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Old 15th June 2011, 03:13 AM   #1
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Default Will Tillman Preamp improve acoustic guitar sound?

I need some advice. I have a Samich acoustic/electric guitar...nothing special, I think I paid about $250 for it. It has controls for volume and tone. I took apart the circuit and traced it out (I am an electrical engineer) and I have attached a picture of the schematic.
I play at my church. The 15 foot cord from my guitar plugs into a simple, passive DI, which plugs into a ~200ft snake that goes to the mixer which is located at the other end of the auditorium.
I know this is a very open-ended question, but do you think if i installed the Don Tillman FET Pre-amp in my guitar I could improve the sound quality from my guitar? I just think that when my guitar is hooked up to the church PA system it lacks the "full" sound that I am used to hearing.
Is this a typical application where the Tillman Pre-amp would be beneficial?
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Old 15th June 2011, 04:03 AM   #2
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If the giutar is not already active then I am sure that a preamp would/could make a vast improvement on your sound quaity as a passive pickup on a 200ft run of cable can introduce quite a bit of loss in signal strength aswell as alot of loss on the high end by the time it gets to the board.
What does it sound like going into the board whithout the use of the snake (shorter cable at the board)?

jer
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Old 15th June 2011, 04:14 AM   #3
tinitus is offline tinitus  Europe
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is this not a 'situation' where line audio trafos are used ?

maybe the passive DI is the main issue ?
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Old 15th June 2011, 12:36 PM   #4
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I thought "line audio transformer" and "Direct Box (DI)" were the same thing?
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Old 15th June 2011, 01:16 PM   #5
tinitus is offline tinitus  Europe
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maybe they are
I'm no expert
just fumbling

but with passive guitar pickups, I think you will need a pre with gain, and not just a buffer
maybe look at 'foot switches'/guitar effects, for inspiration
or look up 'line driver'

one speciality with passive guitar, you need at curcuit with very high input impedance
could be one reason why tube design often work well, along with the gain
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Old 15th June 2011, 02:38 PM   #6
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Yes, bringing down the impedance on the line will do lots of good things; reducing signal loss, improving frequency response, cutting down on buzz and interference pick up. All positive. But I don't believe that present volume/tone circuit (well, I do, because I've rewired other guitars, but I try not to). Did they really wire the two pots as rheostats? Shorting out the pickup (I assume that's a magnetic pickup, not a piezo?) and dropping the high frequencies faster than the bass? A fixed resistor guaranteeing you can never get all the drive out? And I don't believe the pot values, either; they wouldn't stay that precise even if they started that way.

Do you need the volume/tone controls? Tillman suggests (and my experience tends to support him) that a guitar pickup needs a minimum load impedance of 1 meg to give high frequency sparkle; and this one's feeding something like 220k (can't say quite what without the value of R3), and lower. If you're building it a first buffer direct from the pickup, and a second (could be transistor rather than FET) after the volume control, with the tone after R3, giving both decent loading and good line drive, might be a good solution, though it might be a bit 'toppy'. (wind down the treble at the other end of the cable; there went thyristor buzz, hiss, short clicks… There again, we don't know what equalisers they've got on the system.)

Switching the power to the preamp on and off is always a problem (and at the price nine volt batteries cost, an important one, ignoring the ecological disposal problem); the "switching jack" solutions are responsible for so many crackles and unforeseen program breaks. But a guitar with a wall wart plugged into it is less than aesthetic (and what connectot to use that doesn't tend to work loose?).
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Old 15th June 2011, 02:49 PM   #7
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@chrispenycate - Now that you mention it...I think you are probably right about that circuit diagram not being correct. I will re-check it later tonight.
In regards to not needing Volume/Tone controls...would you mind sketching out a circuit of what you are talking about?
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Old 15th June 2011, 03:16 PM   #8
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Wireless guitar ? Costs money, but bypasses that snake.
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Old 15th June 2011, 05:14 PM   #9
kevinkr is offline kevinkr  United States
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Just wondering what sort of sound system the church has, and whether that is not at least partially responsible for the sound quality issues noted? What I am getting at is whether the issue at hand includes things like excessive hum & noise and rolled off highs/lows that would be mitigated by an active pre? The other option would be an active DI which would have no problem driving a long snake. (Most passive DI actually sound pretty mediocre IMVLE when driven directly by a typical guitar pick up..)
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Old 15th June 2011, 09:07 PM   #10
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Quote:
Originally Posted by andersonee View Post
@chrispenycate - Now that you mention it...I think you are probably right about that circuit diagram not being correct. I will re-check it later tonight.
In regards to not needing Volume/Tone controls...would you mind sketching out a circuit of what you are talking about?
Ah, pictures. I'm not very good at pictures here, but I'll try. Actually, that might well be the circuit; guitar makers tend to be better with wood and metal than components, I've found, and that would do more or less what the pots said; it's just horrid.

Quote:
I thought "line audio transformer" and "Direct Box (DI)" were the same thing?
With a passive DI, they can be; but generally a line isolation transformer will be 1-1, while a DI transformer steps down the signal, and the impedance, while balancing and isolating the source. The Tillman output won't be happy driving anything less than about 10k ohms (which for amps is fine) while the console mic inputs (a DI goes into a balanced mic input, not a balanced line) are around 1 to 2 kilohms. So the step down transformer does help (rejoice; in my youth, loZ mic inputs could be as low as 200 ohms, sometimes even fifty, to keep noise levels down).
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