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Old 26th December 2008, 02:49 AM   #1
kimbal is offline kimbal  Australia
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Default More information wanted on this Phase Splitter Circuit

Hi All;

I am in the throws of designing myself a new multi-amp sound system for home. In the throws of studying the phase splitter circuits, I came across this circuit attached here in a 6Y6 push pull amplifier. No information was given other than it was considered unusual.

There are some similarities in part to the twin triode differential Schmidt design of which I believe it has originated from that.

I would like to know if anyone is familiar with the below phase splitter circuit. I drew the circuit out using the evaluation version of Micro-cap 9 so my apologies if the drawing looks more complex than it needs to be.

Please advise as the what pros and cons this circuit has ( such as Linearity, Symmetry, Distortion, Impedance, Gain; etc) and any history about it.

So far, I am very happy with the Schmidt design as to what its performance is capable of, but I will use this circuit if its "better" despite the extra triode.

My personal email is > electricfiretuberesearch@yahoo.com <

Cheers.
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File Type: pdf phase splitter schematic.pdf (80.6 KB, 133 views)
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Old 26th December 2008, 08:41 AM   #2
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I haven't seen this circuit before, but it looks like a pretty basic LTPI to me. In this kind of basic LTPI with a tail resistor (as opposed to a CCS) balance between outputs is not perfect because the second triode (X2) gets its input signal from the common cathode resistor, and there is some voltage drop across this resistor.

This circuit seems to be balanced better (likely, why use an extra tube otherwise?) because outputs are taken from plates of X2/X3, and both of those take their signal from the cathode resistor of X1/X2. AC from X1's plate is dumped to ground via 10 μF capacitor. If you ask me, I would rather use a normal LTPI with f.e. 47k tail resistor instead of 10k, or better, a CCS instead of a tail resistor.

As a sidenote, considering the very high input impedance of X1's grid circuit, 0.25 μF input capacitor seems huge to me and may cause some issues like unwanted farty distortion, although this may only be an issue when overdriven. 0.022 μF for that one should be enough for good frequency response though. And I can just hope this makes sense because I'm writing this 6:43 am local time..
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Old 26th December 2008, 02:40 PM   #3
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Doesn't look like a true LTP to me... the input is a follower, the phase inversion comes merely from driving X3 from the cathode of X2. Eliminate X1 and that's all you have - a badly balanced phase inverter.

The output of X2 and X3 will never null (a simple test for balance) because one is DC coupled at the cathode and one has an icky electrolytic baypass cap in the cathode.

Otoh, who knows, maybe it sounds good?

There are better phase inverters, but I think what this one does that is interesting is that it provides gain while doing the phase inversion, although the potential voltage gain of the input X1 is not used.

LTPs don't balance quite right either with simple resistive loads, so they may or may not represent a better alternatives - also the LTP is low in even order harmonics and high(er) in third and odd order harmonics... something to consider.

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Old 26th December 2008, 03:35 PM   #4
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Quote:
LTPs don't balance quite right either with simple resistive loads
With a good CCS, the limitation in balance is how tightly you can match the plate resistors and the following stage grid resistors. That will be true for any active splitter.
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Old 26th December 2008, 08:35 PM   #5
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as long as it is a tube CCS, it is "legal"!

These sand based devices mess up the free electron field flow...


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Old 27th December 2008, 10:07 AM   #6
kimbal is offline kimbal  Australia
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Default Thanks All;

Thanks All;

I agree with most of what has been said.

If any one knows more about it other than their own obvious circuit assessment, I would still be interested.

The theory I have is, the lack of gain available in the standard LTP was seen as a "waste" of a tube / or pair of tubes and so the current circuit I have submitted was developed by someone to get more from the original design with the need for an additional tube stage added in.

I do remember in years gone by it was financially advantageous to use as few a stages as possible for maximum gain. This mean't some weird circuits were developed and implemented. technical aspects like harmonic quality and balance was not always seen as top priority by some designers; especially where public address and low-fi audio was involved.

My application is to build a truely good quality sound system with just tubes - no transistors in this one. I am happy to sacrifice a few extra tubes to attain a better quality of signal processing rather than take short cuts. With the cost of tubes being so cheap now adding more gain with a few extra stages is no issue.
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