New Member Roland Cube 20 Orange question

[monfi]

Hello I'm new here, and new in building amp, but i've some experience in pedals, so I've a question.
I will build a orange cube 20 i've found the schematics in net and I hope are right I will build only with clean and overdrive sound no tremolo.
I've remove from scheme the thing i not wanna to build, and I hope I've do it right.
I can use a normal dual trasformer 220 (i'm from Italy) to +24/ground/- 24 in diagram is 24.5?
Other question, if someone had a all transistor (no IC) similar or most simple with more common transistor and with only one current need like 12 15 18 24 or 36 can post or send me the schematics?
Thanks in advance

[phatt]

Hi Monfi, welcome  :tu:
That amplifier circuit  has a discrete power amp stage and if you are not conversant with these I'd advise you to build the preamp section up to mater volume (as you have shown) but use a chip amp power section. That will save a lot of time and sound just as good.

Even an LM1875 on split rail will get you  10~15 Watts.
It might look complex but Split supply rails is the better option.
Others here will likely give you good advice on details and how to build. 
Phil.

[monfi]

Thanks, you mean some like this?

inviato e basta

[phatt]

Yep it's that simple and unlike the Cube 20 power amp stage,,, Chip Amps come with built in protection. :dbtu:

Power amplifier circuits like the Cube 20 have no short circuit protection and one tiny momentary short on the speaker end can blow the whole Amp.
They rely on the speaker being internal with no outside connection so it never gets shorted out.

Don't worry about the supply voltage being exactly 25V a few volts either way matters little. the rail voltage drops a bit as power increases which is normal.
Phil.

[J M Fahey]

Fully agree and add: that LM1875 20W amp uses the exact same power supply and sounds exactly the same as the 30 years old Roland amplifier design, so build the modern one.

You will find many LM1875/TDA2050 kits in Italy itself or within EU , which will also offer you the proper transformer, a great help.

So your work is simplified, just worry about the preamp.

You will have to design a PCB or (since it's only 1) , Veroboard or Perfboard.

If in doubt, search and post links to a couple Electronics shops which offer such kits.

Maybe Velleman has something useful to you.

Does the "Nuova Elettronica" magazine still exist?

It was a great hobby magazine.

[monfi]

Hello,
tnx for helping, "Nuova Elettronica" mag, from azines is not more in publishing from mid 2012.
I've only found this kits:
http://www.ebay.it/itm/Amplificatore-TDA7294-80W-in-Kit-da-montare-/131597756420?hash=item1ea3d66804

http://www.ebay.it/itm/Scheda-Amplificatore-mono-70W-TDA7294-DIY-KIT-MONTATO-/271983979669?hash=item3f53822c95

Other I find have less output...from 1 W to 7 W :duh

So i not use this amp with all current they need, so i think with 24v is less power...
For my amp i've a 30 watt 8 ohm speaker 8 inch.
Tomorrow i design the prototype scheme  8| and post here

[J M Fahey]

Hi: here you have an Italian kit which may help you, it's 20+20W`Stereo, includes Power Supply but not the transformer:
http://www.elettronicaclub.eu/shop/kit/aa002-kit-amplificatore-stereo-20w/


You may buy only the PCB and build just 1 channel, obviously you buy components from your favorite shop:
http://www.elettronicaclub.eu/shop/pcb/aa002-pcb-amplificatore-stereo-20-20-watt/


what they not include in the kit (or charge extra)  is the power transformer, heatsink and a couple connectors, but it saves you the time to make the PCB.

This is the basic project, straight from the datasheet, they suggest the datasheet PCB which frankly is very ugly but gives you an idea to draw your own:
http://digilander.libero.it/nick47/50wm.htm


As of the preamp, you can make it on perfboard .


Inn this page you have a nice explanation of TDA2050 and shows one built on perfboard:
http://hack-attacks.tumblr.com/

[monfi]

 :dbtu: Great!
Thank you very  much!!!!!!! :tu: :tu: :tu:

[monfi]

Ok, this can be final prototype....
What you think about simple Tone control...i will do a similar to this
and this is the drawing...sorry if i do this in paint

[J M Fahey]

Well, you *can* use the simple one, of course, but sound will be somewhat crude.

The *Roland*  sound , among other things, lies in that tone control, which by the way is basically the same as what found in its larger brothers.

You are basically building a "mini" Roland JC120  :dbtu: and with a good speaker results will be very good.

Jensen Factory (SICA)  is there.
Jensen MOD series are excellent and not too expensive, a MOD1050 is perfect for that amp.

[monfi]

Ok , let the tones as they are not much 3 potss and a handful of resistors and capacitors that make the difference ; )
In fact I thought to build me this amp to study , because I'm about to start a course in jazz guitar for beginners .
Then I'll know that speaker give me from my wife for Christmas.
But i will add a little overdrive like "electra distortion" or trotsky drive

I'm working about electrical scheme...when I've do it...I'll post here

[monfi]

Finally i've design first circuit, i put tda2030 because in my multisim there isn't tda2050...but for power amplifier I will use a ready to solder kit...
please can check if seem all ok :tu:
Thanks guys for help

[phatt]

Even with a kit power amp the task you face is a long hard road, even more so if you have limited experience.

Build the PSU and the poweramp kit,, then work on the preamp.
Don't complicate matters,,I'd scrap the fancy front end for now and just breadboard the preamp circuit and get that working.

If you commit to soldering it all up in hope,,,  it's much harder to fix later.
I R&D nearly all my circuits and trust me you learn a lot more that way and it's often the shortest path to a successful build. hint. 8|
Phil.

[monfi]

So I've thinked a lot about that you say, and beacuse is my second work I not will complicate too much mi life :lmao:
so this is the next idea
one 12v simple power supply and this simple 2 transistor preamp, preassembled power stage.
So the question, where to put tone stack? I prefer a simple one knob stack...ideas?
mpf102 have nice clean sound suitable for jazz?

[J M Fahey]

Don't reinvent the wheel ... yet

I suggst you breadboard and build this simplfied version of Peavey Solo, an excellent Peavey 12V Battery amplifier, already adapted for such a supply.

You can use just one TL072 for preamp, for just 1 channel which is good for Electric Guitar and its associated tone control.

I blocked out what's not needed (mic preamp and channel mixer), connected the "auxiliary" channel (electric guitar ) straight to tone control, you need to reverse the coupling cap polarity, and showed the preamp/power amp separation.

You can use your own 2 x TDA2003 power amp or what they suggest, TDA2005, which is exactly the same: 2 x TDA2003 in a single package.

You can also use that same preamp with a larger 50/60W amp and a 12"speaker if you wish, it will sound quite similar to a Polytone


EDIT: I forgot: rise R10 to 1M .