I changed out R10 to a jumper and that did seem to solve the hum problem. However, I still have the loud thump. Anybody out there have any thoughts ?
If you turn on the amplifier last and it thumps, I would think that is an issue with the amplifier, not with the preamplifier.
Try turning on the amplifier with the preamp off. Does it thump?
Try a different preamp, and turn the preamp on before turning on the amp. Does it thump?
Try turning on the amplifier with the preamp off. Does it thump?
Try a different preamp, and turn the preamp on before turning on the amp. Does it thump?
I measured the voltage across the output of the FE and it registered 10 volts on start up and then immediately started to decrease. After about 5 minutes it had dropped to .002 volts and stopped. At that point I checked the other channel output and it was still showing 10 volts but also started decreasing immediately. I then checked my ACA mini outputs and they showed very negligible voltage on start up. When I checked the mini I did not have the FE connected to it.
I hooked up my Starving Student to the mini and when I turn it on there is a small pop after about 10 or 12 seconds which has been a normal thing with my mini's, ACA's and my Aleph.
Yes, it didn't start going down till I put the meter on it and that was after the FE had been on for probably 7-8 minutes.
If there was no amplifier connected to the preamp the whole time, there will be DC voltage at the FE output as there is no path to ground at the output of the FE output capacitor. So if you measured VDC at the output of the FE when there was nothing connected to it, then that is normal. My FE has high VDC at its output too if no amplifier is connected to it.
Try waiting a few seconds after turning on the FE before turning on the amplifier.
Try waiting a few seconds after turning on the FE before turning on the amplifier.
You can add a 200k resistor across the RCA output of each channel of the FE. That drops the VDC at the FE output quickly at turn-on when there is no amplifier connected. That will help reduce the thump if the amplifier is turned on immediately after turning on the FE.
The 200k should not affect the performance of the FE and most amplifiers connected to the FE.
Note that many amplifiers have a resistor to ground at their input so that would discharge the DC of the FE output capacitor. But some do not, and the ACA Mini is in that group.
The 200k should not affect the performance of the FE and most amplifiers connected to the FE.
Note that many amplifiers have a resistor to ground at their input so that would discharge the DC of the FE output capacitor. But some do not, and the ACA Mini is in that group.
Bad juju can happen turning on the amp first then preamp... No No.
Pre on then amp on...
Amp off then pre off...

Pre on then amp on...
Amp off then pre off...

Ben Mah, I installed the 200k resistors across the outputs this morning and put a meter on it and turned it on, no voltage at the outputs! Hooked it back up to the system and turned it on and no thumps! Thanks so much for the assist!!! 😎
Hi, could you guys confirm, that the connection is correct? Front End 2022 V0R1 PCB
IN- and VG connected
RCA Input GND connected to VG
RCA Output GND connected to VG
PSU -24V connected to V-
PSU 0V connected to VG
PSU +24V connected to V+
IN- and VG connected
RCA Input GND connected to VG
RCA Output GND connected to VG
PSU -24V connected to V-
PSU 0V connected to VG
PSU +24V connected to V+
When you circuit is up and running, perhaps you might consider moving the zero volt wire (yellow) to midpoint of supply capacitors, not the 'ground' connection of the signal path - the capacitors are the 'on-board' power supply to the circuit hence the +/0/- - it may not change anything but well worth a try
The audio ground and power supply ground are both at "VG" on the pcb, and "VG" is located between the two power supply capacitors.
Perhaps I am not understanding what you are proposing.
Perhaps I am not understanding what you are proposing.
Sorry Ben for the confusion
In some 'schools of thought' it's regarded as optimum to use the 0Volt point between the supply caps as the main or principal ground point of a circuit like this, rather than the signal ground, despite the fact that there's a copper track between that power supply 0 volt (between the caps) and the signal shield point - sometimes it makes quite a difference hence the idea to try it either way.
In power amp power supplies it's much more significant as the + & - rail caps aren't receiving current charging pulses at the same time (alternate 1/120Hz) so ....
In some 'schools of thought' it's regarded as optimum to use the 0Volt point between the supply caps as the main or principal ground point of a circuit like this, rather than the signal ground, despite the fact that there's a copper track between that power supply 0 volt (between the caps) and the signal shield point - sometimes it makes quite a difference hence the idea to try it either way.
In power amp power supplies it's much more significant as the + & - rail caps aren't receiving current charging pulses at the same time (alternate 1/120Hz) so ....
Thanks I used it this "school" in my tube amp, I'll try it, but because of the relative short VG track probably there will be no difference.In some 'schools of thought' it's regarded as optimum to use the 0Volt point between the supply caps
Another question, if I want to use the Fron End directly after the output transformer of my DAC is it possible to skip C1 and C2 input caps?
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