First project 1W hybrid practice amp questions...

[funkjunk2]

Hi,  new to the forum and guitar projects in general.  I am attempting to build a hyrid practice amp based on the Ruby Tuby design but using parts that I have scrounged and have on hand.  I have some questions regarding the possibilty/sensibility of substitutions and a couple questions on reading the schematics.

SOme background on me and the project.  I want to build this for/with my son who will be getting a guitar for x-mas. It is a learning experience for the two of us to do together.  I have lots of donor electronics we have been stripping parts from.  The basis of this project was and old 60's vintage LaFayette tube based multiplexing unit that yeilded a 12AX7, 12AU7, and a 6BN8 along with some hardware that could be re-purposed.  Since this was strictly a line level device with no speaker level output, we decided to build an IC based output amp.  Our goal is a versatile little practice amp.  The Ruby Tuby seems to be a pretty good starting point as it utilizes 2xx7 type tubes paired with IC output amp. 

Additional scrounging around the garage has turned up a TDA2822, speakers, speaker grills, jacks, pots, 12VDC wall warts and 12VDC/15VDC regulated power supply as well as miscellaneous caps and resistors.

At this point I have a new chassis base constructed out of sheet metal and the 12AX7 and 12AU7 mounted on it ready to get wired up.  will likely do this without a PCB, just wire wrap and point to point wiring.

My questions to start out with are:

1. I there any design problems with using one of each tube rather than having them both the same?  I realize it will have a slightly different sonic signature but as long as it is functional I am ok with that.
2. What circuit mods would need to be made to replace the LM386 with the TDA2822? 
3. Since the TDA2822 is a 2 channel IC, can I use one channel as the TL072 amp and the other as the LM386 or is this impossible?  I can probably scrounge up another amp IC if need be but was just wondering about the possibilities here of splitting the chip.
4.  The parts list does not spell out the type of caps to use, just the values.  What criteria should be used to select Electrolytic, ceramic, metal film, poly, etc.

I am open to suggestions if anyone is aware of a desing that better fits the parts I have on hand.  If I have to buy a couple things I will but the goal here is to keep it made from recycled part if at all possible.

Sorry for all the questions and forgive me if they are stupid.

[boppy100]

Welcome to our wacky world.  This should be a fun project.
The Rubytuby is a great project, but since you are already going a different direction with the amplifier portion, I would simplify  the preamp a little.
I would break the project up into two parts.  First get your amplifier working with just the TDA2822(M).  This will power a speaker all by itself and is a simple project.  Getting it up and running gets results quickly and boosts confidence.
The TDA2822 can be used as a single channel amp with the 2 channels bridged, giving 1.5 to 2 watts.  Check the datasheet for  a schematic.  Point to point is not real easy with  these kind of chips and I would recommend vero(strip)board or perfboard as well as a socket for the chip.  If you click on "Layouts Gallery" at the top of the page and scroll down to Renegadrian, you will find a good vero layout on his page 12.  Not the exact circuit as the datasheet, but works well.
Get this working and I would recommend working on a "Valvecaster" for a good 12AU7 based preamp for your next step.  There is a whole 175+ page thread on this simple but great sounding project. As you will see, Renegadrian has several vero layouts of this as well.
As far as caps are concerned, use what you have.

I am sure others will have good advice as well.  Ask questions and keep us up to date with your progress.

[GibsonGM]

Welcome, Funk!  Good post with good questions.   This will probably be a nice project for you guys.   Here is the Ruby Tuby schem:


1) You should only need the 12AX7, as it's a dual triode...it has 2 gain sections in the glass envelope, which is what the circuit calls for     V1A, V1B are one tube...one socket, one heater...

2) I don't think you'll need to change much at all to use the TDA2822...however, an LM386 can be had for like $1.50 - I would just get one (well, 5 or 6 because you'll want to build other things!).   The other 1/2 of the TDA would be unused, most likely.   You could always come back later and change out that section (modify it...) after you know it all works!

3)  No, get the TL072.....actually, as only ONE opamp is required there, a TL071 would work fine (it is exactly the same thing, but only 1 opamp in the IC) - they likely just have the other 1/2 of the dual opamp "parked" and are not using it, which is wasteful....

4) Big caps like 220uF, 2.2uF, 3.3uF are electrolytic---non-polarized if you can easily find them, or watch where that + is pointing.  The others should be poly types (polystyrene...).  You can get a whole kit of various values off Ebay for about $10.   Or, get some at SMALL BEAR, where you'll also find the TL071 and 386....total, <$20....or, if you just get the few caps you need, probably <$10. 

Trust me, for a first build, it's best to get the parts you need rather than try to re-engineer it....it'll go smoother and easier, and you'll get a working thing that your son will be able to use right off!   I know you want to recycle, so look up a TDA2822 stereo amp or something!   No knowing if it's even good right now, is there?

Your wall wart will need to be a couple volts ABOVE 12V, unfortunately, as the regulator needs a couple volts to operate.  One 14, 15V should be fine, as long as it can supply oh, 200 to 500mA.   I would add a heatsink with some thermal compound to the list...the heater will take about 150 mA,  and the regulator is likely to get hot!    Just to be sure...

Ruby Tuby site (Sopht): http://www.sophtamps.ca/mambo/index.php?option=com_content&task=view&id=28&Itemid=39

Small Bear Electronics, for parts:  http://smallbear-electronics.mybigcommerce.com/  Owner is a member here, and I have had nothing but positive interaction & buying history with him. 

Hope this is helpful, and again, welcome. There are no stupid questions!

[funkjunk2]

Thanks guys! That helps a lot and was really quick.

I know the TDA2822 works (AM/FM/Cass we stole it out of was working when we cannibalized it)  but it does not say it is an (M) variant.  Have read different things on this, some folks saying it will or won't take a 12V power supply.  Are there any other differences?  I know there is less margin for failure if I go with the LM386 and stay according to the original schematic but I have read various things about LM386 oscillations and other issues as well as it not having the same output capacity that the TDA2822 is supposed to.  I'm trying to learn here so please tell me, would the TDA2822 provide a better sounding more stable amp with higher output making it worth a little more trouble?  I know I can buy a LM386 for less than $2.00 but I'm trying to also teach my son that you can often turn "Junk" into something very unique and valuable.  We are on dumpster watch!  LOL.  If the TDA is as good or better and I already have it and know it works then I would prefer to use it.  I know one of the posts I read on here the guy claimed the TDA2822 was toward the top of his list in several categories and mentions the ruby. http://www.diystompboxes.com/smfforum/index.php?topic=99271.msg898079#msg898079

Thanks for pointing out my schematic reading error.  I was seeing that as 2 tubes rather one.  Overlooked the "A" and "B".  (although now I have 2 holes in my chassis when I only needed 1   Oh well,  I can make another tonight.)

I am considering the idea of having the pre-amp and amp sections separate which was suggested.  Somebody elsewhere suggested building a "Real McTube" as a separate section which also uses the 12Ax7 variants.  Not sure what the difference in sound between it and the Valvecaster would be.

The guitar he is getting is a Yamaha Pacifica 112V.  Nothing fancy but supposedly a good beginner guitar for a 14yr old.  He wanted something different than the hundreds of Squires out there and it appears this is pretty versatile.  Hoping the Ruby project will compliment it as well.   

I'm sure I'll have a lot more questions along the way and will keep posted on the progress.  Hoping to have it finished by Christmas.

[GibsonGM]

If you're set on using the TDA, I suggest finding a schematic on the net for a guitar amp made from one....then you can use the tube section as a preamp, as you mentioned you'd do (making 2 separate 'things' and combining them).     The TDA will probably be better, offer more power (I haven't used on, not looking at the sheet at the moment.    The 386 is fine, so simple that if you had an issue, it is easy to correct.   Your call!  Xmas is coming     
Depends on your build skills, I'd say.    386 is just fine at practice levels - it has more to do with the speaker, really.

McTube used 2 12V transformers to generate 120V AND the 12V for heaters...neat first "high voltage' tube project, again depending on how comfy you are with higher voltages and build skills....the Valvecaster is low voltage, similar to Ruby Tuby.   Nice project, too.    I'd do Valvecaster, then McTube, then something with a nice high B+, like the "GTFO" (but you'll want a 'real' amp for that). 

Remember, with what you build, if your son is using it as a practice amp you may want to stay to 15V type stuff right now, just in case, y'know?  HV has been known to really bite (or kill) the hand that plays with it and all that.  There are lessons to learn prior to handing off a circuit over those voltage levels, IMO.

My opinion would be to get a few builds under your belt..you can do them together, even...THEN go for the 'golden project'.  Build the power output (TDA or 386), be sure it works...then the Ruby...cob them together....there ya go.   The power section will be its own project to do first...13.8V to 15V wart, regulator, a couple caps and a heatsink....12V all day long      If you can't do it by Xmas, then don't...no sense ruining a good project by rushing.   It is not inconceivable that you'll get something going by then, tho!! 

[PRR]

http://www.diyaudio.com/forums/instruments-amps/299985-cannibal-guitar-amp-project.html

[funkjunk2]

PRR,

That was my post on the DIY audio forum.  Stompboxes forum seemed to have more activity on low voltage based tube projects.  Majority of feedback I was getting on DIYaudio was pushing me in the highvoltage full blown tube amp direction.  The feedback I was geting there didn;t seem to have much love for hybrid type designs.  I plan to update that thread just the same though and I am grateful for the help they did give me.

[funkjunk2]

Last night was very productive.  We did some more scrounging through junk and found a goldmine.  I had a couple peices of old telephone diagnostic equipment stashed.  Opened it up and guess what we found!  Behold, 2-TL071CP's, and an LM386-n3, all in sockets and a neat set of knobs and some LED's.  There are a couple of pots but didn't see any values on them.  Will need to check them once I strip the boards (which I think I can also re-use with a little creativity.  I also found a 78L12.  Add to that I found my old stash of Resistors still carded up and discarded from electronics class at a community college and a few more goodies.  I think I now have just about all the required parts for a text book Ruby Tuby. 

I checked my "regulated 12v/15v" power supply and sadly found that it is not working correctly.  I am sure the transformer is good but I think some of the downstream filtering parts are faulty as it is putting out about 8v.

My scrounged 12VDC wall wart transformer is actually a bit on the hot side.  Showing 16.3V on the meter.  Looks like I still have some work to do on the power supply section of the unit but otherwise things are looking up.

A few more questions:

1. In the Ruby schematic I am working off of, R13 is listed as a 500K "driver".  What does this mean?  It just says 500k 40% in the schematic above.
2. will any pots work ok or do I need a specific type (ei, linear, audio taper, or other style)

Regarding 12V vs 15V:

The LM386 variant I have (n3)  appears to have max input voltage of 12V
The 12AX7 filament heater is supposed to use 12.6V. 
The 78L12 will limit the circuit to 12v correct?  How does this all work together?  Would it be better to connect the tube filaments before the 78L12 and leave the regulated portion for the LM386?


I will try and get some pictures up here soon.  Have to play with the hosting a little and see how it works as I haven't tried that yet.  The link PRR posted above shows pictures of the beginning of the project.

[funkjunk2]

Also found a LM348N.  Quad channel opamp?  Any creative uses for it?

[GibsonGM]

Hi Funk,

Good deal on the finds!  Love when that happens. 

"Driver" likely is meant to be taken as "Drive", or "Gain"....it's a feedback resistor for the opamp, which will set your input level to the first tube.  Adjust by ear when done...

Any "type" of pots will WORK here, but may not sound right. The general rule of thumb is if they're not labeled, use "B" (linear) taper.  Often a volume pot will be "A", log type, as that is how we hear.   If one sounds 'weird', replace it with "A".   

Your wall wart will read "16V" etc. UNLOADED, that is normal.  It's not regulated...so, it says "12V 500mA" or some such thing.  That means it will provide 12V AT 500mA of current draw (power supplies sag...).   You may in fact be able to use that with the regulator, if it does not sag below the required voltage above regulation (13.8, 14v....), you can try it.       The Ruby Tuby and 386 draw VERY little current, just a few mA....the tube heater will draw like 150mA....you can simulate this with resistors to see what voltage you get from that wall wart at that current draw....

Brings us to heaters - yes, feed them BEFORE the regulator, BUT - you have to be sure how you do it.  Keeping it pre regulator keeps that power out of the reg., so it will not get so hot - won't get hot at all really, if you only feed the tuby and 386 with it.    HOWEVER - now you are tossing like 16V at the heater, which wants 12.6V.   
So you'll need to drop some on the way there (via a dropping resistor) - do you have much background, doing ohm's law calculations etc?

The resistor will be the voltage DROP divided by the expected load current...so, for 16v measured on the meter, and you want 12.5 or so, you do: 3.5v/.153A   ~~ 23ohms 

You could put 2 common 50ohm/10Watt Radio Shack cement-type resistors in parallel, and get 25 ohms, and that would be FINE for this.   A bit higher is ok (30 ohms etc).     Power dissipated here would be just over 1/2Watt, so you could find some combination of other resistors to do the same as long as they can handle their respective amounts of power.      This is a common problem when using tubes...another way is to yes, feed it with the regulator, but you then have to deal with heat....I just use the big white cement resistors, myself.  Heaters aren't critical, but should be within 10% of their rated voltage or they can burn out, or underperform.     If they glow BIG AND HOT, unplug fast!!    Be sure what they're getting for voltage....

Quad opamps are cool and have other uses, yes, like tremolo/phasers uses, they give you 4 stages of amplification.  Or a buffer, 2 gain stages with tone controls in between and an output buffered distortion...


Oh - the regulator just takes "input power' from the wall wart etc., and using its internal circuitry keeps it to a steady output voltage, unless shorted or over-heated, when it will shut down.  That is why you need a couple volts above the rating, as it needs some juice to run.   You really need to check how hot it's getting often when the circuit is 'new', until you know what's going on.  It can get hot fast, and the output will quit.   If you can't keep your finger on it for a few seconds, it's too hot!
That is also why the closer to "2 volts above" you can stay, the better - the more it has to 'reject', the hotter it will run.

[J0K3RX]

No use in creating a new post since this is on the topic... Thought some may find it useful.

5000 IC audio amp circuits
https://dl.dropboxusercontent.com/u/11178619/Audo_Amplifiers/5000%20IC%20Audio%20Amplifiers.pdf

[funkjunk2]

Thanks! hoping to start wiring some things up tonight and testing voltages/loads.  You guys are awesome and thanks for the great reference reading as well.  Looks like a great read and handy reference guide/cookbook as well.

[funkjunk2]

Started soldering some stuff up tonight.  I ran into a couple things I have questions on.

First, in using the TL071, I apparently need to know if my input is inverting or non-inverting.  The ruby schematic does not show the pin numbers for the TL071.  I suppose this is simple for those who have done it numerous times?

Second,  For the capacitors on the power supply (C1& C5), it calls for 2 1000uF caps.  I do not have any 1000uF but I do have two 2200uF caps.  I assume larger is better in this scenario and it is a suitable substitute?

Third,  The capacitor in the output (C6) is called out as .01uf.  Can I place 2-  identical .02uF  caps in series to achieve this without causing issues?

[duck_arse]

for your pinouts, get the datasheet. the inverting is shown (-), non-inverting (+). pins 2 and 3 on a single opamp.

the 2200uF caps, as long as the voltage rating is adequate, will do OK. should do ok.

probably just use a single 20nF cap, close enough for jazz. more bass for jazz?

[GibsonGM]

You might start saving sheets like this when you find them, for a 'reference library'...  http://www.ti.com/lit/ds/symlink/tl072a.pdf   Page 3, top left...this data sheet is for the "TL07X series", which are just more opamp sections on a chip.

Note the chip's pinout - find that little 'cutout' on it, and held with cutout at "top", pin 1 is to the left, and so on.  Messing up the pin numbers can destroy the chip
Your input pin is pin 3, "IN+" input.   Noninverting.    Yes, you start to remember the pins as MANY opamps use this pinout, same for dual opamps like the TL072 and so on.   

I have a chart I made with drawings of common transistor and chip pinouts, and tubes, of course, hung like a poster in my work area.

[funkjunk2]

Thanks guys,

I got a data sheet last night.  It shows two different setups.  One for inverting and one for non-inverting.  Sorry if I am sounding rather dense on this.

The data sheet lists the pinout for the TL071 as follows

1.  Offset null
2. Inverting input
3. Non-inverting input
4. -VDC
5. Offset null
6. output
7. +VDC
8. NC


So if I am getting this correct,

Pin 2 connects to RC network between R13 & R14
Pin 3 connects to input jack
Pin 4 connects to -12VDC/GRD
Pin 6 is output to C10
Pin 7 is + 12VDC

Pins 1, 5, & 7 are ignored.

Is this correct? 


I got the amp section completed last night and begin work on the power supply and pre-amp sections today!

[GibsonGM]

Absolutely correct dude!   

Pin 4 is going to be ground unless we're using a BIPOLAR SUPPLY (which we're not, here), which would have both +V and -V, as well as a ground. 

Not to confuse, but R11 and R10 are splitting the voltage in half, which becomes AUDIO GROUND (or voltage reference, VRef, bias....)...point being, when you are done with the power supply you should read about 1/2 your input voltage there.   So you are looking for 12V, about 6v there, and ground (zero volts) at ground points, as referenced to ground (black probe on ground).   

You going to measure your voltages and such at the power supply before you hook that power to the rest of it?   

[funkjunk2]

Absolutely!

Moving forward!

testing picture posting.. If it works, these are the speakers we took out of a big screen TV and plan to use.  6"


And here is a rendering of roughly what it should look like when complete...

[GibsonGM]

Cool!  It should turn out to be a nice DIY recycled project that you'll learn tons from 

[funkjunk2]

I have been making some progress.  I have all the circuit board completed and soldered up but have not connected them together and powered them up yet.  My power supply section is still reading an output of 16VDC without load.  Was concerned it might be too much, need to put a load on it and see waht happens.  I powered up the output amp stage using a 9v battery and I could here it power on, appears it is working.  Pre-amp/tube stage is not yet tested.

Have spent the last few days working on the cabinet.  Thought I would share a few pictures of the cabinet.  The housing is made from 1/2" spalted Tulip poplar. Speaker baffle is 1/2" marine plywood.





He wanted to be able to see the tube lit so there is a hole in the top of the cabinet you will be able to see the tube lit through.  Still need to drill the front panel for knobs and input which brings up a question.  Do I need to isolate the input/outputs from ground or is it ok to fasten them right to the metal front panel?   Will post up some pictures of the recycled circuit boards with new components a little later.