Any small- pedal size guitar Power amplifier layout?

tedsorvino · Post by **tedsorvino** » 22 May 2018, 18:07

Hi there.
Is there any good working guitar power amplifier layout (or simple schematic)?
Around 50-100w . Small size would be more preferable.
I just need to have my preamp and power amp on my pedal board ((or being able to carry them easily) and plug directly into a cabinet (8 or 4 ohm).
Thanks in advance.

tonyharker · Post by **tonyharker** » 22 May 2018, 18:54

If you want it on your pedal board then you want small - thus Class D. this will probably do what you want. TPA3118 on ebay here https://www.ebay.co.uk/sch/i.html?_osac ... 8&_sacat=0

tedsorvino · Post by **tedsorvino** » 22 May 2018, 19:41

I 've read some quite bad reviews for these amps. About their sound and built quality. Any personal experience?
What do you think about something like that?

https://quasarelectronics.co.uk/Item/31 ... er-tda7294

Manfred · Post by **Manfred** » 22 May 2018, 21:20

I bought this LM3886 poweramp kit and made the current feedback loop mod as shown in the schematic.
The current feedback gives the damping behaviour of a tube power amp.
The gain is 23

tedsorvino · Post by **tedsorvino** » 22 May 2018, 21:37

Thanks Manfred. Have you got the layout (the schematic is pretty clear but I ask just in case). Have you put it in a box or something? What 23 means?

Manfred · Post by **Manfred** » 23 May 2018, 04:36

tedsorvino wrote:Thanks Manfred. Have you got the layout (the schematic is pretty clear but I ask just in case). Have you put it in a box or something? What 23 means?

No, I got no Layout, but I got a second board.
I make a better photo of it, then i will draw in the part values into the image.
Please be patient, as this drawing takes a bit time.
The horizontal mounted capacitor C10 is glued on the board, the resistor R7 is mounted outside.
I do not needed a box, because an burnt poweramp unit was subsitute by this board.
I mounted the board on the heat sink using angular metal sheets.
The LM3886 is available in two different packages,
the LM3886T has a metal flange on the back of the case, and the LM3886TF is all plastic.
Thus to different heat sink types are necessary, LM3886T: 1 °C/W and LM3886TF: 2 °C/W.

tedsorvino · Post by **tedsorvino** » 23 May 2018, 09:01

What kind of power supply does it need?
Where could I place a master volume knob?
How many watts is its power?
I need it to be more than 60w cause I want it to drive either a 4 ohm 85w speaker or an 8 ohm 100w.

tedsorvino · Post by **tedsorvino** » 23 May 2018, 15:20

is this the same?

https://www.ebay.com/itm/LM3886-Hi-Fi-A ... 1438.l2649

Manfred · Post by **Manfred** » 23 May 2018, 16:22

tedsorvino wrote:is this the same?

https://www.ebay.com/itm/LM3886-Hi-Fi-A ... 1438.l2649

No, that is not my board, I fear it is no longer available, but there are similar boards or kits on the market.
You can buy any LM3886 Mono Board PCB or kit.
When you have bought then you can send me the instruction to insert the CFB modification.

tedsorvino · Post by **tedsorvino** » 23 May 2018, 17:01

But it's still an LM3886 Mono board kit. So I guess I can use it. Is this correct?
What value of master volume pot would you use for such a kit, (i guess it goes to the output)?

Manfred · Post by **Manfred** » 23 May 2018, 18:57

So I guess I can use it. Is this correct?

Yes, you can use it.

What value of master volume pot would you use for such a kit, (i guess it goes to the output)?

Substitute the resitor R5 by a potentiometer.

: LM3886ModVolumePot.jpg (18.35 KiB) Viewed 1746 times

tedsorvino · Post by **tedsorvino** » 24 May 2018, 10:28

Seems straightforward so far. Could you please help me with the appropriate power supply (transformer, regulator and rectifier) values?

phatt · Post by **phatt** » 24 May 2018, 11:50

LM3886 is a good chip but you will need a decent power supply (and same for heat sink) to run it which will take up a lot of space on the pedal board.
This should give you some idea of what you will need.
http://www.circuitbasics.com/design-hi- ... -VA-Rating.
LM3886 is about 50Watts @ 8 Ohms,, assuming 30-0-30 supply.
Personally I would rather a power amp in a separate case,,, unless you can find a clever digi power stage to save space.
Even those still need a big power supply,, often those fancy Digi amps are sold with Smode supply but still take up a large space,, about as big as those old laptop PSU's.
Phil.

tedsorvino · Post by **tedsorvino** » 24 May 2018, 12:04

Yes. It seems reasonable to build the power amp in a larger case.
Some people suggested this one
https://www.ebay.com/itm/Bang-Olufse...AAAOSwIWVY90Hp
with this case
https://www.ebay.com/itm/ASX50-MXR-A...cAAOSwRJ9XgfXL
But it seems to me way too expensive for a guitar power amp.
What do you think?

tedsorvino · Post by **tedsorvino** » 24 May 2018, 20:12

Sorry about that...the links don't work.

I mean this expensive module http://www.profusionplc.com/parts/icepower50asx2-btl (actually it doesn't need a power supply)

with this also really expensive case
https://www.ebay.com/itm/ASX50-MXR-A-DI ... SwRJ9XgfXL

W

phatt · Post by **phatt** » 28 May 2018, 11:15

No, you will find it does need a power supply,, you have to read the fine print

Seems expensive,, you may as well just buy one off the shelf?

This one was recently superseded but likely still some in stores around Australia.
https://www.jaycar.com.au/2-x-75wrms-di ... r/p/AA0505
These were over $200 au but now reduced to $80 au.
I've personally tested one of these with my audio mixer and they are impressive but the Psu is larger than the amp

The Bass goes down to DC so for guitar you might need a hi pass network in front.
Phil.

plush · Post by **plush** » 28 May 2018, 13:01

phatt wrote:No, you will find it does need a power supply

Icepower has onboard selectable (100-130/200-250v) switch-mode power supply.
They are making quite decent stuff

phatt · Post by **phatt** » 28 May 2018, 14:03

Thanks for the correction,, I must have read the wrong part of the blab which was not clear to me at least.

Phil.

tedsorvino · Post by **tedsorvino** » 29 May 2018, 11:07

Finally I ordered an LM3886 board mono PCB

https://www.ebay.com/itm/HiFi-LM3886TF- ... 2749.l2649

with the appropriate rectifier board (i may use just two capacitors instead of four in order not to choke the amp so much).

https://www.ebay.com/itm/Dual-Power-Rec ... 2749.l2649

It seems an affordable and ok size wise solution.
I think I have a +-25V transformer somewhere. Maybe it will be more like a small rack.

Manfred · Post by **Manfred** » 04 Jun 2018, 12:50

I made a PCB-Clone layout of the ordered board to insert the NFB wiring.
The gain of the poweramp is ~23.
The board mod has not yet been tested.
Power amp schematic without mod:

Power amp schematic with mod:

Power amp layout without mod:

Power amp layout with mod:

Power amp mod wiring:

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