Thank you.
As others may have already mentioned, the line stage is inverting.
I do not think this is a big problem, because you have to take the
absolute phase of the whole system into account and then probably
reverse the speaker leads if you consider it necessary.
At the time lots of coupling capacitors, and most of them electrolytic,
have been standard. Today people try to avoid them, by using dual
supplies, complementary push-pull circuits etc.
Both considerations are legitimate, but strong proponents of "correct"
absolute phase should know that in the studio recording process and
in record pressing there is never any means to preserve phase integrity.
In tape recorders absolute phase is even undefined.
I think it would be useful to incorporate a phase reversal switch in a new
preamp design if only to prove that most people will hear no difference
with most program material.
And finally it would be nice to compare a well preserved Radford ZD22
to contemporary or vintage "high end" preamps.
As others may have already mentioned, the line stage is inverting.
I do not think this is a big problem, because you have to take the
absolute phase of the whole system into account and then probably
reverse the speaker leads if you consider it necessary.
At the time lots of coupling capacitors, and most of them electrolytic,
have been standard. Today people try to avoid them, by using dual
supplies, complementary push-pull circuits etc.
Both considerations are legitimate, but strong proponents of "correct"
absolute phase should know that in the studio recording process and
in record pressing there is never any means to preserve phase integrity.
In tape recorders absolute phase is even undefined.
I think it would be useful to incorporate a phase reversal switch in a new
preamp design if only to prove that most people will hear no difference
with most program material.
And finally it would be nice to compare a well preserved Radford ZD22
to contemporary or vintage "high end" preamps.
Will add here a couple of links with Radford schematics,
maybe someone will find them useful.
https://www.drtube.com/radford/
maybe someone will find them useful.
https://www.drtube.com/radford/
@sgrossklass
Off topic but thank you for the information on the leach preamp. I bought one in the 1970s because of the low input capacity. Leach advertised 20 pF of input capacity.
Off topic but thank you for the information on the leach preamp. I bought one in the 1970s because of the low input capacity. Leach advertised 20 pF of input capacity.
Hi AS Audio (and StevenOH),
According to my simulations (and measurements), the line stage is indeed NOT inverting. Regarding the Dr.Tube website (which is housed not far from my home): this site has only documents on Radford amplifiers with electronic tubes (or valves, for our friends from the UK). Paul Kemble has a page on the Radford solid-state amplifiers. You can find it at: https://www.angelfire.com/sd/paulkemble/sound8j.html.
According to my simulations (and measurements), the line stage is indeed NOT inverting. Regarding the Dr.Tube website (which is housed not far from my home): this site has only documents on Radford amplifiers with electronic tubes (or valves, for our friends from the UK). Paul Kemble has a page on the Radford solid-state amplifiers. You can find it at: https://www.angelfire.com/sd/paulkemble/sound8j.html.