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Author Topic: LM3886 Guitar power amp schematic suggestions  (Read 12312 times)

mladenu

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LM3886 Guitar power amp schematic suggestions
« on: May 07, 2015, 06:36:16 PM »
HEllo guys, me again.. :)

Like a subject says, please give me advice with schematics for guitar power amp with lm3886 (because i have one), and a power supply which power up this chip to throw ~20-25watt output.. For practice amp needs surely.. :)

Again Thanks in advance.

Mladen
« Last Edit: May 07, 2015, 06:51:13 PM by mladenu »

JHow

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Re: LM3886 Guitar power amp schematic suggestions
« Reply #1 on: May 07, 2015, 08:21:52 PM »
Are you familiar with Elliot Sound Products?  He has a lm3886 project...even a pcb.

http://sound.westhost.com/project19.htm

galaxiex

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Re: LM3886 Guitar power amp schematic suggestions
« Reply #2 on: May 07, 2015, 09:20:46 PM »
Check http://chipamp.com/

He has pcb's, complete kits, power supply kits, etc for the LM3886 and others.
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mladenu

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Re: LM3886 Guitar power amp schematic suggestions
« Reply #3 on: May 07, 2015, 09:34:24 PM »
Tnx ppl, i`m familiar with all of that schematics, and i am aware that many posts are written about this particular chip, but i want advice, exact LM3886 circuit which is best proved in practice for the guitar amp, taking into account the input and output impedance... And of course, the most important thing is how to design PSU to achieve about 20-25w output... (17v bipolar i guess)..

Enzo

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Re: LM3886 Guitar power amp schematic suggestions
« Reply #4 on: May 07, 2015, 11:02:39 PM »
There is nothing special about using a 3886 for a guitar power amp.  It will just be a power amp.  What makes a guitar amp special for the guitar is the preamp.  And of course an appropriate speaker.

Did you look at the chipamps web site Galaxie posted a link to?  Under the LM3886 kits section there is the instruction manual.  It includes schematics, as well as the available boards ready to solder the parts to.

With a suitable preamp, this ought to work fine.

teemuk

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Re: LM3886 Guitar power amp schematic suggestions
« Reply #5 on: May 09, 2015, 01:47:05 PM »
There is nothing special about using a 3886 for a guitar power amp.  It will just be a power amp.  What makes a guitar amp special for the guitar is the preamp.  And of course an appropriate speaker.

...Then again it's just a matter of adding some external circuitry to turn the power amp "special" as well:



As much as I respect Enzo, I do believe engineers of likes of Pritchard, Quilter, Peavey, Vox, etc. would entirely disagree with him. I basically falls down to whether you want to design just another "HiFi" chip power amp with LM3886, or a power amp that behaves more like a tube power amp... also using an LM3886 chip. LM3886 is just one high power "opamp" and like with everything else regarding opamps it's the surrounding circuitry that defines the function.

Enzo

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Re: LM3886 Guitar power amp schematic suggestions
« Reply #6 on: May 09, 2015, 08:32:01 PM »
I don't disagree with you or those experts, however, in the context of the original poster's questions, I don't get the impression he is at the level of designing esoteric chip amp circuits to emulate tube gear.  I may be wrong.  So my answer was considering the needs of someone wanting to build a very basic circuit.

J M Fahey

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Re: LM3886 Guitar power amp schematic suggestions
« Reply #7 on: May 10, 2015, 09:23:26 AM »
Both are right, of course.

A "datasheet" LM3886 amp is already incredibly good, and we all know that in most SS guitar amps, sound is basically created in the preamp, using a lot of clever tricks, and the power amp basically clean amplifies that.



Also a few advanced designers, some of which are mentioned above,  are trying new ways to do things.

mladenu

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Re: LM3886 Guitar power amp schematic suggestions
« Reply #8 on: May 10, 2015, 03:28:20 PM »
I don't disagree with you or those experts, however, in the context of the original poster's questions, I don't get the impression he is at the level of designing esoteric chip amp circuits to emulate tube gear.  I may be wrong.  So my answer was considering the needs of someone wanting to build a very basic circuit.

Mr. Enzo, if you read some of my latest posts, you may find that i`m in search for suitable solid state design who will able to produce good side of characteristic valve sound... as much as possible... IMHO i think that i close to that factors, so look for your generous help to carry out my wishes, in the form of ideas and suggestions, and I'll know how to realize... if I were good to design, I would had a desire to share it with you, but since I'm not, I'm here to explain you what I want, hoping that you will help me..

This teemuk Peavey PA example (Transtube variant) is good point of my original question..
Again, although I'm not proficient, I'm aware that (J M Fahey wrote) LM3886 datasheet amp is excelent example.. But, without current feedback...

So guys, help me with that esoteric valve like circuit! :D

Thanks again all of you... :)

Enzo

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Re: LM3886 Guitar power amp schematic suggestions
« Reply #9 on: May 10, 2015, 07:49:46 PM »
Fair enough.  Just consider that the power amp does not sit there alone, it is part of the overall system.  Making special approaches to make the power amp more "tube-like" will be just one small step towards a good amplifier.  In my personal opinion, the speaker you use will have a far greater impact on your sound.  Also, the preamp will be a tremendous part of your sound - the guitar does not plug straight into a power amp.  So perhaps you could tell us the preamp you are intending to use this power amp with.  You mentioned practice amp earlier, so I assume you intend lower volume use, but do you also intend to gig with the amp?  A 25w amp is one thing, but if you operate the amp with the volume turned low, it will produce considerably less power than that.  In fact for bedroom use, 5 watts would be plenty.

Roly

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Re: LM3886 Guitar power amp schematic suggestions
« Reply #10 on: May 10, 2015, 08:19:26 PM »
Quote from: mladenu
i`m in search for suitable solid state design who will able to produce good side of characteristic valve sound... as much as possible...


I once had a conversation with a Bright Young Electronics Engineer that went something like this...

BYEE: "Why do you bother with all that old technology?  You could model the valves in a DSP and use a solid state output stage".

Now I've done a bit of programming in my time and I know that in one mouthful he was talking about a space project.  I also knew that to faithfully reproduce a 100 watt valve amp sound would require a s.s. power amp with considerable headroom.

"Yeah, I could do all that" I replied, "but here's a novel idea; if I want value sound, why don't I just use valves?"

e.g.
http://www.ozvalveamps.org/ava100/ava101lamington.htm

I subscribe to the school of thought that the (average quality) output transformer is a major contributor to valve sound (through progressive magnetic compression).


{I'll shut up now.  :-X }
If you say theory and practice don't agree you haven't applied enough theory.

mladenu

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Re: LM3886 Guitar power amp schematic suggestions
« Reply #11 on: May 10, 2015, 09:00:28 PM »

"Yeah, I could do all that" I replied, "but here's a novel idea; if I want value sound, why don't I just use valves?"


Thanks Roly,
Many times i was faced with this decision, but always stop because of following:
I do not like higher voltage and valve depreciation over time..  :-\

So i want to make a compromise... :)


Fair enough.  Just consider that the power amp does not sit there alone, it is part of the overall system.  Making special approaches to make the power amp more "tube-like" will be just one small step towards a good amplifier.  In my personal opinion, the speaker you use will have a far greater impact on your sound.  Also, the preamp will be a tremendous part of your sound - the guitar does not plug straight into a power amp.  So perhaps you could tell us the preamp you are intending to use this power amp with.  You mentioned practice amp earlier, so I assume you intend lower volume use, but do you also intend to gig with the amp?  A 25w amp is one thing, but if you operate the amp with the volume turned low, it will produce considerably less power than that.  In fact for bedroom use, 5 watts would be plenty.

Enzo,

I have to admit that for years i informed about what you've written to me .. And then gained just that kind of conclusions ... I have no doubt about the importance of the preamp and speakers role .. The only thing was somewhat remained unknown is the power amp and hence i concentrated on this question ... not because of importance for valve character .. :)

Yes, my intention is a gig-able amp as well.. I'm thinking to make PhabbTone pasive preamp or Jfet Bender preamp, even though the last one is in the development stage and i have dilemmas about schematic..  :-\

Roly

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Re: LM3886 Guitar power amp schematic suggestions
« Reply #12 on: May 11, 2015, 08:31:44 AM »
Quote from: mladenu
I do not like higher voltage and valve depreciation over time..  :-\

As you like, but I have to remark that over a hundred of these have been built by complete amateurs without a single injury, fatality, or dead cat.  The output valves are not run hard and will have a life in average duty of decades.



A circuit using a LM3886 with mixed voltage, R19, and current, R18, feedback.



Oh, and you're going to need a BIG heatsink;




If you say theory and practice don't agree you haven't applied enough theory.

mladenu

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Re: LM3886 Guitar power amp schematic suggestions
« Reply #13 on: May 22, 2015, 08:03:24 PM »
What about this? Is this have any chance to be stable for guitar amp? Or if answer is no, what to improve for stability? I like this simplicity, but not for any price...

Roly

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Re: LM3886 Guitar power amp schematic suggestions
« Reply #14 on: May 22, 2015, 08:51:17 PM »
Given a large enough heatsink there should be no stability problems with this circuit.

Current feedback was first tried with valve Hi-Fi amps back in the 50's but never really caught on because it increases the output impedance of the amplifier, and because of the infatuation of Hi-Fi-ists with damping factor the ideal was seen as an amplifier with zero output impedance, i.e. the speaker sees a dead short and therefore has maximum damping.

Solid state amps came along that go pretty close to that ideal but the Hi-Fi world had/has other objections to them, some well based, others only subjective fantasy.

So about the only place you find mixed voltage and current feedback these days is in solid state guitar amps where the current feedback gives a highish output impedance and more "valve sound".  Therefore I would say that any design like you have posted with mixed feedback was most likely aimed at guitar amp use.

I found the source of your circuit here;
http://8085projects.info/lm3886-based-power-amplifier-circuit.html

...but unhelpfully it has no commentary on its intended application at all, but I think we can be pretty sure it wasn't Hi-Fi.


For a good overview of guitar amp design I suggest that you read;

http://sound.westhost.com/articles/guitar-amps.htm

Rod knows what he is talking about.   :dbtu:
If you say theory and practice don't agree you haven't applied enough theory.