Building the Tiny Giant amp

[jogina111]

I think it will be alright if it would sound lame since it will only be for practice. I juat became worried when  I read somewhere that the amp would overheat when the speaker demands more output current etc..

[Ben N]

Taylor, if you ever do a v.2 of the board, it might be nice to include holes for the extra bits to give the 072 some gain, for anyone who does want to insert a tone stack and compensate for the signal loss.

[Taylor]

Taylor, if you ever do a v.2 of the board, it might be nice to include holes for the extra bits to give the 072 some gain, for anyone who does want to insert a tone stack and compensate for the signal loss.

Hmm, what did you have in mind specifically? You can increase the gain of the opamp stage by changing the 220k feedback resistor to a larger value or pot, and/or lowering the value of the 100k from inverting input to ground. But I think you know that so I must be misunderstanding what you mean.

[Ben N]

My bad, Taylor--I didn't look at the schematic before commenting, and assumed that the feedback loop was hard-jumpered on the pcb for unity gain. 

On another matter, I spotted a cheap easy speaker cab that might be perfect for some TG projects: http://www.diystompboxes.com/smfforum/index.php?topic=108964.0

[PRR]

> assumed that the feedback loop was hard-jumpered on the pcb for unity gain.

If he did that, sensitivity might be low and/or idle hiss might be high.

I do not have the plan at hand, but *usually* a guitar amp must run preamp - volume pot - power amp.

It is difficult to get enough gain in a power amp to bring-up a small signal like guitar.

A power amp usually has higher input hiss than a for-purpose preamp.

It usually works out best to take a moderate gain before the volume control, the rest after. Good target values are 20mV sensitivity at guitar jack and 50mV-100mV sensitivity at power amp. Preamp input should also take 300mV~500mV without distortion (at lower volume-pot setting).

> insert a tone stack and compensate for the signal loss

Ah, a new can of worms. If you compensate all tone-stack loss in the front, then the preamp will have high gain and high output level. Assume Fendery stack with 10:1 loss. Present preamp gain is 3.2, so we hack preamp for gain of 32. If we put in a 500mV signal the preamp outputs 16V, which won't happen cleanly under a 12V supply.

Without a much higher supply voltage (say 30V), the "optimum" is probably preamp - volume - booster - tone - poweramp. Two small stages.

Isn't that a dual opamp? Then he "could" pad-out the idle side and let users do what they will. Stock would be jumper Out to In- and In+ to Vref. Mods could be most anything, which is why _I_ would not encourage it or support it (too many ways for buyers to screw-up and complain).

[Ben N]

I would assume (here I go again) that most builders are using supplies of 15-19vdc, but, yeah, I hear the point, Paul. I personally wouldn't mind having the flexibility to use the second opamp, but I get why Taylor would want to keep the platform simple and clear--as it is, there are nearly 900 posts on building it.

[PRR]

> using supplies of 15-19vdc

The Tiny Giant has an on-board 12V (11.9V?) regulator. The power-amp chip is designed for "12V" car audio.

Yes, it could stand more; or the preamp supply could be higher than the power amp supply. But going from 12V to 15V is not a big increase of signal handling. And we do need some filtering or protection for the preamp, so 15V input might be 14V at the preamp.

Yeah, we could double a cleaned input to 28V, or buzz it thru a transformer for 300V. Many things are possible. But as-designed the Tiny Giant does a very useful thing-- guitar to LOUDspeaker, DIY, without the huge box needed to stand out on a showroom floor.

[fatecasino]

hi all!
I built the tiny giant and it works fantastic!
The only problem   is that I was using a friend's 19V adapter. My own laptop adapter is 21.1V...do you think that it will blow my tiny giant up??or is it just the heat issue?

[PRR]

> do you think that it will blow my tiny giant up??

Sorry, no, it won't blow up. (If I thought it would, I'd ask you to get video!)

Slight extra heat should be no big deal, unless it is blistering hot now.

[fatecasino]

true! it works just fine with 21.1V 
thank you very much!

[fatecasino]

 
Sadly, after being lucky for long time, something went really wrong while I was experimenting with the power adapter.
Now, when the Volume goes higher than 60% the amp produces a loud distorted synth-fuzz-like fart. If the volume is lower it plays mostly normally. It is also a bit random, at times when I switch it on it gives this terrible sound at volumes less than 50%
Which parts do you suggest I should replace first???!

[jogina111]

072 oe the tda7240

[Shoeman]

I wanted to take a look at Taylor's site, but my Trend Micro security program has it flagged as a possible malicious site.  I can't imagine that's true.  Anyone else seen that happen?

Geoff

[Luke51411]

It happens on my pc.

[bluebunny]

Anyone else seen that happen?

Nope!      And I'm on the inside of a vast corporate network with doubtless all manner of firewall and anti-virus things going on.  If something needs to be blocked, then it's blocked!

[Ben N]

I haven't been able to get into Taylor's site, either at home (Avast) or at work (government network), in a dog's age due to malware alerts. I know he has struggled with this, and assures that there is no real threat.

[Luke51411]

I have avast as well and that blocks me out every time.

[Shoeman]

So is the site considered safe by those of you who use it?  Taylor?

[Taylor]

To my knowledge, the reason this happens is that at some point in past years, the site got hacked a few times to insert a bunch of links to prescription drugs, I think as part of some SEO scam (if lots of pages link to your site, Google indexes it higher in searches; scammers place links to their stuff all over the web to inflate their apparent significance). The links weren't clickable, possibly not even visible but in the page source code. I deleted all of that stuff and upgraded to newer software, etc. When I go to the site, I don't get any malware warnings and as far as I can tell there hasn't been any weird stuff inserted into the pages in a long time. To my knowledge there was never anything on the site that actually attempted to get onto your computer or mess your browser up.

Web development is not really my forte, despite having been pretty slick with HTML back in the last millennium. It's gotten a lot more complicated and my available time to become expert on things has drastically declined. So based only on my limited knowledge, I can speculate that maybe the site got flagged by anti-malware software back when it was hacked, and perhaps there is no automatic mechanism to get unflagged over time.

Since I haven't personally seen the warning in a long time, and I still receive orders and emails through the site's submission form, I don't have any way of figuring out how extensive the problem is, nor do I really know how to fix it. I will be thinking about how to figure it out - in the meantime if you can't get to the site and would like to order something, you can email me directly at taylorlivingston at yahoo.com.

[Shoeman]

Excellent explanation.  And I know what you're saying about HTML vs. whatever it is nowadays.  My age has a 5 as the first digit       I can bypass my antivirus's warning and go to the site, so I will.

Thanks!
  Geoff