The stereo volume control pot. is located between the 2 stages, if that isn't already obvious from the PCB traces, the 2 original schematics showing the circuits component types and the pics of the assembled product which shows the shielded connecting leads to and from the pot.
Start by removing the signal connections taking the signal to the pot - marked (3) on the PCB. You can then connect your input signal direct to the disconnected pot. lead and thus listen with only the TA filter in place. After testing, restore the connection and remove the connection marked (2). Then you can connect the output lead to your amplifier to the lead you removed in order to test the operation of the gain stage. So in either case, you will still have volume adjustment. Then you can adjust it appropriately and connect the preamp sections to the test signal source and the amplifier respectively.
Notes:
1. I've only spoken of one channel. You need to test and compare both.
1. Without the gain stage, the volume with just the filter in place will be quite low. You may need to increase the source volume, if possible.
2. Maintain the earth shield connections of the signal leads and your signal inputs whilst messing with signal connections. Otherwise you will get noise, hum and uncontrolled levels.
3. MPSA12 is a Darlington type transistor which is used to switch the relay current. Don't confuse this transistor type with the low-noise signal transistors. They may actually work for a time but they are not compatible.
Start by removing the signal connections taking the signal to the pot - marked (3) on the PCB. You can then connect your input signal direct to the disconnected pot. lead and thus listen with only the TA filter in place. After testing, restore the connection and remove the connection marked (2). Then you can connect the output lead to your amplifier to the lead you removed in order to test the operation of the gain stage. So in either case, you will still have volume adjustment. Then you can adjust it appropriately and connect the preamp sections to the test signal source and the amplifier respectively.
Notes:
1. I've only spoken of one channel. You need to test and compare both.
1. Without the gain stage, the volume with just the filter in place will be quite low. You may need to increase the source volume, if possible.
2. Maintain the earth shield connections of the signal leads and your signal inputs whilst messing with signal connections. Otherwise you will get noise, hum and uncontrolled levels.
3. MPSA12 is a Darlington type transistor which is used to switch the relay current. Don't confuse this transistor type with the low-noise signal transistors. They may actually work for a time but they are not compatible.
Is your iPod lightning or wide 20+ pin connector?
I am using either lightning DAC output or line out analog output to get better sound to preamp inputs, no headpone output.
I am using either lightning DAC output or line out analog output to get better sound to preamp inputs, no headpone output.