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LM3886 stereo guitar amp + Phatt passive tone stack + stereo effects loop

Started by Zappacat, August 19, 2009, 03:02:00 PM

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Zappacat

LM3886 stereo guitar amp + Phatt passive tone stack + stereo effects loop.  I'm wondering if this is a practical goal.  I need a stereo guitar amp with basic tone controls.  The stereo effects loop is for plugging in my POD XT when needed.  Could I integrate Phatt's passive tone stack in an amp based off of this Non-Inverting LM3886 Stereo PCB Set http://www.chipamp.com/orders.shtml and add a stereo effects loop in the signal path somewhere?

Also, does anyone have transformer recommendations for this build?

Thanks in advance.
I put my pants on just like the rest of you - one leg at a time. Except, once my pants are on, I make gold records.

joecool85

Quote from: Zappacat on August 19, 2009, 03:02:00 PM
LM3886 stereo guitar amp + Phatt passive tone stack + stereo effects loop.  I'm wondering if this is a practical goal.  I need a stereo guitar amp with basic tone controls.  The stereo effects loop is for plugging in my POD XT when needed.  Could I integrate Phatt's passive tone stack in an amp based off of this Non-Inverting LM3886 Stereo PCB Set http://www.chipamp.com/orders.shtml and add a stereo effects loop in the signal path somewhere?

Also, does anyone have transformer recommendations for this build?

Thanks in advance.

Sounds like it would work just fine.  I would recommend this transformer: http://www.parts-express.com/pe/showdetl.cfm?Partnumber=122-625

It is 250VA, perfect for two LM3886 running a guitar amp, and 25+25v means you will get full potential from the chip.  Well worth the money.
Life is what you make it.
Still rockin' the Dean Markley K-20X
thatraymond.com

ponchojuan

Steve has the same MFG/model toroidal at 100VA for 17.95.  Possibly another option.  2 for $36.

http://www.apexjr.com/miscellaneous.html#Toroids

poncho

Zappacat

I've been doing a LOT of research on this topic.  Mostly because I'm a complete newbie and I need to learn.  Recently I got around to purchasing the chipamp.com boards and I've started to assemble the.

My first question is:

There's a lot of talk on the internet about using the LM3886 as a guitar amp but none of the posts/discussions ever really get to the point of someone actually posting finished projects with information on how they took the guitar signal and fed it to the LM3886 inputs.  Does anyone have a SIMPLE schematic(even without tone stack) explaining how to do a simple preamp stage from the guitar output to the LM3886 input.  I'd like to either use Phatt's passive tone stack or the eighteen watt DIY pedal at GGG for a preamp.  I'm missing the part about attenuating the signal exiting the preamp(Phatt or eighteen) and getting it to the amp input.

Second question:

What would I need to implement a switchable tonestack/preamp.  Ultimately I would like to have the Phat passive and Marshall eighteen on the same amp with a switch to toggle between them.


Any help greatly appreciated !

I put my pants on just like the rest of you - one leg at a time. Except, once my pants are on, I make gold records.

va3ux

I can't answer your questions but I can tell you that the Peavey Envoy and Peavey Studio Pro both use the LM3886.  The very early versions of these models use discreet components in the power section but from about 1999, they use the LM3886.

phatt

Hi Zappa,
        Not sure I fully understand exactly what you are trying to do but I'll share my thoughts which may help you come to grips with what can be excedingly complex.

The pic attached is what I take to my local mucic club when I don't take my Valve reamp setup. The Amp is just an old Laney *Keyboard Amp*
The white front unit on top is the *PhAbbtone* (Left) Then into a 3 knob Drive circuit partly based on a *Nobels SS1* Headphone amp from the 70's and I liked what it did so I tweaked the paremeters to suit a *Live rig*.

Then the signal goes to a 30 year old HiFi Graphic EQ (All 3 preamps are bypass if needed) then onto the Laney which has a very simple Bass Treble and gain on each of it's 3 channels.
So All done by Cheap simple and effective Equipment.

One word about *Efx loops in Amps*  I never got that joke, I just can't see the use of such needless complexity. I've never been able to find a use for them?
Unless it is a *paralelled EFX with a blend knob* attached then all rather pointless dodads.
As you obviously wish to use the pod thing then you've got most of what is needed anyway, just plug straight into the front of any SS Amp and go.

My thoughts on signal path setups.

My Rig; Tone box > Dist > Graphic > clean SSAmp
As you have the Pod then mix an match until you find what works best.
Try inserting the Pod after a Graphic before Clean poweramp.

My thoughts on the Amplifier in general.
I like most just wanted *Everything + more + more* All in one neat pakage.
It took me 20 years to fully grasp that it's a very limiting approach.
By keeping everthing seperate you can mix and match and when an amp goes fut you have not lost *Everything All at once.* If my laney breaks down I just use another cheap SSAmp.
I have a Killer SS Stand alone spring reverb and because It's in a seperate unit I can take that reverb unit to any Amp I wish.

As to getting a signal from a preamp unit into a poweramp just use a 100k pot from the last stage. A simple opamp buffer and a 100k pot will work here. If you have trouble with getting enough signal swing then easy to introduce some gain in the buffer.

The Marshall tone stack you are thinking of is likely to be uninspiring.
If you assume a marshall sound from it's use you will be quite disapointed.
Just having a marshall tone stack is like having a racing car with no engine.
(going nowhere fast)

Marshall amps (old) the tone controls actualy don't do much at all once you crank them up high as the power tubes and output transformer just produce one basic honky wall of tone/sound and you either work with it or sell it as they don't do much else.
This won't happen with the circuit you wish to use as it's only one small part of a very big picture.
You will need a Cab sim type circuit or similar to get that wall of sound to happen.
My SS1 does a decent job for those sounds.
Interesting to note that when I use a Real Tube Amp After my preamp I have no need to use the SS1,
I just use the PhAbbtone to tweak the tone.
SS1 is only needed when running into SS Amps.

Oh yes Stereo only works on recordings.  Live situation *forget it* there are enough problems to overcome already. :'(

phatt


phatt

Hi again Zappa,
               Just a thought on the Pod.
I have an old Quadraverb which I could never come to grips with.
Short story is, Once I hung a *Cab Sim After it* it did bring it to life and became far more convincing.
Cab Sim *Before it*  did nothing much but *After it*,,, Wow big improvement.

The reason I mention it is because I wonder if a Cabsim may have a similar benifit *After* the Pod. :tu:

I used the Cab Sim Circuit from the JTM 30/60 Marshall.
Google *Ed Rembold Cabsim* if you want to find the circuit,
or I can post mine if you get stuck.
Cheers Phil.

joecool85

Quote from: Zappacat on October 22, 2009, 05:17:00 PM
I've been doing a LOT of research on this topic.  Mostly because I'm a complete newbie and I need to learn.  Recently I got around to purchasing the chipamp.com boards and I've started to assemble the.

My first question is:

There's a lot of talk on the internet about using the LM3886 as a guitar amp but none of the posts/discussions ever really get to the point of someone actually posting finished projects with information on how they took the guitar signal and fed it to the LM3886 inputs.  Does anyone have a SIMPLE schematic(even without tone stack) explaining how to do a simple preamp stage from the guitar output to the LM3886 input.  I'd like to either use Phatt's passive tone stack or the eighteen watt DIY pedal at GGG for a preamp.  I'm missing the part about attenuating the signal exiting the preamp(Phatt or eighteen) and getting it to the amp input.

Second question:

What would I need to implement a switchable tonestack/preamp.  Ultimately I would like to have the Phat passive and Marshall eighteen on the same amp with a switch to toggle between them.


Any help greatly appreciated !



I don't have pics, but I used a LM386 Little Gem in front of my LM3886 for a preamp, sounded sweet and was real simple to build.  Schematics for the Little Gem can be found over at runoffgroove.com
Life is what you make it.
Still rockin' the Dean Markley K-20X
thatraymond.com