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Author Topic: Power supply suggestions  (Read 332 times)

mattbianconi

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Power supply suggestions
« on: May 20, 2021, 03:04:52 PM »
I got the kit that came with the 8 ohm speaker.  All assembled and currently powered with a 9-volt battery.  It seems I have to have the volume absolutely cranked to be heard over the guitar strings themselves. Turning the gain up obviously gets past this a bit.
I tried to use a 12 volt DC wall plug but that introduced a ton of hum into the amp.
What are you using as power for this little guy? Would an A23 battery work?
Thanks

galaxiex

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Re: Power supply suggestions
« Reply #1 on: May 20, 2021, 06:30:21 PM »
I got the kit that came with the 8 ohm speaker.  All assembled and currently powered with a 9-volt battery.  It seems I have to have the volume absolutely cranked to be heard over the guitar strings themselves. Turning the gain up obviously gets past this a bit.
I tried to use a 12 volt DC wall plug but that introduced a ton of hum into the amp.
What are you using as power for this little guy? Would an A23 battery work?
Thanks

Install a 10uf cap on pins 1 & 8 to maximize the gain.
The pads are on the board so it's easy to do.
If it ain’t broke I’ll fix it until it is.

mattbianconi

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Re: Power supply suggestions
« Reply #2 on: May 20, 2021, 10:48:51 PM »
Thanks, I'll try that and see how that sounds.

joecool85

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Re: Power supply suggestions
« Reply #3 on: May 21, 2021, 10:33:58 AM »
To get the most clean sound out of it you will want 12v or so.  I use a 12v SLA that I have hooked up to solar for charging my cell phones and other devices at home.  While it works well, clean power is limited on this little guy.  The best clean sounds can be had with higher voltage and a 16 ohm speaker with high SPL ratings. 

The 4" speaker sold with the kit is rated for 90db @ 1w.  This is fantastic for such a small speaker (most this size are between 83 and 86db, sometimes lower).  Large guitar speakers can be significantly higher than this though.  Many 12" speakers are around 102db @ 1w.  This means it would be over twice as loud for the same wattage going into the speaker.  So, for max volume, a 12" guitar speaker at 16 ohms, rated at 102db/w and using a power supply of 16v power supply (yielding 1.2w clean power) would give you 103.6db at 3'.  To put this in perspective, your current situation running on 9v with an 8 ohm load (yielding 0.5w clean) on the stock 90db/w speaker gives only 87.8db at 3'.

Your options on the stock speaker are to increase power to 12v which does give you a little bit more headroom (a total of 0.6w clean or so) and then you can play with increasing the gain on the LM386.  I think you'll find though that given that small speaker, that's about as loud as you will get clean.  If you find a way though, please share!  I love being wrong on this kind of thing!
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mattbianconi

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Re: Power supply suggestions
« Reply #4 on: May 21, 2021, 11:23:12 AM »
Thanks for the clear explanation and comparisons joecool85.  I'll keep playing around and digest the circuit more to try and understand what I'm doing. Always learning. 

joecool85

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Re: Power supply suggestions
« Reply #5 on: May 21, 2021, 11:36:20 AM »
Also, if you are looking at only using this clean, you might want to consider running this without the overdrive circuit at the front.  The board is set up to be able to run the MPSA13 as a buffer in front of the LM386 if so desired.  I had thought this would mostly be for a bassist or keyboard etc, but could be used for clean guitar for sure.  The notes for "clean buffer mode" are on the bottom of the schematic.
Life is what you make it.
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