Solid State Guitar Amp Forum | DIY Guitar Amplifiers

Hi people. I have been designing, developing and building a few different Guitar Amps over the past few (many!) years.
This is my latest effort.
I would much appreciate any thoughts and/or critiques that you may have.
I have actually sold a few of these to mates and acquaintances... but am now at the point where I would like to retire from my retirement... if you know what I mean!?
I'm just getting to old for this stuff! :-\
So if you, or anyone you know might be interested in picking up the chalice I would be glad to hear. Depending on their context there may need to be some "nominal costs" attached.

Anyways... enough of that... the technical stuff follows...

In its simplest from the unit mimics a "regular" guitar amp...
* Outputs up to 50 watts or so
* Has a standard FMV tone control stack
* Both gain and volume can be separately adjusted
* Standard HI / LO high-impedance Inputs
* Etc... etc.

Now for the good bits!...
* Is built in a much smaller and lighter case than a "regular" Amp - actually in a standard Hammond case... roughly 6 x 8 x 6 inches... and only a few kilos in weight! (No more lugging a huge Marshall Amp up the stairs!)
* IMPORTANTLY... uses a (discrete) FET based preamp that mimics the characteristics of a triode valve preamp... e.g. the ubiquitous 12AX7. How this is done is somewhat technical. Google "Dimitri-Danyuk FET Triode Emulator" for a full description. His Paper on this was originally presented at an AES conference some years back.
* (In this version) Uses a high efficiency Class D amplifier (pre-built) module... but
* Can also be built with a TRANSFORMER coupled output stage that I have developed driven by power MOSFETS. While a little larger now also gives a nice power amp overdrive tone... and 100+ watts of output power... just like the "standard" EL34 / 6CA7 config.
* Using the preamp and power amp in combination can produce anything from clean "jazz" tones to all-out crunch!
* Has the standard HI / LO (unbalanced) input connections - on 1/4" TS connections... but...
* Also has a low-impedance BALANCED input connector - on a 1/4" TRS connection which provides really nice tones on guitars using an acoustic pickup. This input has a separate Gain control (as shown)
* (Looking along the front panel) Has a "BOOST" switch that (in a simplified view) alters the characteristic of the preamp that produces a more "edgy" tone. This can also be controlled by a simple (pull to ground) Footswitch through the adjacent TS connector. Great for switching clean to edgy tone quickly and cleanly.
* (Next along the row) A simple Line Output Jack that can be easily connected to a Mixer, Bigger Amp, Foldback Amp, etc...
* Also has an "INSERT" TRS Jack that can be selected as PRE or POST EQ... if you prefer to use an (outboard) EQ in lieu of the standard FMV EQ... or any other devices... Foot Pedals even!

OK... enough words... will await your thoughts.
Some pics attached. The one of the inside was from a prior version and does not include the front panel I/O's or the purpose built PCB's that I have subsequently done.

Cheers,
Graham

Nice work! I really like these compact designs and I'm going to, at some point, try something along those lines myself (sadly, no time to tinker at the moment). At first glance one might get the impression that you're plugging your guitar into some test equipment :D I've actually been thinking about shoving a guitar amp circuit into an old radio enclosure or something like that. Just for the what-on-earth-is-that-thing effect ;)

One question, if I may. I understand that you're powering the class-D module from the transformer through the rectifier and related circuitry. What VA rating does the tranny have for 50W of audio output?
M.

Good question. The tranni in the pic is only 30VA. However given that the amp is 90+% efficient and is (obviously) not running at continuous full power 30VA seems to work well. I have run music (not tone) through it running at full power and the tranni (and the PA) are barely warm.

Thanks for the reply. That's good to know.