The Toy Story ...

[Mangas]

It has been quite a while since my last post. Meanwhile, "The Howler" project experienced a lot of iterations and reached its final stage (I'll talk about that some other time). Anyway, the new idea was born and materialized based on the same concept. I would like to share it with you.
Practice amp with switchable 1 to 4 Watts output power (yes, solid state amp with built-in power attenuator), AUX input for "backing track use", integrated 50 mW headphone amp with dummy load (not just plane disconnection of the speaker and attenuation of the output power level), emulated output for recording, built-in FX module (my design, PT2399 based (only one chip used), not the infamous Belton brick) ... And yet, I tried to make it as simple as possible (only plane volume and tone controls, middle boost and boost switches, single coil/humbucker switch ... And ... I named her "The Toy".

This is the result ...

https://youtu.be/j47IyNkgv2M

https://youtu.be/UsENW2NEOBI

Videos were recorded with shitty camera microphone, Fender Stratocaster straight into the amp, no effect pedals, just a little of my "PT2399 'verb" ...

The middle boost switch and the attenuator were not built in the prototype (I added them later), but I think you'll get the idea 

Cheers ...

[Mangas]

I've just read the message again and saw the part "If you are interested ..."   xP  :loco

Sorry, didn't mean "interested in the terms of purchasing". I apologize to all forum members and visitors for that.
Just ment that I am willing to share some additional informations considering project if anyone is interested in technical terms.

Message "fixed", hope no harm done ...

Mangas

[mckayprod]

Hey, that's got a sound!  Very nice if a little bright for my taste...rolling off the tone on the guitar should fix that, or a humbucker box of some kind.  Good playing, too.

[Mangas]

@mckayprod

Thanks for the kind words. I totally agree with you considering the tone :tu: (a little to bright), but I wanted to present that strat tone "as Fendery as possible". It is a little exaggerated ("guilty as charged", tone pot was pretty high - around 3 o'clock) but I also wanted to show that solid-state tone is not necessarily "ice-picking" in it's clean or overdriven form. Just roll back the tone knob on the amp - problem solved without tweaking guitar tone controls.

The idea was, also, to produce an amp that sounds good both with single-coils and humbuckers. I think you'll agree that without decent amount of treble, with humbuckers, amp tends to sound a little dark. That's why I implemented single-coil/humbucker toggle switch and voiced the amp this way.

Best regards ...

[phatt]

I've just read the message again and saw the part "If you are interested ..."   xP  :loco

Sorry, didn't mean "interested in the terms of purchasing". I apologize to all forum members and visitors for that.
Just ment that I am willing to share some additional informations considering project if anyone is interested in technical terms.

Message "fixed", hope no harm done ...
Mangas

We know what you meant,, it's all ok. 
Impressive :dbtu: :dbtu:
Yes post the technical stuff,, some here eat that stuff for breakfast. :lmao:
I'd be interested in how you approached this and solved problems.
Phil.

[Mangas]

A little bit about concept and technicalities ...

Specification :

Single channel amp
Speaker : Celestion 8"
Output power : 4W (switchable to 1W)
Front panel layout : Input, Single-coil/Humbucker voicing switch, Boost switch, Volume, Middle boost switch, Tone, Intensity, Effect On/Off switch, Delay, LED indicator, Main's power switch
Rear panel layout : Main's power input/Fuse holder, Speaker output, Speaker On/Off switch, Output power switch, Headphones output, Line output, AUX input
Cabinet dimensions : 450mm x 360mm x 230mm

At that moment I had Celestion Super 8 in possession. Cabinet is made of 15mm thick plywood, finger-jointed. I've chosen plywood over pine because I wanted a little tighter sound. By the way, I apply 7V, AC to a speaker for 12 hours in addition to loosen up it's cone.

The final goal was to produce a practice amp, as simple as possible, with all necessary features according to "my specs" and at the lowest cost, using simplified Howler's bulding blocks. Naturally, above a certain, defined criteria. "Amp has to take pedals well" condition, referring to preamps, boosters, TS derivates etc, is a must on. That automatically determined a part of the concept. There has to be a stage, in front of the volume control, that will "cope with problem". The rest of the layout is pretty much ordinary as you can see in the block diagram, except for the output stage.

"At the lowest cost" criteria determined use of a chipamp. Considering that and the output power, the reasonable choice was TDA2030A. Datasheet schematic was used only as a starting point. The stage is operating in a mixed mode feedback regime with implementation of a few nested feedback paths. Personally, I don't like to use chipamps in output stages and since the project exceeded expectations, I'll probably replace it with one of my own discrete designs. You can see the output stage in the second picture.

The last picture shows the amp's guts ...

[gbono]

Why use conformal coating on the PCBs? This makes repair or modification a messy ordeal.

[exztinct01]

In the block diagram what is the sigma symbol referring to?

[Mangas]

@exztinct01

Letter "sigma" is summary sign, so that block represents the summing stage (mixer).

Best regards ...

[exztinct01]

oh, I missed that one  :cheesy:

Is it another active stage or the two pre (guitar and aux) just linked to a single path (wire) there?

[Mangas]

@exztinct01

It is active circuit (OP Amp based) with optimized feedback network (gain and structure). The gain for each input is different to achieve optimal level and ratio of mixing signals at the output.

Best regards ...

[exztinct01]

ahh ok tnx 
can I have schematic for the whole circuit? I'd like to try it
also, instead of using a dummy load when headphone is used, can i just disconnect the speaker and remove that attenuator circuit?

[Mangas]

Sorry, but I am not going to publish full amp schematic (no hard feelings). Will share some conclusions, solutions and experiences acquired during the building process. I sincerely hope that it will help others to focus mind and work in their own, right direction.

[exztinct01]

no problem
great job BTW