I did not want to interfere with your previous videos when you were unhappy, but I am glad you got the amp working. What is left is to get the off-set right then you would have a symmetrical clipping and slightly more power and less distortion, but yes well done at figuring it out. Class A is an amplifier in that it works great but if it distorts, i.e. the rails are not at what they were designed for the sound just falls apart. Also chose your heat sink well, class A runs very hot, playing music or standing idle.
I saw those wago clamps on another channel, home electrician type channel. He claims they are like second generation wire nuts, and way better than wire nuts. He said the wire nuts can cut the wire, and multiple removals could cause a failure. He was looking at it from a high voltage perspective. He said these clamp, and don't damage the wire, and can be reused indefinately. They certainly look like a good idea, and I bet for bench work they are 10 times better!
Glad you checked my math...we seem to agree. ;) Klipsch are generally very efficient if you have a ported bass style cabinet >100dBA @ 1W/1M. The amp you have reminds me a lot of the amp I cut my teeth on in my second job out of school. (It was for Jim Fosgate prior to the Rockford buyout/sale/partnership.) The Punch 20 was a 20W/ch stereo amp for automotive applications. 13.6Vdc input with a switching transformer dc/dc power supply. Provided about +/-25Vdc at the output rails. The input was the 5532 op amp but was used as a buffer to a driver pair of transistors with a gain of 2 to drive the output Class A push/pull amplifier pair. There was nothing on the market at that time in its power class that could touch the sound quality of that amp. (Mid 1970s technology)
@@JasonLeaman I had mine for over 20 years and nary a problem. I worked for Jim before the Rockford hookup...the products were solely Fosgate in the early days.
I find this type of video very useful where you fix a bad design. It made me think through the problem while you explained the issue. Not just interesting, but helpful (to me).
I voted for scrapping the boards, I see now I was wrong , good video, but I would like to se some more measurements of them, and yes a video on working principle and biasing class a and a/b would be awesome.
Thanks Thomas! I too was leaning towards getting my money back;) They are relatively expensive boards and it was a risk that the output transistors and other parts would have to be swapped out too. I’ll do a follow up and show the measurements and set the bias current.
@@KissAnalog Hi Eddie, I think that you still should get some money back for fixing their board. You should charge them royalties for adding your repair to their production! 🤣
Hi Eddie. I'm so pleased that you decided to measure the output power by both voltage and current and display these parameters on the scope. Your current probe clearly indicates that the voltage and current aren't in phase with that 200W load connected which only goes to confirm my suspicion that these load resistors commonly used on many electronics channels to measure the output power of audio amplifiers are indeed NOT non-inductive as many think they are. These resistors look suspiciously like the braking resistors used on elevator motors to slow down the lift car as it comes to a stop by placing a low impedance load across the motor windings thus exploiting the back EMF generated by the motor into the load as an electric brake. Given these rectangular aluminium boxed wire wound resistors are used for this purpose there would be no need to go to the additional expense of reverse bifilar or Ayrton-Perry winding them where in a lift braking system they would be totally unnecessary. Can I suggest that for the benefit of answering the question to the viewers curiosity you spend a few minutes with one of your better LCR meters and measure the inductance of one of these resistors at say 100Hz, 1kHz, 10kHz and 100kHz to evaluate just how much inductance these so called "non-inductive" loads have. I think you may be shocked. A short video demonstrating this would certainly dispel any doubts or misconceptions about purely resistive or at least low inductance loads for testing audio power amplifiers. Perhaps even a low power test comparing these lift braking resistors with known low inductance resistors such as carbon film, metal film or metal oxide types? BTW, I enjoy watching your channel. Keep up the good work. :)
Thanks Alan for that great feedback! I’ll do a video about this very soon. BTW, at the time I was doing this video - I think I made a mistake. I need to go back and watch, but maybe its not in the video... I appreciate this informative feedback!
It's not easy getting affordable non inductive wirewound resistors... I found Mills non inductive on digikey for my last build. Needed 8 of them, cost about the same as the output transistors!
Hi Eddie, Thank you for this great video. What stuck with me the most is what a wonderful feeling it is to fix something, rather than throwing in the towel and just ordering something new. Good job! And, yes, I'd love a video on A/B amplifiers and especially how to avoid crossover distortion. Cheers Mark
Thanks Eddie, great job! Over the last few days I listened to all kinds of music from solo guitars to Bach's cello suites to U2 and Beethoven's 9th all with the class D amp driven by a 12AU7A preamp to see if I could get the flavor and benefits of both technologies working with each other. I really like the sound and the dynamics that are missing with the class A amps. They seem to be good with a limit range of music but once you hear the sound stage and dynamics of the class D amps it's a whole other experience. I still have some things to try with class A but what I think going toward is high power class A. Once you get over about 250 watts a channel the distortion to produce clean music is lower that's why these class D's run so much power. I just SPICE modeled a new preamp interface for the class D amp but the Chinese are still out on holiday until Thursday so my modded 12AU7A boards won't be back until next week. If you want to play with one PM me (I just closed my website, sorry) or give me a way to get in touch and I'll get some interesting boards out to you when they come in. I even made one to roll different tubes on. I just tried to support you and buy the DP10007 but you did such a good job talking about it that Amazon is out of stock! That was fast. Rob
Good job fixing the amp so it worked properly. That would perfect for a good bookshelf sound system. If you get a chance could you possibly see if you could reach out to Loto and get one of their scopes to demonstrate on your channel? I would be interested to see how good the signal generator is and really test the FFT on it It supposedly does 16K points which is better than what my Entry level rigol can do. Learn Electronics tested one today but he didn't really show off the FFT much.
Thanks for this great question! Loto actually sent me a scope, so I'll do a review with it. I was hoping to see more with Paul too, but it seems that he doesn't spend as much time on his scope reviews as he once did. I think he is trying to keep his vids on the short side. There is a positive in releasing more videos than fewer longer ones as I do. I publish more minutes but less videos. His math works better in getting more views I think. But I am in this first to educate, and that just takes more time...But I really like Paul;)
That is a terrific idea;) There isn’t a lot made on dampening factor. Great idea for a video! What are some of the common design errors that you would suggest that I talk about?
Yes to a Video on Class a vs class a/b :) Good video sir ! Not sure why you can't get more than 20watts tho, the Jean Hiraga uses 45v rails and gives you 58Watts RMS with a single pair of Outputs. Good Video
Thanks for the question. Do you want to see my power supply schematic? I have a playlist of videos on this project, and some of those show the schematic of this amplifier.
Hi again eddie. What makes a amp really great is a good stiff low noise power supply, you are a power supply guy so why not go in depth with that, for example a Jean hiraga is a amazing amp, but its pssr is terrible, so people go to great length to build it, some use clc crc , big expensive indicators and so on, others try capacitance multipliers, switch modes with extra filtering to remove switching noise, really clean dc is very hard to get with some current involved, I'm right now experimenting on my hiraga amp, by powering the entire input section with a very low noise regulator from amb.org the sigma 22, I hope noise will go down at least 10db, anyho great channel you have, I do like the leaned back humorous approach, keep it up.
Thank you Thomas! I appreciate you! I am always learning so please share;) I agree with you and I'm considering using a CLC in this, but I am limited in space;) Also, I think this design will have very good PSSR. I need to test that in a video;)
@@KissAnalog in olden days clc "π" filters were the norm...& should be re- introduced today.. then they were acceptable , (there were already many other bulky components in there)... even though load current demands were low ..one more didn't matter.. Then came the solid state era and ampere demand shot up..so these chokes became the first victim..
As in " there's a hole in the bucket"... ..and so on... "USE WATER DEAR HENRY- DEAR HENRY...USE WATER " so also" USE BATTERY PACKS DEAR THOMAS..DEAR THOMAS...USE BATTERIES"...
you have great components ON, which as you know are great at passing current and are high voltage, remove the regulation and mind the current through the phase splitter and see what you can achieve from it.
@@KissAnalog Thanks for your response, that sounds very interesting I'll take a look. I have built a 40 Watt version which I have yet to test and tweek, there never seams to be time these days. I will document it and upload it when time allows.
Check out the Cedar DNS 2 channel Dynamic Noise Suppressor. It will cut the low fan hum in your videos and clean up the vocals. There are also plugins that do the same thing, but being a live engineer I prefer to cut these noises during capture if possible.
@@KissAnalog So they did sort of know what they were doing. I think the original kit may have had the correct diodes perhaps to be fitted after all OK but that may have got lost along the way. I never realised that was what the voltage drivers actually did so it's been a very good experience for me, learned a lot from this. Big Thanks.
Great you fixed it! It was not quite clear to me what you did. Did you put in the 2 22V Zener diodes? What did they replace since I can see a diode on the silkscreen? On the topic of comparing I would be interested to see a comparison between a class-A and a comparable class-D amplifier.
According to this premise: 1 m2 = 10,000 cm2 gives 1 degree at 20 Watt. So 10,000 / 20 = 500 cm2 gives 1 degree at 1 watt, = 1 degree / watt. That is a plate of 22.3 x 22.3 cm. It originally in dutch Google translate it
One more thing. You're using Klipsch horns which I think are high efficiency. I'm using Dynaudio's with a sub, they are only medium efficiency (86 SPL) so these low power amps just don't drive them dynamically as well as the Klipsch speakers.
This "fix" looks strange without more details. One does not simply raise voltage. How about quiescent point, shifted bias, voltage/current rating of components, thermal issues?
Great questions - thank you! Have you seen the previous videos? This one I show the problem and with this one I hope it makes more sense. Let me know what you think. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE--VRcelNAcP0.html
What did you do change out the diode for 22 volts. What about current being off phase is that an issue how do you bring it back. You never replied to my other question about using a class D amplifier as the power supply for class A or class ab, I would have thought it would work well it's a clean sort of power
Perform a test with your final heat sinks running for a few hours and then take the temperature of your heat sinks ?. Unfortunately music clips for them to sound good . 1: A good clean uncompressed recording. 2: not in a small square room with hard floors with sound reflections off the walls and floor that cancel out 3: good microphone even binaural monitoring the recording level to make sure it’s not clipping 4: and a few other tricks of the trade maybe you can ask Ron @ NRD ( New Record Day ) 5: otherwise it all comes sounding the same after RU-vid compression a speaker with a wet rag over it or playing within a cardboard box 📦
@@JasonLeaman that is 100% true. It sucks listening to music through compression. But he can sound better when done right. Listen to NRB music channel on RU-vid there test tracks. I build my own clase A Nelson Pass amplifiers and preamplifiers line stage headphone amplifier For class A Tube stuff I build Pete Millet designs. Build my own linear power supplies from scratch so I don’t have to listen to any of that switch mode power supply stuff.
@@coldfinger459sub0 IMO SMPS arn't that that bad, they just have ot be implemented properly. a BAD linear psu can sound bad if not setup properly too.. I just put out a video on my channel about this, and soon to be doing some heavy measurements with my QA401 with linear vs SMPS.
@@JasonLeaman I completely agree with you SMPS have come along way and they now deserve to be used in some high-end audio applications. I believe in energy efficiency and conserving in all applications of life except my audio lol 😂. I enjoy building them and tweaking them and testing them. Linear Power supplies have that old time nostalgic look and if you live in a cool climate like San Francisco it’s a free source of heat while you’re listening to your stereo. And if you get very creative with copper and brass and custom ornate wiring you can make some really cool steam punk looking art out of your power supply and not cover it and have audio equipment nobody else has or nobody else can afford at a reasonable cost. My sons and their friends absolutely love when I make a power supply and audio equipment on a wooden board Venere and pure copper or on a copper 1/8” thick chassis plate With grossly oversized wiring that had all the insulation stripped off everything polished like a mirror and then lacquer coated. With all nuts bolts and washers source than made out of pure 100% copper or brass It’s difficult to make a SMPS look sexy or Art Deco or Steam Punk yes and I just realize I already watch your channel
Whats the cheapest way to accurately test THD? I have been designing a board and im not rich and it sounds great but I want to measure some things properly.
@@KissAnalog I don't, I have a super cheap $30 scope from amazon that I used just to make sure I wasn't clipping and even that was hard to tell. I am trying to save up for a lower end scope but things keep happening in life unfortunately.
This isn't rocket science. If you have V volts peak-to-peak into a load of R ohms, then you get W = V²/8R watts out of it with a sine wave. So for example, 18Vpp will give you (18*18) / (8*8) = 5 watts into an 8 ohm load. Conversely, if you want to get W watts into a load of R ohms, then you need √(8RW) volts peak-to-peak available. If you want to deliver 20W into an 8 ohm load, you'll need your amp to swing √(8*8*20) = 36Vpp.
Great question! I tried different OpAmps on this project series, so maybe you've seen the other videos by now. I am using near the max on each different OpAmp that I've tried. Here's a video where this helped me achieve 29 Watts: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-olIbJruCuzk.html
@@KissAnalog I always use to power the opamps with 3 or 4 volts less than the max voltage rated and I notice that gets the lowest distortion. When o was powering the opamps with the max voltage rated yes I was getting more amplification but also the distortion was high so I recommend always to don't go to close with the max voltage rated
Ok, here i go again.... 18:25 this in not the way that you should test a class A power amp... you should have a proper setup, stereo system, put yourself in the middle, chose some Audiophile track, and tell us about 3D soundstage that you can hear...
That's a valid question. To learn anything from the exercise two things are relevant IMHO. Yes, schematic (both before and after) as well as the PCB layout as this too can influence the performance of the amplifier in terms of distortion and stability.
Thanks for the question. I'm happy to see others interested too. I just about have the schematic ready. It has taken some time to trace the circuit. I'll have it in Microcap for anyone interested;)
