another newbie

[heineken]

Good point, sometimes I get excited and try to jump in balls deep.
I'll start with the 3886

[heineken]

what are the main differences between the LM3886 and the TDA7294? is one more reliable than the other?

[heineken]

CAn you use any old power transformer, or is there specific ones that work with specific circuits? I have a dead head out of an old Samick 60W amp, where the transformer seems in good shape. there's also a lot of good parts in there I can use I think, like the circuit for the effects loop, and I may even just grind the chassis down and paint it to use in my project.

[phatt]

Hello heineken,  
LM3886 is 50Watt cont output into 8Ohms. 135W instantaneous power
Using 35/35VDC rails.

TDA7294 is 60Watt cont output into 8Ohms. 100W instantaneous power
Using 38/38VDC rails.
Edit; In answer to the reliability, it's not really an issue with most of these chips.
I'm not the expert but LM3886 is proly the better one.

Re, the POWER AMPLIFIER 200W-K8060
There is one thing that those starting out should bear in mind when hunting for power ratings.

I'll use that K8060 as a good example.
You read 200Watts and you get all excited BUT?? hang on look carefully at the real power.
It's only really a 70 Watt Amp. (I quote from page,,,70W rms power @ 8 ohm load)
Not so flash in the real world,, only just above average. 8|

If we hung a 2 Ohm load off the output we could make it look like a *killer watty*
You would likely get over 300Watts @ 2Ohms and the thing would also blow up in a faily short time.

It's always wise to convert any *Whatty* numbers into 8 Ohm Loads as 8 Ohms is generally the ideal load for such things.

Always look for x amount of Watts RMS @ 8 Ohms ,, that will give you a fairly good idea of real power.
Get those *Peak music power* rating out of your mind they always make things look better.
Even worse when you see PMPO ratings. :duh

If you want more power than 50/60 ish Watts then IMO forget chip Amps and go dicrete components for power Amps.
This means big Transformers, big filter caps and a serious heat sink.

The *Samick 60 Watt* you mentioned is likely a chip amp so at a guess the PSU inside is only capable of 50 ish Watts,, any more and you just waste money.

Yes you could drop a great big poweramp inside it but it will only deliver 50 ish watts as the transformer is not designed to give what it has not got. You would likely fry the trans windings anyway.
Cheers, Phil.

[heineken]

okay. sourcing a new transformer as we speak.
If I wanted to have a clean channel as well as a gain channel, can I do this with one LM3886 Stereo kit? Seems like I should be able to, but I've been wrong before.
and I believe I've read before you could take most overdrive/distortion pedal schematics and turn them into a preamp? I was thinking either a Krank distortus maximus or the Dr. Boogey as my high gain channel, both of which I've found the schematics and veroboard layouts. do you need to make any major adjustments to them? I'm sure it's probably already been covered somewhere in this forum, I hate coming along late in the game.

[phatt]

okay. sourcing a new transformer as we speak.
If I wanted to have a clean channel as well as a gain channel, can I do this with one LM3886 Stereo kit? Seems like I should be able to, but I've been wrong before.
and I believe I've read before you could take most overdrive/distortion pedal schematics and turn them into a preamp? I was thinking either a Krank distortus maximus or the Dr. Boogey as my high gain channel, both of which I've found the schematics and veroboard layouts. do you need to make any major adjustments to them? I'm sure it's probably already been covered somewhere in this forum, I hate coming along late in the game.

Hi heineken,
                    You can have multiple preamps with only 1 Poweramp, You just have to sort out how you want to switch between the channels.
Unless you are a relay building guru building such circuits can really slow progress.

IME, it's a lot easier to have a totally seperate unit for preamp/s as that can be a self contained floor unit seperate from PowerAmp.
My reasoning is simple,  any channel switching can be done with direct (mechanical) switching which makes design simple.
(Of all the amps I've repaired more than 50% of issues are in relay type circuits that switch something via a remote pedal.
This fancy relay circuitry is only needed because ALL the controls are in the Amp,,,
Soooo if all the preamps are on the floor unit and most poweramp unit don't need any controllers then why make life hard. 
Just build all the preamps and switching arrangements inside one dedicated floor unit.

Yes a lot of pedal circuits can/are built into a preamp circuitry But I strongly advise you to Bread board test it all first.
It took me a few years of frustration and failed circuits before I caught onto the realisation that no matter how simple some of these
mix an match may look,,,,.a LOT them will no doubt  be a waste of solder and time. Hint trust me I've been doing this for over 30 years.

Of all the stuff I've built (seemed like a fantastic to good to be true circuit at the time) only about 5 circuits have been seriously useful.
Does that make Me a bad designer,, or am I just refusing to except crap circuits? LOL

Poweramps (especially chip ones) there is not much to tweak and most of them don't colour the tone greatly
BUT with all Preamps there are just so many different ways to effect a change to Tone/ Dist/ OD/ Crunch.
So when you read the blab on some of these sites with schematics and build instructions be warned you are taking on someone else's opinion
of what constitutes a fantastic sound.
And will it work with your Guitar /Amp / Speaker /musical style. 
In my experience ,,it's a big gamble to etch a board,, build it ,,,and have it all magically come together.
but it's possible no doubt.
I've got a whole bottom draw chock full of dud PCB's that will end up as land fill no doubt.

It's rewarding long term but you do need to have the patience  when things don't go as planed.
Phil.