More thinking on the lm3886 guitar amp

[Joecool85]

I already figured I want to it like this:

In
3 band passive EQ
LBP-1 preamp
lm3886
Out

Now, here is the question, originally I was going to leave both the volume control on the preamp and the lm3886, now I changed my mind and one will have a trim pot.  But which one?  Any ideas to which would give better results?  Trimpot the LBP-1 to make up for loss in the passive EQ, and then control volume via pot on the lm3886, or trimpot the lm3886 and control volume via LBP-1?

Right now I'm thinking trimpot the preamp and adjust volume directly on the poweramp section...

[ninoman123]

Wire them both up with pots. Play with it awhile. If you find out that one should be a trim pot then make it one.

[Joecool85]

Well, thats probably what I'll do anyway, I just wanted to know what you guys thought.

[MR COFFEE]

The overdrive charactristics of the LM3886 are horrible. It does not clip like a well-behaved guitar amp - it generates AWFUL spikes (note that the overload protection scheme is appropriately named).

You will regret it if you don't reconsider your design.

Don't mean to sound negative - just the facts... check out the scope traces on the LM3886 data sheet and you'll see what I mean. DON'T GO THERE. IT WILL TURN YOU OFF TO DIY FOREVER.

DIY CAN SOUND GREAT.

[ninoman123]

Nothing is wrong with his design. Hes simple running pedals in front of the amp. Hes not overloading the amp at all.

[Joecool85]

Trust me, I know all about the built in SPiKe protection.  I'm not doing this to overdrive it, the LPB-1 is there to regain lost db from the passive EQ I have in there.  I will either have it set up with a trimpot so that the LPB-1 is basically getting the signal back to guitar strength, or I will use a trimpot to keep the poweramp "turned down" and turn up the preamp.  Like I posted earlier, I think that trimpotting the preamp to a lowlevel, and then using the pot on the lm3886 to control volume will probably be wisest.  We'll see. 

The other cool thing about doing it that way is that I could probably work it out well enough that with the preamp down enough, I could crank the volume on the lm3886 to full (or almost full) without kicking in the SPiKe protection.  That way I don't have to worry about it, I can just plug in and play.

[RDV]

You'll probably want a buffer in front of the EQ also.

RDV

[Joecool85]

I was thinking about that too.  One kinda like what is on the ruby maybe?  Now, even though I had thought of it, I didn't know what exactly it would help with...I know it has something to do with input impendance or something.

[RDV]

I was thinking about that too.  One kinda like what is on the ruby maybe? 

That one would work fine.

Now, even though I had thought of it, I didn't know what exactly it would help with...I know it has something to do with input impendance or something.

Yes, and to drive the tonestack.

RDV

[Joecool85]

Now, if I put in a buffer like that, would I need the LBP-1 preamp or no? 

Also, with the buffer, will it accept pedals pretty well? 

I'm not building any sort of OD/distortion into the amp, its just a clean poweramp with a 3 band eq that I can plug pedals into 

[RDV]

Now, if I put in a buffer like that, would I need the LBP-1 preamp or no? 

Also, with the buffer, will it accept pedals pretty well? 

I'm not building any sort of OD/distortion into the amp, its just a clean poweramp with a 3 band eq that I can plug pedals into 

Put buffer into the search and start reading, but the answers to your questions are Yes and Yes. A buffer does just that, it buffers, or acts as a line driver.

READ.

RDV