DIY Audio Projects Forum

Thanks!

I finally got around to getting a 12V UPS Battery, but I am still having problems with clipping at relatively low input volume. I also just rebuilt the entire amp, just in case I made a mistake, but to no avail. I also noticed, while running some tests, that the signal is being inverted. Should this be happening?

Is the clipping audible?

The amp is very simple and has virtually no noise cancellation. The best way to avoid this would be to use a differential "long tail" pair on the input or something similar with two tubes. I designed the amp to be very simple, unfortunately transients will be amplified along with the music signal.

Since the signal is derived from the the anode of the tube it will be amplified and 180 degrees out of phase with the input. If you scope the cathode of the tube you will see the signal at unity gain, and in phase. There are some other amps out there "like the yaquin" that use a tube as a "buffer". In this amp I use the mosfet as the buffer.

Hope this makes sense.

Rogers

After a few days of steady use my amp has seemingly suddenly started clipping and putting out static like crazy.

Does anybody have any ideas about what could be causing it?

Maybe I let something get too hot? Maybe I broke my tube? Any thing?

UPDATE: Never mind. My wife had iTunes' volume maxed out and her laptop volume maxed out *and* the amp maxed out. Once I had her turn down iTunes and her laptop a bit everything was better

I am wondering about something, this build doesn't use any kind of heatsinks. In an early stage i mounted a heatsink for both the mosfet's and the LM317 regultors, because i think it was necessary.

My argumentation for doing so, was to avoid the mos-fet's selfregulation, not constantly trying to cool down. Maybe i'm wrong, but i think heatsinks are needed. I don't know about the sound getting better with or without heatsinks.

The build of mine is a 10 Ah batteryversion mounted in an old PS cabinet, with a charger. At the frontpanel i've got a switch, so it can be charged when necessary, there's also a LED to show the condition charging / driving. It has been running for over one year now and i still like the hybridsound very much ...again thanks to Mr. Gomez for both the build and this supportthread.

If anyone are interested, i will add some pictures of my build.

I used, at first, a small heatsink of the type you might find on an older VGA card - just a square, with some stubby little bumps (hardly even fins). This got pretty hot, so I stepped up with a heatsink of the same size, but now with some definite fins. It's pretty warm, but stable - i.e. it reaches a temperature and stops rising.

This is the older heatsink; the new one (no photo yet) is just a little more aggressive than this one:

http://mikeyancey.com/photo/One-Tube%20Amp/test_run.jpg

As you can see, all 4 ICs are underneath that square:

http://mikeyancey.com/photo/One-Tube%20 ... e_prep.jpg

I recommend it simply because it's going to (1) stabilize the temperature of the ICs (and possibly audio quality), (2) it'll reduce the likelihood of them going into thermal runaway, and (3) it's just not that pleasant to have something that sizzling hot where a finger can get to it...

Mike Y

Exactly, temp. stability and avoidance of thermal runaway, i couldn't have said it better.

The circuit does remain stable with a 12V supply provided that the devices are exposed to outside air, but they do get hot. However, if you prefer to box up the amp or run it off higher voltage/current some level of heat sinking will most likely be required. Small flat heatsinks like those that can be salvaged from computer power supplies are often sufficient.
Cheers

_________________
[ DIY Mains AC Power Cable Cord ] - [ Gobo LM1875 Amp Kit ] - [ Tang Band D4-1 Horn Speaker Kit ] - [ Monoblock Push-Pull KT88 Tube Amp Kit ]

John and Mike,

I agree that heatsinks are prudent for the amp as it will contribute to the mosfets running in a more stable "on-resistance" area of the curve.

When I designed the PCB and tutorial, I took this into consideration, but decided to omit the heatsinks for three reasons.

* The amplifier is designed for brand new builders, some of whom have very limited electronics experience. As you know the tabs of the Mosfets are at B+ and the tabs of the regulators are at a +vdc. I wanted to avoid the chance of someone accidentally shorting the tabs out to a heatsink, or ground. Instant smoke on first power up is very discouraging.

* I ran some calculations and decided to run the class A current at .125 @ 12v. This will dissipate about 1.5w max, which is barely under the max dissipation to ambiant air (~1.6w +/- 20%). The mosfet itself drops about 6v @.125A so about 750mW
After a good month with the unit on I have not experienced any thermal runaway.

* The distance between the semiconductors did not leave enough space for off-the-shelf heatsinks.

Now for those who have successfully built a working unit, and desire to lengthen the life of their semiconductors, heatsinking will be a great upgrade to the amp. I recommend that each TO-22 package be heatsinked individually, as this will avoid the usage of insulators and nylon washers. I have seen some folks use coins, washers, and pretty much any metal as heatsinks. For this small amount any clip-on type or small piece of tin or aluminum would do the job. Just make sure that there are no shorts to ground or other components before power up. You can see that I fashioned some heatsinks on my internal amp because it runs B+ at 18V. The large heatsink is a 7812 for heaters (now that little guy can get hot, so I sinked to the chassis as well)



Thanks for the input

Rogers

Really awesome project! Simple and something that won't kill me for now
Though I can't seem to get mine to work. I've tried different power supplies so I'm fairly certain that is not the issue. The issue I'm having is instead of sweet, sweet music coming out my cans (cheapo earbuds for now) I get buzzing. Not even distorted sound, just incessant buzzing. Buzzing is the same on both channels.

I've tried a walwart and the PS i made for it (which makes far better sounding buzzing, but not music ), and i've checked over the wiring a bazillion times. I've made sure the MOSFET and other things that shouldn't be aren't shorted to ground.
I just can't figure it out.

I'm using an MP3 player as a source and it works (hooked up the earbuds straight to it and i hear the music fine) and it hasn't exploded, so it doesn't look to be shorted anywhere. Also went with 4k7 resistors for bias instead of pots.

For all i know it could be the wiring (i've made mistakes before... lots of mistakes ) but it would help to know what to look for given the symptoms.

Thanks in advance!