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Guitar Preamp = MIC Preamp = other preamp ,,are they all same?
Guitar Preamp = MIC Preamp = other preamp ,,are they all same?
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Old 12th March 2008, 07:53 AM   #1
Paswa is offline Paswa  India
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Default Guitar Preamp = MIC Preamp = other preamp ,,are they all same?

Hi,

Once I made a Condenser Microphone preamp using two BC549 transistor. Now I've built a preamp with LM358. It sound is neither too good nor too bad.

I saw many people to make preamp using LM741 and TL072.

Now my question is

1> my primary aim to connect the preamp with a acoustic guitar pickup. I want very good audio quality. And I'll also buy a good pickup. Which preamp circuit will I use?

2> the duty of preamp is to amplify the gain. So in this term, guitar preamp, tape head preamp, microphone preamp all they are same. is it right??

3>Will I need any special preamp for guitar pick up

T h a n k Y o u
T H E O
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Old 12th March 2008, 05:16 PM   #2
myhrrhleine is offline myhrrhleine  Belize
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Default Re: Guitar Preamp = MIC Preamp = other preamp ,,are they all same?

Quote:
Originally posted by Paswa
Hi,

Once I made a Condenser Microphone preamp using two BC549 transistor. Now I've built a preamp with LM358. It sound is neither too good nor too bad.

I saw many people to make preamp using LM741 and TL072.

Now my question is

1> my primary aim to connect the preamp with a acoustic guitar pickup. I want very good audio quality. And I'll also buy a good pickup. Which preamp circuit will I use?

2> the duty of preamp is to amplify the gain. So in this term, guitar preamp, tape head preamp, microphone preamp all they are same. is it right??

3>Will I need any special preamp for guitar pick up

T h a n k Y o u
T H E O

Hi.
The preamps are similar, but not exactly the same because of noise issues, filtering, and other needs.

Modern op-amps, such as the OPA134 may be a better choice for you.
Even the older NE5534.
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Old 3rd December 2019, 08:24 PM   #3
Jimbo724 is offline Jimbo724
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The specs for my guitars say they all have preamps. Are typical built-in guitar preamps adequate to plug the guitar into a power amp, say, an LM386 (first amp project) or LM3886 (second amp project)?
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Old 3rd December 2019, 10:51 PM   #4
MAAC0 is offline MAAC0  Portugal
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Say You have am amp that needs 1V for full power on the output.
Say Your pre-amp can only 500mV. What gives ? Only half the power.
Now Your amp needs 500mV but Your pre can 1V. You will clip the amp, but wait ....You a have a volume / gain pot for that on the amp input.
Guitar pickups have usually very high impedance (MegaOhm), so a JFET op-amp is a good choice, but as Your guitars have pre-amps built in, they probably have low impedance output.
You have to make sure that output impedance is always lower than the amp input impedance (impedance bridging) or You will get that thin sound.
On the other way, mikes have low impedance, so every op-amp should work with them.

To answer Your question... Pre-amps are all basically the same but ...Gain differs between types, but for Tape & Phono for example You need equalization networks and more gain. For Mikes gain is similar, but for a Tuner or CD player or even Your Guitar perhaps You don't need high gain. That's why mixers have gain pots and tone controls.
And Yes they should work with any "normal" amp. Bear in mind that some PA intended amps need a higher voltage on the input say 2V, compared to consumer mV levels.
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Old 4th December 2019, 12:06 AM   #5
Galu is offline Galu  Scotland
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Quote:
Originally Posted by Paswa View Post
1> my primary aim to connect the preamp with a acoustic guitar pickup.
What kind of pickup are you considering - magnetic soundhole pickup, piezo bridge pickup or internal microphone?

The majority of acoustic guitar pickups come with preamps - you'll see their small control panels situated on the top or side of the guitar.

If the pickup doesn’t have a preamp, it can be plugged into any acoustic amplifier, DI / mixing desk or preamp pedal.
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Old 4th December 2019, 03:55 AM   #6
dotneck335 is offline dotneck335  United States
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An excellent guitar preamp design is one of the most difficult in audio. You cannot just provide clean, flat, quiet gain----it may sound terrific for a phono cartridge, a microphone, or a tape head but it will sound TERRIBLE for a guitar. Guitars don't want clean or flat. Perhaps one of the best, most affordable guitar preamps is the Joyo American pedal. If you want to build your own, I suggest an emulation of that.
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Old 4th December 2019, 05:51 AM   #7
Jimbo724 is offline Jimbo724
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Thanks, MAAC0!
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Old 4th December 2019, 10:04 PM   #8
Gnobuddy is offline Gnobuddy  Canada
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Quote:
Originally Posted by Jimbo724 View Post
The specs for my guitars say they all have preamps.
This is extremely unusual for electric guitars. There were a some electric guitars with active pickups (which contain preamps) in the 1980s, but very few today. Bass guitars frequently have built-in preamps, but basses aren't guitars.

Are you perhaps talking about electro-acoustic guitars, as Galu suggested? Those are very different things, and the requirements for an acoustic guitar amp and preamp are very different, compared to electric guitars.

Can you tell us more about your guitars? What makes and models are you referring to? As Galu said, what sort of pickups are in them? If you give us that information, it will be easier to answer your other questions.

By the way, the LM3886 is ancient in electronics terms: it dates from the late 1990s, about twenty years ago. (Note that this thread dates from 2008, eleven years ago!)

The LM3886 is a fine example of a class AB integrated circuit power amplifier chip from the last century, but this type of amplifier requires a huge, heavy, and expensive heatsink, and lots of clean DC from its power supply.

Because high-powered class AB chip amps have to get rid of a lot of heat through a small area of metal (the chip is very small), they are really not very good choices for amplifying musical instruments - they tend to have poor reliability when driven hard.

For a power amp in a little guitar practice amp, these days I would suggest using one of the many class D amplifier boards available on Ebay, Amazon, etc. These are much more efficient than the venerable LM3886, so they don't need a huge heatsink, and they draw less power from the power supply. Many of these newer class D chips also operate in bridge mode, and that means they also need less supply voltage, which makes it easier to find a suitable power supply.


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Old 4th December 2019, 10:13 PM   #9
Galu is offline Galu  Scotland
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Quote:
Originally Posted by Gnobuddy View Post
Note that this thread dates from 2008, eleven years ago!
Jings, I hadn't noticed that and was referring to the original poster!
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Old 4th December 2019, 10:14 PM   #10
Gnobuddy is offline Gnobuddy  Canada
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Quote:
Originally Posted by dotneck335 View Post
You cannot just provide clean, flat, quiet gain----it may sound terrific for a phono cartridge, a microphone, or a tape head but it will sound TERRIBLE for a guitar.
I was thinking the same thing at first, but I think Galu may have successfully read Jimbo724's mind, and figured out what he didn't actually say: Jimbo might be talking about acoustic guitars, or rather, electro-acoustic guitars, i.e. acoustic guitars with onboard piezo or mic pickups and onboard preamps.

If this is the case, a flat-response preamp and speaker system are fine. There will probably be at least three bands of EQ built into the guitar, which will be sufficient for tweaking the sound for non-critical situations. Usually the output level is closer to mic level than line level, so a fair amount of voltage gain might be needed.

IMO it's really nice to have more sophisticated EQ available to take away some of that stinging treble and too-deep bass that electro-acoustic guitars are notorious for, but that is a whole other kettle of fish. I've used a cheap little Danelectro Fish and Chips graphic EQ pedal do do this job; it isn't manufactured currently, but there are somewhat similar graphic EQ pedals available online.


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