The FQP parts as well as KSA/KCA are on their way plus some spares. I am on standby for the 2SD2014 to become available again which will act as the 2SD2081 replacement - so the Darlington's will be the 2SB1257/2SD2014 combo as per suggestion.
I'm gonna work on a PCB that is a bit smaller than the original one, a shrunken HPA-1 if you like, and make this headamp my 2024 project. As I have other things to spend my time and money on, progress will be slow, but I will share when there is some exciting news. The case design will be inspired by
Oneminde
I'm gonna work on a PCB that is a bit smaller than the original one, a shrunken HPA-1 if you like, and make this headamp my 2024 project. As I have other things to spend my time and money on, progress will be slow, but I will share when there is some exciting news. The case design will be inspired by
Finished my build a little while ago, but still debugging an issue with the relays... Could really use tips or ideas on how to proceed.
I have used the PCB design by Jeff Young, but building it - I changed the U4A and U4B Flip-Flops by lifting the input pins (SET and CLR) to replicate U3A behavior. That way, on power-on all 3 FFs are ON. That means SRC1 is enabled, PHONES is enabled and PRE is enabled.
The Q output of all 3 FFs work as expected, but only relay K1 is closing as expected. The other 2 relays (K3 and K4 for PHONES and PRE) are still not passing signal across
I found online an advice to measure R across relay (when amp is off), so I tried that. K1 (for SRC1) - measure 366kΩ, but K3 and K4 measure 1kΩ.
Any ideas?! Any help is VERY welcome... 🙏
I have used the PCB design by Jeff Young, but building it - I changed the U4A and U4B Flip-Flops by lifting the input pins (SET and CLR) to replicate U3A behavior. That way, on power-on all 3 FFs are ON. That means SRC1 is enabled, PHONES is enabled and PRE is enabled.
The Q output of all 3 FFs work as expected, but only relay K1 is closing as expected. The other 2 relays (K3 and K4 for PHONES and PRE) are still not passing signal across
I found online an advice to measure R across relay (when amp is off), so I tried that. K1 (for SRC1) - measure 366kΩ, but K3 and K4 measure 1kΩ.
Any ideas?! Any help is VERY welcome... 🙏
Have you checked if the relays are functional outside of the circuit and can you measure what is happening with the supply rail / voltage to the relays upon power up ? ... that is some basic functionality you can check and start tracking back to the issue. Could be a track or component that is not working as intended, put in backwards and so on.
Since the PCB is installed inside the case, and it is a BIG undertaking to remove it (need to unsolder wires to the PCB and remove switches from the back panel) - I am trying to exhaust all possible ideas first, to find the root cause. I never thought of testing the relays before soldering to the PCB, since all 4 were bought new from Mouser or Digikey. Weird coincidence that SRC1 works, but PHONES and PRE relays do not.
All supply rails are stable and correct voltages. Are you asking about power-on sequence from 0V to stable and correct voltages? What are you suspecting could happen that explains the current situation?
I am not a EE, but a colleague of mine is, so I asked him to verify everything looks good. He confirmed all non-symmetrical components (diodes, transistors, etc.) are assembled correctly. He also used a scope to verify a 1kHz test tune feeding the amp gets all the way through the amplification circuit and to the "doorstep" of the output relays (PHONES and PRE).
He also confirmed all 3 FFs outputting '1' and the transistors operate as they should.
At this point, I am still trying to explain to myself (or prove somehow) what are the chances those 2 relays (PHONES and PRE) both arrived bad or "blew" while the SRC1 relay works perfectly.
If anyone has any idea what else can be tested without removing components from the PCB - I would highly appreciate it!!!
Some more information:
I do not have buttons in my build. That is the reason I want SRC1, PHONES, and PRE to be enabled always at power-on.
I only have 1 input, and I want headphones and PRE to always receive signal. There is an external switch between PRE output on the PCB and the actual RCAs, so I can flick the PRE off externally (when using headphones).
The change I made (from Jeff Young's design) was connecting SET and CLR pins of U4A and U4B to those of U3A. See:
Now, all 3 FFs behave identically.
Q43 and Q44 as a result behave the same as Q41 (as far as I can tell).
Yet, K3A and K4A do NOT behave like K1A. K1A lets signal through (relay is closed) while the other 2 relays do NOT let signal through them (relays are open).
Obviously possible, but I think it is a weird coincidence if both relays used for K3 and K4 arrived defective (or died on me), while K1 just happens to be good... Any way to tell for sure (without removing from the PCB) whether the relays (K3 and K4) are malfunctioning? If I have a definite proof that K3 and K4 are both malfunctioning - I will reluctantly take apart my build and remove them.
Thanks for any help 🙏
I do not have buttons in my build. That is the reason I want SRC1, PHONES, and PRE to be enabled always at power-on.
I only have 1 input, and I want headphones and PRE to always receive signal. There is an external switch between PRE output on the PCB and the actual RCAs, so I can flick the PRE off externally (when using headphones).
The change I made (from Jeff Young's design) was connecting SET and CLR pins of U4A and U4B to those of U3A. See:
Now, all 3 FFs behave identically.
Q43 and Q44 as a result behave the same as Q41 (as far as I can tell).
Yet, K3A and K4A do NOT behave like K1A. K1A lets signal through (relay is closed) while the other 2 relays do NOT let signal through them (relays are open).
Obviously possible, but I think it is a weird coincidence if both relays used for K3 and K4 arrived defective (or died on me), while K1 just happens to be good... Any way to tell for sure (without removing from the PCB) whether the relays (K3 and K4) are malfunctioning? If I have a definite proof that K3 and K4 are both malfunctioning - I will reluctantly take apart my build and remove them.
Thanks for any help 🙏