The connections inside the wire nuts are soldered, with the wire nuts used as insulation.
I am using the grounding jumper between the two output terminals for testing. As in the schematic, I will run both leads to the amp section and the power ground star there. Is that what you mean by PSU ground, or am I missing a connection, completely?
The fuse is in a panel mount. It's the closest of the three dark thingies.
Insulating the AC connections sounds like a good idea. Those disconnects will come in handy, now. I can sleeve the connections in shrink wrap.
Thanks for the feedback, everyone. It really helps take the anxiety out of the experience.
--Mike
I am using the grounding jumper between the two output terminals for testing. As in the schematic, I will run both leads to the amp section and the power ground star there. Is that what you mean by PSU ground, or am I missing a connection, completely?
The fuse is in a panel mount. It's the closest of the three dark thingies.
Insulating the AC connections sounds like a good idea. Those disconnects will come in handy, now. I can sleeve the connections in shrink wrap.
Thanks for the feedback, everyone. It really helps take the anxiety out of the experience.
--Mike
A little more progress:
I've mounted everything on the other half of a RS 279-150 board that I had left over after my first learning project, the Tangent variation of the CM headphone amplifier. I realized after the fact that there is no need for me be building so small on my prototype effort.
That white .22 Ohm resistor is a little clumsy...
I've tested power at [the holes for] the power pins to the chip at 24.7 VDC, but haven't powered up with the chip in place. I need to solder another wire or two, and make the binding post and input RCA connections.
Any words of wisdom before I finish this off, and hook up an old speaker for testing?
Thanks,
--Mike
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An externally hosted image should be here but it was not working when we last tested it.
I've mounted everything on the other half of a RS 279-150 board that I had left over after my first learning project, the Tangent variation of the CM headphone amplifier. I realized after the fact that there is no need for me be building so small on my prototype effort.
That white .22 Ohm resistor is a little clumsy...
I've tested power at [the holes for] the power pins to the chip at 24.7 VDC, but haven't powered up with the chip in place. I need to solder another wire or two, and make the binding post and input RCA connections.
Any words of wisdom before I finish this off, and hook up an old speaker for testing?
Thanks,
--Mike
Llamas said:
I would get rid of that resistor. Next time you built a circuit try to place caps closer to the chip and resistors where convenient. Not everything has to be on that board and input resistor can hang as well to RCA socket and if you insist on a big 0.22 ohm output resistor it can be mounted directly to the binding post.
Banned
Joined 2002
The great thing is, I didn't have to ask that "how big of a heatsink question do I need?" question; I tricked you guys into telling me. Well, at least that it's too small. If I could figure out how to tap a CPU heatsink, I'd be in business. Until then, I'll play at low volume, for short periods, purely to test.
I'll be driving 4 Ohm speakers, at least at first. That's why I used an 18V toroid instead of a larger one. I should be within spec on voltage, but it sounds like I need to find a bigger piece of metal to heat up.
I've pulled that unsightly resistor. When I make the second channel, I'll try locating the caps closer to the chip in the layout. How important is the physical proximity? Presently the power caps are about an inch from the pins.
Thanks for the feedback. I'm going to try to get this one operational before I go to bed, tonight.
--Mike
I'll be driving 4 Ohm speakers, at least at first. That's why I used an 18V toroid instead of a larger one. I should be within spec on voltage, but it sounds like I need to find a bigger piece of metal to heat up.
I've pulled that unsightly resistor. When I make the second channel, I'll try locating the caps closer to the chip in the layout. How important is the physical proximity? Presently the power caps are about an inch from the pins.
Thanks for the feedback. I'm going to try to get this one operational before I go to bed, tonight.
--Mike
I don't know how important physical proximity of PS caps really is, but if I have a choice to place coupling resistor and cap in that space or PS electrolytics, I would go for the latter. The feedback resistor should be also very close (directly on pins prefferably). I made some experiments and it seems like it creates a difference.
Ron Clarke posted 3 reasons for distortion in another thread...leading me to...
It is bad if one of the secondaries of the transformer is showing 6V, and the other 18V?
I pulled the transformer, and placed #2 in it's place. Tested its outputs as even, and powered on. Silence.
Then I started the source. Silence.
Then I turned up the 100K pot. Music!
Bad transformer? I am more willing to believe in my own fallibility. I had a bad connection with one of the quick connects, somewhere, I think. I stripped them off, and hooked up the "bad" transformer again. Now both channels are even.
Now to find a tap kit to attach bigger heat sinks...
--Mike
It is bad if one of the secondaries of the transformer is showing 6V, and the other 18V?
I pulled the transformer, and placed #2 in it's place. Tested its outputs as even, and powered on. Silence.
Then I started the source. Silence.
Then I turned up the 100K pot. Music!
Bad transformer? I am more willing to believe in my own fallibility. I had a bad connection with one of the quick connects, somewhere, I think. I stripped them off, and hooked up the "bad" transformer again. Now both channels are even.
Now to find a tap kit to attach bigger heat sinks...
--Mike
Really, Ron, you can't let your dental health interfere with my amplifier building! Remember your priorities! Heh... It was a post of yours that helped me fix the problem, so you did, in fact, lead me to the solution.
Next item...what's with the long arm on these Radio Shack potentiometers? I'm going to have to mount the pot away from the enclosure panel to get the knob to set flush...
I'm going to put these in wood enclosures. Any suggestions on shielding? I've seen general references to copper foil, but no specifics.
And again, earth ground? My transformers don't have a lead (like I've seen in some diagrams) for earth ground, and I don't have a conductive chassis. Bind it to common ground, or let things float?
Thanks again for the help!
--Mike
Next item...what's with the long arm on these Radio Shack potentiometers? I'm going to have to mount the pot away from the enclosure panel to get the knob to set flush...
I'm going to put these in wood enclosures. Any suggestions on shielding? I've seen general references to copper foil, but no specifics.
And again, earth ground? My transformers don't have a lead (like I've seen in some diagrams) for earth ground, and I don't have a conductive chassis. Bind it to common ground, or let things float?
Thanks again for the help!
--Mike
For RF sheilding i use copper sheeting from the Hobby Lobby or you can use alum foil.
I have gotten away from conventional pots and use motorized 20K pots (shunted to ground with a 10k in the signal path), with the motorized pots the pot can be right close to the chip and with 2 momentary buttons there is no volume control knob.Press the red button at the top , its gets louder press the black button at the bottom the volume goes down.
All i use is wooden cabs as i am an old speaker designer and builder and i find wood is easier to work with and makes a good looking cab.
ron
I have gotten away from conventional pots and use motorized 20K pots (shunted to ground with a 10k in the signal path), with the motorized pots the pot can be right close to the chip and with 2 momentary buttons there is no volume control knob.Press the red button at the top , its gets louder press the black button at the bottom the volume goes down.
All i use is wooden cabs as i am an old speaker designer and builder and i find wood is easier to work with and makes a good looking cab.
ron
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