I would think that you know this trick, but, for those who do not... For two transistors that you want to be equivalently thermally influenced (example: matched pairs)... when you layout the board, position them face to face, with their faces actually (just) touching... Before you populate the board, put thermal paste on the faces of the transistors. Populate the transistors on the board, square their faces and solder them into place. Wrap their heads (together) with Kapton tape to keep their faces in contact. Thermal movement can occur, otherwise. Only wrap around the side of their heads, to allow heat to escape off of their tops. Make a note to the Boardhouse instructing them to proceed with manufacturing the boards with the transistors paired as placed. Your board software may complain that the transistors' courtyards have been violated, but this may be ignored. Just make sure none of the pads are shorted. This is an old trick... Not mine, of course.
Yes, I'll be showing the final version of the PCBs when I have made the SMD version of this amplifier. My soldering job was a bit crummy and I didn't want to get in too close to that with the camera haha, so I'd better get JLCPCB to assemble all the surface mount parts for the updated version! Hopefully next month :)
@@PhilsLab No worries, under no circumstances would I have started to critique the soldering job. Good work on the design though. Did you use any spice program to simulate the circuit or portions of it ?
If you want, you could make guitar pedals too. I have to say I find the content excellent, clearly explained and no extra fluff. This is some great engineering learning material.
Am I the only one here who has no idea what the hell is being discussed? This is actually the 4th or 5th video that I have watched.... it started out as an autoplay from some other video about how cell phone storage works (I have no idea how I wound up down that very unfamiliar rabbit hole to begin with) and I stayed on the first few bc I liked the sound of your voice. lol And then I saw your guitar videos..... 😍 So, now I am just stuck here drooling listening to you talk about things that I am so clueless about.... kicad, FIR, PID, ratios of r15 and p1.... D1, D2.....and although this is greek to me, I could listen to you talk about nerdy shit all day. But, I also noticed that you weren't wearing a wedding band, so I am just holding out hope.
Really nice video! Just had an exam on power amplifiers this year and I'd like to point one little thing: if you were to use heatsinks for those power transistors, you'd ideally join the transistor responsible for the Vbe bias too, as the heat difference will affect the transistors beta value (or hfe), shifting the bias value. By clamping all three transformers to the same heatsink, the temperature of all three transistors would be the same, so the beta value would change at the same rate, hence avoiding the bias shift.
Thank you very much! Hope your exam went well as well. This is true for a typical Darlington configuration, however things are different for the Sziklai pair. The output stage should not be directly coupled thermally to the Vbe multiplier (see sound-au.com/amp_design.htm#s31).
Hi Phil, That’s awesome - I’m a HUGE fan of Rod’s (and sound-au.com), so thank you both for providing such great content there. If you do get the chance, I would really appreciate it if you could say thank you to Rod as well. I’m pretty sure I have read every article (no joke) on the site!
@Phil Allison That's great, thank you very much for that, Phil. That's awesome, you must've seen quite a number of things during your years working on all that audio equipment (only something I can hope to say about myself one day!). Did you end up designing some of your own tube guitar amps as well then? Yes, I finished university last year but to be honest most of my engineering experience I seemed to have gathered from just going out and 'making stuff' in my spare time.. Thanks again for your message. Phil
Tisk tisk! Current mirror doesn't current source make! Variation in supply voltage will vary current mirror current, and this in turn will end up in the stages fed by the mirror! Oh and those transistor on the output will need a heatsink, 10W at class B will result in at least ~4W of power dissipated.
Another great video Phil. Thank you. Can we request a guitar solo? Lol? Something without distortion so we can hear this great amplifier again. How about the solo from Sultans of Swing
0:00 bend it more! you _neeeeed_ to hit the pitch right! apart from that the execution was sooooo nice... clear, with rhythm also, you have VERY FEW VIDEOS 😁 we want more 🤗
Awesome video this is becoming one of my favorite channels. Do you have an ETA for that FPGA video you mentioned ? I actually have a couple of Lattice iCE-40s lying around and I'm looking for some board layout ideas :)
Thank you! Yeah, I wanted to put in an order but unfortunately the FPGA that I wanted to use (or rather the only one JLCPCB has in their inventory) is currently out of stock. The board is finished, just need to wait now.. Really want to get my hands on that thing! I'd love to do something on Lattice FPGAs as well sometime.
@@PhilsLab Great I'll be waiting for that. Hope they stock it soon. The iCE40HX1K's that I have seem solderable by hand and are quite cheap so they might be a good choice for a future project. There is also an open source toolchain out there for programming them
I like the number of safety features and current mirror in the pre amp! Have you considered removing output capacitor, adding bias potentiometers and using some direct current protection IC? Maybe i missed something, but LEDs signaling footswitch state may be useful as well. Best regards!
If the output cap C6 was removed, the amp would supply a continuous average 12VDC to the speaker. Aside from continuously pushing the speaker in or out, that would be a constant 36W into the (4 ohm) speaker, doing nothing useful, and heating up both the speaker and the amp. There's no easy way around that capacitor with a single-supply amp.
Thank you! Yeah, as Graham said the output capacitor is necessary, as it is a single-supply design. For a split-supply design, it'd be interesting to play around with some bias servo ideas to try and minimise the DC offset at the output. And yes, some more advanced footswitch options would be cool as well :)
Beautiful design and nicely compact layout. In the voiceover, when you say "you can get them for as low as $2 from JLCPCB," I presume you're referring to their generic service, and not your particulat board. Which is a shame, because I'd *really* like one of those (especially if they were able to populate it for me, though I'd be more than satisfied with just the board and a full parts list!). I don't suppose...? Oh, well, a lovely dream. And a lovely amp.
Thank you, Scott. Yeah, generic service is $2 although this amp's board (despite its size) isn't much more expensive - something around 10 to 20 USD for a set of 5 I believe. Component cost of course not included.
Pretty much just used LTSpice. Predominantly DC analysis to ensure operating points (current + voltages) are what they should be. Other than that some frequency response analysis.
Awesome as usual. Can you guide me to learn these stuf as a beginner ? I've currently just finished electronics course at the University and I don't think I'm gonna see any of this in the carriclum. Is there any specific topic/s or an online course to get started with these stuf? Thanks
Thank you! But yes, as others have said there's plenty of material online and in books. Check out 'The Art of Electronics' or if you're particularly into audio, check out books by 'Douglas Self'.
I am pretty new to analog electronics and audio stuff. What I do not really understand is why not use a simple opamp? What technical advantages does a custom BJT amplifier circuit offer? Does it have economical advantages? If you would implement this amplifier with ready-made opamps would it sound worse?
There's quite a lot to that. I'd suggest Douglas Self's book 'Power Amplifier Design', several hundred pages long but covers all the details very well.
Nice work. Could you give feedback on output bias drift as the output devices reach temperature equilibrium. Also what Icq did you decide on for the output pair
That's one great video on power amplifier design! I have a question, why does the active load in the VAS increase the gain? Thank you! I would love to see more videos on audio amplifier design.
Thank you very much! In general, for a common emitter amplifier the gain is approximately equal to transconductance * impedance of load. Since a current source typically has a very high output impedance, if used as the load, the gain is increased by a large amount. I'm planning on making a couple more videos on more analogue design as well! :)
I'm planning to make a guitar amp, I think I'll choose your design, but should I put a preamp, before this, or not? (sorry if I wrote something badly, I'm not English)
Great video & nice chops! Are you running any effects with the amp for this recording? Also, is this design scalable (e.g., 30w)? I saw a post where you might be doing some additional videos that include the preamp. If so, I'm looking forward to that.
Regarding to the post below: Anyone having suggestions in this? Could it help to add some kind of differential/balancing thing to somehow cancel out that nasty buzz based on 70-100 V AC between secondary PSU MINUS and the mains AC safety earth. Added to this: It's he same 70-100 V AC between secondary PSU PLUS and the mains AC safety earth. Might this be more simple than we think? I have no idea right now...
Maybe someone can help me. Why isn't the first stage replaced by a low noice op amp? And then fed into the class A part. And why does almost no one use smd components (bjt or resistors) for the low power part? As the same technology like melf resistors are available.
I understood nearly everything on your STM32 custom pcb tutorial, but in this tutorial I do not. Don't know where to start to get what everything means.
So, I’m very new to all of this stuff. I found a schematic for a Fender Champ which appeals to me because it’s extremely simple; however, the schematic is a 5watt tube amp. Would you be able to offer some advice on creating a 15 or 30 watt solid state amp based off of a tube amp design?
Thank you! I designed for a single-rail DC power supply for the following reasons: - Much easier to get a single rail (no centre-tapped transformer needed). - Can get my DC rail directly from something like a laptop power supply, therefore no messing around with designing AC to DC power supplies and lethal voltages.
@@PhilsLab Thanks for your reply. What about switching hum/buzz (50/60 Hz) with that wallwart, the voltage - in Sweden it's 70-100V AC/50Hz between AC safety earth and secondary minus on all switched power supplies (PSU) that i have tested - which may be passing via a small capacitor from primary to secondary in the PSU's what I have read. So to get rid of that buzz/hum when I use switched power supplies (have tried plenty) I have to "neutralise" that AC 70-100V with a connection from PSU secondary minus to wall socket AC saftety earth, which is no fun. Here's an example: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE--toarxIohKY.html .... Any ideas anyone?
Thank you! I'm currently changing the board from through-hole to surface mount and then I'll be releasing parts of the amplifier, e.g. the power amplifier. Not sure about the whole thing yet but who knows!
@@PhilsLab I think the through hole design would be great for my son to do himself. He recently started playing the bass and one of his amps is a bit dodgy. He could then replace the amp inside it and keep the driver. He likes to tinker but not sure where to start so I think this would be a great introduction.
in the words of the great nelson pass: what's the point of 100 W if it sounds like shit at 1 W? also, generally, instrument-centric speakers like those you see on cabinets, have _very_ high sensitivities, something like 110 db/W/m so 10 W is enough to play in small studios
@@GeorgeTsiros Yes, that does make sense, I'm used to speakers in the HiFi area of 85/89 db/W/m or so where 90dB would be classed as very efficient. I remember my cinema days of years ago when 20 watts could fill a 1000 seat auditorium.
I don't understand this actually... You agree to use a big capacitor in the output, but object to use it on a negative power supply rail. Why digital domain engineers are so scared of negative voltages? =) A current must flow independently in complementary ledges. From Vdd to GND, and from GND to Vss.
