Wicked circuit, just discovered your channel. Super interesting hearig you justify differenet transister choices and outpout topologies. I believe you were correct about the diode in the original circuit, it is to bypass the resistor in the charging phase and force current through the second half of the pot during discharge. Thanks
@@AstrosElectronicsLab i apologize for my rudeness. I just don't t understand how those archaic puppies work is all. Always wanted one as a kid. When i went to middle school in the early '90's those things were in the schools secret storage room of outdated equipment that no longer stood as pertinent science tools according to the schools budget. Wish i knew the principals of their usage though before i opened my big mouth.
@@Steve-nf7gp no offense taken :). I don't remember seeing any leaking caps, either... maybe a load of that brown circuit glue, however. The fact it works now, is the good thing ;)
You got lucky. Bought one about a year ago and it was a wreck both mechanically and electronically. I had to make quite a few corrections including replacing the output op-amps. If your interested I did 2 videos on it #0060 and #0071 over on my channel. It's nice to see some people get good ones!
The up on the left corner I believe adjusting the contrast of the display. And the one on the middle have to do with calibration of the function generator.
I am currently working on that model receiver and have found similar problems with the bad solder joints. Others with this problem have noted that this was one of the first models that Sony made with lead free solder that that combined with the high heat around the preamp modules and other hot components causes the problem. I also suspected a high resistance in the output relays so I did one of my redneck repairs I have done on other amps. I drill a small hole in the top cover of the relay and shoot it full of DeOxIT contact cleaner. It has worked for several months for me in the past.
I had a similar problem and it happened to be a NAD. Look around for why the opposite voltage isnt getting through to (balance) it. I chased my tail for ages with -27V on the output chasing -ve voltages. Someone on one of the forums suggested I should be looking for missing +ve voltages. I think mine was a shit join on one of the drivers trans . You probabaly already have but, check the work you have done for solder bridges or lifted tracks. The fault wasnt there before so it's something youve introduced. Good luck.
The fault was there before, and nothing I've introduced. It had a shorted MJ2955 transistor collector to emitter. And currently, it keeps blowing the new transistors. I think the driver transistors (which are 33 years old) may have become electrically leaky between junctions. I'm at the stage now of calling it non-repairable as it's not economically viable.
C"mon. I'd hate to see you give up! But you do have to know when to fold em. Throw it on the shelf. Something might come to you when you least expect it as most anwersin life so often do. I'm actually chassing down a similar fault now on one channel of an ancient Jans J600S PA my brother dropped off. What makes it even better is I cant get a schematic for love nor money. This thing is Australian Made from the early 70s so look like I'll be trying to trace out and draw myself, which I'm pretty sh1t at. Just keep on swimming.
@sanolivo6867 That's your opinion, however the point of this is to see if it can be repaired (there will be a follow-up video soon) before I condemn it as "parts only".
@bobisyouruncle1 One thing I forgot to film or mention was this originally came from the Mornington "Tip-Shop" (resource rescue) for $120!! They sold this thing to someone for $120 in an non-working state! This is not uncommon for this resource center, which is why I rarely go there lol. Also, the purpose is not really they want it repaired, only "if" it can be repaired. I won't be making much off of this. However, having said this, I don't know if it was originally working and the person that bought it didn't just blow it up by shorting the output...
Checked the electros, replaced a few and still same issue. However, I have now found an issue that may possibly be causing the -14V across each pin of the Vbe multiplier transistor. A new video will be coming soon about it, and what I found, I'm also not happy as to what I've found...
I checked that, that's just the plastic disc that's expanded over time. You push on it and it goes down flat to the aluminum top of the actual capacitor. Good eye, though ;)
The isolated PSU (USB power) makes this Osc. useful. But Bode plots (Frequency measurements) are important in the audio world. Is it possible to get the internal Gen and FFT function (lots of hidden modes) to work for this in this scope?
Great video. I've question: will this voltage reference work for esp32c3 and hx711? To prevent excitation voltage from interfering with load cell readings?
@user-mg3ju8tl3q this is just a reference diode, and provides 2.5V stable voltage to whatever its connected to. I don't know, you'd have to experiment.
Ok i see two transistor pushpull But how many transistor have in circuit? Op amp as drivers? Diodes are vbe multplier and phase spliters? Dont havent bias generator transistor in heatsink
I had an old window fan that seized like that and all I did was to squeeze some bicycle chain lube at the stem where it meets the casing, then let it seeps, turn the stem a few times and that's all it takes.
Dextron II ATF contains dissolved bronze and is preferred lubricant for sintered bronze bearings. I have used it in small motors (and these fan motors) bearings for decades, never a problem. Do not ever use Singer sewing machine oil, guaranteed to emulsify and gum up sintered bearings. Cheers.
Congratulations! It's been an excellent series to watch and you've done a great job not only building, but teaching along the way. I hope it gives you years of pleasurable listening. Cheers!😎
Thanks for sharing and making the video. Am I seeing inductive spikes on the scope trace? If so, would placing a reversed biased bypass diode (I hope I worded that correctly) across the fan motor help? You mentioned the noise. As you know, a good bit of that could be from the breadboard construction. I also saw in the comments that you are going to have PCBs manufactured. That will answer the question as to if the breadboard is the noise culprit. Please do a followup video with the PCB build and testing. It will be interesting. Cheers.
Unfortunately, the power dissipation isn't evenly shared between the parallel connected 2.2 and 22 ohm resistors. Because the resistors are in parallel, they will have the same voltage and so the 2.2 ohm resistor will dissipate 10x the power since P=V^2 / R. When the 2.2 ohm resistor is dissipating its rated 10W, the 22ohm will dissipate 1W, so the effective load rating will be 44W not 80W...
Nice amplifier. I have the AVR-1306, 70wrms@8ohm x 5, since 2007. Still running beautifully and great sounding. These early 2000 amplifiers still have proper psu's. Good purchase.
It is pretty ok, the sound is a little harsh, but I as I said in the video, it's most likely a stupid EQ setting. I've ordered a remote for it for like $25, which is pretty good! So, I'll need to find a HDMI capable monitor to go through the settings, etc.
I possibly misunderstood you, but I got the impression you said that cross-over distortion was due to "the way transistors work". As far as I understand, crossover distorsion is not present at all when you run a single transistor ( or a tube ) in pure class A, which is the main beauty of it. The cross-over distorsion arises when you run a pair of transistors in push-pull configuration, and bias for class AB operation, i.e. positive half of wave taken care of by one of transistors, negative by the other, and merge the two halves together. The mismatch between the two non-identical ( or non-symmetrical ) halves , or the timing mismatch, gives crossover distortion.
No, I meant on a Class-AB amplifier on a bipolar supply. Class-B can have severe crossover distortion if it's not designed/biased right. Class-A has none on both bipolar and single ended.
This is not the "correct" way to do this. The ground line is usually connected to the potentiometer as well to create a voltage divider circuit. This might work perfectly well, I dont know enough to say that it is bad necessarily, but from my understanding, it is not the typical way to do it.
This is an Amazing little sub. I have 2 of them. One stopped working just before covid and took it to a repair shop. This guy lost it or sold it. He asked for proof, so I showed him a photo I took of the serial number of the sub......sitting on the floor of HIS shop. A week later i gave him the original Box with the same serial number. He then gave me $450 for it.
LOL! Epic, dude! There are some shifty people out there, and the most likely issue originally with it was the Sanyo STK4040V IC (I'm assuming), and good luck to him to find a genuine one. And, yes. I've been using the sub now for 4 days, and with a little fiddling of the crossover and gain pots, I think I've got the perfect amount of bass to compliment my Accusound speakers.
I just got the mt21 as well... Hooked it up to an oscilloscope. And switching noise is really there. The way they implemented the filters is truly inadequate... I got it somewhat looking good by adding my own filters. But it sill looks quite horrible
Why didn't you use the secondary voltage for the soft start circuit, instead of using the primary and creating a specific RC timed circuit that isn't really universal for different projects? Just curious. Switch the primary of the circuit, based off of the secondary voltage rising to a certain level.
With the right probes, yes. As this is isolated from the mains earth, it should be fine. Just be aware of the high voltages, use an isolation transformer and common sense.
Yes. The transistor at that point will no longer function. It's done. There should be no shorts between base-emitter, base-collector or collector-emitter.
Also, remember that in circuit, the transistor can "appear" to be shorted due to other things in the circuit. There is an in-circuit transistor tester (which is basically an oscillator, similar to an ESR meter) which will save having to remove it to test it.
