Discrete audio amplifier project PT11.3 output bias and thermal stability

[@paulpaulzadeh6172]

Very good channel, I have M.SC EE 35 years HW design, learn a lot by your channel John.

[@roblastem2905]

Hello! Great video, awesome channel. I am an EE, myself. I’ve been designing PCBs for over 10 years, mostly DC/DC SMPS, EMI MIL-SPEC power filters, microcontroller driven USB devices, video display driver boards, LI-Ion battery charge controllers, USB Audio DACs and so on. You mentioned laying out a PCB for this project with a BOM. I highly recommend using PADS or DipTrace software for board layout creation. I’ve used both everyday for years - they are quite capable of just about anything you can imagine. Cheers 🍻

[@1959Berre]

To fall asleep on the bench... been there, done that.

[@stephanc7192]

Great video and explanation. Really enjoying this series

[@hansgruber2861]

SNICKERS The trusted assistant rules

[@nathanjames5949]

Can't wait to order your kit!

[@JohnAudioTech]

I hope it gets that far!

[@twotone3070]

Good video as usual, thanks John.

[@ملكةزماني-ذ4ر]

😷 🙏🏻 Thank you

[@pedroneamps]

Great video! It’s the first I’ve found that shows the real problem and its solution. Do you think putting some thermal resistance between the compensation transistor and the heat dissipador would be another solution? In my point of view… if we have some overcompensating we need to put some “ Thermal distance” to the compensating element. What do you think of it? Thank you.

[@100amps]

Getting there. I like your cautious, methodical approach. I can't help but be concerned about using BD139/40 for drivers, only because they are so outdated and have a known slow (but undocumented) gain/bandwidth/speed. 2SC4793 and its partner are probably better, or MJE15030/31 if I have those numbers right.

[@JohnAudioTech]

I've not heard about that with the BD139/140. They have a nice flat gain response for the range of current they will be used to drive the outputs so they seemed like a good choice. If they can't keep up at 300ma or so, I'll have to find something else.

[@pliedtka]

MJE 15034/35 might be very good drive alternative 4A, with a bit higher hfe of 100 than 15030/31 devices. The BD139/140 is kind of old for the new 30MHz devices. But for John's design they might be fast enough - only 100W 4ohms, and I think they will do a second pair for 200W. MJE 15032/33 are common in many amps. The Sanken, Toshibas, Hitachi are faster, but 1.5-2A devices and may need base stoppers - they work great as long as someone doesn't ask them to drive 10 out pairs in 1000W 2ohm design. Helpers - they love things with wires, open books, keyboard and occasionally they play with the mouse. I think it's the warm environment they enjoy under the desk lamp. Nice to see the progress.

[@MsFireboy2]

Question John on your Transistor matching video does the frequency of 10 kHz make a real big difference?

[@peep39]

I'm familiar with biasing a push-pull stage, although everything I've done uses a pair of diodes between the bases to generate the 1.4v drop. In your design, how will you trim the actual bias voltage itself (to tune the idle output current and voltage)

[@anindyamitra5091]

Hello Mr. John, please help me out; I was building a tda2030a ic bridged amplifier circuit, but when I connected a speaker (an 8Ω, 60w woofer and a tweeter with crossover circuit) on the output, a high frequency hissing sound is present till the ics remain powdered,i.e. the 10,000uF capacitors remain charged. I am running the circuit with ±17v supply (12-0-12v 4A, transformer with rectifier). I think the hissing sound is too loud when the ics are idling, i.e. the volume turned all the way to zero, again the board (dot perfboard is well built, as there is no problem of 50-60Hz humming in the circuit. It doesn't as well have the 100-120Hz hum, because the power supply is well filtered. The hissing is less noticeable if the speaker (box) is connected to only any one output and the ground. I think you'd take a look at this matter, and I'd be very happy if you reply on this matter as I am really suffering from this particular hissing problem.

[@JohnAudioTech]

This sounds like the amplifier is oscillating. There could be several causes. Proper layout of the ground traces are important. Be sure the grounds carrying heavy current such as the return from the output are not flowing in the "small signal" grounds such as the input and feedback returns. There are a few videos on my channel about circuit layout.

[@anindyamitra5091]

Firstly, thank you for your attention in this matter. Secondly, as I have mentioned earlier that TDA2030A ics are in bridge configuration(exactly like this encrypted-tbn0.gstatic.com/images?q=tbn%3AANd9GcQVy_rjN_qPvuwHFplOhi04369PNLxFo5q8Z3_K3NsLH22ikD5i , it is an image of the circuit, you can open it) so there is no return path of the speaker to the ground. Are you talking about the return path of the 0.22uF capacitor with the 1Ω resistor in series and connected to the output to ground? Or is it due to using carbon resistors instead of metal film resistors? Or none of them? I am using star ground on the perfboard, where the input ground is far away from the power ground.

[@anindyamitra5091]

PROBLEM SOLVED: This amount of "hissing" is normal for the bridge configuration of TDA2030A, I didn't know about it and just exaggerated the amount (though the ic gets a bit hot while idling compared to STK4141, which doesn't have any of the problems) and it would depend on the cross over circuit, so I think adding a suitable inductor in series with the tweeter will reduce the problem. What do you think?

[@pliedtka]

@@anindyamitra5091 We listened to my DIY SB spkrs connected to friends Yamaha receiver that uses STK433-133 IC - wow was my word - clean, dynamic, good bass, really very surprised how well it coped with 4ohm 2way - we managed to clip it on some organ music but it was quite loud, much louder than many people listen to. A yes way better than some older Sony AVR thing I have for watching TV, that uses IC chip as input driver-VAS and pair of Darlington Sankens.

[@abdadkhbqefkehfkf]

Hey John. Kindly review the TDA7498 dual channel amplifier board. It has the best rating I've seen yet. Thank you.

[@christophermcdonald5578]

What do you think about doing a phono preamp after this project is complete

[@Asyss_Complex]

Hi, How do you protect your components from electrostatic discharge? How do you store your components?

[@1pcfred]

BJTs are not particularly sensitive to static. That is more of a FET problem. With improved manufacturing, materials and design ESD is mostly a problem of the past today anyways. I tend to blame susceptible components more than handling. If parts blow up toss them and use better parts. Problem solved!

[@shawnmc8159]

@johnaudiotech If I send you a broken Pyle amp would you be interested in determining why it failed?

[@JohnAudioTech]

Yes, it could possible end up as a video. Thanks! Please give me a heads up if you do decide to send it.

[@mikedrz]

Looks like I'm early... ah what do I do in the mean time? I'll like the video before watching it.

[@petesclark]

I like the video to let me know that I've seen it.

[@ملكةزماني-ذ4ر]

What is the minimum value of the DC biasing current in class A output stage? Explain you answer.

[@johnknightiii1351]

more please

[@petesclark]

I made the first comment!!!

[@CraftAero]

Your Mother must be very proud... well done !

[@petesclark]

@@CraftAero It doesn't happen very often.

[@MagruderSpoots]

Dammit.

[@madalinbetea9871]

hello Jon plase make a discrete 'hi-fi' clean audio amplifier with complementary BC transistors in final 12V/8 ohm i need for a hf reciever.

[@felixcat4346]

How fucking silly is it to make a pink resistor? Don't say "bias spreader", say "voltage divider".