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Old 3rd October 2004, 11:58 PM   #11
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I'm also building me a guitar amp, already bought 2, 80 watt Celestions. I'm setting it up to where I’ll have 3 sections, a pre-pre-amp section, basically just an op-amp gain stage, as a buffer, and to bring the input signal up to line level. I might have a comparator circuit which will indicate with an LED when the signal is at line level, 2 volts peak to peak or so. Then the second stage will be a tone shaping and effects sage, with effects loop connections, I probably wont have any voltage gain in this stage just for tone shaping. And finally a power amp stage, just a basic hifi design, volume control will happen here. The second stage I'm planning on being a separate modular unit, so I can upgrade and develop it over time, for now its will just have a few tone controls, a parametric equalizer, and a tube based distortion circuit, already have a few 12ax7c’s.

Keep in mind that there are many considerations to keep in mind as far as the enclose goes, the type of wood, size, whether it has an open or closed back, all affect the sound of your amp. I’m going for a read oak “inner shell” and a maple “outer shell”, mostly for a very clean sound. The softer the wood you use the more warmth the box will add to the sound. Red oak and maple are fairly hard woods, so should produce a fairly clean sound.

Also the power supply is often used to add to the “feel” of the amp, especially in vintage amps, tube rectifiers are sometimes used for their slow response, thus affecting the players “attack”, sounds like a lot of BS to me but whatever.

Although you might not be interested in distortion, consider using a few pre amp tubes in your pre amp, from what I understand warmth is what jazz guitarist look for, especially if you’re using a hollow body.
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Old 6th October 2004, 12:59 AM   #12
BbbyBld is offline BbbyBld  United States
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I would keep the amp VERY simple. I play a Gibson ES-135 when I'm attempting to play jazz, and all I want is a gain control and a flat eq so I can adjust the tone with the guitar controls. Design the pre-amp with high input impedance. The less you load the pickups, the more subtleties of the guitar will be heard. I think this is one of the reason I like a tube preamp.

If I were going to design a solid state amp for jazz right now, I would definately throw in a compressor circuit. That would be the only complex part. I hate it when I'm switching back and forth from chords to moving passages and I play a string a little too hard. It totally interrupts the mood of the song! A compressor makes octave solo patterns sound better to me. Some people I've met think a jazz guitar amp should have a ton of headroom though.

If I were going to design a jazz guitar amp for myself, it would be an all tube design, since I'm one of those people who have convinced myself that tube amps sound better.

Either way, I would build a semi-open back pine cabinet with a 12" eminence. All personal preference of course.
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Old 6th October 2004, 05:07 AM   #13
Enzo is offline Enzo  United States
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A tube rectifier is no BS. You may or may not like the results, but it has a very real effect. We call it sag. When you play something loud, the extra draw from the power supply causes the B+ voltage to sag due to the tube's effective resistance.

I don't think of it as an attack reducer so much as a compressor, but it does reduce attack. When you bang on the amp, the peak drops the B+ for a moment, and the output of the amp drops with it. Then as the note rings out, the caps charge back up and the B+ climbs back to where it was, the output of the amp rises with it. Thus the sound level of the amp is more even. This tends to give you more sustain on notes held. In that way it makes the amp more expressive for the blues player. The death metal guys are not into it.

In fact the tube recto can maybe serve as the compressor Bbby wants.

Makes the amp sing. Or cry, as your needs may be.
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Old 7th October 2004, 03:34 AM   #14
BbbyBld is offline BbbyBld  United States
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I believe there is something to power supply sag, but I also know you can get the same effect from using silicon rectifiers and adding series resistance to duplicate the high voltage drop of a tube rectifier. Even knowing this as a fact, I would still use a tube rectifier because of the mojo factor.
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Old 7th October 2004, 05:59 AM   #15
Enzo is offline Enzo  United States
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Yes, we sometimes add sag resistors to small amps. SOme commercial amps have selectable rectification - Fender Prosonic comes to mind
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Old 9th October 2004, 02:48 AM   #16
rljones is offline rljones  United States
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This may not be the way you want to go for building a guitar amp from scratch, but I'll decribe the approach I took.

I recently built a 12" guitar amp, planning on using one of my amp modules along with a preamp module to keep it "clean" sounding, figuring I'd use pedals before the preamp section if I wanted to add distortion. I was also planning on adding a spring reverb tank to the amp.

As I got the project going, I read about the Carvin preamp TN100 (Frank Gambale design). So I scrapped my preamp section, bolted the TN100 to the top of the cabinet and used only my amp module (a 100W/8ohm MOSFET with power supply). The driver is a Weber 12" AlNiCo (40oz/60W/8 ohm). After listening, I added 4 series/parallel Bohlender Graebener NEO3 Planar Tweeters (Parts Express). I put a switch between the amp and the X/O to allow using the 12" by itself or with the X/O and the 4 tweeters.

The TN100 is a very good preamp with amazing effects, which include reverb and chorus. As I was assembling it, I heard vibrations that sounded like a spring reverb unit (but if you look inside there's none to be seen). The built-in effects are quite varied and are programmable and it has a cool blue display. The effects can be switched remotely with a simple foot switch. (See the Carvin site for details.)

So basically, you can add this preamp/effects processor to any amp module you choose and have a really good guitar amp. One nice feature is all the holes and inut jacks are already in the preamp, so except for wiring up the amp and power supply, it is almost plug-n-play.
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Old 9th July 2009, 12:42 PM   #17
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Question question

Hi
I have a question about transtube used in Peaveys, please follow the link and answer: peavey amp
thanks in advance
P
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