Building the Tiny Giant amp

[StarGeezers]

 OK, Thanks Prut !!!    Now where is that Hum coming from ....  turned off ALL my appliances, lights, everything , even tried different guitars .... still Hums ... 

[bluesman1218]

OK, Thanks Prut !!!    Now where is that Hum coming from ....  turned off ALL my appliances, lights, everything , even tried different guitars .... still Hums ... 

As long as it's keeping the beat and in the right key, seems to me you saved having to buy a vocal harmonizer!

Sorry, had nothing useful to say but HAD to say something...... Now back to our regularly scheduled programming.

[phector2004]

I had a strange hum a while back with a chipamp. The second I'd touch the strings it'd be silent. Not light or appliance related. I have absolutely NO IDEA what made it go away, as it magically disappeared one day.

The only clue I have, as to its origin, is that I would unplug and move this amp often (always in the same room, same plug socket, though). Also, of note is that it still hasn't been boxed. Can't make any sense of it, nor do I care now, but it'd be good to know what caused it for future builds.

[space_ryerson]

> Although the synth has a volume control, the amount of noise

Raise the mix-resistor on the line/synth side to 33K, 100K, or more.

Ideal goal is for synth hiss-floor to come out the speaker similar to room noise-floor (different in the midnight lab or the happy-hour saloon, some judgement required), and for synth maximum output to come out at or slightly above the Giant's full ~~20 Watt limit.

It may not be possible to meet both goals in a quiet space. But in a paying-gig situation, when the max-output gain is right, the hiss is often a non-issue (below crowd noise).

This also improves gain in the preamped path, by shifting the mix from 50:50 to something like 80% preamp 20% line.

Thanks Paul, your description clears things up nicely. As a test, I tried a 100K pot in series with the 10K resistor to get a sense of noise floor vs. max-output. With the pot set at 60K (70K total resistance), the noise floor had dropped considerably (I had to shut down my computer to hear it), but the synths I tested were definitely loud enough. The amp still clipped with the synth volume going past 2/3rd's. I could probably increase the resistance a little more to make the maximum volume not as clipped. I'll likely use an 82k resistor.

[pruttelherrie]

Now where is that Hum coming from ....  turned off ALL my appliances, lights, everything , even tried different guitars .... still Hums ... 

Well, normally* ground is grounded to earth through the amp you're using (IEC receptacle). The Tiny Giant uses a laptop PSU which most probably isn't grounded/earthed. So if you use just the Tiny Giant, speaker, guitar, it won't be earthed until you touch the strings, ground of the plug, case (if grounded), etc.
As far as I know, earthed shouldn't be necessary but it won't hurt. Can somebody else with more knowledge chime in here?


* normally = 'standard' amp

[bluesman1218]

Well, normally* ground is grounded to earth through the amp you're using (IEC receptacle). The Tiny Giant uses a laptop PSU which most probably isn't grounded/earthed. So if you use just the Tiny Giant, speaker, guitar, it won't be earthed until you touch the strings, ground of the plug, case (if grounded), etc.
As far as I know, earthed shouldn't be necessary but it won't hurt. Can somebody else with more knowledge chime in here?

* normally = 'standard' amp

Makes sense and, if that is the case, just make sure to get a PSU with a grounded plug, they are out there. On the other hand, making sure the guitar is properly shielded and all connections are solid might help, too. It doesn't matter if there's no hum with other amps. You figure what the problem is when and where it occurs.

[p_wats]

Posted more pics of mine, along with the homemade cab I'm using.

http://dogisblue.com/another-homemade-amp-tiny-happy-giant/

Still might drill in a 9v out jack for powering pedals though...

[Taylor]

It should be no problem to add a regulated voltage output for your pedals - it was one of the things I suggested that people could do, actually. Keep in mind though that it will be closer to 12v than 9v, so make sure your pedals can handle that and will sound normal at that voltage.

[StarGeezers]

You guys are spot on ... my IBM PS only has 2 wires ... no ground .... grrrrrrr!!!!     Back to Flea Bay ... 

[StarGeezers]

 Had to do some searching for a 3 wire AC adapter...  found this one ... http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=250694483500#ht_3489wt_922   Ordered it .... hopefully that will solve the Hum ...   I Like this amp too much to be bothered by any little hum problems ... 

[space_ryerson]

FWIW, I'm using a IBM PS (2 prong), and I don't have any hum to speak of.

[bluesman1218]

I am pumped! Looked in my garage and found my old Laptop PSU - 16vdc, 4 amps. I'm gonna build it, gotta go check parts!

[StarGeezers]

  Taylor , consulted one of my Mentors about the TG Hum ... here was his reply ... Just FYI...  QUOTE: " Just to ask do you have the input jack set up to short the input with no cable plugged in? If so do you get hum when you turn the volume up with no cable? The other question would be does the hum go away with the volume turned down. What I am thinking is maybe the hum is power supply noise in the box that gets canceled out by out of phase noise going into the box. That would explain why the humbuckers or running two single coil pickups would have higher noise, less noise going in. The op amp is set up with a resistor divider across the power supply so any noise from the supply will be coupled into the input of the op amp. But now that I think of it with the input shorted the 100nF cap will be tied to ground and filter any noise from the supply, so to see if it is supply noise the input will need to be open. If it is noise getting through the LM338 a 10uf from the adjust pin to ground will improve the ripple rejection of the regulator.

A couple of quick ideas the 10uf connected to the 100k on the feedback of the op amp could be lowered to 22nf to 47nf to reduce 60Hz gain. Also if you change the 1Meg ohm resistor at the op amp + terminal to ground to 2.2 Meg ohm and connect the capacitor hooked to the 100k on the feedback of the op amp to the ground of the input jack you will have differential rejection of noise common on the inputs of the op amp. This will reduce the op amp gain to +2 instead of +3." 


Taylor you have any comments  about that  ??   Thought I'd consult you before making any changes ... 

[Taylor]

He's right about the 10uf cap connected to the 100k. That will be about 3db down at around 60hz. I wouldn't do this personally, since I am a bass player, but for guitar, your lowest fundamental is 82hz so it's a good idea.

I'm not a power supply whiz, but it seems unlikely to me that 60hz hum would be coming from the power supply, since the supply is a SMPS. Hum is obviously an issue with linear supplies, but I thought, but could be wrong, that in a switching supply, the power is going to be heavily filtered and chopped to the point that the mains frequency is completely gone. Hopefully one of the more learned gurus will chime in.

Did you ever try a 3-prong supply? I am using a grounded supply and I have  never had any hum, even with the first perf board prototypes that weren't in metal enclosures.

[p_wats]

I've tried mine (3-prong) supply all over lately and I get/don't get hum depending on where I am (crappy electrical in my apartment=hum with just about any audio equipment...).

[StarGeezers]

Extremely Good news !!!    The 3 prong PS arrived last evening ..so  this morning , plugged it in and NO HUM !!!     It was the IBM 2 prong PS  all along .... Grrrrrrr!!!!!! 
Guys,   I really appreciate all the help with this matter!!!!!!!!   ...  All Good now , and the TG sounds Great !!!   

Big THANKS !!!!   

[Taylor]

  Glad it all got sorted.

[StarGeezers]

  Me too ...     

[StarGeezers]

 Taylor , if you're able , please join us here  http://www.wattkins.com/node/17514  for more TG discussion ...

[StarGeezers]

  Guys , got my TG all checked out , sounds Great , and it's getting double duty , not only as my Studio/practice amp , but I'm also throwing it in the gig bag as a "spare" amp ...  a back up for the gig tonight  , just in case ...  I Love that idea !!!    
 Now I just need to make another one so I can leave it there...     Er, Taylor , you got any kits left