Terry, can you put 8.2 ohm or 4.7 ohm 5W resistor from output to ground with no input signal then measure voltage. Connect bulb in series with transformer just in case to save mosfet.
I wanted to stay with laterals if possible so it wouldn't need thermal compensation.I had this sort of working with the TL071 but not well. I made the new layout so I could try dual opamps because I have a variety of those. It won't help if I can't get it working.
OK I connected a load an that brought the offset down some but I have .800mA draw on the + rail and 13mA on the - rail so something is still not right. I am using a lightbulb so I can't get the rails up high enough for the zeners to fully turn on but I have +8V on the output of the IC so the SK1058 is on hard. Both channels are doing the same thing so it must be my layout and I'm just missing something.
I found it issue. I had installed 2R2 instead of 2k2 in R15. Now with the correct value the offset is gone. The amp works but will need some changes in the compensation somewhere because the 10khz square waves are almost pointed. I'll post up some pictures soon and maybe Mile can make some recommendations. One other thing of note is that the amp draws a lot of current once a signal is introduced. I have the bias set at 70mA per rail and for only 7vac output the current raises to 450mA.
I have been listening to it for about a half hour. Sounds fine. Gain is a little low but would be fine with a preamp. Here are some scope shots.
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Wow,
Your efforts finally paid off! and wow again. great going. Must be the simplest amplifier on earth with only 2 transistos and an op-amp.
reg
prasi
I don't know. I have the values installed that are in the schematic I posted with my layout above.
Thanks, It is pretty simple and a good layout man could make it very small. I am still learning and just wanted to get it working and have a pair fit on a 4" x 6" board so there is a lot of wasted space on mine. Looking forward to improving it as suggestions come along. All part of the fun of this hobby. As long as I am still learning it will remain fun. 
Blessings, Terry
Blessings, Terry
Hey Folks,
a long time i've been a silent reader, especially in this thread. I just wanted to tell you that i'm actually working on an Apex A23. After Rod Elliots P3A, this will be my second audio amplifier project. I've just registered here espacially to thank you guys for publishing your great ideas and work. Even if there are already Layouts available, i'd like to make my own to give it a personal touch.
Thanks guys, please don't stop making great DIY work
a long time i've been a silent reader, especially in this thread. I just wanted to tell you that i'm actually working on an Apex A23. After Rod Elliots P3A, this will be my second audio amplifier project. I've just registered here espacially to thank you guys for publishing your great ideas and work. Even if there are already Layouts available, i'd like to make my own to give it a personal touch
.Thanks guys, please don't stop making great DIY work
An externally hosted image should be here but it was not working when we last tested it.
Hey Folks,
a long time i've been a silent reader, especially in this thread. I just wanted to tell you that i'm actually working on an Apex A23. After Rod Elliots P3A, this will be my second audio amplifier project. I've just registered here espacially to thank you guys for publishing your great ideas and work. Even if there are already Layouts available, i'd like to make my own to give it a personal touch
Thanks guys, please don't stop making great DIY work
A23 is one of the best in this thread
https://www.youtube.com/watch?v=4I6khZgsI4o
Regards
Gain can be increased by adding 10 ohm to 47 ohm resistor in series with R19, increasing value will increase gain. At 56 ohm amp will be clipping with 2V input.
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Thanks, I try that. I listened to it all day today. Really very pleasant. I can't hear the high roll-off. Cymbals and hi-hat sound very natural. Electric guitar is especially nice. I listened to a lot of Larry Carlton. Beautiful.
I'm thinking that I probably should have added some caps to the rails but I sounds clear and dead quiet. Speaking of that, I had reported earlier that when testing one of the protection boards that I thought I heard a ground hum but I hooked one of them up to this amp and still dead quiet so I was mistaken.
Now a question for Mile or anyone who might know. The "Pro" circuit on the protection circuit, hooks to the emitter of the output transistor or in the case of this amp the drain. My question is does it work on an amp that doesn't have an emitter resistor like this amp?
Thanks, Terry
