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Why not help out the phase splitting with the input transformer?

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In Reply to: RE: EL-34 PP schematic posted by mqracing on February 09, 2008 at 22:07:59

If you're going to use an input tranny you might want to consider integrating a preamp circuit with the total design too. From what experience I have with input transformers, I�ve found I couldn�t use just any preamp to drive it. If the design focus was shifted so that the input transformer was now a preamp output transformer it could handle the phase splitting too. Little tiny transformers split phase very well.

Built it and lets us know how you like it.

Follow Ups:

RE: Why not help out the phase splitting with the input transformer? - mqracing 09:45:01 02/13/08 (0)
Hi Scholl:
you wrote:
::::If you're going to use an input tranny you might want to consider integrating a preamp circuit with the total design too.::::
as drawn this circuit would be for someone who wants to go direct from their cd player to their amp--- but need provisions for volume discrimination. The 10K input impedance should be sufficiently light enough load for the vast majority of cd players with solid state outputs.
As well as many tubed cd players with sufficiently low output impedance.
:::From what experience I have with input transformers, I�ve found I couldn�t use just any preamp to drive it.:::
this is a bit too vague--- big difference btwn driving say a 600 ohm (or lower) input trans and an input trans with a 10K or higher input impedance. And, of course, quality of the input trans comes into play--- as well as how lossy it is (i.e., what the insertion losses are).
And the above of course is also dependent on the capabilities of the source--- what is it's output impedance and etc.

::::If the design focus was shifted so that the input transformer was now a preamp output transformer it could handle the phase splitting too.::::
awe... but that component (preamp output trans) would be in a preamp not the front of a power amp---
point well taken--- that you can split phase on the output of your preamp--- our B7 preamp outputs have 500\600 ohm nominal center tapped secondaries--- from which you could derive a differential signal by simply grounding the center tap.
But in that case I would build that person a different amp--- deleting the volume control as well as the input trans--- and going directly into the LTP with the differential signal from the preamp.
Once you move past the really straightforward implementations--- say just having a simple RCA single ended input--- then you need to do a moreso through systems analysis--- to see what a person needs or doesn't need.
But your point on splitting at the preamp level (small signal) is well taken. But what I had in mind in initially drawing up the circuit as shown is the person wanting to go from cd player with single ended output directly to the power amp.
MSL

Edits: 02/13/08

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