3.28v across R15 on the right channel, compared to 4.67v on it left. R15 is 125 ohms and has .412v across on the right, .916v on the left.
R4 sets the current of the J113 (Q3). The current should be around 10mA.
I assume R4 is 125 Ohm, not R15 as you mentioned.
Left channel current = 0.916V/125R=0.0073A = 7.3mA, close enough for the circuit to work.
Right channel current = 0.412V/125R=0.0033A = 3.3mA, too low, resulting in the voltage at R15 being too low, and therefore Q6 not functioning.
What needs to be done is R4 in the right channel to be reduced in value. This will be by trial and error. Try 50 Ohm or so first. Then measure the voltage drop across the resistor and do the calculation as above. The target current is 10mA.
I assume R4 is 125 Ohm, not R15 as you mentioned.
Left channel current = 0.916V/125R=0.0073A = 7.3mA, close enough for the circuit to work.
Right channel current = 0.412V/125R=0.0033A = 3.3mA, too low, resulting in the voltage at R15 being too low, and therefore Q6 not functioning.
What needs to be done is R4 in the right channel to be reduced in value. This will be by trial and error. Try 50 Ohm or so first. Then measure the voltage drop across the resistor and do the calculation as above. The target current is 10mA.
Is this just a normal production variation of the J113? If so I have 6 more that I can test for a better fit. And you are correct, that was a typo and should have been R4.
Yes, production variation.
You can do the test as you had posted earlier and select a J113 that gives you 10mA, or if you have some resistors handy, just change the resistor.
The J113 is just a constant current source so the resistor change is not detrimental to the sound. Not having the 10mA current is detrimental to the sound. So changing the resistor to attain the 10mA will sound the same as finding a J113 that works with a 125R resistor for 10mA.
You can do the test as you had posted earlier and select a J113 that gives you 10mA, or if you have some resistors handy, just change the resistor.
The J113 is just a constant current source so the resistor change is not detrimental to the sound. Not having the 10mA current is detrimental to the sound. So changing the resistor to attain the 10mA will sound the same as finding a J113 that works with a 125R resistor for 10mA.
When I started testing them, I forgot that I had apparently already soldered two in place. oops
Thank you for your help. It's greatly appreciated.
If you do the test, put a 125R resistor in place of the 100R resistor that is shown in your test rig schematic. 10mA across 125R= 0.010A x 125R = 1.25V.
@Ben Mah
Having read so many discussions/troubleshooting advice about getting 10mA across R4 I just have to ask, how much is too much? Is there an advisable upper current above 10mA not to exceed?
Having read so many discussions/troubleshooting advice about getting 10mA across R4 I just have to ask, how much is too much? Is there an advisable upper current above 10mA not to exceed?
Interesting that this comes up again. I just received an assortment of resistors and some sockets, and so tested 10 - 125 ohms on my right channel. Previously it had not worked at 125 ohms, and did work with half that, about 62 ohms. Somewhere between 75 and 90 ohms it probably stopped working, though I didn't record the voltage at DC1. As I decreased resistance from 65 to 10 ohms the current rose from about 4.5mA to 7.2mA. At this point I tried some 3.3, 2.2, and 1 ohm resistors which gave 7.83, 8.05, and 8.4mA, respectively, two 1 ohm in parallel gave about 8.5mA as well. At this point I hooked up a source and made a set of rca speaker cables, and verified I got sound out of the right channel even with R4 shorted.
Meanwhile my left channel came in at 9.9mA with a 90 ohm resistor.
Meanwhile my left channel came in at 9.9mA with a 90 ohm resistor.
Lots of variations in J113. Looks like you need to change the J113 if you want 10mA.
The key is getting 4.5V or so across R15 to get Q6 to get going.
The key is getting 4.5V or so across R15 to get Q6 to get going.
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I finished my build of the ACP+ today and can report limited success. I haven't plugged in headphones and source yet, but voltages are looking good at roughly 8mA and 9mA per channel with 23.5 ohms for R4. I'll dial in the right values tomorrow and give it a listen!
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I ended up with 12ohms for R4 on one channel and 16ohms on the other. Sounds so good I'm eyeing the ACA.
Someone asked about using 2Sk216 in the ACP+.
You only need to learn to use the search function.
No need to PM me.
Amp Camp Pre+Headphone Amp - ACP+
Amp Camp Pre+Headphone Amp - ACP+
Cheers,
Patrick
You only need to learn to use the search function.
No need to PM me.
Amp Camp Pre+Headphone Amp - ACP+
Amp Camp Pre+Headphone Amp - ACP+
Cheers,
Patrick
I want to build the ACP+.
My problem is that I don't have part Q3 J113, but I have 2N7000 instead. I got the 2N7000 as equivalent part for the J113 from a local store. They told me in the store that the 3 pinouts are different and I can turn them around so that they match with the PCB.
J113 pintouts: D S G
2N700 pinouts: S G D
(When the printed side is on the front side.)
Is it possible to build the ACP+ with the 2N7000?
My problem is that I don't have part Q3 J113, but I have 2N7000 instead. I got the 2N7000 as equivalent part for the J113 from a local store. They told me in the store that the 3 pinouts are different and I can turn them around so that they match with the PCB.
J113 pintouts: D S G
2N700 pinouts: S G D
(When the printed side is on the front side.)
Is it possible to build the ACP+ with the 2N7000?
I looked it up and the 2N7000 is an enhancement mode FET whereas the J113 is a JFET, which is depletion mode. So it is totally different and cannot be used in the ACP+.
Hi guys so I ordered the parts following the BOM on post #661, I realised for R16 and R17 its 33.2 ohm, and the mouser prt number links to 33.2K ohms instead, is that intentional?
Also the BOM or Mr Pass's BOM doesnt include any part for R22 7.5k, is that not nessesary?
Lastly, I have these RCJ-053 CUI Devices | Mouser 香港, RCA jacks as per the #661 BOM, seems like the orientation of the pins dont fit the board like it should?
Thanks for your help!
Also the BOM or Mr Pass's BOM doesnt include any part for R22 7.5k, is that not nessesary?
Lastly, I have these RCJ-053 CUI Devices | Mouser 香港, RCA jacks as per the #661 BOM, seems like the orientation of the pins dont fit the board like it should?
Thanks for your help!