Small Class-D Amplifiers

[mwelch55]

A while back, I ordered a couple for different small cheap Class-D amplifiers on eBay (similar to the attached photo).

Each one had the same problem.  I used one of my clean boost pedals to drive it.  When I strum the guitar, the note decay is "sputtery".  It sounds like an impedance mismatch, but I can't find any specs on any of them.  Does anyone know what the input impedance of these type of amps are?  Are they intended to take low-impedance signal or a higher impedance signal from an op-amp or similar device?

Has anyone had any experience with this?  What did you use as a preamp?

[smackoj]

I don't know about the input imp., I would think that a clean boost should drive that circuit alright. Sounds more like a failure of the power capacitors (The Surface Mount Devices use tiny parts so who knows what the little capacitors are made of?  But, I have built several of the discreet solid state amps where I buy the PCB(s) and source the parts myself. One of them was a kit that included the devices. But you have to be careful who you buy from. The best DIY amp PCBs out there are called Gain Clone aka Chipamp. Here some info on them:  http://liquidaudio.com.au/lm3886-chip-amp-project/    Or another way to have clean, usable power at literally pennies on the C-note is buying something like this:
  https://www.ebay.com/itm/VINTAGE-DUKANE-TRIUMPH-1A1520-MONO-PA-AMP-20-WATT-SOLID-STATE-USA-FREE-SHIPPING/202403766475?hash=item2f203460cb:g:ASsAAOSw0xRZmK6Q:rk:8:pf:0


 

[shooter]

the little capacitors

the cap between C21 and C1 looks like the bottom solder is kinda crappy.

monitor the 24vdc see if you can catch it glitching

"sputtery". 

does the signal sound like it cuts out?  Not sure if the cpu senses signal clipping and shuts down for 27mS

you can scope the in n out and see, standard TS rules apply 

[shooter]

I did some google surfing of TPA 3116 chip.  It does have a faultz line, here's one link;

http://www.icstation.com/tpa3116d2-2x50w-dual-channel-class-amplifier-50w50w-mini-digital-amplifier-board-module-m562-p-12548.html

[PRR]

> Does anyone know what the input impedance of these type of amps are?

Like we would know off the top of a head.

http://www.ti.com/lit/ds/symlink/tpa3118d2.pdf

It can vary.

Why are you thinking "impedance"? Class-D amps are notorious for sounding like crap when over-driven. There must be fixes; they are used in some new guitar amps. I'm not sure about naked random choice on eBay.

Indeed, some self-defend when clipped hard.

[mwelch55]

Thank you for the replies.

I have bought several of types of these and couldn't get any of them to work correctly.  I was just hoping someone had experience with these type of cheap amps.  Class-D seems too good to be true, so I was just trying it out (since they are so cheap).  I know there are successful implementations of Class-D, but so far I've been unsuccessful.

[pompeiisneaks]

Thank you for the replies.

I have bought several of types of these and couldn't get any of them to work correctly.  I was just hoping someone had experience with these type of cheap amps.  Class-D seems too good to be true, so I was just trying it out (since they are so cheap).  I know there are successful implementations of Class-D, but so far I've been unsuccessful.

There was a thread on the ampgarage about class d and many had gotten it working quite well, but I think they bought the sample units from the manufacturers of the chip and paid a pretty penny for them, not the cheap chinese stuff.  As has been mentioned, it may be they're designed for really light input and the protection circuit is cutting it off.  Try a pot in front of the input and dial it way down to start and slowly increas the input to see what level doesn't cut out etc.  Maybe then you can figure an input resistor to attenuate the current a bit and help it? 

~Phil

[1blueheron]

A while back, I ordered a couple for different small cheap Class-D amplifiers on eBay (similar to the attached photo).

Each one had the same problem.  I used one of my clean boost pedals to drive it.  When I strum the guitar, the note decay is "sputtery".  It sounds like an impedance mismatch, but I can't find any specs on any of them.  Does anyone know what the input impedance of these type of amps are?  Are they intended to take low-impedance signal or a higher impedance signal from an op-amp or similar device?

Has anyone had any experience with this?  What did you use as a preamp?

Just a shot in the dark here but what are you using as a power source for it?  I messed with some of those cheap amps for a while and found they acted as you described when the power supply was inadequate.  Might try a beefier power supply and a larger filtering cap? I found they ran better at the higher end of the voltage spectrum.  Most of them say 12-24V or some such.  What chip is the amp based on?