Hello!
I would like to thank lineup and Zoran. Their suggestions led me to the following circuit:
The output power is 3.5W into 8 ohms:
Despite the lack of global negative coupling, THD is ~ 1%:
The frequency response extends up to 350kHz:
lineup: https://www.diyaudio.com/community/threads/sound-of-the-bipolar-transistors.402327/post-7437895
Zoran: https://www.diyaudio.com/community/threads/sound-of-the-bipolar-transistors.402327/post-7480371
I would like to thank lineup and Zoran. Their suggestions led me to the following circuit:
The output power is 3.5W into 8 ohms:
Despite the lack of global negative coupling, THD is ~ 1%:
The frequency response extends up to 350kHz:
lineup: https://www.diyaudio.com/community/threads/sound-of-the-bipolar-transistors.402327/post-7437895
Zoran: https://www.diyaudio.com/community/threads/sound-of-the-bipolar-transistors.402327/post-7480371
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Hi Walor,
The drift doesn't seem like it would matter much. I couldn't expect it to be stable without some form of DC feedback, and for guitars you don't need response to 20 Hz even. I'd leave it the way it is.
Looks like a great little practice amp.
-Chris
The drift doesn't seem like it would matter much. I couldn't expect it to be stable without some form of DC feedback, and for guitars you don't need response to 20 Hz even. I'd leave it the way it is.
Looks like a great little practice amp.
-Chris
The only thing I would be concerned about is getting rid of the heat with the surface mount outputs you're using. Beyond that, it seems to fit your use nicely. What's great is the simplicity of the circuit.
lol!
On a decent heat sink, you can't blow them at those power levels. You could easily use TO-220 devices with no worries. I thought your listed devices were surface mount.
On a decent heat sink, you can't blow them at those power levels. You could easily use TO-220 devices with no worries. I thought your listed devices were surface mount.
Ahh, nice.
Yes, depends on power dissipation (bias current).
Nelson Pass might like this. Simple and effective.
Yes, depends on power dissipation (bias current).
Nelson Pass might like this. Simple and effective.
Those look like TO-3Ps, which will be fine. Better heat transfer than TO-220’s
Its not too little for 19volts. It’s just physically in the wrong orientation. Run the fins vertically and it will cool way the hell off. Just flip it and you’ll see - it will become apparent in about 30 seconds.
Its not too little for 19volts. It’s just physically in the wrong orientation. Run the fins vertically and it will cool way the hell off. Just flip it and you’ll see - it will become apparent in about 30 seconds.
The transistors won't break, but I wouldn't want to touch the heatsink with my bare hand. I estimate the thermal resistance of this heatsink to be around 2K/W. The power dissipation of the amplifier is 19V*1.3A = 25W. Therefore, in addition to the ambient temperature we have 25W*2K/W = 50°C, i.e. a total of > 70°C. And actually after 10 minutes the heat sink noticeably starts to radiate heat, so I don't dare touch it.
70 C ambient with 12.5 watts dissipation per output device is nothing. Internal temperature rise will be another 15-20C. Just add theta JC (plus C-S) times Pdiss to what you physically measure.
70 C with 50 watts per device and I’d be worried. Then you’d be pushing the max junction temp.
Also why TO-220’s are horrible. Case to sink is stupid high, even if junction to case is low. TO-3P is better about this.
70 C with 50 watts per device and I’d be worried. Then you’d be pushing the max junction temp.
Also why TO-220’s are horrible. Case to sink is stupid high, even if junction to case is low. TO-3P is better about this.
Hi wg_ski,
Yes, you're right about thermal transfer. But for low power applications a TO-220 can be fine. His dissipation here it a bit high for a TO-220.
TO-3P cases are obviously much better. The TO-220 case outputs have been successfully used for 25 watt per channel receivers since forever. Sometimes higher, especially in cap amps.
Yes, you're right about thermal transfer. But for low power applications a TO-220 can be fine. His dissipation here it a bit high for a TO-220.
TO-3P cases are obviously much better. The TO-220 case outputs have been successfully used for 25 watt per channel receivers since forever. Sometimes higher, especially in cap amps.
Hi Walor,
That's with the fins vertical? 25 watts of dissipation is actually a lot. A small fan may help, a little air flow can make a huge difference.
That's with the fins vertical? 25 watts of dissipation is actually a lot. A small fan may help, a little air flow can make a huge difference.
20 watts is my cutoff point for a single TO-220, and that usually takes a BIG heat sink or forced air. For 5 or less watts no problem at all. 25 watts per channel class AB dissipate less than that (on average) per device.
The fins arent vertical, which is why it’s getting so hot.
The fins arent vertical, which is why it’s getting so hot.