PeterW wrote:This was discussed extensively on another thread.
If you wish to create a permanent partnership between the PAS and an amplifier, it becomes a (minor) exercise in matching the impedance such that the PAS "sees" about 50K.
Dynaco described the process for a 100K Load (ST-120) as follows:
To do the impedance mod - per the Dynaco literature:
1. Obtain two 100,000 ohm, 1/2-watt 10% tolerance resistors.
2. Unsolder and discard the two 510,000 ohm (green-brown-yellow)
resistors connected to the audio-output sockets on the back panel of
the preamplifier and replace them with the 100,000 ohm resistors.
Solder all connections.
3. Snip out and discard the two 62,000 ohm (blue-red-orange) resistors
on the PC-5 circuit board adjacent to eyelets 8 & 18. This completes
the modification.
With that in mind and given the 75K on the VTA 70, you will need to calculate the proper resistor in parallel with 75K to get to 50K (150K) and substitute that for the 100K listed in the procedure.
Go for 5% screened resistors as well.
You might find this already done if your 3X is well-and-truly a 3X. However, early versions of the 3X were hit-or-miss.
NOTE: This matches *THIS* PAS with *THAT* amp. If any other amp is introduced, the resistors will have to be changed in order to get the 50K preferred match. If the amp has an input impedance too low to allow such a match, then the buffer becomes the best option.
I sort of pulled this out of another thread and created my own thread before i really knew what i was trying ask.
I had been wondering if the 510k ohm resistors on the outputs of my PAS 3 were 'holding it back' paired with my vta st 70, being that this was intended for the original ST 70.
I was really curious and just snipped both connections.
Wow! what an improvement.
Im still learning, so forgive me for sort of duplicating a thread in a way.
With that in mind and given the 75K on the VTA 70, you will need to calculate the proper resistor in parallel with 75K to get to 50K (150K) and substitute that for the 100K listed in the procedure.
With this above statement in mind, having exactly this combination of amp / pre. im a little confused by the 'to get 50k (150k)" part.
I dont seem to see 25kohm resistors, so essentially i need to build like 24k + 1k = 25kohm x 2 (one per output) to get 50k ohms total?
Mods feel free to merge this new thread back into the thread from which i quoted.
