05 September 2002 at 05:40 AM.] |
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Jim Smith
From:
Midlothian, TX, USA
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Posted 5 Sep 2002 4:40 am
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Darren, another Jim here. I don't know if a matchbox would help. For your other question, Jim Pitman is suggesting to put the ProFex II in the effects loop of your amp, not the other way around.  |
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Bill Moore
From:
Manchester, Michigan
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Posted 5 Sep 2002 4:54 am
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I've used the Profex II plugged directly into my Session 400, it doesn't have an input for "power amp in" or an effects loop. The output of the Profex, on the back, needs to be set very low, in order not to overload the amp. The volume is easily adjusted via normal amp volume control. I've also used it with my Nashville 400, usually plugged into the "power amp in" jack on the back. With this setup, the output level can be set much higher, with the volume adjusted with the output control on the back of the Profex. It works fine either way, the outputlevel just needs to be set properly.
Keith, my hearing is kind of poor, but I really like the way my Hilton pedal sounds. especially at low volume.
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Bill Moore
my steel guitar web page
[This message was edited by Bill Moore on 05 September 2002 at 06:34 AM.] |
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Jim Pitman
From:
Waterbury Ctr. VT 05677 USA
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Posted 5 Sep 2002 6:44 am
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Yes, Any buffer device is designed exactly for this situation. Keith's pedal, the goodrich matchbox, etc, all do the trick. These typically have high input impedance, 300k or greater.
A steel guitar pickup is at least a factor of 3 times higher the resistance and likely 7 times, or greater, higher the inductance than a guitar pickup. If Peavey originally designed this for guitar that explains it.
A pickup's series inductance and the impedance it is driving form a low pass LR filter. The lower the input ipedance of the driven device the lower the freq corner, therefore the loss of highs.
For example I changed the input resistor on an old session 500 from 220k to 470k and improved the high end immensely.
Jim
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DJ Sillito
From:
Lethbrige, Alberta, Canada
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Posted 6 Sep 2002 9:46 am
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Jim Smith,
Thanks for the reply. Turns out I had tried hooking the effects loop "bass ackwards" . it still would work the other way but it was a bit tedious. Thanks for the insight.
I figure I could bypass the loop situation by just using my goodrich box.
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Darren James
Carter D-10 8P 5K
Nashville 400, ProfexII |
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jim milewski
From:
stowe, vermont
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Posted 16 Sep 2002 3:06 pm
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| whats going on here? pitman, I thought I sent you to your room! |
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Sam White R.I.P.
From:
Coventry, RI 02816
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Posted 16 Sep 2002 6:22 pm
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Jim I have my Pro Fex II pluged into my Goodrich Volumn pedal andI also have my super sastain Match box plaged into the amp side of my volumn pedal and Iplug from the Back of the Pro Fex II into the back of my nashville 400 Amp and I runfrom the back of The ProFex II into the back of my Bandit 75 Amp and I have the best sound at our steel show in R.I.
Sam White |
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