Tube preamp for tda3003 ss amp

[Brymus]

I cant answer your question Sean.
But I love the stuff you make ,tell me the spkr goes in the hole in the front.
That would rule.
I never said anything but I really liked the last amp you made too.

[sean k]

Glad you like it Brymus! Thats my job here you see, the place I have alotted my self to be of the most use. I'm not so good at designing things, electronically, well not good at all, Mr hack and tack thats me... but hopefully I'm useful in offering a little inspiration to the rest of you to make use of those things we might not think could be used.
We do it here in New Zealand, not so much anymore, because we're so far away and everything was precious and expensive up to at least the mid seventies so we had to make do. But it's a way of doing things that I think would go a long way on making better use of resources but that another story eh! Not one to highjack threads but hows this for silly.

[Renegadrian]

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 ?

Yeah I'm on Kubuntu 8.04 - Left window$ circa 3 years ago 

[El Heisenberg]

this threads about 4 different things now!

The tda2003 amp desgin I used was from this book electronic projects for guitarists by craig anderton or something. Its on the generalguitargadgets.com site too.

heres the last schem of the amp I made.



http://i633.photobucket.com/albums/uu56/el_heisenberg/ampbug.jpg

[El Heisenberg]

that schematic is old. But really only add ons.

The tda amp has a switch to swawp resistors from pins 2 to 4. I have 880 ohms and 4k7 i think. I keep it on 4k7. The fetzers are quiet I think.

I think my troubles might be atributed to my using MPF102s for the fetzers, but I have tried j201 get the same result from the second stage! I just wanna get a freakin tube workin in there and be done with it!\

edit: one thing i should note about the problem with the second fetzer stage. When i play throught the marshall cab sim through my PA, i get the splatteriness in different places using the trimmer. But overal it works better through the cab sim. WTF?

[sean k]

I've been somewhat busy but my efforts are such that this is occuring.


The amps can go to about 200x by the look of the resistors people are using. I started off, in the previous amp, with 220 ohms and 22 ohms which I didn't like so I swapped out the 22 for a 2.7 which is definitely more like it. Thats slightly less than 100x so on this one I'm going for +200x...

The triple transformer, theres another underneath, but it's what I had and all the other parts are just surplus lying about. All I bought were a 12V reg, the NPN power transistor, a 3.3 ohm 1W resistor and 2 x 10uf electros for the cathodes.

The resistors on the 12V reg allow one to lift it above it's spec'd output voltage which has  divided into it, 12/.025 = 480 so 470's close enough, then the difference between what you want and what the spec is, I wanted 14.4 so 14.4 - 12 = 2.4/.025 = 96 so 100 ohms while the MJE2955 npn allows one to run much more current than the spec'd 1A of the 7812.

Now I just gotta start cuttin' up wood to make the box. The speaker I'll use is an ol' alnico ribbed paper 12" at 10W so I'll be cutting it fine if I play it at loud. It's going to be lovely. That heat sink on the back is from my first computer CPU... with the middle fins removed.

[Brymus]

Gawd I love this place.

[El Heisenberg]

I just noticed the title of this thread says TDA3003 instead of TDA2003. Dammit!

[sean k]

You're right, didn't even notice it... it's proof we only read a few letters/numerals into a "word" from the back and front.
  TD_ _ _03   must be a 2003.

[sean k]

Well, I've been busy. All wired and sorted except for one final rip down then test to see if it works and sand and finsh the box.

I actually quite like this one. The woods a bit soft but I do like the colours. Can't remember what it is though... maybe it's even redwood but I don't think so as redwood actually, I think, is more like oregon and spruce with the easily identified difference between summer and winter growth. Might be Lawsonian Cypress.

You can just see the bottle to the right and do like these alnico magnet'd 10W 4 ohm speakers I got years ago NOS from the Southern Island.
Once I finish it I carry on, if if all works properly, in the pictures thread.

I'm going to get all arty with aluminium strengthening strips around the edges and copper corners... all hammered and attached with brass nails.

[Brymus]

I am at a loss for words Sean 
This is just incredible , Now that is an amp with some serious MOJO "MAGIK" in it and on it.
Let us know how it sounds.
WOW

[Renegadrian]

[El Heisenberg]

lol, man you gotta help us out with our simpler designs. Me and this other guy are just trying to get it done. Just one tube a tonestack and the TDA2003.

[El Heisenberg]

Man that looks awesome

[sean k]

Just found a bunch of parts I haven't seen on this site for a good long while and happened to find this.
http://www.diystompboxes.com/pedals/schems/shakatube.gif

12AU7's tend to be used in circuits to push more current and have less voltage gain. The 12AX7 is a better voltage amp and inbetween the two is the 12AT7. Way back when I started out I mainly used 12AT7's as I found a ready supply of them for cheap and they would work in a design for a 12AX7 but the gain was lowered and so a 12AU7 would exhibit even lower gain.

Using data sheets for the tubes the 12AT7 usually wants a 50k plate resistor and the 12AU7 can go as small as 10k, with higher voltages, and this is because the various tubes are designed to do different thing. 12AU7's make great microphone preamps because they push more current and I think this is because of the nature of microphones and the predominance of input and output transformers.

You've now got a bunch of different options to work from and the idea is to simply make a decision and start into design and build and hopefully it'll work beautifully or it'l, at worst, at least let you know what you do actually want.

I used 2 x 240/12V @1A each transformers in parallel because the filament requirements for the tube at 12V is 300mA which leaves me with 1.7A for the TDA... and I hope that thats enough because these little output amps are very hungry for current. They were designed for use in cars which a surplus of current but only 12V nominal. In discussions about these amps, 12V car amps, it's not unusually to give them 2.5 to 3x the output wattage you want so a 10W amp should require a 30W power source, to be completely safe about getting clean sound from them. Hopefully I can get away with 20.7W. I've recently found some schematics of the TDA in bridge mode which are good for 20W audio output but I think I'd have a devil of a time finding a 12V@3.5A.

[El Heisenberg]

sean K, mine uses ONE 120v/12v 1.2 A transformer. I use the GGG.com desgin by craig anderton. I also run a marshal cab sim, a digital reverb and two fetzer valves off two lm317s in parallell for DC power . Is this a problem? Im haveing problems adjusting the bias for the second fetzer stage. I was wondering if Im not getting enough current.


A while ago I tried this same design with a 24v 3A transformer, and used the 317 to get it down to 15 or 14 v but it got too hot. went down to 12, but the 317 got too hot..

[sean k]

I am still learning about these things myself and I'm not absolutely, well even remotely, sure as I'm basically at a loss to understand the data sheets but I"m somewhat of the idea that the dissipation of the amp is added to the output power. Those data sheets also show the output transistors as being in class A which would account for the high current use as they are biased at half supply. Well they are like the npn's in a discrete amp I use and I went through a bunch of transformers before I got something that provided enough current.

The maximum Voltage for these is 28V and they'll take 40V for 50mS so maybe you should try the 24V at 3A and find a small choke somewhere to hold it down to 24V. Seems a pity to waste such an apt power trannie for the want of a choke. These same chokes are used in carstereos to smooth the power lines to the amps from mush generated elsewhere in the car. Whether the henries of those particular chokes are great enough to store all the excess peaks to bring it down to the rms value I don't know and you'd have to do further investigation. But I think you'd be better off with more current. than just more voltage.

Your fetzer valve, second j-fet?, is taking voltage gain off the drain so it's not drawing much current at all though the digital reverb may be sucking quite a bit. Clip some leads from your multi meter to what you have and fire it up then bring up the volume and see if the voltage reading drops.

All that said I don't worry too much about what my amps do, whether they are clean, break up early or late or even come with a little too much noise. I just use them with what they've got so as far as fine tuning yours to do what you want it's a bit out of my league to undersatnd exactly what your hoping to acheive. But then again sure help comes in the form of substitution of things that are known to work well. Does the setup you have work well into another amp and with the other amp can you get the sweet spot on the drain of the second j-fet. Seems to me the sweet spot, on stuff I do, is anywhere between 50k and 10k... all sounds the same to me.

Persevere buddy. Sometimes it helps to put stuff aside for a bit and let the information you've gathered settle in and then it's amazingly simply to see problems that you couldn't while you were willing it to go well with all of the power available to you.

[El Heisenberg]

well this has been an ongoing project for like the past 4 months. I've built and rebuilt it prolly over 10 times. It's always the same problem. The second JFET after the tonestack wont work at half supply voltage on the drain. It only works at something like 1.5 v or 2.2v from a 12v supply!!! When building these Ive begun just setting the first one for half voltage and then just adjusting the other by ear. This has been a problem since before I put any of the other stuff in the amp at all.

Another thing is for the S resistor I just used 1k trimmers this time. I shoulda just used 1k5 fixed or something but I thought it might help solve the problem. It didn't.

Im using two MPF102s, does this matter?

[sean k]

I have no idea at all. I don't even bother measuring voltages on drains because no matter where or how I use fets, after following schematics, they all sound fine so I think if your happy with how it sounds then all's well.

If your not happy about the sound and think that the biasing of that fet is at fault... try some other ones and see what happens (ah!, you've tried J201's but gone back to mpf102's). If you've done that and still have no luck then change it to something that you know works. I'm not knowledgable at all but stuff seems to work regardless... most of the time. Maybe add a resistor in series from the gate to the volume and put a 22uf cap on the source so it's basically the same as the one at the beginning.

My one with the tubes I'll test tomorrow but I'm thinking it'll be as dirty at high volume as the other one I made. This new ones at 200x gain and the last one was at 100x and at anywhere after half volume it just turned to dirt and motorboating, but in a good way, so I don't know what your expecting from these little amps.

Valves have less gain and are a little noisy what with the filaments  so it really does depend on what you want from these little $5.00 amps.

[El Heisenberg]

Mine works fine. Im concerned it could work better. I've never owned a guitar amp in my life, besides a danelectro bacon n eggs pedal if you know what that is. I dunno how it should sound. But the two fetzer stages and the tonestack is the best Ive gotten the TDA2003 circuit to sound. But people are doing different things like tubes in front of tda2003s or opamps instead of FETs. So i wonbder if I could get better results another way. I havent gotten any responses regarding the 2nd JFET in any of the threads or posts ive put up here ocver the past few months. Ive just lived with it. You're the first person to even address it I think. I have no idea what the problem is, the problem shouldn't be there, it's a mystery. I know really little. Is it the load of the amp stage? Is it that it's two MPF102s? Is it the voltage? What could it be?