Building the Tiny Giant amp

[Taylor]

Wow, that will be a great unit when it's done. Looking forward to seeing it.

[DocAmplify]

I have a question about the input.  The FAQ for this site suggests a stereo input so that the input can act as a switch.  This build shows a mono input.  It seems to me that switching via the guitar input isn't necessary (or even desired).  Am I correct that the mono input is a better choice for this particular build?

[DocAmplify]

While I'm at it, I plan on building a couple of effects pedals (probably an orange squeeze and a tube screamer clone).  These both need 9V, but it looks like I have 11.6 volts in the circuit (since I'm asking, the power input can be between 15-20 V - but the schematic specifically says 11.6 - I'm guessing this is a precisely controlled voltage).

Can I just run the 11.6 from the output?  With the voltage drop on two pedals, will the couple of extra volts do any damage or change the nature of the effect?  Is a voltage divider overkill for the sake of two and a half volts? 

[waltk]

I have a question about the input.  The FAQ for this site suggests a stereo input so that the input can act as a switch.  This build shows a mono input.  It seems to me that switching via the guitar input isn't necessary (or even desired).  Am I correct that the mono input is a better choice for this particular build?

Yes, a mono jack is better for this.  Switching the power by using a mono plug into a TRS jack is a convenience in pedals that are battery-powered.  It saves the battery and/or allows you to eliminate a separate power switch.  In this case, the power is always external, so the reason for doing it doesn't apply. 

Also, I would be concerned about switching a lot of power (as required by this amp) this way.  Here's why... Using the TRS switching method, you normally connect the power ground to the ring of the jack, and the circuit ground to the sleeve. When the mono plug is inserted the one long stretch of plug connects the ring to the sleeve, and completes the power circuit for the effect.  The problem is that there's a moment (fractional second) while you're inserting the mono  plug when the tip of the plug is in contact with ring of the jack, and the shaft of the plug is in contact with the sleeve.  This would momentarily try to complete the power circuit through the device that is connected to the plug (maybe a guitar or other effect).  Do you really want to expose the device to a jolt of 15 volt/4 amp power?

While I'm at it, I plan on building a couple of effects pedals (probably an orange squeeze and a tube screamer clone).  These both need 9V, but it looks like I have 11.6 volts in the circuit (since I'm asking, the power input can be between 15-20 V - but the schematic specifically says 11.6 - I'm guessing this is a precisely controlled voltage).

There are a couple other posts in the thread about powering other pedals using the TG voltage regulator output.  I would use an additional 7809 regulator for this, and power the other effects in parallel.

[DocAmplify]

Thanks.  I am documenting my build as I go (I didn't get the printed circuit yet, so I'm starting with other components). 

I want to etch the enclosure, so I started with wet sanding.  The bottom of the enclosure is the factory finish, and the top is sanded (220, 400 and 1000 wet sand paper)



My first solder joint was on the pot.  Looking at the terminals, I think I got the pot designed to be placed directly onto the board.  I want to use wires so I have freedom to place the pot wherever I want.



Here are the LED, switch and pot soldered and insulated with heat shrink.



I had designed my graphic earlier this week.  Before I altered the enclosure, I decided to glue the printed graphic to a piece of cardboard and check the fit of the components.  As you can see, I didn't leave enough space between the switch and the pot. 



Here it is from behind.  My wiring looks pretty deep - I'm nervous about how much space these three components will take.



Here it is with the pot moved north.  I like the aesthetic of the three components, but it messes with my graphic.  My daughter's name is Victoria, and since this project is based on Taylor's Tiny Giant, I thought I'd make a play on my baby girl's name and her sharing a name with Queen Victoria (with a nod to Freddy Mercury in there as well).  If I want to keep the name "Tiny Queen", I'll have to find a spot that looks right. 

[DocAmplify]

There are a couple other posts in the thread about powering other pedals using the TG voltage regulator output.  I would use an additional 7809 regulator for this, and power the other effects in parallel.

I found another link on the 7809.  It suggests that it should have .1uF capacitors on the input and output sides.  The schematic doesn't state polarity, so can I use a ceramic cap?  It also doesn't state the voltage - probably a 20V?

[waltk]

I found another link on the 7809.  It suggests that it should have .1uF capacitors on the input and output sides.  The schematic doesn't state polarity, so can I use a ceramic cap?  It also doesn't state the voltage - probably a 20V?

Rules of thumb:
You can always use a non-polar cap of the correct capacitance whether the circuit specifies a polar or non-polar one (the converse is not true - don't use a polarized cap if the circuit calls for a non-polar one).
Always use a cap that is rated for more voltage than it will see in the circuit - it doesn't matter how much higher.
If the cap is in the signal path, film caps are usually preferred - in this case, it doesn't matter.

Within these general rules, the choice of caps is usually determined more by size and cost.  It's rare to find a stompbox circuit that doesn't use .1uF caps - so you should consider buying a quantity of nice .1uF film caps.  They're cheap and readily available in 50V or 100V ratings with 5mm lead spacing.

[evirob]

This amp looks amazing! And in fact, just what I've been looking for. After building a few ruby variants, I've wanted to build something with a bit more oomph, but being relatively new to the game, I'm not ready to risk my life with high voltages. So, I have read this whole thread and have a couple of questions. I think I know the answers, but really I'm not sure, so I hope someone here will take pity..

The first is very noobish (sorry) and kind of general. Regarding power supplies, if you have a 4A supply as is recommended here, does that mean it's pushing 4A into your circuit, or is it that there is up to 4A on tap if the circuit needs to draw it? Or something else. Sorry again for my limited grasp of electrical basics. I tried to answer this question through my own research but don't even really know how to phrase the question so it makes sense, so I hope someone can guide me here.

Secondly, considering the 4A power supply, would I be able to put something such as the Matsumin Valvecaster into the same build to act as a pre-amp? i.e. will 4A cause damage to a circuit that only draws a few hundred mA? I've built a couple of valvecasters, but the strip board I build the circuits onto is only rated at about 1A.

Sorry again if these questions are infuriatingly basic, but I would rather ask than build something that will explode.

[waltk]

So, I have read this whole thread and have a couple of questions.

Welcome, and congratulations on reading the whole thread.

Sorry again if these questions are infuriatingly basic, but I would rather ask than build something that will explode.

Questions are good - especially after reading the whole thread.

if you have a 4A supply as is recommended here, does that mean it's pushing 4A into your circuit, or is it that there is up to 4A on tap if the circuit needs to draw it?

It means that there's up to 4A on tap if the circuit needs to draw it.  Power supplies try to give what the circuit demands, rather than push current through them. The TG draws about 1A on startup, then less than that depending on volume.

would I be able to put something such as the Matsumin Valvecaster into the same build to act as a pre-amp?

Yes. The biggest consumer of current in a valvecaster is the heater - about 150ma.  You can run the valvecaster off of the regulated voltage from the TG.

i.e. will 4A cause damage to a circuit that only draws a few hundred mA?

No. Your valvecaster will draw what it needs and no more.

Also, because the default TG build sets the LM338 regulator to produce 11.6V, you should make one resistor change so that it produces 12 or 12.6V to power the Valvecaster tube heater.  The tube heater will like this voltage better, and it won't hurt the TG.

[evirob]

Oh cool, thanks for your reply, that's what I was hoping to hear. Although I hadn't figured the fact of needing to increase the voltage to ~12V so thanks for the heads up on that!

[papasteack]

> Noise is reduced tenfold

But can we hear the noise now? The simple regulator does have good ripple reduction. The car-amp power chip has very good power supply rejection (a car's electrical system can be VERY noisy).

In most DIY builds, ground layout and wires too close to each other will leak more power supply noise than the chips.

> very good esr ... 0,0125

The elephant in the room is the 3 or 6 ohms of speaker resistance. We want to make other resistive losses "small" compared to 3 ohms. Smaller than 1 ohm. But I would not go to a lot of trouble to get 100 times smaller.

Hi,

I come back about optimizing the regulator. I have understand a bit what is supply rejection...So, the tda has a very good sypply rejection...But what about the tl072 ?  And other circuit that should be connected to the regulator ?
So the need of capacitor on adjustement pin should be justified at leastd for the buffer, and for other circuits. And overall, if there's a distortion circuit with a lot of gain... Am i right?

Damien

[bcalder]

Hi all, a frustrated newbie question here.

I have the TG working by itself, but can't get the stompbox I built into the cab to work without patching it. My setup is as follows, following RG's article (http://www.geofex.com/article_folders/jiab/jiab.htm):

Input --> stompbox --> stompbox volume lug2 --> tip of NC jack 1 (preamp out)
                                                                             |
                                                                              switch of NC jack 1 --> switch of NC Jack 2 (amp in)
                                                                                                              |
                                                                                                               --> tip of NC jack 2 --> TG in

If I patch Preamp Out --> Amp In, it works. If I pull the patch, it doesn't. I can't figure out what I'm missing here!!

Thanks in advance for any advice!!

[bcalder]

Well, even though I've yet to figure out my NC jacks, I wanted to post my 99.9% completed build for you to see:





The build thread is here:

https://picasaweb.google.com/101724142776681014815/LittleBluesAmp?authuser=0&feat=directlink

It's real interesting sounding with the Supreaux front end & the 6x9 speaker - this is not a shredmeister setup!!

I can also bypass the front end & either plug directly into the TG, or plug my Amplitube into it. The 6x9 speaker definitely gives a different twist on the sound.

It's a spanking little setup for home practice, and I may have to take a day off work this week to have some fun.

Thanks everyone for the good knowledge & advice!

[Taylor]

Looks really cool! If you can post a picture of the jacks you're having trouble with, and the way you've wired them, perhaps we can figure out the problem.

[bcalder]

Thanks for the compliment, Taylor!

I'll try to post pictures towards the end of the week - pretty busy ATM.

[DocAmplify]

I just got my kit.  Before I start heating, I want to check.  Under the tl072 there are two holes.  Do I leave these empty, and just solder the 8 pins of the socket here?

[DocAmplify]

I went ahead with it, but I'm having some problems.  As indicated in the instructions, I checked to ensure the speakers and the heat sink tabs were not continuous with the ground.  They were- everything is.  

I was careful and thought I'd be ready to try this, so I had everything assembled.  I slowly began disassembling to look for the problem.

I'm not sure if photos will help.  I fear there's a short somewhere in my soldering.  I'm using the resistance setting of my multimeter to test for continuity and I'm seeing real values (i.e. not infinite resistance) on just about everything I test.  

For example:  

I get 3K ohms when I test across the ground and +ve in.

I get 0 ohms when I test from ground to the sleeve of the input  jack (I expected this).

I get 1100 ohms when I test from ground to LM338 tab (that's removed from the enclosure)

I get .9 ohms when I test from ground to the tab of the TDA

From ground to the red lead of my speaker I get infinite resistance, but from ground to the black lead I get a quick reading that then goes to infinite.  

From the red lead to the black lead of my speaker outputs I get 7.68K ohms.

[Taylor]

Since there are caps and resistors connecting all areas of the circuit, it makes sense that you will not see infinite resistance between all areas of the circuit, right? As long as your meter does not read 0 ohms you are ok to assume two things are not continuous. But I would also recommend getting a multimeter with a beep-continuity mode. I got one for about $12 I think.

The two small holes are called "vias". They are there as part of the internal circuit board design - they connect traces on the bottom copper side to traces on the top. ou don't need to do anything with them, just ignore them. Don't connect them to anything.

[DocAmplify]

Thanks; that's good to know.  I was worried because I was careful and took my time- I couldn't figure out where I went wrong.  I'll probably get a chance to finish wiring it up tomorrow and fire it up. 

[DocAmplify]

It works!  Thanks guys.  Taylor and everyone.  I have never done any type of electronics prior to this - Taylor, your kit was a breeze (despite a few panic moments; but that's my issue, not yours).  From enclosure etching to soldering and understanding the circuitry; this was a group effort between my and DIT stomp boxes. 

I have a couple of suggestions for future builders.  The two IC's that have the heat-sinks that attach to the wall of the amp are tall - in my case, I didn't sink them quite low enough on the PC which means they are in the way of my base.  I can easily shave the base back, but it would have been nice if I had made it just a bit shorter. 

I also decided to use an old plastic gift card as an insulator pad under the IC.  I put a layer of electrical tape over it - mostly to obscure the store logo from the gift card. 











I plan on putting in a 9v regulator on the out, and making a DC out to attach a pedal.  I also need to clean up my DC in. 

On that note, my laptop DC has something attached to the cord on the DC side (it's a small cylinder - smaller than a size C battery).  I have noticed this on multiple AC to DC converters on the DC side.  What is it?  I already cut the stock end off and soldered my power end, but I want to replace it.  Cutting it again will put me very close to this widget.