He's back 

You cannot view this attachment.

Time to do some exercises

You cannot view this attachment.

 

It wasn't meant to be a book, it just got that way. 
I thought I'd write down a few groundig and hum avoidance tips, maybe a page or two. It kept growing as I went and the first draft was over 40 pages. A few illustrations to visualize some points, and...  well, it kind of grew up.

And anyway, some of the best places are the most obscure.   

Hi R.G.,
we meet in the most obscure places😉.
Never knew about your book, thanks.
Greetings,-H

Try reading "Guitar Amp Wiring Notes" here:
https://www.dropbox.com/scl/fi/ywf5o2fpdmu5z8ejldmvn/Guitar-Amp-Wiring-Notes-1-2.pdf?rlkey=4qypic5s25j1i5adnffbblagn&st=6g2lq7x2&dl=0

Kevin O´Connor has an entire book about the subject, although bits and pieces are scattered all over his books.
He speaks of a "galactic" grounding scheme, using a picture of many stars residing in a galaxy. Maybe of interest in this context.

Fenders in fact are wired that way. There is local stars on the turret boards interconnected via a big brass strip "back-bone".

I forgot to mention: There are 48V power supplies that can be used to power a 59W @ 4 Ohm guitar amp.

Example: https://www.jameco.com/z/PSA120U-480L6-R-Phihong-120W-48VDC-Output-Desktop-With-C14-Inlet-and-4-Pin-Din-Connector_2670879.html

Some have a barrel connector like used on effects pedals. I'd stay away from those because you don't want to plug 48V into a 9V stompbox by mistake Choose one with the 4 pin DIN connector. Most have a Universal Mains input so it can be plugged in anywhere on earth. All you need is the right Mains cord for wherever you are. The minus side of the 48V is usually connected to the Mains safety ground inside the brick. For a 50W amp you need something like 125W power supply.

Quote from: blackcorvo on June 22, 2026, 01:17:56 AMAfter almost a year, I have updates.
First of all, my apologies for being away so long, life got in the way and I had to push the project aside.

That said, the updates are:

- I ditched the battery-powered idea, removed the holder, and closed up the holes I had made when installing them (3D printing pen filament and a lighter is a surprisingly effective combo);

- I figured out most of my problems come from the amp being REALLY sensitive. Apparently the mono module board is preset from factory at 36dB for the BTL configuration, giving it an input sensitivity so small you can drive the amp into distortion by just plugging your instrument directly into it;

- I've tested the amp now with both the internal 8 ohms 25w speaker (I mistyped in the first post as it being 30w btw), and an external 4 ohms 25w speaker, at both 12v and 19.5v, and had no issues with it cutting out even when using my Joyo Bass headphone amp pushing it at full volume. It did distort on both speakers and both PSUs, but did take more signal to get there at 19.5v;

- added a series 3u3 50v capacitor with the tweeter, and it helped reduce some distorting on the trebles from it being driven too hard;

Right now, I'm reconsidering what I should do regarding the preamp. Putting the Lead/Bass 12 aside for now, and I'm actually thinking of something more like, perhaps, a Honeytone's preamp, just with a tone stack replacing the single tone control. I do enjoy how those little beasts sound.

[Edit] considering that on average, at 12v on 8 ohms, the amp can put out around a 10v swing undistorted, at a gain of 36dB, the input sensitivity would be right around 150mV. The datasheet's solution is just a resistive voltage divider.
I'm tempted to just use a clipper...

Thanks for sharing this update - glad to hear it is coming together!

Quote from: J M Fahey on July 29, 2025, 01:32:51 PMAt the moment I am designing a new line of amps based around TPA3118, which will be fed from generic/surplus Laptop bricks or LED lighting SMPS, anything between 18 and 24V DC, simply because they are cheap and plentiful.

So I am designing preamps, effects loops, distortion, etc. fed from +24V single supply instead of classic +/-15V or +9V so together they become full amps, both pedal sized and small combos.
Basically what you are trying to do 

In September there is a Musical Expo (think mini NAMM / Expo Música / Frankfurt Messe) in Buenos Aires where I will show these new products, so I must hurry.

Any update on this?  I'm interested in using TPA3122 to do similar.  It's a neat chip because it is through-hole class D and uses 10-30v supply making it pretty flexible.

Thanks for your relevant feedback, I updated the section about balanced inputs with the concepts you describe: https://electrucio.substack.com/i/192899322/electronically-balanced-inputs

I will check also the other references you suggest. Indeed, this is truly a rabbit hole with no exit on the other side .

An interesting aside, fits nicely to the above linked write-up.

I had to convert a HiFi system to balanced due to hum I could not tame with conventional methods. The preamp was converted to balanced by following the guidelines in Jensen AN-003, INTERCONNECTION OF BALANCED AND UNBALANCED EQUIPMENT by Bill Whitlock (fig. 2.4).

Since I expected problems with my makeshift balancing, I bought chips from THAT Co for the input side of the power amp, Series 1200 because:

Quote(...) conventional input stages measure well in the lab and perform well on paper, they fail to live up to their CMRR specs when fed from even slightly unbalanced source impedances — a common situation in almost any pro sound environment.

That sorted the problem out in no time.

Incidentally, it was the same Bill Whitlock that designed the chips for THAT.