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Old 2nd August 2007, 10:59 AM   #1
spresv is offline spresv  Greece
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Default My Guitar Tube Amp. Help needed with Mesa/Boogie pre

Hello, first post here.

I recently built my first guitar tube amp. The amp was based on an AX84 20W Push-Pull project, but came out a bit different. I used a pair of 6L6 instead of the suggested 6V6 with minor modifications on the power amp, chokeless power supply (don't know if that was a very good idea), and amplimo toroidal transformers. So now it's about 40Watts, loud enough for me.

As a preamp i used the Lead schematic from the same site, which was total crap. Wait, to be honest it was not crap, it just wasn't what i wanted. What i wanted was modern American hi-gain tone, a bit like mesa/boogie.

So i'm thinking of replacing the preamp channel with this preamp section from the 2 channel Mesa Boogie dual rectifier. Here comes the hard part. I really don't think i should try this one on point-to-point. Does anyone have the pcb for this preamp? I've searched for a couple of threads, but i didn't see a pcb anywhere... An alternative is a mark IV. (which is, i think, identical with the mesa/boogie formula. I've tried this directly to the power amp and it sounds amazing...)

Any ideas?
thanx a lot
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Old 3rd August 2007, 09:02 AM   #2
PRNDL is offline PRNDL  United States
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I took a quick look at the schematics and it's your basic Marshall preamp with a cascode gain stage, plus a long tail pair PI. This is your basic formula for Marshall tone.

The 6L6 power amp has negative feedback, which is going to give it a nice Fender clean sound, with the preamp distortion on top.

One simple mod may be to lower or disconnect the feedback, which usually adds grit.

Taking out the choke would make the amp more responsive, especially at high volumes.

The big question is what speaker are you using?

I'd recommend against the Mesa Boogie preamp. Stick with the well known: Fender/Marshall.

You may also want to ask on the Hoffman board, which is more for guitar
http://www.el34world.com/Forum/yabb2...ubeAmpBuilding
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Old 4th August 2007, 01:03 PM   #3
spresv is offline spresv  Greece
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Currently I'm using an 1x12" Marshall cab 80 watts (i think celestion speaker) which is not very good. I've played on an 2x12" closed back with Celestion V30 speakers and it sounded amazing. I'm gonna build one of those once i return home.

Why not mesa preamp?
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Old 4th August 2007, 02:14 PM   #4
PRNDL is offline PRNDL  United States
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Quote:
Originally posted by spresv
Why not mesa preamp?
You appear to be a beginner at this.

There's tons of info on Marshall/Fender tone stacks, and a lot of people can offer advice on mods to get the tone you want. Not so with the Mesa/Boogie.

Also, the preamp you chose is for the heavy metal sound. So, there must be something else going on.

I have one of those 10" Marshall speaker cabs (for the mini stack) and replaced the speaker with a Celestion, which sounds much better.

Have you tried major changes in the tone settings? It's not uncommon to have to put the bass and treble at 1 or 2, especially if you want thick mids.

Also, the easiest mod is to put in a lower value bright cap, or remove it. This usually changes a thin sound into thick and heavy.

The guitar is the last piece of the tone puzzle. Single coil guitars sound thinner that humbuckers.

Add all three (Strat, cheap speaker, bright amp) and voila ... a bright and thin amp!
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Old 5th August 2007, 04:06 AM   #5
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if you built the HO preamp, I don't know why you had problems with it as it nails the early marshall tone dead on, and has loads of gain. You gotta have good tubes however. I have a JJ 12ax7 in V2 location and a '64 sylvania 12ax7 in V1. Replace V1 with a 12au7 and you've got vox ac-30 sounds. I have loads of early RCA cleartops that sound great in this amp

the HO will not do mesa-boogie style distortion, but you should consider putting a pedal in front of it and see.

EDIT: My amp is the SE 5 watter... I have gigged with it live with a drumkit. Couldnt believe how loud it was through a 2x12 cabinet..( for 5 watts) till I checked the bias ... 60ma @ 275v!!!!! Must have crept up on me.. Best of luck!
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Old 5th August 2007, 09:05 AM   #6
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You can easily build the rectifier preamp point-to-point... I did, (no channel switching) and it is still my favorite amp.... all that vintage marshall and fender stuuf never did it for me....
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Old 5th August 2007, 03:56 PM   #7
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Just build it P to P. And build a couple of other channels of different designs whilst you're at it, as you can never know whether the tone is right for you until it's plugged in and running and the rest of the band are telling you to turn it down.
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Old 5th August 2007, 07:36 PM   #8
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If you strip away all the bells and whistles, the Dual recto preamp is just ripped off the Soldano SLO. Go to the SLOclone forums to find PCB and also turret layouts for it. I have built several variants of that style of preamps myself in both turret board and free wired true PTP, and it is just fine if you have the component layout and wire crossings right.
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Old 5th August 2007, 09:11 PM   #9
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Default Re: My Guitar Tube Amp. Help needed with Mesa/Boogie pre

Quote:
Originally posted by spresv
Hello, first post here.
Welcome!


Quote:
So i'm thinking of replacing the preamp channel with this preamp section from the 2 channel Mesa Boogie dual rectifier.
If you're a beginner, good luck getting that thing stable!



Quote:
Here comes the hard part. I really don't think i should try this one on point-to-point. Does anyone have the pcb for this preamp?
I sell generic tag and turret boards. PM me if you're interested.

Cheers!
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Old 7th August 2007, 06:58 PM   #10
spresv is offline spresv  Greece
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Thank you all for your replies!

Quote:
Originally posted by PRNDL


You appear to be a beginner at this.

Have you tried major changes in the tone settings? It's not uncommon to have to put the bass and treble at 1 or 2, especially if you want thick mids.

Also, the easiest mod is to put in a lower value bright cap, or remove it. This usually changes a thin sound into thick and heavy.

The guitar is the last piece of the tone puzzle. Single coil guitars sound thinner that humbuckers.

Add all three (Strat, cheap speaker, bright amp) and voila ... a bright and thin amp!

What gave me away

I've done all that. along with a stopper resistor, plain 1.5K on the cathodes, 150 instead of the 470pF in the tone cotnrols, and a switchable cap in each gain control. It sounds much more bright, less harsh gain, more distortion, but it still isn't what i want. Great tone for classic rock though.

Quote:
Originally posted by aletheian
If you strip away all the bells and whistles, the Dual recto preamp is just ripped off the Soldano SLO. Go to the SLOclone forums to find PCB and also turret layouts for it. I have built several variants of that style of preamps myself in both turret board and free wired true PTP, and it is just fine if you have the component layout and wire crossings right.
This is really interesting. I'm waiting authorisation from the admin to see if i can find anything usefull.

Thank you all!
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