Any small- pedal size guitar Power amplifier layout?

tedsorvino · Post by **tedsorvino** » 04 Jun 2018, 15:29

Thank you very much Manfred. Excellent layout and schematic. Really really helpful. I will keep you posted when i finish it.

Manfred · Post by **Manfred** » 04 Jun 2018, 20:08

Sorry, I uploaded the intermediate results of the schematic drawings.
Here the corrected schematics:

schematic without mod:

schematic with mod:

I would add that the I kept the original components of the board except R1 and added only the components which are are highlighted in yellow.

Manfred · Post by **Manfred** » 05 Jun 2018, 03:11

C10 was connected with the wrong polarity, and must be flipped.
Only in the schematic drawing, in the layout it is correctly stated.

Manfred · Post by **Manfred** » 27 Jul 2018, 22:26

Tedsorvino built this amp using the mods.
Thanks Tedsorvino for pointing out the faults.
He contacted me regarding potentiometer setting issues.
The reason was a fault in the layout and also in the wiring instruction.
Faults:

Corrections:

The first 1Kiloohms resistor in seriell to the potentiometer terminal 3 is omitted now.

tedsorvino · Post by **tedsorvino** » 28 Jul 2018, 08:25

I have to say that without Manfred this very helpfull and great sounding little box (under 10 cubic cm) wouldn't have happened.
Sound-wise it's fantastic. Trust me, I own some great sounding tube amps, I'm a recording and gigging musician and this one is a small "miracle" that can save the day. Cheaper and louder than the commercial solutions and equally good sounding. No there is no footswitch on it

....

I mean.... useful for small gigs, with just any cabinet or combo speaker (4 or 8 ohms, the most usual ones). I 've tried it with 4 different ones so far. And any preamplifier (I 've used it with pedal ones, tube ones and rack ones). The sound quality varies from passable to great according to the quality of the preamp.
This is not like any Hi-Fi ss power amp. It has a certain color but it doesn't dictate the sound. It just makes it more like a well maintained tube guitar amp (without the natural noise and absolutely great power amp tubes breakage- yes I'm a fan of tubes).IMHO if a tube guitar amp is not well maintained, it's plain rubbish. Of course rubbish tone may be desired (and at times it's useful). Totally subjective.
It's also really useful as a backup amp for larger gigs, in case something happens to the main amp.
And of course with a good pre amp, it's better than most cheap commercial ss combos (you can alway use the combo's speaker), for rehearsals and jams.

Once again all credit goes to Manfred. Without his advice, hard work and help I wouldn't be able to make it.

It works with a 29V - 0 - -29V DC external diy PSU (easily built). It's really easy to build and really cheap (around 70 euros, including the cost for the diy PSU - the AC - AC transformer is the most expensive part).
Of course you can construct it in a rack along with the PSU (or even a preamp, reverb etc.), with similar results but that would be much larger and less portable.
The external design is not something I care about on my pedals.

Here are some images:

Needless to say, once again: THANK YOU MANFRED.

Manfred · Post by **Manfred** » 28 Jul 2018, 14:03

Thank you very much for all the nice words, but I would also thank you for your best teamwork.
I appreciate your work very much.
We have done it, and done it together.

HENK · Post by **HENK** » 29 Jul 2018, 11:56

Great Work,Guys

How much Current for the Transformer,please?

Manfred · Post by **Manfred** » 29 Jul 2018, 15:37

HENK wrote:Great Work,Guys
How much Current for the Transformer,please?

2x22VA 130W

Manfred · Post by **Manfred** » 29 Jul 2018, 19:27

Manfred wrote:
HENK wrote:Great Work,Guys
How much Current for the Transformer,please?
2x22VA 130W

Sorry typo!
2x22VAC 130W

tedsorvino · Post by **tedsorvino** » 31 Jul 2018, 21:51

I work it with 2 x 19VAC, 100W , 2,5A per rail. 4 ohms stress it a bit. Perfect for 8 ohms. I hope it will last (I don't intend to use it that often) because I mainly use it with a 4 ohm / 85w speaker.

sixthfloor · Post by **sixthfloor** » 30 Oct 2018, 16:54

Manfred, what is the use of R12 ? My guess is it is used in order for a small amount of the current flowing through the speaker to be fed back to the LM3886.

Its the first time I see a resistor of such small value in a schematic.

Manfred · Post by **Manfred** » 30 Oct 2018, 17:53

Hi sixthfloor

Manfred, what is the use of R12 ?

R12, R11, und C10 forms the so-called current feedback loop.
The purpose of current feedback is to increase the output resistance respectively to decrease the damping of the amplifier.
Due to the lower damping the speaker resound long and add overtones mixed into the tonal picture.
A tube power amp got this higher output resistance, so the current feedback solid state amp simulates this.

Its the first time I see a resistor of such small value in a schematic.

Have a look at Marshall Valvstate schematics or some Peavey solid state amps schematics
you can find the CFB many times.

sixthfloor · Post by **sixthfloor** » 30 Oct 2018, 20:03

Thanks Manfred, much appreciated

swt · Post by **swt** » 06 Dec 2019, 12:06

Hello. Is there any printable pcb layout for this? Thanks.

Manfred · Post by **Manfred** » 06 Dec 2019, 16:45

swt wrote:Hello. Is there any printable pcb layout for this? Thanks.

I had copied the layout shown above of an asian kit to draw in the "Current Feedback" modification.

LM3886BoardTracksUnderside.pdf: (4.1 KiB) Downloaded 61 times

LM3886BoardTracksUpperside.pdf: (3.17 KiB) Downloaded 50 times

I think it is better to buy and modify one of these cheap Asian LM3886 kits than to make a double sided circuit board,
If the identical kit is no longer available, I can help you modify another one.

Manfred · Post by **Manfred** » 08 Dec 2019, 00:40

Here the SprintLayout 6.0 File for it:

LM3886_PWR_3_layout.zip: (23.4 KiB) Downloaded 55 times

swt · Post by **swt** » 09 Dec 2019, 01:20

Thank you so much

Manfred · Post by **Manfred** » 10 Dec 2019, 09:12

I just saw that the last schematic doesn't match the layout, the resistor coil combination at the output was omitted.
Here the corrected schematic:

I have a one-sided circuit board for it in work.

Manfred · Post by **Manfred** » 10 Dec 2019, 23:48

I found another drawing errors C10/R11 were incorrectly connected these have to be connected to pin #9 instead of pin #10, C3 I had forgotten.

Manfred · Post by **Manfred** » 11 Dec 2019, 22:19

Here the single-sided layout as announced, the components for the current feedback modification are now included on the PCB.
P1, P2, P3 are the connection points to connect the potentiometer.
Both 0R33 resistors for 4 Ohms load one for 8 Ohms load.

LM3886_NFB_PA_PCB_ComponentSide.pdf: (10.98 KiB) Downloaded 44 times

LM3886_NFB_PA_PCB_SolderSide.pdf: (3.09 KiB) Downloaded 41 times

SprintLayout 6.0 -file:

LM3886_NFB_PA_singlesided.zip: (17.7 KiB) Downloaded 43 times

Any small- pedal size guitar Power amplifier layout? [schematic]