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Author Topic: LXH2 - marshall preamp for guitar amp.  (Read 14459 times)

TomHealey

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LXH2 - marshall preamp for guitar amp.
« on: July 11, 2012, 08:48:22 AM »
Hello everyone!

Few days ago I've completed first pre-amp for my new project, a solid state guitar amp. I've bulit LXH2 "marshall" and test it, sounds fantastic! This week I will build "fender" version and cabinet 2x12". Still not sure what speaker should I choose, Eminence or Jensen.

LXH2 project is already gone and withdraw from site: http://home3.netcarrier.com/~lxh2/marsh.html. Attached you will find schematics and PCB for both Fender and Marshall.

I have made few changes to the original schematic, I used AAP153 germanium diodes instead of silicon one, also I resign to use last stage after buffer and level control as I will have level controls and master volume on other PCB connected to the PA.

Here is some photos:

 

I've recorded this way: Ibanez RG370DX + LXH2 + Roland Quad-Capture + CabSim 2x12" from Amplitube. I cannot upload sound clips (RAR is small enough but doesn't allow yet ZIP is too big), so you can download from here:

Sound Clips

I know that final sound coming from real cabinet will be slight different, but I assume won't be worse or even better  :)

Kind Regards!
Tom.
« Last Edit: March 23, 2013, 02:06:32 PM by TomHealey »

spud

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Re: LXH2 - marshall preamp for guitar amp.
« Reply #1 on: July 12, 2012, 04:22:27 PM »
Hey, I remember those plans.  Cool project.  Very nice clips.  I was fascinated with this project when i saw it back in 06.  I had saved a bunch of his (Krister Sundstrom) stuff.  This is Marshall stuff but I also have the Fender stuff somewhere too. 

I have more clips but will need to post them elsewhere and link because they are pretty large.  (The clips are not me, I just saved them from the original developer's page (Kirster Sundstrom) and posted them here as that page is no longer available.)

Jim
« Last Edit: July 12, 2012, 04:24:29 PM by spud »

spud

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Re: LXH2 - marshall preamp for guitar amp.
« Reply #2 on: July 12, 2012, 10:56:15 PM »
Ok more clips:  All of them are from Krister Sundstrom. 

http://soundcloud.com/spudjds/sets/lxh2-1/

Jim
« Last Edit: July 13, 2012, 01:18:51 PM by spud »

TomHealey

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Re: LXH2 - marshall preamp for guitar amp.
« Reply #3 on: July 14, 2012, 04:38:20 AM »
I know those clips, there are quite different. As far as I remember he recorded through LXH2 cab-sim (but not that simplified "fender"), but very good though. Anyway, good point of reference, not bad for a non-tube pre-amplifier  :)

newbiediy

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Re: LXH2 - marshall preamp for guitar amp.
« Reply #4 on: September 09, 2012, 12:55:43 PM »
Hi, I'm interested in building this preamp for my next amp. Do you have noise problem at high gain setting? How do you filter your power supply?
Thanks before.
Sorry for my bad English. We say "laik dis" instead of "like this" in Facebook. :P

TomHealey

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Re: LXH2 - marshall preamp for guitar amp.
« Reply #5 on: September 22, 2012, 06:29:36 AM »
At hight gain there will be always noise, that's quite normal. When I have extreme gain then I use noise gate. But all in all I think there is less noise at high gain than comparing to the tubes amps.

If it comes to the power supply - I use LM317 and couple of caps/resistors (standard application). No big deal. As a addition, I put ceramic cap (around 100n) between +/- soldered under PCB for each op-amp.

allan_belt

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Re: LXH2 - marshall preamp for guitar amp.
« Reply #6 on: October 07, 2012, 12:20:06 AM »
Hello everyone here.. i`m writing from Peru.. Cool project by the way but i just found an error in th schematic and in the layout.  :(
In the Original schematics of a Marshall amp in the tonestack the 22n is conected to the wiper of the Mid Pot.   ::)   I'm i right ?  ;)

i made first the Layout posted here without mods.. and comparing with the moded tone stack with the marshall specs. i found that the first one sounded Fenderish an the second almost like a real Marshall .  :duh
what dou you think?  8)


« Last Edit: October 07, 2012, 12:31:27 AM by allan_belt »

TomHealey

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Re: LXH2 - marshall preamp for guitar amp.
« Reply #7 on: October 07, 2012, 05:37:20 AM »
You can consider different connections as an error, but it is not in term of workability :) In other words, it works good and it is simplification. Tone is exactly the same (as the tonal characteristic stays, look at the attachments), the only difference is - if You turn down middle, treble and bass - you will shout down the signal, there will be no flow. In Marshall style tone stack, it is not possible because middle pot cannot be shout to the ground by the wiper, as there is no connection between wiper and bass potentiometer.

If it comes to the sound, I like it as it is, but of course anyone can do any modification they like  :dbtu:

allan_belt

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Re: LXH2 - marshall preamp for guitar amp.
« Reply #8 on: October 07, 2012, 11:33:00 PM »
You can consider different connections as an error, but it is not in term of workability :) In other words, it works good and it is simplification. Tone is exactly the same (as the tonal characteristic stays, look at the attachments), the only difference is - if You turn down middle, treble and bass - you will shout down the signal, there will be no flow. In Marshall style tone stack, it is not possible because middle pot cannot be shout to the ground by the wiper, as there is no connection between wiper and bass potentiometer.

If it comes to the sound, I like it as it is, but of course anyone can do any modification they like  :dbtu:
Thanks man for the explanation.. maybe i should say : "i Think there is an error .." sorry 'bout my poor english I`m from Peru.   :dbtu:
If you did the schematics like that on porpouse .. then there is no error..  ;)
by the way one question..  ;)  mids bottom goes to ground right? and mids lug connected to bottom? .. thanks in advance..  ohh and very good idea to put a buffer at the end.  :dbtu:
 

TomHealey

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Re: LXH2 - marshall preamp for guitar amp.
« Reply #9 on: October 08, 2012, 12:35:40 PM »
No hay problema mi Amigo :)

Regarding mid pot, if You look at the PCB from the top (middle pot pins): left goes to the potentiometer wiper, and right goes to the bottom pin of potentiometer.

Having buffer at the output is always a good thing :) But in my case - don't need it, so I didn't place it as I have buffer before end stage (power amp)

Saludos!

jrc4558

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Re: LXH2 - marshall preamp for guitar amp.
« Reply #10 on: March 19, 2013, 12:36:38 PM »
Hello everyone!

Few days ago I've completed first pre-amp for my new project, a solid state guitar amp.
...
Kind Regards!
Tom.

Hi Tom,

I noticed that the attached Fender project files are referencing my layout. I would advise not to use it. I made it a long time ago when I knew quite little about doing it properly and the resulting build was insanely hissy. Just an FYI for people who may decide to pursue it.

TomHealey

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Re: LXH2 - marshall preamp for guitar amp.
« Reply #11 on: March 23, 2013, 02:05:48 PM »
Hi Tom,

I noticed that the attached Fender project files are referencing my layout. I would advise not to use it. I made it a long time ago when I knew quite little about doing it properly and the resulting build was insanely hissy. Just an FYI for people who may decide to pursue it.

Hey!

Quite frankly, I have never built Fender version of LXH2 using this layout, I just have found it at Aron Nelson gallery (no copyrights). But indeed if you look closely, it doesn't look right (ex. loops/antennas). I have removed old layout, tomorrow I will upload new version, my own layout to whom it may concern ;)

Regards!

TomHealey

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Re: LXH2 - marshall preamp for guitar amp.
« Reply #12 on: April 13, 2013, 06:02:24 AM »
Ok. Now, finally I'm posting new improved schematic. I have omitted highpass filter and amplifier after LEVEL control at the end as it is useless for me, I just don't find it necessary.

Mirror PCB has ratio 1:1.

Enjoy!

EDIT: few updates, there is place for bypassing cap on the PCB for higher freq. however there is now bright switch - as I think, it is better to be done 'on wire'. Also below you can find attached two photos of built fender sim. I'm looking forward to post sound clips soon, say maybe this week.




I have utilised used parts so to keep cost lower :)

Saludos!
« Last Edit: June 04, 2013, 04:01:25 PM by TomHealey »