I guess the bottom line re impedance compatibility with the BAT is that a reasonable case could be made on either side of the issue.
Earlier in the thread I referred to the possibility of audibly significant phase shifts occurring as a result of the impedance interactions that would arise using the BAT with your amplifier, in addition to a slight amount of deep bass rolloff. If I recall correctly Ralph of Atma-Sphere has said in past threads here that to be sure that audibly significant phase shifts will not occur frequency response should extend beyond the audible range by a factor of 10, meaning 2 Hz to 200 kHz. While his designs meet that requirement, at least at the low frequency end (and at both ends in the case of his preamps), obviously many well regarded designs do not. All or nearly all SET amps for starters. (I note, btw, that your X350.5 is specified down to 1.5 Hz).
And in this case, given that the preamp’s output impedance rises from 414 ohms at mid-frequencies to 4600 ohms at 20 Hz, it will not come close to supporting bandwidth down to 2 Hz in conjunction with a 30K load.
So it seems to me that while use of the BAT in this application represents a compromise in terms of impedance compatibility, the degree of that compromise is sufficiently marginal that its acceptability is something reasonable (and knowledgeable) people can differ about.
Regards,
-- Al
Earlier in the thread I referred to the possibility of audibly significant phase shifts occurring as a result of the impedance interactions that would arise using the BAT with your amplifier, in addition to a slight amount of deep bass rolloff. If I recall correctly Ralph of Atma-Sphere has said in past threads here that to be sure that audibly significant phase shifts will not occur frequency response should extend beyond the audible range by a factor of 10, meaning 2 Hz to 200 kHz. While his designs meet that requirement, at least at the low frequency end (and at both ends in the case of his preamps), obviously many well regarded designs do not. All or nearly all SET amps for starters. (I note, btw, that your X350.5 is specified down to 1.5 Hz).
And in this case, given that the preamp’s output impedance rises from 414 ohms at mid-frequencies to 4600 ohms at 20 Hz, it will not come close to supporting bandwidth down to 2 Hz in conjunction with a 30K load.
So it seems to me that while use of the BAT in this application represents a compromise in terms of impedance compatibility, the degree of that compromise is sufficiently marginal that its acceptability is something reasonable (and knowledgeable) people can differ about.
Regards,
-- Al