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Amp Camp Amp Kit 1.6/1.8
Amp Camp Amp Kit 1.6/1.8
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Old 13th June 2021, 05:27 AM   #981
Mooly is offline Mooly  United Kingdom
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Amp Camp Amp Kit 1.6/1.8
The important voltage is the midpoint at the junction of the 0.47 and 0.68 ohm resistors.

I don't follow your readings, they show around 12v on Q2 source which is good but you then show Q1 source has 11.4v present. That should be ground (zero volts).

Don't overthink it.

Have you connected the speaker sockets correctly? Remember the ACA inverts and so the sockets are wired differently to how you expect. Red goes to ground and black goes to the amp output.

Make sure you haven't inadvertently added a short across the speaker socket by wiring them incorrectly. You should hear the speaker thump at switch on.

If the voltage on the PLUS end of the 3300uF cap is 12 volts and adjusts and if the FET's are hot then its probably all OK circuit wise and you have a simple wiring error in the speaker or inputs.
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Old 14th June 2021, 12:13 AM   #982
nacarp is offline nacarp  United States
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Default Measuring Resistor values once the board is packed.

ACA v1.8

I have a general question. R12 is 39K, once it is in a completed board should it still measure as 39K, or does the rest of the circuit, especially capacitors now make it impossible to measure the resistor in situ?

I think the value may be out, as in situ it is measuring as 20K.

This is my second DIY project and don't know all the basics yet. I imagine to measure it accurately now I will have to remove it from the board?

Thank you.
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Old 14th June 2021, 07:31 AM   #983
Alan4411 is offline Alan4411  Wales
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R12 should measure about 39k on a populated board.
Double check by measuring from the GND (ground line) to the RCA input centre pin. That should read 49k to 50kΩ and is R11, R12 and R14 in series.
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Old 14th June 2021, 07:52 AM   #984
Mooly is offline Mooly  United Kingdom
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I'll add my two penneth here seeing as this was the day job for many many years and this scenario crops up on a daily basis.

Checking resistors in circuit is totally unreliable and not only because of surrounding interconnected components affecting the result.

The DVM type, its internal test voltage used for resistance measurement, the range you select and set and the polarity of the test leads all contribute to errors.

On the ACA, anything connected to the input (via R11) can also affect the result.

On a practical level if a low value resistor reads OK in circuit then it probably is so. If a higher value one does the same and reads exactly correct then it to is probably OK.

If you do not see the expected result then isolate one end and retest.
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Old 14th June 2021, 09:41 PM   #985
nacarp is offline nacarp  United States
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Thanks, I'll isolate and measure again, and will check the end to end resistance also. I had 39K on one channel, but 20K on the other, it is this discrepancy I did not like. Awaiting a better multimeter at the moment but will post my results when I get them.

I've found Step 56, so I'll check some voltages too.
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Old 15th June 2021, 05:28 AM   #986
Broth is offline Broth  United States
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Hi Mooly
I checked all connections for input and speakers and I had them wired correctly but I went ahead and reflowed it all to be sure. Also I found minor solder spatter between S & D of Q1 ( where S read 11v instead of 0v) it didnít look even close to bridging the two but I scraped everything clean prior to powering up.
Let it warm, adjusted voltage and rechecked S on Q1, now it reads 9v instead of 0v. What would cause that?
Anyway I plugged in a preamp and CD player and fired it up. Didnít hear the bump but did hear the caps charging so I hit play and it worked!
Should I be concerned about the voltage at S on Q1?
When I build my second one and it reads 0v on that one will they sound different from each other?
Thanks for your guidance. Iím feeling more confident about building #2.
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Old 15th June 2021, 06:09 AM   #987
RafaPolit is offline RafaPolit  Ecuador
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Just to confirm: there is no thump on startup of the ACA, only those charging caps sounds. Depending on your setup (stereo, balanced, bridged, etc.), there is a power off thump, but very minimal.
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Old 15th June 2021, 06:14 AM   #988
Mooly is offline Mooly  United Kingdom
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Q1 is the lower FET and the source should go to ground (zero volt line). I think you are mixing up the terminology here That point should always be zero volts, even if you have a fault or a short anywhere else.

The middle lead of Q1 is the drain and that should be adjustable to either +9 or +12 volts depending on whether you are using an 18 or 24 volt power supply.

If it will not adjust then first question has to be whether the input FET (Q4, the 2SK170) is a genuine part.

If you can not achieve that 'half supply voltage' setting on the middle pin of Q1 then you have an issue, either Q4 is suspect if not genuine or you have a component error.
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Old 15th June 2021, 07:57 AM   #989
Broth is offline Broth  United States
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The middle lead of Q1 is where I adjusted voltage. The lead marked S on the Q1troubleshooting photo indicates 0v. This is the lead that shows 9v not 0v on my white board. Am I still confused? Yes I am
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Old 15th June 2021, 08:21 AM   #990
Alan4411 is offline Alan4411  Wales
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Quote:
Originally Posted by nacarp View Post
Thanks, I'll isolate and measure again, and will check the end to end resistance also. I had 39K on one channel, but 20K on the other, it is this discrepancy I did not like. Awaiting a better multimeter at the moment but will post my results when I get them.

I've found Step 56, so I'll check some voltages too.
Before you do anything else, make sure the rear switch is in the 'Central' position. If it is in either of the other positions you will have parallel connections between the 2 inputs...
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