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Old 3rd June 2003, 05:06 PM   #1
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Default help with matching input impedences.

I don't have a gutiar amp because i figured the 600watt r.m.s. dj amp would work out nicely. my problem is that i cant get the amp to sound right because it wasn't meant for guitar. i don't really know much about the input impedence thing but i think it is the problem. is there any easy way to remedy this problem. clean the guitar sounds good. put any distortion pedal inline, it doesn't. my amp only has rca and phono input.
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Old 3rd June 2003, 06:36 PM   #2
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Default hi or low

car guy,

When you say "not good" what does it sound like? Too low/high in volume, distorted, hum/noise? Can you describe the symptoms? Is there some volume control that influences it?

Jan Didden
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Old 11th June 2003, 11:24 PM   #3
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it is hard to explain how it sounds. the easiest way to describe it though would be that it is similar to hooking a set of headphones right up to a distortion pedal but louder. it sounds thin, no tone from my les paul is getting through. it is also really distorted, not the good overdrive tones but a rough scratchy distortion. it is the same at all volume levels. i was told by some tv repair guy i know, that my input impedences aren't matched. i need some help. is there possibly a circuit i could use, like a headphone amp for a guitar ? that would be ideal. if anyone knows of a simple circuit that they could point me to, i would greatly appreciate it.
-John
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Old 11th June 2003, 11:41 PM   #4
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A Dj amp is meant to be a "low" distortion device. In other words: Distortion is bad - design the amp to make it distort as little as possible.

A Guitar amp is a "high" distortion amp. In other words: Distortion is good, (we like the sound of the distortion) let's design the amp to be able produce alot of it.

The main cause of a lack of distortion (or guitar amp sound) is probably not because of an impedence mis-match, but because the amp is not designed to be over-driven. Over driving a guitar amp is the biggest source of the guitar amplifier sound.

Ironically, you would be more likely to get more of a guitar sound if you bought a smaller amp, as in 25 - 100 watts.

Your best bet would be to find a foot pedel (or if you got the bucks a guitar pre-amp) that would go between your guitar and the amp. The pedel would generate the sound you are looking for, then let the DJ amp do the power gain. This foot pedel should also correct for any impedence mis-match and needed gain.

If you are good with a soldering iron, you could make your own guitar pre-amp/foot pedel type of device. The good news is that all the things that make an amp cheap and easy to build are the things that introduce the distortion (or guitar sound) you are looking for.

Have fun,

Aud_Mot
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Old 12th June 2003, 12:35 AM   #5
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okay there seems to be a misunderstanding. i am not trying to overdrive the amplifier as it would result in a very undesirable super hard clip. i am talking about when i USE a distortion pedal inline. like i said before it sounds the same as hooking up a pair of headphones straight to the distortion pedal but louder. the rig is as follows les paul guitar -to- ibanez ds7 distortion pedal -to- 600 watt r.m.s. dj amp. all i'm looking for is the cheapest way to clean up the sound. i'm not opposed to building a preamp that would correct the mismatch but i've been having a hard time finding one that is resonably simple. i've used a dod distortion pedal with a headphone output that sounded great on my amp, but when i tried using the 1/4" output on the same pedal it sounded like mine does right now.
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Old 14th June 2003, 02:44 AM   #6
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caraudiophile,

Well you need to do a little experimentation.

The DJ amp you are using, is there any source that works with it? Example a tape deck, phono/turnatable pre-amp, microphone mixer etc. What is the label on the input jack that you are using?

Does the DJ amp have any microphone inputs? The output of a guitar is closer to mic level than line level. (I used to put my bass guitar into the mic inputs of my cassette deck so that I could play it on my bedroom stereo.) If you can, plug into a mic input, turn down the guitar and the amp and bring them both up very slowly, while picking on a couple of strings.

If you are using some sort of pedal/guitar pre-amp, I will assume that your problem is not an impedence mis-match. The pre-amp's output impedence should be low enough to drive the input of a audio amp.

You might have a gain problem. You can make a breadboard gain booster to go between the pre-amp and the DJ amp. This does not have to be anything fancy, you can do it with a $1.29 op-amp, 3 or 4 resistors, 2 capacitors and a 9V battery. How are you with schematics and soldering irons?

The other choice is to drag your guitar, preamp and amp to the local guitar shop and ask them what it will take to get the sound you are after. That is what they are there for. You don't have to buy anything.

If you have access to some test equipment (an O-Scope and signal generator) you could just measure the signal levels.

Let us know what what works.

Aud_Mot
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