Building the Tiny Giant amp

[Taylor]

Hi, I've already successfully built one of the tiny giants and recently finished my second. This time I wanted to add a switch volume pot and led. I've gotten the led to light up and turn off when the switch is switched however there's no sound at all. At first I had the power wired wrong but fixed that. Any tips?

What do you want your switch to do? Standby or power? Was the amp working before you added the switch? How did you wire the switch?

yeah, i didn't explain myself there right, it's true, the TG really gives what you send to it, i just wanna get a bit more treble without changing the TG circuit with tone stacks and eq, so i was thinking if i add a preamp circuit this will fix my problem or not?

The traditional guitarist solution is a treble booster like a Rangemaster. There should be more treble booster circuits than you could ever dream of if you search this forum. I'm not a guitarist so I can't recommend a good one - I'd probably pick the simplest one-transistor silicon one I found.

[garcho]

Runoffgroove.com is a great place to look for what you're asking. Their English Channel project might be what you're looking for.

[trem7]

I want the switch to be power, I have the switch wired between the positive on the dc jack and the board. I'll try taking the switch out and see if it works.

[YouAre]

Built my first TG. It's great!

Like many others, I plan on creating a preamp with some ROG designs. I'm going to try the Professor Tweed tonight, but thought about adjusting the negative feedback arrangement.

On the actual Princeton Amp, the negative feedback is tapped off the speaker, and feeds back into the cathode. In the Professor tweed, it feeds off the FET that simulates the 6v6, and goes to the last preamp stage's emitter.

Would I be safe in tapping the feedback off the speaker output from the tiny giant? I know this is something I can simply test after making sure the pedal works stock, but I want to make sure I want harm any components with this idea since it probably hasn't been done before. Would I need to do away with the 1uf feedback cap? Or would DC muck everything up?

Thanks again guys.

[Taylor]

I'm hoping PRR or RG (or somebody else who knows way more than I do) will weigh in on that, but what exactly are you hoping to achieve with that?

I should also say that, until somebody who knows tells you that you should do that, I would recommend that you don't.

[trem7]

So I've gotten the amp to work, I removed the LED and resistor which was before the switch. There's a pop when switching on and off so I will be adding a standby switch. In which part of the circuit should I wire the LED?

[garcho]

The LED should be wired in parallel to the circuit, that is, it's not part of the circuit. It will turn off when you switch the power off, it will turn on when you switch the power on, regardless of what the Tiny Giant does.

Positive voltage -> power switch -> 1-2K resistor -> LED anode (+, the longer leg) -> LED cathode (-, the shorter leg) -> ground.

see here if you're confused

[YouAre]

I'm hoping PRR or RG (or somebody else who knows way more than I do) will weigh in on that, but what exactly are you hoping to achieve with that?

I should also say that, until somebody who knows tells you that you should do that, I would recommend that you don't.

Hoping to use the TG as a poweramp for some FET preamps to sound relatively close to the tube amps these preamps emulate. I understand that the Professor Tweed uses the negative feedback from the section that simulates the poweramp, but it actually comes from the speaker tap in the real thing. The ideal goal is to get a closer simulation to the real thing, and I'm hoping that the possible increase in bandwidth from the global negative feedback will help. I know you'll say that the TG is already a very flat amp, but this could potentially be very helpful for the voicing of the preamp as well, since we'll be feeding the signal back the last or second to last stage. There will be a sacrifice in output gain, but the TG has lots to spare.

Also, this opens us up to the use of the more feel based amp power controls, like Presence, Depth, and Speaker Damping. This could really be great for guys who want to build a great sounding SS amp that emulates it's bigger tube based brothers.

I'm really inspired by the possibilities of a tiny loud and clean amplifier. So I think I'm doing it justice by pushing the possibilities as far as imagination will let it run.

Thanks again for all the awesome designs.

[trem7]

Thanks for the help guys. Still pretty new to DIY electronics. So the switch I have is a pot with a switch. Can I make this work or will I need a different switch?

[garcho]

If you're up for spending a buck or two and have the patience or time to order the part, I suggest this type of switch, with built-in LED:

[PRR]

> Would I be safe in tapping the feedback off the speaker output from the tiny giant?

No.

> I know this is something I can simply test after making sure the pedal works stock

There is much risk for burning-up the power chip. While TDA7240 is pretty bullet-proof against load mis-connections, wrapping feedback around that many stages is pretty sure to oscillate, probably hypersonically, which gets all the internal power transistors VERY hot in a way that the internal protection systems are not designed to handle.

The TDA7240 _has_ NFB, internally, for the same reason the Princeton takes NFB from output to driver. This means the TDA7240 _controls_ the speaker, no deviation.... it does what the Prof Tweed tells it to do.

BTW, the TG has _two_ speaker outputs. Unlike Princeton, neither side is grounded.

[YouAre]

> Would I be safe in tapping the feedback off the speaker output from the tiny giant?

No.

> I know this is something I can simply test after making sure the pedal works stock

There is much risk for burning-up the power chip. While TDA7240 is pretty bullet-proof against load mis-connections, wrapping feedback around that many stages is pretty sure to oscillate, probably hypersonically, which gets all the internal power transistors VERY hot in a way that the internal protection systems are not designed to handle.

The TDA7240 _has_ NFB, internally, for the same reason the Princeton takes NFB from output to driver. This means the TDA7240 _controls_ the speaker, no deviation.... it does what the Prof Tweed tells it to do.

BTW, the TG has _two_ speaker outputs. Unlike Princeton, neither side is grounded.

Makes sense! I guess I can mess around with the feedback in other stages of the pedal feeding the TG. Thank you for the heads up!



On a separate note. I've been noticing the common complain that the TG is lacking in the high end department. I understand it's because we're used to most guitar amps having that high frequency boost, but it does affect how ROG pedals sound as preamps. Has anyone modified the TG's opamp section to have a high end boost? I was thinking decreasing the cap size and increasing the feedback resistor. This would hopefully keep the lows/mids at the same volume and only boost the highs if my understanding of non inverting HPF's is sound. Any thoughts?

[YouAre]

Sorry for replying again (couldn't find edit button for some reason).

But I just wanted to add that I did build it, and I found myself missing that high end available in typical guitar amps.

My goal is the have the TG resemble a typical guitar power amp as much as possible, to utilize ROG and ROG-esque tube-to-fet pedals as preamps. I will modify the preamps as necessary. I'd ideally like to avoid adding the high end in the pedals, so I'm thinking adding the "sparkle" to the poweramp section would be the way to go.

Any suggestions besides modding the input opamp section of the TG (which I'm going to experiment with this week)?

Thanks guys.

[PRR]

> complain that the TG is lacking in the high end

I think many people overlook or mis-read these good words in the manual:

"It's designed to be a clean full-range amp without any inherent EQ curve or distortion. This allows you to pair it up with your favorite effects, preamps, and/or equalizers to build your own custom amp."

Here's a simple high-boost (added R and C) plus alternate bass cutoff "try" cap values (the very extended bass "may" overwhelm treble).




> couldn't find edit button

On this forum: "edit" goes away in a day. You can edit your post for about 24 hours, then it is locked to reduce time-warp confusion. I know other forums with perpetual re-editing, rarely someone will abuse that. Very reasonable, but a bit confusing if you have quick-edited here then find a reason to re-edit a day or more later.

[Jdansti]

The LED should be wired in parallel to the circuit, that is, it's not part of the circuit. It will turn off when you switch the power off, it will turn on when you switch the power on, regardless of what the Tiny Giant does.

Positive voltage -> power switch -> 1-2K resistor -> LED anode (+, the longer leg) -> LED cathode (-, the shorter leg) -> ground.

see here if you're confused

I don't think that the wiring scheme you refernced will work for the TG.  The chip that the TG uses has a standby switch connected across a capacitor that is connected to pin 2 on the chip and not a traditional power switch like most of our stomp boxes.  There is no main power switch where you could place an LED in parallel.  You also have to be aware that the output (speaker) has to be connected to the chip and not to ground. Here's the schematic:




One option might be to jumper across the standby switch connection on the PCB so that the "switch" is permanently closed and then add a DPDT switch to the output of the power supply. You could add the LED and limiting resistor to the new DPDT switch.

[YouAre]

I think many people overlook or mis-read these good words in the manual:

"It's designed to be a clean full-range amp without any inherent EQ curve or distortion. This allows you to pair it up with your favorite effects, preamps, and/or equalizers to build your own custom amp."

Here's a simple high-boost (added R and C) plus alternate bass cutoff "try" cap values (the very extended bass "may" overwhelm treble).

Absolutely. Didn't miss that section at all. I'd just never built anything completely "flat" before, so I'd never had a point of reference for what flat really sounds like in terms of guitar tone. So believe me, I'm not whining about the TG at all. I just want to make it closer to a typical guitar power amp. I will definitely experiment with the EQ changes you've suggested, and other options I've come across as well.

Thank you again.

On this forum: "edit" goes away in a day. You can edit your post for about 24 hours, then it is locked to reduce time-warp confusion. I know other forums with perpetual re-editing, rarely someone will abuse that. Very reasonable, but a bit confusing if you have quick-edited here then find a reason to re-edit a day or more later.

Makes sense. I figured that was the case. Thanks for clarifying.

[Lieuwe]

I just finished building my first TGA, and it works, kinda. Only problem is that the volume is incredibly low (whisper-like). Does anybody have any idea where I went wrong? I can post pictures or anything if needed. Did all the checks in the PDF. Thanks in advance!

[waltk]

Does the volume level change at all when you turn the volume pot?

A picture might help.

[Lieuwe]

Does the volume level change at all when you turn the volume pot?

A picture might help.

The volume is only whisper-like at max-volume. Anything below that and it's inaudible.

I just found out that my camera can't really do macro pictures, so the ones up close are a bit out of focus. I hope they help. You can see there is a second pot, next to the volume, that isn't connected. This will be the tone knob, but first I want to get it to work without it. It has an internat speaker, 4 ohm, and a jack for external speaker next to the power jack. It has a switch for standby and led, and a switch for internal/external speaker. I really have no idea what I did wrong...

Oh, and the heatsink is normally attached to the bottom plate, so it isn't just dangling around in there, as it looks like now.

[waltk]

It's too bad your camera doesn't have macro focus - very difficult to see anything clearly in the photos.

It looks like your volume pot might be mis-wired.  On the PCB, the pads for the pot numbered 1-2-3 are connected to the yellow-red-orange wires. It looks like the red and orange wires are connected to the pot on terminals 1 and 2 (can't tell which is which from the photo).  The yellow wire should be on pin 1 (top terminal in the photo).

It's hard tell how things are connected from the photos.  As a general debugging technique, you should probably use your meter to check continuity for all the off-board wiring.  Is there continuity everywhere there is supposed to be?  Is there isolation everywhere else?  For example, with your standby switch off, make sure there is no continuity between the standby pads on the PCB.  With your speaker switch set to "internal" make sure the speaker pad on the PCB have continuity with the terminals on the speaker.  Make sure the speaker actually has some resistance between the terminal (about 3.2 ohms of DC resistance).

-Walt