Some questions about Van Scoyoc X-coupled splitter - diyAudio
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Old 1st September 2004, 12:12 PM   #1
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Default Some questions about Van Scoyoc X-coupled splitter

I've seen some info, in this forum and elsewhere, about the cross-coupled phase splitter invented by Van Scoyoc. However, I would still like to get answers to the following questions:

1. Is it necessary (or desirable) to use the same tube type for both the first and second stages? e.g. would it be OK to use 6SN7 for the IP c/f followed by 6SL7 for the voltage gain or should both tubes be the same?

2. If both tubes should be the same, would it be better to use a pair of 6SN7s or 6SL7s?

3. What causes the limited amplitude of IP signal that it can tolerate and how can this be maximized in practice?

4. Whatg are advantages or disadvantages of this type of splitter, compared with a long-tail pair splitter?
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Old 1st September 2004, 08:21 PM   #2
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Hi,

Quote:
1. Is it necessary (or desirable) to use the same tube type for both the first and second stages? e.g. would it be OK to use 6SN7 for the IP c/f followed by 6SL7 for the voltage gain or should both tubes be the same?
1. Not necessary at all. The splitter likes to be driven from a low impedance source, hence the CFs in front of it.
Whether you use a 6SL7 or something else should mainly be dictated by the drive requirements of the stage following the splitter: triodes, penthode, etc.

2. See 1.

3. The CF input will take an awful lot of IP signal, the following stage needs to be scaled accordingly. This is true for any cascading stages, I don't see why it would be typical of the Van Scoyoc design.

4. Pro: excellent balance
Contra: extra tube or xformer, reputed to be rather "dead" sounding...
Neither of the above: been used to death by ARC.

Cheers,
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Old 5th September 2004, 09:17 AM   #3
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Thanks for your response.

Quote:
3. The CF input will take an awful lot of IP signal, the following stage needs to be scaled accordingly. This is true for any cascading stages, I don't see why it would be typical of the Van Scoyoc design.
I have read that there is a limitation on the size of signal that the Van Scoyoc splitter can handle and I guess that must be why it always appears as the first stage in a power amp.

Thinking more about this, I suppose that the input stage (a c/f) can be given a negative rail, if necessary, allowing for a high amplitude input signal. However, the second stage will have limited bias, because of the way it is fed from the c/f. If I'm right, then the signal handling capability of the splitter will be limited by the bias voltage of the second stage. E.g. a 6SL7 with 250v plate voltage and -2.5v grid bias could handle a signal of around 4v p-p or 2.8v rms, which should be enough. Or am I barking up the wrong tree?
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