JP please read more carefully.
"Put in my stepped attonator but problem remained."
Intention was to leave it out and it was indeed taken out and only then it stopped working wasn't it? Then, as a solution, the protection itself was removed isn't it? Double good 🙂 Anyway I read installing volume control of sorts as a temporary attempt to get the amplifier alive again. As adviced in post #3.
What was the exact cause? Do you know the "why?" now?
What was the exact cause? Do you know the "why?" now?
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What exactly earned me this insult?
Do you really need an schematic to know what a skipped attonator looks like?
Yes. Because it makes no sense that if you skip the attenuator that the entire amplifier does not work anymore. Either the amplifier is something special which does not allow you to do that. Or you skipped the attenuator in an improper way (no insult intended, happens to me as well). Or. Or. Or. Like I say it is not normal so every bit of information is needed. Which is the original circuit and the modified circuit.
I see too many threads here describing an hardware problem where the OP did not go all the way to provide every piece of information. Like inspector Derrick used to say: "Can you tell me everything you saw, leave no details out, no matter how unimportant that might seem to you". After all the OP is asking for free advice and then we (who must provide the free advice) are entitled to know the OP made every effort possible to collect as much information as possible. No insult intended.
And again, my advice to short the contact with the hot side of the potmeter was sincere and should be fail-safe.
The pot was probably the DC ground reference that sets the input bias, and now there is no ~47K "Rin" as in the data sheet notes. Unfortunately, the first diagram in the data sheet has no such resistor because it is very conceptional and would only work if the input source is a DC path to ground. Shame on TI for publishing a misleading drawing, or perhaps assuming the customer knows better.
Without a schematic, we cannot see enough detail to be certain what you have done. If the only thing connected to the +IN is the capacitor then this is your problem.
Without a schematic, we cannot see enough detail to be certain what you have done. If the only thing connected to the +IN is the capacitor then this is your problem.
The first diagram is not capacitively coupled - the later one is and requires the 47K to ground reference the input voltage. The OP is using a capacitive coupled input and also got rid of the required ground shunt. Just pop a 47K (or whatever you want your impedance to be) from the end of the capacitor going to the amp to ground (replacing the pot) and all will be well. Or, use the original pot for the required shunt if that makes you happy. I think (my opinion only) that the prior comment about providing a legible schematic was, in addition to being a very good and helpful idea, also implying that to make electronic modifications to a circuit like this you should at least know a little about electronics and how it works first.
Thanks guys.
Found the Problem: Original pot had ground on the mounting shaft but my stepped attonator dos not. Signal ground on the Chassis is strange. They must have provided the 47k resistor from chassis to input signal somewhere in this birds Nest.
Klaus
Found the Problem: Original pot had ground on the mounting shaft but my stepped attonator dos not. Signal ground on the Chassis is strange. They must have provided the 47k resistor from chassis to input signal somewhere in this birds Nest.
Klaus
Hi, chassis and covers normally only needs to be connected to PE for safety (and shielding as a bonus). Chassis is not and should not be part of the audio circuit! IMHO your amplifier did not have a ground reference at it inputs because of a user error and therefor oscillated. Did you measure with an oscilloscope to see what happened?
My tip is to first make a picture of how a device is, then think if things really need to be changed and think things over both positive and negative, then decide if action is needed. The last is action. After action comes testing/measuring/evaluating. As a procedural sequence mistake was made and we never saw pictures how it originally was we can not see what exact error was made but the person making the mistake asks us what is wrong 🙂
BTW the PE connection (in wrong color so against code just like the bare wires) is only done to the back cover. This is inadequate in case the aluminium is anodized and stuff does not make good contact. You may want to add/daisy chain a second green/yellow wire 1.5 or 2.5 mm2 with 2 ring connectors M4 to the bottom cover. Just to be sure it has a good PE connection.
It would be very wise to repair the speaker protection circuit (think of positive consequences) when the fault has been corrected. True audio OCD also would notice caps not to be orientated directionally.
My tip is to first make a picture of how a device is, then think if things really need to be changed and think things over both positive and negative, then decide if action is needed. The last is action. After action comes testing/measuring/evaluating. As a procedural sequence mistake was made and we never saw pictures how it originally was we can not see what exact error was made but the person making the mistake asks us what is wrong 🙂
BTW the PE connection (in wrong color so against code just like the bare wires) is only done to the back cover. This is inadequate in case the aluminium is anodized and stuff does not make good contact. You may want to add/daisy chain a second green/yellow wire 1.5 or 2.5 mm2 with 2 ring connectors M4 to the bottom cover. Just to be sure it has a good PE connection.
It would be very wise to repair the speaker protection circuit (think of positive consequences) when the fault has been corrected. True audio OCD also would notice caps not to be orientated directionally.
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@Radian , when making modifications, you should check everything, measure everything and draw schematics. It is easy to draw the schematics here, everything is point to point except for the DC speaker protection. If you had sketched the schematics, you probably would have seen the problem right away. Otherwise mistakes are possible and you could burn the amplifier. The grounding of the amplifier and housing also needs to be solved here, as far as I can see it is problematic. Removing the potentiometer is not expected to cause the amplifier to lose the signal GND, gain a DC offset or start oscillating.
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What good is it to contemplate on how it normally should have been done?
Fact is that the ground lug on the old attenator is connected to the shaft and therefore conducting with the aluminum front plate.
Fact is also that I did nothing else than to move the signal wires straight to the coupling caps and the ground to input ground. In practice like any power amp out there. None of the many amps I did this on has ever malfunctioned and this one shouldn't either.
I will install the 47k resistors and see If it fixes the problem.
If you don’t want to see how things can/should be done right for good results that is fine. In this case an error is corrected with another error. The device may be built so so: it did work OK originally.
It is Verschlimmbesserung to work on assumptions. I dare to bet you haven’t measured if it oscillated or not. Many here will think and react similar as a result of the way of working. After all that is what you asked from us.
It is Verschlimmbesserung to work on assumptions. I dare to bet you haven’t measured if it oscillated or not. Many here will think and react similar as a result of the way of working. After all that is what you asked from us.
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You took this once more the wrong way.
I do electrical safety installations as a living and I am in this hobby for over 40 years.
Got a cheap Chinese amp without schematic that developed a fault after a change that should have never caused this. Didn't have the means to do a thorough investigation as I am on the road.
I ask here what people think of it and got a few good hints but others start to lecture and insult me. I can read data sheets, draw schematics and do simple mods even though I might not be able to understand complex circuits.
A few good hints would have done without the insults or the hidden sarcasm.
Klaus
I do electrical safety installations as a living and I am in this hobby for over 40 years.
Got a cheap Chinese amp without schematic that developed a fault after a change that should have never caused this. Didn't have the means to do a thorough investigation as I am on the road.
I ask here what people think of it and got a few good hints but others start to lecture and insult me. I can read data sheets, draw schematics and do simple mods even though I might not be able to understand complex circuits.
A few good hints would have done without the insults or the hidden sarcasm.
Klaus
Haven’t seen a picture of the type and implementation but the problem occured after removing the potentiometer (that was out of the signal path in full open position anyway except for its reference to GND). That is what I tried to determine. There is also no picture of the replacement and I am by no means clairvoyant.
It is hard enough already to “see”/determine what someone else causes and to find a cure to undo a fault. IMHO your comments in post #32 are unjustified in a few aspects. You got both other peoples time and you got quite good advices from various members but you didn’t get the clue I guess.
It is hard enough already to “see”/determine what someone else causes and to find a cure to undo a fault. IMHO your comments in post #32 are unjustified in a few aspects. You got both other peoples time and you got quite good advices from various members but you didn’t get the clue I guess.
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Perhaps it would have been instructive to say up front that you bought it this way and the "point-to-point" wiring is not your own work, not "your fault". I confess that I too assumed that any such creation w/o a printed circuit board had to be DIY. The internet is full of videos of terrible hacks where they wire components together in a similar manner, unsuitable for anything but a quick bench experiment, without any of the features that make a circuit useful long term. Would you approve a 480V 3-phase installation with exposed bare wires hanging out on the floor? It's hard to believe that anything without a PCB is offered for public sale.
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