Tube preamp for tda3003 ss amp

[El Heisenberg]

Id like to try to replace the two fetzer valves i have drivin my fender tone stack into my tda2003 amp. It runs off a 12v 1.2A transformer. I have two 12AU7 tubes. Are there any designs out there or is this pretty easy to do?? Ive tried to search but cant find what really what im tryin to do

[Brymus]

If you look at the thread you had before ,I gave you a link to a guy in South America who builds these with a 12ax7 and the TDA2003.
If you watch the vid from the link I gave he posted his schematic,It might help.

[PRR]

> look at the thread you had before

http://www.diystompboxes.com/smfforum/index.php?topic=81123.msg671579#msg671579

> a tube preamp running on a 12v 1.2A

Tubes are skinny pipes. They don't flow much at low pressure.

Someone mock up this plan.



You need to connect the heaters, of course.

Trim the "15K" resistors to set the plates about half supply voltage.

It may give enough gain to drive TDA2003 directly. Most tube-Fender tricks apply (a brite cap on the volume control, etc). It's gonna overload real easy.... I hope that is a feature and not a flaw.

> im so sloppy with things id surely melt one of my eyeballs out or somethin.

Please don't do that. Learn to be less sloppy; it really helps when working in electronics.

[El Heisenberg]

Thanks. The video you had directed me to a while ago was wht i had in mind. Im just terrible with the search feature.

[El Heisenberg]

I mean the mexican video with the tda2003+ 12aux7

[El Heisenberg]

Ugh all the videos on utube are in spanish! And no schematics.

If i replace the fetzer jfet stages in my tda2003 amp with the tube preamp will i get the same output volume/wattage?? Is it as simple as just swapping out the stages?

[El Heisenberg]

Also im unclear on what the schematic above says. The output goes to the tda2003 design rite? But the resistor to ground is circle with a dotted line and labled tda2003??

[Brymus]

I think that resistor is a load to represent the input of the chip amp.
Here is your thread I was refering to.http://www.diystompboxes.com/smfforum/index.php?topic=79439.0
And the link http://www.youtube.com/watch?v=8LZRRJvh5A4
The schematic is shown from 8 seconds in until 22 seconds hit pause and copy by hand.
Whats nice is the extended sound clip after he finishes building the amp gives you a good idea of the tone you could get.
I bet it would sound even better with a different spkr.
Looks way simple he even shows how he builds it.

[Brymus]

The schematic above looks good except the cathode resistors look a bit high to me but maybe thats cause Im used to 12ax7s.
Does a 12au7 need that high of cathode resistors or are those values something to do with the low plate voltage?

[El Heisenberg]

A the schem in the vid is a little blurry. But i also just have a little hard time reading the power supply portion. His caps are marked in ways i havent read before either.

His tda2003 drsign is different from mine.

Anyways thats two good schems for me to work from. Thanks.

[El Heisenberg]

What does "mock up this plan" mean??

[Renegadrian]

the schem in the vid is a little blurry.

[PRR]

bieber45's plan uses high voltage for the tubes. This will obviously work.

A 12VDC scheme is obviously neater. I'm 99% sure my vales will "work": something come out. I'm less sure that "enough" will come out, though the TDA2003 does not need much drive. Only way to know is try-and-see.

> Does a 12au7 need that high of cathode resistors or are those values something to do with the low plate voltage?

Yes and yes. Try it.

[El Heisenberg]

Renegadrian I tried to open that pic to see it bigger, but the photobucket type site you had it at won't let me see it. It's all in spanish too. Sex ads and stuff.

[Renegadrian]

[Brymus]

Renagadrian how did you copy the pic like that?
I couldnt right click it when I tried.

PRR thnx will try when I get back to my hybrid stuff.

E look at and listen to Bierber45s other vids,his prototype vid of that Bluesman amp has an incredible sound clip.
I am going to have to try that when I get a chance.
There is also a vid showing how to do a terminal strip TDA2003 amp.

[Renegadrian]

Bryan, just paused the video in youtube, pressed the STAMP key and pasted it in GIMP. That's it!!!

[Brymus]

Bryan, just paused the video in youtube, pressed the STAMP key and pasted it in GIMP. That's it!!!

OK thanx.
So your running a Linux distro then ?
Or is Gimp on Windose now ?

[sean k]

I've just done a TDA2003 using the schematic from the data sheet with all sorts of stuff between pin 4 and pin 2. Do you reckon I'd get better output with the simpler schematic above with just the 4.7uf cap over the 1k to ground on pin 2? Is the feedback network holding this amp back?

I'm running 18V at just under two amps into the 2003 then into a Vifa 6ohm speaker. Because pin 3 is earth I just bolted the amp to the enclosure which is an ol' pressure cooker pot and drilled holes around it to increase the surface area for heat dissapation.


This is the amp on it's stand.

[sean k]

Just as an aside, after mentioning I've gat a j201 ahead of the TDA2003 with the output off the drain, that I tried an 8 ohm, a 6 0hm and a 4 ohm speaker on this amp and the 8 ohm was the best but it was a 12" so I can't use it. The 6 ohm was almost as good and the 4 ohm wasn't so good at all so the sensitivty of any speaker seems far more important, at these levels, than the ohms of the speaker.