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Old 7th October 2006, 10:50 PM   #1
ashade is offline ashade  Brazil
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Default building guitar amp... first project! help

hello, I'm a 4th year electronics student and i'm about to make an amp for my guitar... it's going to have tone, volume, balance controls, it'll be stereo, 40W per channel... it'll have a distortion / overdrive pedal. I'm going to use lm4766 for amplification, lm1036 for tone/balance/volume controls and a pedal that i found on this forum... I'm thinking of connecting the guitar to the pedal, the pedal to the lm1036 and it to the lm4766... is it right?? any recommendations, etc?
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Old 7th October 2006, 11:22 PM   #2
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Default Re: building guitar amp... first project! help

Quote:
Originally posted by ashade
hello, I'm a 4th year electronics student and i'm about to make an amp for my guitar... it's going to have tone, volume, balance controls, it'll be stereo, 40W per channel... it'll have a distortion / overdrive pedal. I'm going to use lm4766 for amplification, lm1036 for tone/balance/volume controls and a pedal that i found on this forum... I'm thinking of connecting the guitar to the pedal, the pedal to the lm1036 and it to the lm4766... is it right?? any recommendations, etc?

Op-amps are supposed to sound absolutely awful when overdriven or abused. (They're the exact opposite for tubes in this respect).

I've got threads both here and in the Tubes thread on a tube-gainclone hybrid amplifier. You could probbably do something similar with a low-power FET amplifier.

What happens if I put a clipped INPUT into a gainclone?

Help wanted for a truly loco project. (A Tube--gainclone hybrid guitar amp!)

It's a nice solution - Assuming you use an el-cheapo power transformer (about 3$, less if you rip it out of something else) for the interstage transformer, and can find a cheap transformer for the 200v needed for the tube stage (rip apart another amplifier!), the total cost of the tube stage is well under 50$.

As an added bonus, the transformer eliminates DC offset on the inputs, and you can do some interesting things by oversaturating the transformer by adding a DC offset to the tube stage, and by adding current-limiting resistors on the power supply.

Plus, the tube stage is completely isolated from the power amp stage!
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Old 7th October 2006, 11:55 PM   #3
ashade is offline ashade  Brazil
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tubes?! I thougt i though it was left behind decades ago.... well, thankx for the help, i'll think about it...
PS: are you sure op amps are not goodfor overdrive, even the highest quality ones?
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Old 8th October 2006, 12:55 AM   #4
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Quote:
Originally posted by ashade
tubes?! I thougt i though it was left behind decades ago.... well, thankx for the help, i'll think about it...
PS: are you sure op amps are not goodfor overdrive, even the highest quality ones?
I've heard from everyone I've ever met that they're abysmal, but you don't have to take my word for it.

Tubes are clunky, fragile, and inefficient. However, because they're more or less electromechanical (google the Thermonic Effect), they do many interesting things in very non-linear ways under certian situations. This is generally considered desireable.

(They also do a much better job of distortion. Distortion is bad most of the time, but most of the "effects" on an electric guitar are just forms of distortion. Overdrive is just the preamp overdriving the power amp, fuzz is often formed by adding diodes (with their breakdown voltage and voltage drop) in the signal path, et cetera.)

Of course, because you need a massive output transformer built to exact tolerances and lots of tubes, big tube power amps are tricky; usually, they largest are not above 50w. However, we can take the same signal (with all the distortion intact) and feed it through a Gainclone. If the input is clipped, the output will be clipped, but without sounding nasty. (For example, if you have a 2.5v signal into a gainclone with 30v rails and a gain of 10, the output will clip at 25v, but within the 30v of the gainclone- it will output it like any other signal).

Plus, you can use a cheap-0 power transformer in place of the fancy, expensive transformer, and you only need a very small power transformer.
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Old 8th October 2006, 01:10 AM   #5
ashade is offline ashade  Brazil
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sorry, but I still doesn't understand what is the problem with ic amps... i know distortion clips the signal to a voltage, and the ic will amplify it etc, but what is wrong with it??
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Old 8th October 2006, 01:33 AM   #6
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Quote:
Originally posted by ashade
sorry, but I still doesn't understand what is the problem with ic amps... i know distortion clips the signal to a voltage, and the ic will amplify it etc, but what is wrong with it??

When an op-amp clips, it severely distorts the signal, but in a manner that sounds horrible.
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Old 8th October 2006, 02:14 AM   #7
ashade is offline ashade  Brazil
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but what is supposed to clip the sound is the pedal, not the amp
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Old 8th October 2006, 02:41 AM   #8
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Quote:
Originally posted by ashade
but what is supposed to clip the sound is the pedal, not the amp

"Overdrive" = pre-amp clipping the power amp. Trust me, no guitar amp has zero distortion.
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Old 8th October 2006, 03:55 PM   #9
ashade is offline ashade  Brazil
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i thought it were different... let me give an example:

input signal: a sine wave with 2V peak
pre amp overdriven signal: the same sine wave, but clipped at, let's say, 1,5V.
power amp output: the same signal multiplied by a gain factor, let's say, 20 times, which means a sine wave with 40V peak, but clipped at 30V... if the power amp is fed from +- 50V for example there will be no problem in my opinion... (the output signal is the same distorted signal from the pre amp).

Am I thinking the wrong way?
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Old 8th October 2006, 05:01 PM   #10
Nordic is offline Nordic  South Africa
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Getting it to clip is not the problem, the actual sound of opamps clipping, is.
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