I think I need to focus on the protect issue first. The noise may not be present with woofers instead of a small full range speaker.
The driver board in a socket is a bad design. It should have been soldered in. The ones that do use pluggable connectors, typically use two pins for each connection to prevent intermittent connections (which can lead to blown outputs if a connection is intermittently broken).
You still need to see if applying pressure to any components or parts of the board will make the noise change like it does when flexing the board.
You still need to see if applying pressure to any components or parts of the board will make the noise change like it does when flexing the board.
So the only thing that makes any difference is if I touch the top of c3 and c3 cap with my fingertip makes a buzzing noise like if you tap the end of a rca to an amp. And I tiny scratching if I move rt1 temp sensor for the output fets.
Is c3 the electrolytic between the RCAs and the speaker outputs?
You mentioned a 'frequency adjust pot' in one of your posts but I don't see it on the PCB photos. The only POT I've ever seen in MMATs 4080's is the high current limit adjustment pot. Did you mess with it? Or were you referring to the crossover frequency adjustment pot?
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No and this one does not have a pot. He was getting rid of dc offset in that post.
Post 53 is what confused me.
'Off of those feeds there are c8 and c15 filter caps to the frequency adjust pot.'
People find the multi-turn limit adjustment pots in these and mistake them for offset or rail adjustment pots. I just wanted clarification that you didn't find something like that I couldn't see in the photos and start turning it. I'm late to this party so i'm trying to get myself caught up and rule out any user error in the process.
'Off of those feeds there are c8 and c15 filter caps to the frequency adjust pot.'
People find the multi-turn limit adjustment pots in these and mistake them for offset or rail adjustment pots. I just wanted clarification that you didn't find something like that I couldn't see in the photos and start turning it. I'm late to this party so i'm trying to get myself caught up and rule out any user error in the process.
Thank you for clarifying. Precisely which pin of the comparator is driving the protection LED? Your chart is sideways and confusing. Some of your pin data looks incorrect in one of the posts.
The protect led is out put 3 of the comparitor. The paper says thermal but it is the protect output.
You're oversharing a bit. We don't often have the luxury of comparator block numbers on a schematic so I ignore those. I go for inputs, outputs, and a datasheet on the part. That's the sure way and it works every time. So output pin is pin 14.
Here is a format that helps:
8 (- IN): 3.37v
9 (+ IN): .35v
14 (OUT): .04v
Using Perrys explanation:
'When the '-' input is higher than the '+' input, the output will be 'low'.'
This comparator block is functioning correctly. We now have to look at the input signals because the part is doing what it's being tasked to do properly. But this is where I run into another problem with the posted information that needs clarified/corrected.
From post #53: 'Pin9 high input for 3 goes to soft start pin14 of sg3525.'
The soft start on a 3525 is actually pin 8. Pin 14 of the 3525 is a PWM output. If you reference the D3 schematic posted then pin 9 of the comparator is tied to the 6v BIAS line for the entire pre-amp. Except I don't see that voltage there. If it was, the comparator output would go high.
To be clear, those readings were taken with the amplifier powered up and producing sound but the protection LED on?
Referencing chassis ground, what is the DC voltage on pin 7 of the 4080 socket? You can take this measurement from the open pins on top of the eliminator PCB, amp at idle, no signal. Be gentle and don't slip.
Ok yeah my pin numbers are all screwed up, my phone thinks it knows what pin number I want and is auto correcting. My apologies. It was to pin 8 of the sg3525. When the amplifier is powered up and producing sound the protect light is not on. The protect light is only on when there is b+ and b- connected and no remote connected.
So what information do you need going forward. I will double check all info before I post, just in case autocorrect tries to change anything.
First i'd like sort a few things out so we have solid data. I don't think pin 9 of the comparator goes to pin 8 of the 3525 but you say it does. I say this because the soft start should provide a slowly ramped DC voltage > 4.5 when the 3525 is enabled. But that's not present on pin 9 of the comparator. And it doesn't connect to this on the D3 schematic. I need to validate or invalidate the D3 schematic against your amplifiers circuit.
We can confirm one way or another by taking a voltage reading from each pin (9 of the comparator and 8 of the 3525). If they are connected, they will be the same. Take the measurements and post them here.
To work forward a little, I'd also still like the DC voltage measurement I asked for from pin 7 of the 4080 socket.
For both of these readings the amplifier needs to be in a 'working' state. You need no load or signal. But you'll have to do the power wire dance to bring the power supply up as you have been.
We can confirm one way or another by taking a voltage reading from each pin (9 of the comparator and 8 of the 3525). If they are connected, they will be the same. Take the measurements and post them here.
To work forward a little, I'd also still like the DC voltage measurement I asked for from pin 7 of the 4080 socket.
For both of these readings the amplifier needs to be in a 'working' state. You need no load or signal. But you'll have to do the power wire dance to bring the power supply up as you have been.