I build it, and it sounds amazing. PG and SG should be connected. It's the same Ground point. With two LME49710 it has zero noise at max volume with no signal. Thank you for schematic! UPD: I replaced 47uF caps to 100uF. Not sure, but feels like sounds better.
So all PG and SG are connected to the same ground? is the 0V.? I have a problem with the ground and the PNP transistor gets hot quickly so I have to disconnect the power.
Just finished my version of this circuit last night. It works for sinewave on 30 Ohm load - now I have to hook up earphones and take a listen. Running on two 9v batteries with NE5532 front end. Thanks, John, for the simple circuit.
Great as always! My favourite channel, I wish I had the means to try out what you create. Did you also try it without the feedback? Some say amps sound better without, this would be a great test for that.
I didn't try that. With the output stage not in the global loop, the output impedance will be higher which could affect the sound. Adding a series resistor to the output can also affect the sound with some phones.
Great video John. Im just starting out messing about with op amp circuits and was wondering why you used a 2.2uF cap on the input as this seems high to me due to it passing frequencies as low as 7Hz. (im sure you have a good reason for it). I have yet to build it but, it will the next one into my breadboard later this week and Im looking forward to trying to get it to work for my 250 ohm Cans. Cheers.
John, this is a winning amplifier design. Nice work. What's a good source for some genuine BD139 and BD140 transistors? What diodes did you use on this John? Thanks!
Hey John. I hope you read this comment in this 6-year-old post. I came across your channel recently and been enjoying watching your videos a lot. Thanks for sharing your knowledge. I'm interested in building this headphone amplifier to power my old Beyerdynamic DT331 (40 ohm, 86dB/mW) at no louder than 80dB (to not make my tinnitus worse lol). DC power would be from a 19V 1.5A SMPS adapter I have. Assuming DT331 dips to 20 ohms and its sensitivity measured at 1kHz (I couldn't find an impedance graph or detailed specs), I estimate I would need 7mA (both channels) or 28mA (for +6dB headroom at low frequencies). Biasing the transistors would require 4mA, and the NE5532 idle draw is 8mA. Thus my total estimated peak current requirement equals 40mA. I'm thinking of using a TLE2426 IC to split the rail. Would you agree with my current estimation and do you think TLE2426 would work in this case (or too close to its limit)? Thanks. Bill
Hi Bill, Thanks for watching the channel. You can make a split supply using resistors and capacitors as I did in my last video. I would recommend larger capacitors, though. 1000uf would be sufficient.
Hello! Very good video! I was looking for a headphone amplifier when I accidentally bought a behringer mx400, which is a mixer instead of a headphone amplifier, so it means four imputs instead of four outputs.. The look of both, this one and the ha400, is almost the same, I was wondering if I could turn it into a headphone amplifier easily, both has 4 channels with volume pots and the AC input is the same... Thanks!!! and just subscribed to your channel! :)
Great video, John! Do you think this design would work as a booster amp for MP3 player/smartphone ->> auto AUX IN? I find player output direct to aux in requires full volume from player and the car audio system.
You don't need a power stage. Just configure any audio opamp you have for voltage gain. If you don't have a bag full of opamps, maybe consider getting something like rc/njm4580 or ne5532. The former is more versatile because you can sometimes get away with running it off 5V and can do higher current, the latter is more established in projects you'll find around the net. Either will cost you a dollar for a bag full.
Hi John if I want to drive 32 ohm headphones (half impedance as yours) what change have to make to the circuit ? or use It just live the values as you stated un this video ? If you can take a minute to unswer this question I´ll order the parts to build one for myselt (probably put an output capacitor just in case one off the output transistors fail and pass DC to my headphones (cost me a little fortune), you know there are knock t off ransistors offs). Thanks in advance
Did you think about thermal stability when driving lower impedance loads? You don't have thermal contact between the 1N4148's and output drivers as far as I can see. I guess those 10 ohm emitter resistors are going to prevent destructive currents, but I wonder if the bias current is prone to wander around without some stabilization?
In a finished amp, I'd consider mounting the diodes along with the transistors on a small heatsink. All of that is not practical on this show and tell breadboard amp. The 10 ohm resistors do help keep the bias stable. It's been awhile but I recall the transistors barely got warm even when testing.I'd stress test it before deciding on the final design.
Would you be able to design one of these for two isolated stereo inputs to a single output? Would be *incredibly* useful for we nerdy gamers (eg; TV audio out from consoles and PC audio combined and amplified, to be fed into good high-impedance headphones)
Just found ur u tube channel 2 days ago and im. Glad i did i love seeing this stuff done i just got a pionner 1021-k reciver and learned out after i bought it that they had a flaw in them from the factory for the dsp chip what happens is it will get hot then loose conection with the board and heating them up to reball them is only a temp fix mines working fine but i was wondering what u would do to fix that problem or is there anyway i could stop it before it happens to mine i was thinking of putting a heatsink on the chip with a fan to blow on it other thing i noticed is heatsink pionner put in there gets really hot when u use the reciver so i was thinking of putting a fan on it aswell hope to hear back from u john
Seems like a very simple but impressive design, I have a question though. When do you know when to use polarized (electrolytic) vs. non-polarized (film or poly) caps?
I try to use film caps where feasible. Above a certain value they start getting large and expensive, so I use electrolytic. Contrary to popular belief, electrolytics won't harm the sound quality *IF* they are used properly.
I made the "Power amp" version of this. With darlingtons. 8W 8Ohm, 6Amps, short circuit proof etc :D 10Hz-50 kHz linear. Simple but perfect circuit. Of course the soul of it the perfect IC. If you dont need darlingtons, BD-s are much better for High frequencies.
Hey! Nice one there. I was just wondering if you could explain what are the characteristics of well designed PCBs as far as audio amplifiers are concerned. Thanks.
Most important is the grounding layout. It is important to arrange the ground traces so that high currents are not flowing in the small signal grounds which will cause higher distortion and/or instability.
very clean hp amp indeed.. i have a question, if i want it to be battery operated and compact, can i use a buck converter (probably 9v step up to 18v) and use a rail splitter capacitor? will it sound as clean as using 2 9v battery?
As long as the power supply is clean, it will work. two 9v batteries will work but the current draw is around 25ma so run time will be limited to a few hours. If your phones are in the 32 to 64 ohm range, you could run the amp at +/- 4.5 volts but you might need to adjust the biasing resistors if bias drops too low.
Hi John.. I am pleased to say and want to thank you for this video. I wanted to DIY a headphone amp and I have implemented your schematic and made a headphone amp with some modifications. Also made schematic and PCB design and the PCBs are being sent to me as I am writing this. The sound quality of this amp is astoundingly good. I would like to thank you and share with you my project. Please let me know how I can do so.
Dear john, I build this amp for someone about 2 years ago, he had hi end types of headphones, recently i dont know what went wrong in the circuitry, but my friend lost left side of his headphones. I need to request that it would be a good idea to hv a speaker protection based on upc1237h in this final diagram. Im not good at working with relays john. That's why im requesting.
70 ohms is low for a headphone I would have thought. Most headphone outputs would expect 600 ohms... unless im wrong. But the point is, in which case, its actually over loading
So I built this kind of headphone amp but its got bugs. I see how you put power to wrong pin, then I looked up internet data pin out to double check if I did that and I get a "wrong" pinout and go switch pins and ... well not good. LOL.
Hello John. Can you give any tips on how to figure out bias resistor values. I'm building output stage on Darlington BJT's and this thing is not wanting to cooperate)
JohnAudioTech I need bias resistor values for diode biasing approach (like in this video). I'm using 2T827A (n-p-n) and 2T825A (p-n-p) transistors (hfe=750-18000, Ic=20 Amp, Uce=100 V, Ueb=5 V).
I don't recommend biasing a power amp this way. Use a current source otherwise output swing will suffer under load. In a darlington config, there are 4 base to emitter diode drops to deal with, so you need 4 diodes. Better to use a transistor, IMO.
Thank you very much! I discovered your channel a few weeks ago and I have to say that your videos are very helpful to me. Thank you again, and sorry for my English :)
There's little reason not to use class a for a low powered headphone amp. Simpler and extremely low distortion, very little to gain from class d. Perhaps a bit more volume if you are limited to a voltage though, without converting the power. Without biasing, a class D can theoretically swing closer to the rail of the power provided.
john I wish you build a circuit board and schematic to show us all how to build so we can download .im tierd of coking my brain with wifi headphones if you have the time it would be great I realy like clean sound like class a
Where I'm supposed to plug the ground of my headphones jack? On the 0v rail? Or the - 9? Because in reality the 0v rail is at 9v and the - 9v is at 0v...as the +9v is at +18v...i dont get it :( My transformer is +20v 0v -20v so if I take the ground of my headphones jack and connect it to the 0v rail, will I send 20v straight to my cellphone?
Hi John, I tried your circuit but I couldn't get it to work :o( The only way I could get it to work was to have the Opamp with its own local feedback then take the amplified signal into the push pull network. If I tried your way of including a global feedback, then the output was more of a square wave! Love to know how other people have got on with this circuit.
Strange. You should get the same signal level with the output in the feedback loop. If the opamp and OP stage work independently (as tested in the video) they should work together. Mind your grounding layout (no output return or supply currents should flow in the small signal grounds) or the amp will misbehave for sure.
Thanks for responding John, I will revisit this with two separate bread-boards to help keep the signal and power earths separate. John if its not too much trouble, could you please clarify if you used a single power supply for your final circuit or did you use a split rail power supply? ( I used a single power supply of +18vDC ).
Thanks for responding John, I will revisit this with two separate bread-boards to help keep the signal and power earths separate. John if its not too much trouble, could you please clarify if you used a single power supply for your final circuit or did you use a split rail power supply? ( I used a single power supply of +18vDC ).
you can make a 10x amp and that way any distortion will be 10x , bringing you from 0,2% minimum detection to 0,02 witch is about as good as you really need , you probably know this . one good set of op amps will do that powered by batteries .
So you meant more current output. Oomph it to the headphone. 20 ohm output impedance would be luxurious on looking at your circuit though, you'll drive a speaker at 16 ohms to 1W no problem with that 😂
@@JohnAudioTech Thank you for your answer sir..But where do you control the bias current trough BD139 and BD140? Otherwise there will be cut-off's in the signal? I mean how we determine how much current flows trough those transistors to avoid cutoff's?
The schematic that you are showing does not match what is on the breadboard.. On the breadboard you have an op amp, audio driver, and output transistors'
