do apex audio amp ic's have some kinda special rules? - Page 1
Forum section: electronics / projects

author: coppercone2
author_rank: Super Contributor
timestamp: December 16, 2023, 03:39:39 am
content: I fried three different apex chips. One in a dead bug PCB and two in a real pcb.the first one I broke was like a PA60 or something, obsolete. the other two were from mouser . the old one worked for a whileI got a ESD mat, I checked the PSU rails (it goes up to +-15V in like 2 seconds with no over shoot).The last one was installed in a board with no input and no load (50 ohm termination on the input) and it made a crackling noise and I noticed it was dropping 1/2 an amp through the non inverting pins through the 50 ohm resistor.Do op amps not like having a resistor to ground on the non inverting pin in a voltage follower without a series resistor ? I thought it was just leakage current. I assume it fried on power up.I am not seeing why a power op amp with a measly 50 ohm load to ground and a terminated input just fucking fried on first power up. The input pins should be high impedance right? so long the voltage input is within the rails nothing should happen? am I missing something hereI played with alot of op amps from Ti, LT, AD and probobly some others, I never seen this kinda stuff happen before.its the PA74 chip.I am not getting how the base of the transistor can supply that much current if its OK. I thought its limited to like 500 nA.ima solder some bullshit dual op amp in place of this thing with dead bug wire to splice it in and see if this works because IDK what the fcujkthe only thing that comes to mind is that maybe putting a 50 ohm to ground on the non inverting input pin during startup causes some kind of problem so maybe it should be like 1k resistor from the op amp to the 50 ohm to ground but I swear I never seen that be a requirement. its just a fucking random guess. I feel like I saw aalot of successful shit without any fucking resistor in series with the non inverting pin. Actually I am sure I saw op amps used like that for major projects that sold alot.

author: Whales
author_rank: Super Contributor
timestamp: December 16, 2023, 05:43:03 am
content: Neg input: tied to outputPos input: tied to ground through 50R, somehow pulling 0.5AWhat is ground? 0.5A through 50R is 25V. The part is only rated to 40V (eg +/-20V split rail). So you must mean ground = negative voltage rail; or your 0.5A is only approximate and I'm drawing too many conclusions from it.The datasheet says the common mode input includes the negative supply, so that should be OK.Perhaps the negative voltage rail is not connected to the chip or somehow less negative than the ground you are tying to the input through 50R? Then 0.5A might flow into this chip via VCC and then out of the chip via the pos input, either through input protection diodes or some unintended substrate diode misbehaviour effect.

author: magic
author_rank: Super Contributor
timestamp: December 16, 2023, 09:34:03 am
content: The datasheet says all sorts of things which don't make sense if the schematic also included in the datasheet is trueThe topology they show ought to have phase reversal, the output is likely to go to the top rail if the inputs are brought to the bottom rail or the top rail comes up before the bottom rail and the bottom rail is near ground where the inputs also are.The schematic they show has no protection from excessive differential voltage and base-emitter breakdown of input pair transistors, although absolute ratings say there is no differential limit.Very sloppy datasheet OR a very sloppy chip with a very sloppy datasheet. If it's the latter, the two points above could explain how it blew.Send the carcass to Noopy or ask the manufacturer wtf is going on. Or both.editOn second thought,emitter degeneration resistors may save it from phase reversalehm, no, they can't, apex is clearly hiding something hereBut it's still unclear how it behaves when the negative rail is left floating and it's still unclear if it really has differential overvoltage protection.If you would like to try again, add reverse biased 1N5158 or at least 1N4001 from each rail to ground and few-kΩ resistors in series with each input. Connect a scope and look for anything weird during startup.

author: coppercone2
author_rank: Super Contributor
timestamp: December 16, 2023, 10:57:45 am
content: its 500mA total (250mA per channel). Basically the input is at rail voltage at rail impedance.I don't expect a op-amp input to go to -14V or whatever with basically no limiting. I thought a electrolytic capacitor was shorting, I could not believe it was the 50 ohm resistors on the input..................yeah they are pissing me off I think hiding something proprietary. i think i can do this with other chips that I trust more.I don't think I want to try again because its expensivefor the negative voltage, maybe I can try to probe it under the socket with a grabber hook to make sure the socket is not mesed up. I know the socket pin is getting the voltage. Its new and looks good.But the only way it could provide 250mA from a INPUT to a ground impedance setting resistor is through some kinda unlisted diode right? The base of the input transistor would have to be sourcing alot of power. I thought itt could only source 0.5 micro ampers.oh yeah, its from the negative rail. because the negative side of PSU was reading 0.47 amps with the input resistors connected to ground. So the negative rail is coming out of the inputs. if I remove the chip from the socket, there is no voltage on the inputs BTW. I am not soldering anything. I don't think it could be a bridge. I also don't have bolts on the chip, so its not flexing anything to cause some weird short or whatever, and its o nly a 2 layer PCBi wonderi f its possible the socket is messed up and the positive rail is floating??

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: December 16, 2023, 02:24:41 pm
content: I've had good results with Apex stuff but it was many years ago. Their support was excellent so I'd see what they say. Best case is they might replace it. It should work pretty much as you'd expect, no weird requirements.

author: coppercone2
author_rank: Super Contributor
timestamp: December 16, 2023, 04:31:51 pm
content: i wonder if its a sequencing issue, I need to check that the PSU follow close enough. I know its slow and not over shooting but maybe there is a delay between - and + ?but it never broke op amps beforeok once I ruled out the common suspects, it looks like a feedback loop op amp is doing something funny (composite).When I removed some other op amps the rail went back to normal. Maybe this chip is OK.So to clarify:1)first opamp PA60 on dead bug was from ebay, it died under load grilling a resistor. could be natural causes2) second op amp : dead channel, I think DOA3) third op amp : feedback loop op amp making the protection diodes go crazy?3a) checked the socket by putting grabber hooks under it, no problems3b) power supply sequencing ok3c) no short circuits found3d) need to bench test apex amp again with voltage follower configuration to see if it still works as unity gain buffer as it did on arrival3e) if the feedback loop is making the protection diode blast current into the input pins (not sure how this is happening but its related to op amp next to it i pulled) its possible that the input was dead shorted on OPA#2 and then it caused something in the chip to blow up).so maybe its some kind of solvable problem and not a broken part.I bet what happened is that I heard the other op amp make noises on power up. it has been through 3 prototypes already.

author: TimFox
author_rank: Super Contributor
timestamp: December 16, 2023, 04:56:22 pm
content: I don't know about this specific device, but I have had problems in the past with latch-up due to power sequencing on split supplies.A typical cause of latch-up is when any pin of the device goes negative with respect to the substrate (most negative node of the circuit in normal operation) by more than a silicon-junction voltage (0.6 V or so).With split supplies relative to ground, a possible latch-up sequence is having the positive supply present when the negative supply is still an open circuit or high impedance (such as the output resistance of a linear regulator with insufficient input voltage) to ground.In that case, current from the positive supply through the output stage or other parts of the amplifier can pull the negative supply terminal positive with respect to ground, while at least one of the input terminals is hard-wired to ground, inducing the latch-up, which can persist after the negative supply comes up, resulting in large supply current and overheating.(Some mixed-signal devices, such as switched-capacitor filters running on split supplies, have a "ground" pin which is actually an input, the reference voltage for the digital clock input circuit.)The cure for that problem is to put Schottky diodes from the positive and negative supply pins of the device to ground, to avoid full diode voltage across the relevant circuit with one supply missing.

author: coppercone2
author_rank: Super Contributor
timestamp: December 16, 2023, 05:07:14 pm
content: alright since Im not insane and its mostly through hole without solder screen I can add some diode to ground in a fairly easy way if the op amp passes the bench test

author: magic
author_rank: Super Contributor
timestamp: December 16, 2023, 05:37:43 pm
content: Alternatively, don't use a split rail PSU. (Or use it with the center tap not connected to anything).Generate a virtual ground with resistor divider and connect it to IN+.Connect IN- to the output, preferably with another safety resistor in series.See if it works (OUT = IN+).

author: TimFox
author_rank: Super Contributor
timestamp: December 16, 2023, 05:44:18 pm
content: For an audio amplifier, the output pin must source a large current to the load, which either requires a grounded load and a split supply, or a grounded load and a large series capacitor with single power supply and a low-current bias supply.

author: magic
author_rank: Super Contributor
timestamp: December 16, 2023, 05:50:42 pm
content: Or virtual ground with capacitors to each rail of about the same size as output coupling capacitors.Eliminates input coupling capacitors, avoids turn-on transients, but puts ripple on the virtual ground (effectively: on both supply rails simultaneously) and exercises the amp's PSRR more...But we are getting off topic, I think. I simply suggested a way of testing such devices with lower risk of smoke escape.

author: coppercone2
author_rank: Super Contributor
timestamp: December 16, 2023, 07:04:31 pm
content: wait, I have zener diodes on the rails because the PSU I have can put out 40V and its above the regulator voltage. So I limited it to 1 volt under the regulator voltage. I have seen this PSU explode before and put out 60V, so I added the zener diodereversed biased it should perform the same function as the shotkey diode?

author: coppercone2
author_rank: Super Contributor
timestamp: December 16, 2023, 07:16:04 pm
content: hmm ok something aint right, 200mA flows from PSU center point to oscilloscope negative. it should be floatingis that some kinda ground loop hmmwhat is this loloh ok, the alligator clip I grabbed bnc thing was cross wired (ebay addon). I wanted the grabber hook because its better for this then alligator clip but I will just use the old test lead. (this is a new problem from the last 5 min due to poor cable choice)

author: coppercone2
author_rank: Super Contributor
timestamp: December 16, 2023, 07:35:52 pm
content: alright for testing with a 1KHz sine wave that is from a isolated floating source with a good bnc cableit looks like when its powered on both channels pass a sine wave with the voltage follower configuration. when its powered off you pass a half sine with some bump on top, I imagine that is what the op amp does when its not powered but has a input. Wired with a whole lot of grabbersthe bad amplfiier passed nothing at all with the burned channel or whatever it isso maybe the amp is fine, and the noise I heard was the little amp burning up. not sure how it passes current but at least maybe its not a 100$ burn upima take some time to make some better cables because i fee llike I am at the point right now where I typically blow something up due to lack of proper experiment planning (when I want to run it over)I think a BNC to grabber, proper DMM probe with shrowd, maybe some mini-clips with the hook up dupontand it just fried. trashed. i think i will stick to other manufacturers lol

author: schmitt trigger
author_rank: Super Contributor
timestamp: December 16, 2023, 07:44:49 pm
content: Just curious; how are you heatsinking these devices? The multipin TO-3 package is not very common.And I know, I know. you mentioned that one blew up from the powerup, so it may not be a thermal failure.

author: coppercone2
author_rank: Super Contributor
timestamp: December 16, 2023, 08:06:19 pm
content: whatever i am not doing further research on apex parts. trash cani might solder in a dual op amp in there just to exonerate my PCB but whatever if the regular things I do for all my parts don't work for apex and i don't have some kinda crazy specific requirement for apex then im not gonna use apex. and yes the heat sink is inconveniant and expensive enough that it makes me further not want to use apex (and it was over powered for my application anyway). the savings from the integration minus the pain in the ass from the heat sink in the design minus whatever special thing I am missing makes the net worth negative as fuck. maybe the satilite aerospace people can figure this out but its not what i needim not gonna be terrorized by this huge bastard anymore

author: TimFox
author_rank: Super Contributor
timestamp: December 16, 2023, 08:29:14 pm
content: Quote from: coppercone2 on December 16, 2023, 07:04:31 pmTo prevent latch-up, the diode drop (when it is forward biased, i.e. power supply reversed) must be less than 0.6 V, so a Schottky is required.Zener diodes when forward biased are equivalent to a normal P-N junction.Before retirement, we used TO-3 power op amps from Apex with split supplies (required for DC operation) successfully to drive precision 40 W DC motors. I think we had local protection diodes on the board.The only need for such amplifiers is if you need relatively large output current (as in our DC motor drivers), or for simple audio power amplifiers.

author: coppercone2
author_rank: Super Contributor
timestamp: December 16, 2023, 08:32:09 pm
content: they should put a foot note because thats a pretty god damn huge requirement

author: TimFox
author_rank: Super Contributor
timestamp: December 16, 2023, 09:53:18 pm
content: I don't know that that device is more prone to latch-up than others, but the diodes are a good precaution.Devices that did latch up on me, before a useful engineer at LT told me about the diode trick, ended up almost shorting the +6 to -6V lines (for that switched-capacitor filter), and if the power supply was capable of large currents the devices (DIP package) became painful to the touch and failed.The failure mode is equivalent to grounding the op amp input terminals, open-circuiting the negative pin (which will then go positive wrt ground), and supplying +15V from the positive power pin to ground.

author: coppercone2
author_rank: Super Contributor
timestamp: December 16, 2023, 10:04:07 pm
content: alright but where do you put these diodes. if I make another board with different parts (probobly LT) I might as well add these diodes.Can they be by the power input connector where I have the RF caps, zener diode, TVS? or must I put it near the amp.or should they be after the LDOs?

author: TimFox
author_rank: Super Contributor
timestamp: December 16, 2023, 10:05:01 pm
content: Connect each of two diodes from a power pin to ground, so that each is reverse-biased in normal operation.I would put them close to the device, but it may not make a difference.

author: coppercone2
author_rank: Super Contributor
timestamp: December 16, 2023, 10:06:57 pm
content: but before or after LDOs??this board has pos/neg LDO and powered from DC source (LAMBDA). (LT3015/LT3083)I don't like clutter near the device!I have an accidentally ordered PA74 too. I guess I could give it one more try by doing some fancy footwork with the pins on that so it can solder to the bottom of the socket.maybe some nye fireworksaFTER that one breaks too maybe I can wire the TIG welder into the board and do a stress testanyone notice that by the time you are doing cruel experiments on chips bending the leads and mounting them upside down in grotesque PCB structures the problem ends up being solved? just reroute the elephant spleen into the badger ear and its all good!

author: TimFox
author_rank: Super Contributor
timestamp: December 16, 2023, 11:13:05 pm
content: After the LDOs, directly to the pins of the op amp.The circuit I was working on, lo these many years ago, where I learned about latchup had a 7806 and a 7906 on the board driven from the external +/- 15 V power rails.I found that the 7906 negative regulator had a very high output impedance when the input voltage to it was below dropout.The device was a CMOS switched-capacitor analog filter IC, where the signal voltage was symmetric about zero and the filter needed split supplies to follow it.

author: coppercone2
author_rank: Super Contributor
timestamp: December 16, 2023, 11:21:55 pm
content: what diode do you recommend.I thought a 1n4148 would work but I see that still a silicon diode. the voltage drop is too high. for some reason I thought that was a skI get like 0.6 on that one

author: TimFox
author_rank: Super Contributor
timestamp: December 17, 2023, 12:15:40 am
content: Maybe a 1N5819 DO-41 TH part (nominal 40 V, 1 A).Max Vf = 0.6 V at 1 A.Typ Vf = 0.25 V at 0.1 A.1N5818 rated at 30 V, slightly lower spec Vf.

author: coppercone2
author_rank: Super Contributor
timestamp: December 17, 2023, 12:19:07 am
content: I have 5822 and 5819 in large box 2vdrop is 0.178 on the 5819maybe I should wait till 4am to buy another apex so i can make a comfortable bad late night decisionsoldered them in under a nearby ceramic decoupling capacitor close to the shark cage. anything can happen now

author: coppercone2
author_rank: Super Contributor
timestamp: December 17, 2023, 01:30:06 am
content: alright, I put the diodes on, got the part out of the trash and fixed the leads with a pair of non esd safe knipex pliers.it looks like in circuit now the input and the output are both at 0V and current consumption is low. I need to plug in signals still but either1)the diode eliminates a startup problem2)i broke it more3)i fixed it by handling it like a troll, did I mention the diode polarity was wrong on first attempt, and the negative voltage rail got positive voltage because I swapped the PSU leads to red black red black rather then red black black red. I assume the zener diode did some work for the first time in its lifebut its not stuck at 14V on the output.none the less a 0 signal is less infuriating then a next to rail signal even if broken, so it broke in a better wayits possible the PSU was causing the same problem as it was in circuit with 2x regulators (since that is what it is) during benchtop testing with leadsits kind of ridiclous though about the diodes. they need to add that info in LDO sheets and stuff. like it must be damaging the market not to know if you need low drop diodes there for no good reason. before it requires a 2000 dollar FPGA with polyphasic dsp quantum bullshit to solve a problem because of missing diodes

author: coppercone2
author_rank: Super Contributor
timestamp: December 17, 2023, 03:51:18 am
content: i reattached the 50 ohm termination resistors on the input. no current drawI think those magic diodes did something

author: coppercone2
author_rank: Super Contributor
timestamp: December 17, 2023, 06:52:39 am
content: hmm I don;'t think tis outputting current.but not having 14v on the input seems promising. i need to wire a load test. maybe i will get another one. i just need to believe those diodes will prevent a power on deaththe circuit i have is a lttle weird but with the pa60 it was smoking... power resistors with some seriously ghetto wiring

author: coppercone2
author_rank: Super Contributor
timestamp: December 17, 2023, 07:13:16 pm
content: Ok, so what I am seeing now, is that when its set as a inverter, only whatever bleeds through from the function generator is making to a load.I disconnected the feedback loop (resistor from turret) and jumpered the output to the inverting terminal to make a in circuit buffer amp. It does not appear to do anything.I wonder if those diodes helped or if it just totally broke down inside.

author: jonpaul
author_rank: Super Contributor
timestamp: December 17, 2023, 07:25:10 pm
content: IC body substrate diode latch up is back 50 years.All bipolar ICs have it. Larger hybrids like the Apex power op amps are more suseptable due to large area of the transistors.Dual supply opamps of any type need a reasonable supply turn on.Check the turn on of the setup, +/- PS.Try with a good quality lab supply.Bon chanceJon

author: coppercone2
author_rank: Super Contributor
timestamp: December 17, 2023, 09:04:24 pm
content: like i said, its regulated locally (island regulator principle)i used the same damn method for many circuits with no problem. I think its just the power op amp that needs special attention.is there any other things i can add to a op amp PCB to make it less prone to break on startup? I got the diodes now. When I could not figure out WTF was going on, I cut off the ESD diodes because I forgot the resistors under the PCB were there, I thought the diodes were getting hot. I will reattach those too.To summarize for anyone else trying this: the effect of not having the SK diodes on the rails might be that the op amp inputs are capable of sourcing rail current through something or another.the power supply is LQD422. I bet its the local regulators and not the supply. I think that one is really symetrical. their identical sections, powered from a split transformer.I am also gonna make some SK diodes on lugs so I can put it in front of the power supply for testing with cables.

author: coppercone2
author_rank: Super Contributor
timestamp: December 17, 2023, 09:53:51 pm
content: Lol okOn the PCB,-both channels don't seem to put out current, not high power consumption. the output is 0V. Basically does not respond to input on either channel, you get some feedthrough of the signal (same as powered off) on the output.on wires with the SK diodes at supply.-1 amp on both chips works. the other amp is at rail voltage, Does not respond at all to any activity on the non inverting pin. . they can smoke a resistor. if you connect a resistor to the railstuck output pin, it gets serious juice through it. The other side of the amp gives output proportional to input.IDK if the supply is causing a channel to seize. The board has lots of decoupling (good capacitors) and diodes right near the chips.But it seems if I do the same experiment where i short out the feedback path to make a inverting amp, its not putting out current.so IDK if anything is even broken. Maybe?when I try it from the PSU I have the 2 SK diodes on each channel and then a long tight twisted pair of 18 AWG wire connected to graBBERS. Maybe I need local decoupling or something. I think I need to buy another socket, and make a test PCB with some decoupling capacitors.christ, this is about as easy as starting a old chain sawMaybe I get the old HP dual supply with the 'tracking' function out. Then raise the voltage slowly for the chip.bcause the version of this circuit that worked was1) older amp2) protoboard3) decoupled pretty good (tantalum and ceramic). The PCB version is ceramic and electrolytic polymer (did not want tantalum).4) same power supplyMaybe it does not like ground planes or something but still wants decoupling?? or tantalum caps? maybe I made the rail decoupling ESR too low, I did go kinda crazy with it....

author: coppercone2
author_rank: Super Contributor
timestamp: December 18, 2023, 04:01:58 am
content: lol now with the dual HP supply that has the tracker it looks like the OLD apex chip is stuck with a rail output but the newer chip is pretty much doing the same thing that it was doing with the lambda dual supply turned on to set voltage. (in PCB)they keep changing states!AND IN THE circuit with the new supply I get a symetrical response but its not correct. It seems to have trouble pulling negative. I wonder where the damage occured if the chip was damaged by the mechanism proposed. maybe it causing that. and there is at least a different response when the power is applied and removed. before it was like invariant.I am actually thinking way back when I did have filter circuits that did not work. Not SC filter but still. I wonder if this issue was related. I think I have some research to perform on circuits abandoned long ago. They got so complicated with dead bug soldering I never wanted to take it apart to verify the op amp did not break on start up, I just gave up.

author: coppercone2
author_rank: Super Contributor
timestamp: December 18, 2023, 07:53:48 am
content: also, what is some good integrity test to run on power op amp to check for damage?like most informative tests, etc.I think I gotta take this slower so I am on a cloaked goose huntI thought just inverting/non inverting amp with a resistive load. But are there more telling tests? perhaps just a speaker maybe? good quality audio = good op amp?

author: coppercone2
author_rank: Super Contributor
timestamp: January 14, 2024, 07:04:43 am
content: well the high speed scope shows that something funny is happening when you have a high bandwidth.a test you might want to run on bad amplifiers is to sweep the frequency low pass filter (i.e. rigol) to see if the wave form changes or gets less stable

author: coppercone2
author_rank: Super Contributor
timestamp: January 15, 2024, 11:00:30 pm
content: bought another socket so i can try these on a slowly ramped tracking power supply with diodes in simple configuration

author: coppercone2
author_rank: Super Contributor
timestamp: February 14, 2024, 05:21:26 am
content: Ok I got another socket and I made inverting amplifiers on both sides. It looks like the same part of the opamp is fried on both. I soldered resistors (grounded on input) to the socket to see if 0V - 0V. One side works one side no. It makes me think my board has some kind of defect thats waxing partsfor the non inverting topology, one side responds to input being grounded, the other does not.I wanted to test it by1) connecting it to 0V output dual tracking HP power supply2) slowly ramping it via knob while in tracking mode to +-10V3) dismantle socket configuration and rewire it to non inverting topology and repeat 1&2Can I do this without the damn diodes and capacitors to just see if a new in box chip works with grounded input? I verified the supply tracks with 1mV accuracyWires soldered to socket that are inserted into binding post. the only thing to clip on is oscope lead. connection lenght 6 inches of wire per supply connection (3 wire)the idea is to get the part from the box while wearing a esd strap, insert it to socket, ramp up supply. When powered and set to 0V the supply measures 4.1 milivolts. Though I did not see any overshoot at all during turn on so I guess I can plug it in off too.

author: coppercone2
author_rank: Super Contributor
timestamp: February 22, 2024, 08:00:55 am
content: I made a dedicated test socket for inverting amp configuration. This one I plugged in when it was set to approx 2mV and ramped up to 12V with potentiometer.The third apex chip functions as expected. 0V in 0V out. Hard soldered. The other two are broken.I will rewire the socket just to test non inverting operation, but I suspect either my PCB is breaking parts, or I got two broken parts in a row.Given the fact that both amps have fried at the same position, I am inclined to blame my PCB. Not sure how its doing it.Hahaha and I thought that this board was simple enough to test! Tempted to put the diodes locally right up against the IC and test it again but its expensive proposition.I can wire in a dummy load, and compare to the broken chips in the PCB, to check for latchup conditions. I should have tested the parts first before plugging them in before going on this wild goose chase but I was so confident it would just work.seems to work in non inverting configuration too.

author: coppercone2
author_rank: Super Contributor
timestamp: May 26, 2024, 08:21:42 am
content: Quote from: TimFox on December 17, 2023, 12:15:40 amalright mr. white!third try is the charmI think the 2nd one I fried I had the diodes on the input, not after the LDO. I modified the board a while ago, so the diodes are connected from the socket to ground, but I was too irritated to try to turn it on again because thats one expensive chipfinally, I can power it up and down and the current draw stays low on both channels, and plugging it back into the test fixture, the output is 0 V for both channels.So I guess at least the first problem was the LDOs.Maybe If i can renember WTF i was doing so long ago, I can proceed with the design.I did like 5 power ups now, and the chip is intact. I need to reattach all the random stuff I cut off to try to trouble shoot it, then If it works with the other stuff I can try to plug it into an function generator!!I guess a more proper design would have tracking rather then diodes. might be a interesting circuit to implement. getting tricky now

author: coppercone2
author_rank: Super Contributor
timestamp: October 06, 2024, 07:29:40 am
content: Ok I took a bit of a break from this one, it looks like its not fried and its not oscillating.I need to shore up this board before doing more work thoughThe power rails I had were quite poorly timed. It did not look like much but it was pretty bad, thats what I get for trying to be fancy with local regulators, and the diodes fix the problem.I tried a power sequencing circuit, I think I can get them to track, but the parts count, compared to 2 diodes, is obscene. Really glad its not the PCBI need to clean up my bench to be able to work on this. it really got out of hand LOL. I think I went on strike when I can't fix the 6177A and then this board kept breaking.

author: mawyatt
author_rank: Super Contributor
timestamp: October 07, 2024, 03:07:04 am
content: Here's some AWG Amps that folks might find interesting, one of the HV designs uses an APEX PA443 and another uses the OPA462. Also designs for the LM3866 & LM1855 that we haven't assembled yet, and some other High Current & Power Op-Amp types. PCBs are here somewhere and parts (think) but haven't had time nor need for these just yet, just the HV version were needed and thus assembled.Recall everything runs off 12VDC, and has Dual Output +- 180V HV Switcher on the PCB for the PA443 and +-90V, higher current versions also have on Dual Output PCB Switchers.We botched up the PCB for the PA443 didn't pay close attention to the left and right Op-Amp Inputs/Ouputs and got them swappedhttps://www.eevblog.com/forum/testgear/hv-buffer-amp-for-awg/Note the waveform voltage levels at 50V/div with the PA443!!Best

author: coppercone2
author_rank: Super Contributor
timestamp: October 11, 2024, 04:28:35 am
content: now they seem to be talking to each other, that is one amplifier takes over and the other one does nothingthis amplifier is hard. I had the same circuit working in a bootleg prototype with their older version. I thought I optimized some of the resistors, so I will take my current PCB and change a few values to match the prototype (which was on proto board)I think they want the circuits more physically separated. I made it real tight.usually its the opposite where it works better on a PCB lolI wonder if this has to do with Class - C topology they use.And the working one had wire wound resistors and giant feedback loops with inches of wire. Tempted to take the broken apex chip and solder on an adapter to the cheap-style apex chips to see if it works in the same circuit too. Glad I did not throw away that fried amp yet, I can turn it into a socket thingI am glad i spent a day making a proto type by hand instead of doing the 'strait to cheap PCB' thing and never figuring out that it could actually work.That PCB you made looks useful to drive a ultrasonic thing. but the ultrasonic wand I bought uses a transformer transducer and vacuum tubes, but that one might be able to make a higher frequency wand or something.Ultrasonic styrofoam float clamp? can you position a sphere of styrofoam in a axis by changing phase of two transducers or something like that? that would be a fun shooting game for darts or a blow gun

author: coppercone2
author_rank: Super Contributor
timestamp: November 05, 2024, 02:58:44 am
content: do these things have some kind of problem with cross talk?I did alot of adjustments and the circuit I had working on a perf board with a cheaper apex chip just does not work. There is a 'dominant' signal that takes over the amplifiers outputs. I think it might be unstable or something. Or its damaged again. They should be isolated from each other as far as I can tell, other then having a common groundI think I am jus t gonna go to some normaler chips. I am kind of sick of this thing.

author: Analog Kid
author_rank: Super Contributor
timestamp: November 05, 2024, 03:15:02 am
content: Quote from: coppercone2 on October 11, 2024, 04:28:35 amWait, that can't be right: class C is only usable for RF. High efficiency, high distortion (nonlinearity).Class A?

author: TimFox
author_rank: Super Contributor
timestamp: November 05, 2024, 04:05:16 am
content: Quote from: Analog Kid on November 05, 2024, 03:15:02 amI believe the Apex amplifiers run in class AB, like other op amps.

author: coppercone2
author_rank: Super Contributor
timestamp: November 05, 2024, 06:31:05 am
content: says cAt least I learned like 50 things about actually designing a amplifier prototype PCB to make it... possible to trouble shoot it.

author: coppercone2
author_rank: Super Contributor
timestamp: November 06, 2024, 03:45:23 am
content: I got a pin compatible part that is much older and not from apex.I wanna plug it in and see what happens. OPA2541

author: coppercone2
author_rank: Super Contributor
timestamp: November 09, 2024, 06:43:41 pm
content: this chip starts oscillating and drawing alot of current in the circuiti must have failedi guess i need to do a redesign that was more like my wired prototype instead of using all the pcb layout best practices