Erno Borbely designed it among many others products. Probably the most known audio amp on this planet and relatively simple. This man knew how to make big MOSFET output amps, some push-pull class A. Together with Nelson Pass, John Curl and others he's one of the designers that left massive contribution to DIY. Funny how many of products from 80-90s still work without big problems. To bad Toshiba, Hitachi doesn't make MOSFETs suitable for audio 😥. My Sima amp from Montreal didn't have the relay either but with 120,000uF in total it took forever to discharge. One thing the Differential input section would discharge much faster so there was no big pup on the outputs when turned off. The problem when I was away someone blew one channel and I couldn't get old Motorola transistors to repair it.
That's the problem with mosfet transistor amps. They are all pretty obsolete these days. What a wonderful sound they had when they worked. Push Pull are always class B. They can be biased as AB, but if it is push pull, it is class B. Class A is a single ended amp, and uses 1 tube or transistor. You can have a parallel class B, with multiple class A stages in parallel, and those will warm the room nicely, because at idle the amp will be drawing about half the rated output. So an amp that can deliver 100 watts will be burning up 50 watts just sitting there. That is why the push pull amp was developed. Much more efficient. Now class D is all the rage. The PWM digital amp. Some will argue that they are not digital, they are analog, but really they are digital. The analog waveform is represented by a PWM switching carrier which is either on or off. A 1 or 0, with the time duration between the 1 and 0 state representing the analog waveform. Filter the carrier out and the amplified analog signal returns. Done right and class D can sound very good, and they are close to 100% efficient. I had an opportunity to hear some nice class D amplifiers, and if i hadn't been told they were class D i would never have known.
@@12voltvids The Erno Borbely amps had 5-7 output pairs and biased heavily into class A so crossover distortions were NIL, say 1A per pair instead 120-200mA being the norm. It required big power supply and heatsink of course. The topology was symmetrical, with separate differential pairs for positive and negative half of the waveform, same as the DH 200, but with additional cascoding, etc to minimize distortions. Yeah funny how people call Class D amps 'digital' because of use PWM modulator, however it doesn't DAC at the output, only low pass filter to filter out the PWM signal. And digital output from say CD player can not be directly connected to amps input so it can not be called Digital amplifier. I don't it's possible to produce digital amp being able to work where digital signal can be controlled from input to output without changing it first to analog. Imagine how many bits of processing would be needed to make amp where signals volume control was fully digital with 60dB range and 120dB dynamics. We all know that DACs with 24bit resolution are the maximum possible, above that additional bits of information are buried in the noise from electronic components that DAC chip is made of.
Looks like a good old basic amplifier, no fancy bullshit. A double pole double throw relay with 10 ohm load resistors could be added to catch that spike, but as you said it's not so bad.
I used this one to remove chrome on a car. Some goof parked too close to me and as I passed between cars my watch caught the chrome on the car and the chrome came right off. Damaged the watch band and put a hole in my wrist. Can't help wondering how much it cost to fix the car as I didn't wait around. I was looking for something fix the hole in my arm and then off to the er to get sewed up.
They sell thermistors to protect the power switches on these. They're on eBay. Put one on my XL-280, which is an upgraded DH-220. The power switches were a really common failure item on these.
Jesus Smith, I should have read your first comment first. (A little harsh, don't you think.) But I was putting in my teeth and hearing aids, here at the old folks home, and as I couldn't find my walker, I pissed the bed. Ah, the golden years!
I have found that a resistor of 2.2k across the main positive and negative electrolytic caps will solve your problem when turning off the amplifier. (The RC time depends on the DC voltage)
I have no idea why this is here either. You are correct though. Only the live side should be fused. This has them on both sides. Again it was originally a kit, and as such whoever built it likely wasn't aware. The original units had a 2 prong non polarized plug.
@@12voltvids 1. You insert the tubes on the disconnected wires. 2. move them back, away from the connection 3.Solder. 4 Move the tubes forward. 5. Heat schrink. 6. Done & safe.
@@jacques6753 Duh i know how to put on heat shrink however it is not required. In an area that someone might contact sure but this is inside a unit that has covers on it and the only people that should be poking around are service people that obviously are aware of potential electrical hazards. How many switches have heat shrink tubing from the factory? Perhaps in devices rates for 240v but not so much in 120 countries.
That's not a bias resistor. That's R39 and is between the output common rail and input common. So if that resistor is over heating, the amplifier has gone unstable at some point and was likely oscillating way way above the audible range. Load the output. Scope the input and output under various input levels to be sure it behaves it self. Sometimes they can become unstable at a particular volume level but turn up the volume and stability returns. There should have been some kind of high frequency roll-off. There is really no need for the 100KHz frequency response. But if you have a good one and can maintain it, they can sound pretty good.
Hello, wondering if you could replace my power switch on my Hafler and take a look at it, see what it needs? I've had it since 1980 when the retailer assembled the kit. It works great at the moment.
recently i had a weird thing happen. i listen to music over my pc, its obviously grounded. i usually have a audio isolator between it and my preamp since i had a tube amp that was grounded and had hum, but i changed my setup and removed that isolator since it noticeably degraded sound quality. the signal goes over a rca cable to my preamp (nad 1240) over to two different amps, depends on my mood i turn either one on. one out goes into a nad 2200 amp with no grounding lead. the second output goes into grounded active monitor speakers. now when i listen over the nad2200 and switch on&off the grounded monitors, a really loud pop occurs , sometimes even turn off my pc monitors for a short period. luckly it didnt killed my tweeters. but it heck made me jump i had to break ground from my pc-preamp to my active monitors with a car audio isolator, its not as bad anymore but still happens. now i have to turn them on/off only when the nad2200 is turned off
Hey, hats off to you for actually being interested. Very few people actually take the time and usually come to the repair guys with their own unfounded ideas of whats wrong and think that 'educating' the mechanic is helpful which often times it isn't. Generally recapping only affects a very narrow spectrum of possible issues and in good working order of the system a recap would not give any noticeable effect and be a waste of time and even possibly risk damaging the board, though that's certainly not a risk with Dave. Care to explain why this amp is unique?
I've got a NAD 2100 power amp on the bench now with -5VDC at the outputs and can't find the source. The lower power rail negative voltage is also high. It's driving me nuts.
What's the supply voltage if you disconnect the output amp section. Did you check for faulty power supply capacitors. I would check current for positive and negative supply voltage. Also other filter capacitors. If caps and supply section is OK, something might be draining the current - don't have schematic in front of me so I'm just guessing the obvious.
@@pliedtka Believe it or not, after weeks of troubleshooting, I found the problem. A ceramic 100nf cap was blown (C438) which connects to the -45V rail and one of the output transistors. It must have been causing a "backup" of voltage. Filter caps are fairly new, so I knew they weren't the issue. Thanks for the suggestions.
@@ElectoneGuy That kind of weird, the way they run supply rails. Is VAS, predriver and driver rail much higher than out transistors (I would put slightly higher voltage to avoid clipping the waveform). Funny, ceramics supposedly never fail, I like metalized film foil more, my guess was to keep cost down.
@@pliedtka this ceramic probably failed because the owner blew the entire right channel output transistors and melted the -45V filter capacitor. I've never seen this kind of damage before.
@@ElectoneGuy O s..t , I have seen some output tranies with holes in the plastic, but melted capacitors😨. On the other hand they could have run 2 pairs per channel with this voltage rails. Much safer in case someone decides to try 2ohm load. Then I knew a guy, physics student, who miss wired crossover on Focal dual voice midwoofer and send Audiolab 8000A integrated to heaven, big 17A Sankens - one of voice coils was acting as stopper instead of increasing bass output (out of phase). He used Bass tone controls at max because there were no lows.
Would placing a couple of bleed resisters across the main caps help reduce the offset weirdness when its turning off? I am not expecting it would stop it completely, maybe reduce it?
speaking of caps im sorta in a weird choice i have 4 of these devices (internet like devices i should of added) but 2 of them have blown caps just one same spot within 4 months of each other. however i don't have a 1500uf to replace it with though due to them popping in same area on both. i wonder if the other 2 will is this due to low capacitance anyway or something else?. if i put 2 820's in Parallel to do 1640uf instead would this cause any issue?
Please, I would like to ask a question: would it be worth repairing a Hafler DH200 and pairing it with an AMC CTV 1030 preamplifier with a pair of Dynaudio 52 speakers and an Arcam cd73 CD player?
Now that depends on what is wrong. Those DH200 amps sound great but they are very long in the tooth and I don't even know if the mosfet outputs are even available anymore. I would guess no.
Hey i keep seeing you on youtube when i type in CRTs. I have a Gateway EV910A that I'm pretty sure will support 1080p resolution. It has a VGA input on it and I'm using a HDMI to VGA adapter on it. It works really well and the image is great. However, the CRT after about 10min of using will kick off to standby and then kick back on. Once it starts doing this it wont stop. It doesnt do this with 480p content and only on occasion with 720p. I also noticed some trailing, ghosting, and whites "bloom" when its a dark scene. Do you think there might be a solution to these problems? Im your average joe. That doesnt really know much about electronics. But i have opened this unit up already and tweaked the HV pot and focus knobs on the flyback, because there was a large portion of the image being cut off on 720p and 1080p content. So that has been resolved or at least i get more picture now.
@@incandescentwithrage Exactly. This is what causes this phenomenon is as the capacitors discharge one side discharges faster than the other. This is caused by multiple factors. The tolerance of the caps is only one. Generally one side has a greater load than the other as well, as the preamp stages are usually class A and only require the B+ rail. The B- supply is only required after the phase split. All class B (and AB is just a class B with a slight bias to keep both transistors in slight conduction so that there is no point where they are both in cutoff as that results in class B intermodulation distortion) The slight voltage swing as the amp powers down, or the slight "thump" at power up is perfectly normal on these designs. Later designs incorporated speaker relays to disconnect the speakers during the power up, and power down phases, but these amps, being kits were minimal in design. They are a good, basic solid amplifier design that gives very little trouble and can have the crap abused out of them and still work. I would love to have one of these, and a dynaco tube preamp to drive it. That would be the ultimate combo. Tube preamp for the tube sound, and mosfet PA for some kick ass power. My Luxman LV103 is about as close to that as you can get. Tube preamp, MOSFET output, but it is only 60 watts.
Thanks Dave, for the hum / isolation tnfr update. On a previous video, you worked on a SONY KDL-32 TV. I have a similar model and need a schematic to troubleshoot the main power board. Do you have a link to the schematic ? J K
@@12voltvids Thanks for answering. Have the deck cassette; Renkforce tp-1000 and has quite audible flutter. It has many clones (ion tape 2 pc, Marantz pmd300cp, Pyle Pro .....
Client is concerned that speaker cones pulse when powering down. Babble and rave and repeat yourself numerous times for over TWENTY minutes, yet never even once check for what the client specifically wanted checked (unusual movement of speakers).
Just what do you thing the meter measurement was for? That was to determine if there was a voltage that could damage the speakers. I guess you skipped that part or are too dumb to understand. That or you are a troll. You pick.
@@12voltvids - no, I saw you test voltages however you didn't check (or show) the cone movements. So when you wiggle your hand to indicate the the speaker moving, is that how far the cone moves when powering down on THIS amp? In other words, is the problem big or small, minor or major, irrelevant or alarmingly dramatic? Does the cone move a millimeter or an inch back and forth? Does it move just once or repeatedly? Is the client being alarmist, or their concern a genuine one? It would have been good for us to see what was worrying your client, rather than you simply dismissing it as "normal".
@@johncoops6897 Its a non issue. It happens at power up, not power down. The woofers extend about 5 mm for about and retract back over the next 1/2 second. This is because there is no delayed start relay. All amps with no speaker relay will experience this.
@@12voltvids - I am aware of the usual turn-on thump on amps without speaker on a delay relay. However in the video you said numerous times that the client saw unusual cone movement at POWER DOWN eg: watch at 1:20 and 3:30 and 6:04 etc. You spent quite a lot of time explaining it, but you didn't show the degree that this amp exhibits the phenomenon. I think that would have been constructive to demonstrate, as well as quantify what you consider is "not a huge issue". If there was no associated sound, then an easy solution would be to refit the grill cloths, so that the cone movements remained invisible LOL
@@johncoops6897 That is what he initially said, but there is none on power down, just on power up. What does run on longer on this one than his identical unit with original caps is it runs longer at power down, BUT, this one has larger main filter caps then the other one, so it will run for a few seconds longer if there is still audio being fed in.
The way to keep repeat customers is by not ripping them off. That was the philosophy at the shop I worked at for 20 years. The competition did that and one day they got stung by a TV reporter that planted a blown fuse trouble and exposed them when they were told there was tons of parts bad.
