Hello this is my first time here and I need some advice. I finished up the v1.8 on the weekend and before I fired it up I went through the resistance and voltage diagnostics as per the v1.6 build guide. A couple of problems:
Any help will be greatly appreciated.
- On channel A the S leg of Q1 reads 13.6 V - should be 0 V
- On channel B the resistance on R5 is OL, should be 10.9 kohms
Any help will be greatly appreciated.
Q1 source voltage - perhaps you measured the drain voltage. Q1 source is connected to Ground so unless you have the power supply wires mixed up, it is unlikely that the source was at 13.6V. If the power supply wires were reversed, bad things probably would have happened and you would not hear any music.
Resistance at R5 - is your meter auto-ranging or do you need to set the range? Perhaps your meter was not set at a high enough range. You can also compare resistors on both channels to make sure that both channels are identical.
If both channels are making sound, perhaps there is nothing wrong with them.
Have you adjusted the pot to set the voltage at the Q1 drain at 10V if your power supply is 19V or 12V if your power supply is 24V? If not, do that, and then measure the voltage drop across R1 of both channels.
Post some good pictures.
Resistance at R5 - is your meter auto-ranging or do you need to set the range? Perhaps your meter was not set at a high enough range. You can also compare resistors on both channels to make sure that both channels are identical.
If both channels are making sound, perhaps there is nothing wrong with them.
Have you adjusted the pot to set the voltage at the Q1 drain at 10V if your power supply is 19V or 12V if your power supply is 24V? If not, do that, and then measure the voltage drop across R1 of both channels.
Post some good pictures.
Hi Ben. Thanks for the reply. My responses below in italics.
Q1 source voltage - perhaps you measured the drain voltage. Q1 source is connected to Ground so unless you have the power supply wires mixed up, it is unlikely that the source was at 13.6V. If the power supply wires were reversed, bad things probably would have happened, and you would not hear any music. I am pretty certain the power supply wires are correct. I am also pretty certain that I am getting 13.6 V at the S leg of Q1. I am thinking I may have a short to the D leg?
Resistance at R5 - is your meter auto-ranging or do you need to set the range? Perhaps your meter was not set at a high enough range. You can also compare resistors on both channels to make sure that both channels are identical. It auto ranges. The R5 resistor on the other channel reads right around the expected 10 or 11 kohms so I think that rules out the meter. I am also sure I am not shorting to ground/heatsink because I checked for that before I bolted down the boards.
If both channels are making sound, perhaps there is nothing wrong with them. That would seem logical, but I don't think the sound is all that good, certainly not what I was hoping for based on reviews?
Have you adjusted the pot to set the voltage at the Q1 drain at 10V if your power supply is 19V or 12V if your power supply is 24V? If not, do that, and then measure the voltage drop across R1 of both channels. Yup adjusted to 12 V as instructed
Post some good pictures. I'll see what I can do - what specifically should I be targeting?
Any other suggestions would be welcomed.
Q1 source voltage - perhaps you measured the drain voltage. Q1 source is connected to Ground so unless you have the power supply wires mixed up, it is unlikely that the source was at 13.6V. If the power supply wires were reversed, bad things probably would have happened, and you would not hear any music. I am pretty certain the power supply wires are correct. I am also pretty certain that I am getting 13.6 V at the S leg of Q1. I am thinking I may have a short to the D leg?
Resistance at R5 - is your meter auto-ranging or do you need to set the range? Perhaps your meter was not set at a high enough range. You can also compare resistors on both channels to make sure that both channels are identical. It auto ranges. The R5 resistor on the other channel reads right around the expected 10 or 11 kohms so I think that rules out the meter. I am also sure I am not shorting to ground/heatsink because I checked for that before I bolted down the boards.
If both channels are making sound, perhaps there is nothing wrong with them. That would seem logical, but I don't think the sound is all that good, certainly not what I was hoping for based on reviews?
Have you adjusted the pot to set the voltage at the Q1 drain at 10V if your power supply is 19V or 12V if your power supply is 24V? If not, do that, and then measure the voltage drop across R1 of both channels. Yup adjusted to 12 V as instructed
Post some good pictures. I'll see what I can do - what specifically should I be targeting?
Any other suggestions would be welcomed.
Remember that you can not check resistors reliably in circuit. As long as the correct value is fitted then it is highly likely (like 99.9999% likely) that the resistor is just fine.
If both FET's are running hot (they should be) and the midpoint adjusts to around 12 volts then its likely all is well.
If both FET's are running hot (they should be) and the midpoint adjusts to around 12 volts then its likely all is well.
Easy to re-measure the voltage at the Q1 source. Pins are G D S.
Also measure the voltage drop across R1. The net resistance across R1 is 0.235 Ohm. That will give the current (Ohm's Law), and will likely confirm whether the amplifier is working properly.
Also measure the voltage drop across R1. The net resistance across R1 is 0.235 Ohm. That will give the current (Ohm's Law), and will likely confirm whether the amplifier is working properly.
Hi guys - thanks for the input. I still feel like the sound is not where it should be. Do these things need break in?
First, make the measurement that I suggested in post #5 to check the amplifier to see if it is working properly.
What speakers are you using? Are they low sensitivity? The amplifier does not have a lot of power, 8W into 8 Ohm with the 24V power supply.
Post some well lit and focused pictures of the amplifier. Include shots of the whole amplifier showing all of the wiring and closeup shots of the boards. Eagle eyed members can then check the build.
What speakers are you using? Are they low sensitivity? The amplifier does not have a lot of power, 8W into 8 Ohm with the 24V power supply.
Post some well lit and focused pictures of the amplifier. Include shots of the whole amplifier showing all of the wiring and closeup shots of the boards. Eagle eyed members can then check the build.
Thanks Mooly. Both FETs are definitely running hot (and it seems equally). The voltage was around 10V out of the box for each channel and adjusted easily to 12V (finicky as eveyone seems to find).
So I guess I'll put it down to the mysteries of electronics and just listen to the thing!
It certainly sounds like its OK given those results. The only 'unusual' feature operationally of the ACA is it has a low voltage gain meaning it needs a decent level of input signal to drive it fully.
It should sound great though.
It should sound great though.
Hi Ben. I actually thought I wrote a few days ago but it seems it didn't post. I am arriving at the conclusion that the amp is working okay. The more I listen the better it seems. Despite some weird measurements? I am going to see how it goes, and if I have any doubts, I will pursue your suggestions further. In the meantime, I am running a fairly crappy preamp (Schiit Vali 2) and driving a pair of NHT Super Ones (86 db) in my shop. I am going to move it into my listening room and will be driving a pair of CSS Criton TD1 speakers (also about 86 db) so kind of power hungry. We'll see. The more I have listened the more I like the sound - I think it has taken time to get used to the sound of the ACA. Thanks for your time and support.
