Troubleshooting
Removed keratherm, confirmed no contact with mosfet pins
R13. L=1.0, R=1.18
R4. L=.74, R=.69
R15. L=4.60, R=4.73
Looked at soldering yesterday, added solder to headphone jack and input selector switch, all else seemed ok.
Removed keratherm, confirmed no contact with mosfet pins
R13. L=1.0, R=1.18
R4. L=.74, R=.69
R15. L=4.60, R=4.73
Looked at soldering yesterday, added solder to headphone jack and input selector switch, all else seemed ok.
How do I confirm PSU voltage? Never done that before.
Do you mean the GND Pad next to the power jack thing? I don't see another one.
Yes I have the additional ground plate.
Cannot compare the voltage across R12 before the weekend, but will do that ASAP.
Thanks so far!
ref to Articolo change (decrease) value of R4 to get 10mA through
you can check that as voltage sag across R4 and compute as I=U/R , or observe voltage across R15, expecting 5mA there
or even better - change R4 with trimpot (200R) connected as var. resistor (mid pin and one outer shorted) , starting set to max. resistance and dial it to have output node at 1/2 PSU voltage
you have two wires , bringing GND and +B from switcher to pcb
measure at wire pads what is PSU voltage
Troubleshooting
Thx for the support ZM. Help a bonehead understand what might be happening. The amp worked fine for a few weeks then “tick” and now there is noise. What do the voltage numbers indicate? How can the voltage at DC1 for L and R channels be so different now when a few weeks ago they were close to each other? Why would Q5 and Q6 temps between the L and R be so different? I’m happy to put in a trim pot for R4 just trying to understand why it might be an issue.
Thx for the support ZM. Help a bonehead understand what might be happening. The amp worked fine for a few weeks then “tick” and now there is noise. What do the voltage numbers indicate? How can the voltage at DC1 for L and R channels be so different now when a few weeks ago they were close to each other? Why would Q5 and Q6 temps between the L and R be so different? I’m happy to put in a trim pot for R4 just trying to understand why it might be an issue.
Hi Zen Mod,
thank you for the quick reply. Haven't had the chance to do it yet. Sorry, but I am not native English speaker so please help me out. Here is a picture of the PCB:
20210109 194539 HDR — Postimages
Now I can see a GND hole next to the power jack. What do you mean by switcher and +B? I can solder, but measuring due to house moving currently not available. Thanks again for your patience.
Cheers,
Johannes
Last edited:
after 2sec more of thinking , there is a question - do you know how to test/match JFets ?
see enclosed sketch - you can use 9V battery instead of supply marked as 12V
DC jack , right close to it - pads V+ and GND
set your DVM to Vdc ( range more than 24V) , black probe to GND , red probe to V+, measure , write here
Attachments
Troubleshooting
Hi ZM, thanks again. I did not match JFETS. The L74’s were a matched quad form The Store. The J113’s were a random buy from Digikey. I looks like R4 is too large which I can change to a trim pot or lower value to get closer to the 10mA specified. Could this be the source of the noise/hiss in the R channel and the wierd voltage readings in the R channel? This preamp worked fine for several weeks so I’m very confused. DC1 on both channels measured 11ish volts when I first built it and now DC1 is way off on the R channel. Thanks again?
Hi ZM, thanks again. I did not match JFETS. The L74’s were a matched quad form The Store. The J113’s were a random buy from Digikey. I looks like R4 is too large which I can change to a trim pot or lower value to get closer to the 10mA specified. Could this be the source of the noise/hiss in the R channel and the wierd voltage readings in the R channel? This preamp worked fine for several weeks so I’m very confused. DC1 on both channels measured 11ish volts when I first built it and now DC1 is way off on the R channel. Thanks again?
Troubleshooting
Got it ZM. I assume that means desolder and remove from the PCB. I have an extra car battery, is that an acceptable 12v source or just use a 9v? The JFETs your talking about are the J74’s? Both channels or just the R? Should I remove J113’s and test them too? Am I looking for a specific mA reading on the DMM or just that they are close to each other?
Out a Sea Ranch this weekend for Wife’s 56th so can’t start until next week. Many thanks for your time.
Got it ZM. I assume that means desolder and remove from the PCB. I have an extra car battery, is that an acceptable 12v source or just use a 9v? The JFETs your talking about are the J74’s? Both channels or just the R? Should I remove J113’s and test them too? Am I looking for a specific mA reading on the DMM or just that they are close to each other?
Out a Sea Ranch this weekend for Wife’s 56th so can’t start until next week. Many thanks for your time.
just use 9V
car batteries are nasty - you'll have welder, in case of any mistake or mishap
check all JFets, while you're there
car batteries are nasty - you'll have welder, in case of any mistake or mishap
check all JFets, while you're there
ACP+ V1 R2 Parts and Questions
Hi all,
I bought the PCB Boards for the ACP+ (V1 R2). This is going to be my first DIY project ever and of course, I have a few questions.
I read the article on the Firstwatt website for ACP+ and it seems to me that the Bill of Materials is probably for the R1 board or I just don't understand what I am reading. In any case, has anyone recently built an ACP+ and have a current parts list for it and be willing to share it with me, I would be very grateful.
Also, as I said before, this is going to be my first DIY project and of course, I don't know anything about Resistors and Capacitors and ....., so if someone could suggest a good source for Capacitors and resistor (I went to Mousers but I was a bit lost trying to figure out if I was getting the right parts) and good brands and good versions, I wouldn't mind spending a little more to get nice parts
Thanks in advance!
Cheers
Daniel
Hi all,
I bought the PCB Boards for the ACP+ (V1 R2). This is going to be my first DIY project ever and of course, I have a few questions.
I read the article on the Firstwatt website for ACP+ and it seems to me that the Bill of Materials is probably for the R1 board or I just don't understand what I am reading. In any case, has anyone recently built an ACP+ and have a current parts list for it and be willing to share it with me, I would be very grateful.
Also, as I said before, this is going to be my first DIY project and of course, I don't know anything about Resistors and Capacitors and ....., so if someone could suggest a good source for Capacitors and resistor (I went to Mousers but I was a bit lost trying to figure out if I was getting the right parts) and good brands and good versions, I wouldn't mind spending a little more to get nice parts
Thanks in advance!
Cheers
Daniel
Daniel, check out the link above, or the attachment on post 659. This should cover most everything you need. Looks like everything is available at Mouser. If you copy the part number from the sheet into the Mouser search field, it’ll take you straight to the part. You’ll want to reference Nelson’s original BOM for part quantities (or the schematic)
Daniel- if this is your first project I strongly suggest you practice soldering with a kit such as this, it is quite fun and you will be significantly better at assembling the project when you are finished. 
https://www.amazon.com/Tree-Assemble-Kit-Color-LED/dp/B06Y44CJ4B
https://www.amazon.com/Tree-Assemble-Kit-Color-LED/dp/B06Y44CJ4B
Hi
I need help picking the right Volume pot for ACP+, does anyone have a part number for Mouser?
Thanks
I need help picking the right Volume pot for ACP+, does anyone have a part number for Mouser?
Thanks