systemtruck
Well-known member
Gotcha. Understood! That’s funny that you say that about other RCA boards because every one I’ve looked at the schematic of has had this line booster amp. Can i ask which models don’t have it?
I was going to again mention the theory that perhaps all of this extra gain, and then voltage dividing, is solely to achieve the mono/dual switching function… like I mentioned before, so that two channel bussing loss was met with a similar loss during dual mode, just for user friendliness, when they already needed the summing resistors…
BUT… That theory is now negated because the mono BC-5B and BC-3B boards both also have the line booster amps, as attached below.
And in their post voltage dividers, their values are 18k/6200, which is only a slight difference from the 18k/8200 from BC-6A above.
So even thought they don’t need switching or summing, they kept a significant voltage division/loss between the Booster and PGRM.
So what is the deal then? RCA would not have wasted all that expense and parts for no reason. Doesn’t there have to be SOME kind of operational / sonic benefit to have a summing amplifier be separate from the PGRM output amplifier? Like maybe the 4 stages of 12AY7 is preferable for whatever reason? And the two stages of 12AX7 amplification is a better setup for the Push Pull that follows? I’m just stabbing in the dark here.
And what about that pair of 100K resistors that feed the PGRM 12AX7 inputs in the actual PGRM schematic a few posts ago? How does that relate to RCA’s overkill gain staging?
I was going to again mention the theory that perhaps all of this extra gain, and then voltage dividing, is solely to achieve the mono/dual switching function… like I mentioned before, so that two channel bussing loss was met with a similar loss during dual mode, just for user friendliness, when they already needed the summing resistors…
BUT… That theory is now negated because the mono BC-5B and BC-3B boards both also have the line booster amps, as attached below.
And in their post voltage dividers, their values are 18k/6200, which is only a slight difference from the 18k/8200 from BC-6A above.
So even thought they don’t need switching or summing, they kept a significant voltage division/loss between the Booster and PGRM.
So what is the deal then? RCA would not have wasted all that expense and parts for no reason. Doesn’t there have to be SOME kind of operational / sonic benefit to have a summing amplifier be separate from the PGRM output amplifier? Like maybe the 4 stages of 12AY7 is preferable for whatever reason? And the two stages of 12AX7 amplification is a better setup for the Push Pull that follows? I’m just stabbing in the dark here.
And what about that pair of 100K resistors that feed the PGRM 12AX7 inputs in the actual PGRM schematic a few posts ago? How does that relate to RCA’s overkill gain staging?
