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Author Topic: TDA7294 Power Amp with Fender Clean Sound Preamp  (Read 4851 times)

exztinct01

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Re: TDA7294 Power Amp with Fender Clean Sound Preamp
« Reply #15 on: February 29, 2016, 01:32:27 AM »
oh, I just saw the light  :cheesy:
so all I really need is my transformer, bridge rectifier and filter caps to supply voltage to the +- rails of the power amp circuit. Got it now. Now I only need to do the math, I think (gotta use my major).
However, center tap means three wires (ac volts - 0 volts - ac volts), and all schematics I've seen show two wires from the transformer going to the two ac leads of the rectifier.

So, am I assuming it correctly that the two non-zero secondary volts goes to the AC leads of the rectifier which then creates the +-DC rail?
And that the zero (neutral) volts from the transformer is already the ground which will go to the ground plane of my power amp pcb?
Please confirm.
~ Stephen

J M Fahey

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Re: TDA7294 Power Amp with Fender Clean Sound Preamp
« Reply #16 on: February 29, 2016, 07:19:08 AM »
Yes.
In general (and this can be VERY confusing bto newbies), some things are "taken for granted" , "everybody knows it" , so are not drawn or if they are, in a very minimalistic way.

So it happens what you mention: 2 wires are shown going to the AC terminals of the rectifier bridge: check ; and center tap goes to grounf ... "why waste ink drawing that in full"? ... although in fact since ground is all over the place, drawing it as a solid line connecting all proper points messes the schematic, so just little ground symbols are vdrawn all over the place.

"It is known" that in practice all are joined by some **metal** , either the plain chassis itself, or some dedicated bus wire or plain plastic covered wire.

exztinct01

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Re: TDA7294 Power Amp with Fender Clean Sound Preamp
« Reply #17 on: February 29, 2016, 08:24:36 AM »
thanks J.M., now i can move on to other concepts

anyway, would anyone discourage me in using that autotransformer? perhaps it gives too much voltage for the lm3886 and that my heatsinks (attached in above post) won't be able to handle dissipated heat?
I don't think I'll be using the 18-0-18 transformer for the lm3886 since it gives small wattage. Unless someone tell me +-25vdc is enough to obtain loud volumes from the lm3886 with a not so efficient speaker (good brands are hard to find in our country).

I really did a great mistake in making the title of this thread
~ Stephen

phatt

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Re: TDA7294 Power Amp with Fender Clean Sound Preamp
« Reply #18 on: February 29, 2016, 08:08:48 PM »
Hey do not worry,, mistakes are one of the best learning tools. :tu:
As long as you avoid the Fatal mistakes you will be fine. 8|

Maybe start with someting in a kit form.
plenty of good ideas can be found here;
http://sound.westhost.com/projects-0.htm

Some reading here;
http://sound.westhost.com/amp-basics.htm

And the 100Watt Guitar Amp Here;
http://sound.westhost.com/project27.htm
You will need a transformer with 25-0-25VAC taps which means 25VAC x 1.414 = 35VDC rails.

That big donut transformer used in the right circuit will likely deliver way over 100Watts. <3)
But be careful you need the right circuit for those voltages. That transformer will deliver ~60-0-60VDC after rectification.
Phil.

PhredE

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Re: TDA7294 Power Amp with Fender Clean Sound Preamp
« Reply #19 on: February 29, 2016, 09:01:43 PM »
Hi all. Sorry, I haven't been around in a while.
I was lurking/spying on this thread, it's interesting (and I'll profess a bias toward Fender 'clean' tones..)

exztinct01, was just wondering..
It sounds like you're intent on building your own amp as a solution, but was wondering if you boosted your signal going direct into the mixer using an emulator type pedal/box (that does 'Fender tones') if that might help get you closer (?).  Don't know if your PA/mixer is up to the task, but if it is, then maybe that is a reasonable workaround (assuming you want one of course..) ?

I stick a Joyo American Sound in the front of my signal chain and eventually run it into my smaller Fender SS amp, and really love it.  It gets a range of good Fender-type tones and can really boost up the signal quite a bit (can be noisy... depending on settings). It supposedly has basic speaker emulation included as well.  I will attest, it can do a pretty good Bassman, good range of standard 'cleans' -- eg Twin,  etc. and even some classic tweed sounds as well.  I really love that thing.  It's the best $35 I've ever spent on anything gear-wise.  Reference:
http://www.amazon.com/Joyo-JF-14-American-Amplifier-Simulation/dp/B007L0CH8K

Well, it's just a thought (maybe not even a good  nor practical one).. good luck to you just the same.


exztinct01

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Re: TDA7294 Power Amp with Fender Clean Sound Preamp
« Reply #20 on: February 29, 2016, 11:50:31 PM »
I don't believe our PA system is up to the task, can't even hear much of the vocals, keyboard and guitar when our drummer's in the mood of rocking out a worship song.
I don't have a plan for the preamp yet except for the fetzer (so simple), but I won't stick to it long, i'll build a better one once I finished the power amp.
I have to thank all of you here for answering all my questions above. Right now, I'll try to start building the power amp and hope everything turns out good.
Ciao!!
~ Stephen

PhredE

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Re: TDA7294 Power Amp with Fender Clean Sound Preamp
« Reply #21 on: March 01, 2016, 12:55:46 AM »
No worries. Good luck on the power amp.

And, doh! /smacks forehead ..you can always use the Joyo American in front of your amp to 'shape' the tone -- it really does Fender tones quite well <<forgot to mention the obvious in my earlier post. ..oh well.  You can even go straight out into headphones with it too.  It's a pretty versatile and interesting little beast.

Good luck. Let us know how it goes..

 

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