Dual TDA7293 Pt 2. The Complete Amplifier

[@stevesmyth4982]

Nice job, Mike! You did well to squeeze that lot into the box, proper heatsinking too.

[@adalbertus777]

Thanks Michael. Good to see you back here with new material and interesting thoughts shared.

[@mauriciojv7901]

Hey Mike. So glad to see you back once more. Loving the new videos. Salute from Brasil.

[@MichaelBeeny]

Thank you Mauriciojv your comments are most appreciated.

[@brianwood5220]

Really great to see you again, Michael. Great video, very interesting and thanks for sharing.

[@ronschauer839]

Hello my friend. I am so very happy to see this brand new video on your "closed" channel. 😀 And of course I am very happy for your results. That said, I remain quite partial to L12's for my main stereo system and have no plans to change them. However- I do have a pair of the very same dual TDA7293 boards as yours on order for an AV amplifier project and cannot wait to receive, install and listen to them. I have long been convinced that variations in speaker impedances across the audio spectrum have been at least partially responsible for the perceived deficiencies of certain amplifiers. Notably the common NAP250(clone) and other "single output device" boards. L12's (and presumably the dual TDA7293 boards) with their doubled-up output devices seem to be able to far better cope with any dips in load impedance. BTW, I am not, and never have been, a fan of "passive" preamps or variants thereof, exactly for the reasons you mentioned. You should always run a buffer stage after your volume control that is high impedance in, low impedance out, whether unity gain or more. Similarly, I am not a fan of typical op-amp inverting stages because they tend to unduly load the prior stage or source by their very nature. My own recent experiences with a headphone amplifier kit (Beyerdynamic A2 clone) bear this out. Anyway, BRAVO..!

[@MichaelBeeny]

Hi Ron, I cannot wait for you to receive this boards. I am more excited for you to hear them. Will you like them more than the L12? Will they even replace the L12s as your main amplifier?? I think I am more excited than you lol Thanks, Ron, for your input, much appreciated.

[@billkalina3089]

Hey Mike! What a pleasant surprise to see another video! I was shocked to hear you had gotten rid of the LJM12. We were convinced it would be difficult to topple that amplifier from the podium, weren't we? But being honest, my ears are telling me its the best thing I've built. I swear, if you put it into a pretty box, it would not be hard to convince most people that it is a $3000.00 unit. The sound quality really is superb, especially when you factor in the total cost. I may have to put up some amps for sale, and perhaps build another of these! Hope you are well. Enjoy the music....cheers! .

[@MichaelBeeny]

Hi Bill, see, I do take notice from my subscribers. You said it was good, so I had to try it. This version is however the best. Maybe YOU should try it lol

[@billkalina3089]

@@MichaelBeeny I just may, lol

[@ronschauer839]

I too am partial to L12's. 🙂

[@billkalina3089]

@@ronschauer839 I do like the L12. It was my fave. There's just something about the tda7293/4. Just a bit of extra sparkle? Detail? I don't know, but it's just very appealing!

[@ronschauer839]

@@billkalina3089 I just received a pair of the boards exactly like Mike's. They are indeed nice but a few things about them became immediately apparent to me. First, the HF roll off he experienced without a low impedance pre-driver is due to a heavy-handed input circuit design. The input passes through a 1K resistor to a 2N2 (2200pF) capacitor and then to common. From their junction it passes through a 150 ohm resistor to the master 7293's input. The input signal doesn't go anywhere near the op amp (more on this in a moment). With a typical 50K volume control this will result in a true 1/2 control resistance (25K-25K) setting HF loss of around -6.3dB at 25khz due to the R/C effects alone. So the -5dB he was experiencing at 20khz is totally understandable. Someone else commented about placing a capacitor at the input terminals, which is unfortunately not a solution to this problem. I assume that they meant in series with the input. It will only de-couple any DC present from across the volume control, nothing more. It makes NO improvement to the HF frequency response whatsoever. Sorry to all the passive preamp fans out there, but it is what it is. However, if driven by a low impedance buffer stage (such as directly from a DAC as Mike did), the HF roll off will be minimal (there's that extra sparkle and detail?). It will take me a couple of days to get these wired into a chassis (with a suitable pre-buffer of course) but I fully expect to hear great things from them. 😀 Second, the op amp on the board is not in the input signal path at all. It is in fact part of a feedback loop to effect output null voltage compensation, and it is actually rather clever IMHO. No wonder Mike is seeing single digit millivolt output offsets. However, that also means that changing the op amp for something better is unlikely to have any audible effects upon the board's output. All that being said, I predict that I will be sticking with L12's for my main stereo setup. When I built them I VERY carefully matched components and of course performed Mike's QI adjustment modification and adjustments. I really like them. 🙂 But these 7293 boards should be absolutely great for the A/V amp I am building and I can't wait to hear them.

[@fmuratori]

Great to see you back on KZbin!😊

[@michaellundsrensen2292]

Thank you Michael. It looks like a very nicely built amplifier and you have utilized the cabinet well. It's great if you get 2 x 100 watts/4 ohms out of the 160 VA transformer. You might be overloading it a little bit, but as you say, the music isn't playing at max all the time. Too bad about the Windows files! Thanks for another great video! Take care and enjoy your fine amplifier, but remember we love your videos! Salute from Denmark.

[@MichaelBeeny]

Hi Michael, yes, I don't think the transformer would be over happy with a 300 VA load for long. On testing it did supply that current, but long term it would overheat and eventually burn out, not recommended! Thank you for watching and commenting.

[@MarvinHartmann452]

The small ceramic caps across the main filter are to shunt any oscillations of the power supply.

[@nakfan]

Great info on the not so good passive preamp approach. Thank you so much for taking the time and effort to make the video. Hope you’ll be able to find / restore the video files you lost maybe. BR, Per

[@alabamacajun7791]

Micheal, someone thought changing from Farnell to Silicon 14 on the periodic table. Thanks for bringing this to fruition. Great selection of parts and love the bridging.

[@KP-nd3bx]

Your build looks great. To me You explain it very good. Best of wishes from 🇩🇰

[@MichaelBeeny]

Hi KP. I always try to remember that for many of my viewers English is not there first language. I try to make things as clear as I can. I really appreciate all my viewers from every part of the world.

[@MarkErikEE]

Good point regarding the volume pot. Chinese PCB-s often include a pot position, but I ignore it.

[@ryanchappell5962]

Nice work! It looks really cool

[@MichaelBeeny]

Cool is always better than hot in Audio. lol

[@gilbert2870]

Thank you Mr. Michael🙏I am excited to build this one🤗

[@ford1546]

Hello. Have you ever tried the L20 Class-ab from LJM with 8 pcs. transistors? Quiescent current is incredibly low and doesn't get hot before you play music. I have often wondered if it is a clasd-b amplifier. I have also compared the sound quality with other factory built amplifiers such as luxman m120a and yamaha mx1000. the L20 amplifier board has just as good a sound. This is my opinion.

[@edmundzed9870]

Dear Michael, can you tell me where to get it? I don't see any link here and I want to but build it. Thanks

[@impuls60]

Windows update shouldn't delete anything as long you have several gigs of free space on the C drive. Windows uses the disk as spare memory when you run out of physical ram (which one quickly do when editing). So you might have ran out space and the buffered editing files might have got deleted when the disk was full and you turned of the pc. So always maintain atleast 5-7gig of free space on the C drive. Hope this info helps to avoid it happening again. Congratz on the completed amplifier! Its always fun to test something you buildt yourself.

[@danhorton6182]

I really like your amp build. Would you consider using a 28v-0-28v transformer or would the rectified voltage be too high for your liking? I have a very large number of TDA7294 I would like to start playing with and wondering what voltage I should be at for the rails. Would be interesting to do a large amp running 4 or more in parallel per channel.

[@MichaelBeeny]

The main issue is getting rid of heat. This 2 chip version does cut dissipation in half. Voltage is not the main issue; the spec sheet quotes 60 volts. Not something I would like to do. Probably be OK with 28/0/28 but probably best to stick with 8 ohm load. I have never tested the 7294 so I cannot comment, it looks quite similar on paper. Don't forget these are not exactly in parallel, one chip is the master, and the others are slaves.

[@tilmannschuler3136]

great to see you quite well

[@MichaelBeeny]

It's all done with mirrors and video editing.😇

[@pandouros]

As always windows is a system to surprise you many times.

[@jim9930]

TDA7293's are at best 50 watt 8 ohm amplifiers. Paralleling the output stage only allows them to operate at 4 ohms without activating the protection circuits. ( closer to what typical 'real' 8 ohm speaker loads actually are ) Reliability is a calculation usually under ideal conditions. Plenty of room for marketing hype... A little story to illustrate the point: After the Challenger blew up, I had a discussion with the director of range safety for NASA ( we were on the same dart team at a local bar ). He claimed the calculations were 1 in 10,000 error rate. I told him the actual failure rate was 1 in 25. Serious engineers read the fine print, and assume the worst case. Sooo, you can find switch mode supplies rated at 600,000+ hours; but who tested them 68 years? ...read between the lines!

[@ronschauer839]

I have performed detailed reliability calculations on my own commercialized designs as part of the product release process, so I know how such assessments are made. Your point is very well taken- it may be calculated to be 600,000+ hours, but in the end it is only a calculation (essentially, an educated guess) and the end product is only as reliable as its weakest link. Also to your point, "8 ohm" speakers are typically not anywhere near 8 ohms across the entire audio spectrum. Some are as low as 2 ohms at certain frequencies. Unlike Mike's experience though, I have had linear supplies fail for reasons other than the capacitors (the rectifiers typically). And higher quality switching supplies, if properly applied and not over-loaded, can be quite reliable. I stress "properly".

[@Bengal20]

Thank you very much, Mr Beeny! Can you make a video of how to resolve oscillating problem of op amps on IV and LPF sections of a DAC? I have this problem with my DAC (dual PCM1794A) :((

[@MichaelBeeny]

I'm sorry, I have little constructive knowledge of DACs.

[@Bengal20]

@@MichaelBeeny Thanks anyway, Mr Beeny! 😁👍

[@pabloaraya1223]

Hello friend, do you know where I could find power suply cable or adapter for Wharfedale E90 ?

[@MichaelBeeny]

Sadly this 3 pin plug has long been discontinued. You can still find them from time to time on EBay but at silly prices. A better option would be to replace the socket with 2 x 4mm sockets. This will involve removing one of the drive units to get access. This just speaker connections, the speaker is not powered.

[@max79444]

Well done !!

[@Electrondivize]

How about transfor,mer coupled input 12au7 single 15K plate to 600^line out ? mybe il try it with TDA7294 .

[@MichaelBeeny]

On paper it should work OK but sound wise a transformer in any audio circuit is not recommended or even any valve. A simple circuit with a 5532/4 will do a much better job.

[@vincentopati5406]

Do you think it sounds better than Aiyima MX50 SE?. i want to know before I upgrade to this board

[@MichaelBeeny]

Yes, it does for sure. The MX 50 is amazing value for money. Probably the lowest cost of all good amplifiers. This cost 5 times the price, is it 5 times better? probably not. Is it worth the money? for sure. These chips have been used by a number of up market amplifiers in the past costing hundreds of dollars.

[@vincentopati5406]

Thank you Beeny this will be my next project

[@ronschauer839]

It is based upon a Linn LK140 actually, a dual output chip upgrade to an LK85 which has only a single 7293 at each channel output. The circuitry looks "suspiciously" similar. 🤔 Hmmm....

[@MichaelBeeny]

I did not spot that error Ron; lucky you were paying attention. I always make one major mistake in every video. Maybe I should hand the video editing and quality control over to you lol

[@ronschauer839]

@@MichaelBeeny I think that you do well enough as-is. 😁

[@new-kids-on-the-block]

We need 2 see it my friend ❤

[@ford1546]

Therefore, you should have a capacitor at the input of the amplifier to avoid this frequency change problem. Then the amplifier will not see the load from the potentiometer. I have also read this on the internet. I usually use wisma polyester 5 - 6 uf capacitor. Potenyiometer has always had its own sound and never gives a 100% unchanged sound. Therefore many high quality amplifiers now use volume gaincell as (ps audio) does. Some potetiometers are better than others!

[@ford1546]

Hello. It can't handle 8 ohms in the bridge! and therefore no good amplifier if you ask me! (TDA7293 data sheet) 4.3 Bridge application Another application suggestion is the bridge configuration, where two TDA7293 are used. In this application, the value of the load must not be lower than 8 Ω for dissipation and current capability reasons.

[@MichaelBeeny]

Running a 4 ohm load in bridge is not recommended, it's like a 2 ohm load on a single unit. A 2-ohm speaker can drop in impedance to 1 ohm. The amplifier will see this as a short circuit. Distortion will rise, the chip will get VERY hot or be in protect mode.

[@trondnylkken956]

Yoy revied a amp kit with transistors not IC